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  • 1.
    Acker, Pascal
    et al.
    University of Freiburg, Germany.
    Rzesny, Luisa
    University of Freiburg, Germany.
    Marchiori, Cleber F. N.
    Uppsala universitet.
    Araujo, Carlos Moyses
    Uppsala universitet.
    Esser, Birgit
    University of Freiburg, Germany.
    π-Conjugation Enables Ultra-High Rate Capabilities and Cycling Stabilities in Phenothiazine Copolymers as Cathode-Active Battery Materials2019In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 29, no 45, article id 1906436Article in journal (Refereed)
    Abstract [en]

    In recent years, organic battery cathode materials have emerged as an attractive alternative to metal oxide–based cathodes. Organic redox polymers that can be reversibly oxidized are particularly promising. A drawback, however, often is their limited cycling stability and rate performance in a high voltage range of more than 3.4 V versus Li/Li+. Herein, a conjugated copolymer design with phenothiazine as a redox‐active group and a bithiophene co‐monomer is presented, enabling ultra‐high rate capability and cycling stability. After 30 000 cycles at a 100C rate, >97% of the initial capacity is retained. The composite electrodes feature defined discharge potentials at 3.6 V versus Li/Li+ due to the presence of separated phenothiazine redox centers. The semiconducting nature of the polymer allows for fast charge transport in the composite electrode at a high mass loading of 60 wt%. A comparison with three structurally related polymers demonstrates that changing the size, amount, or nature of the side groups leads to a reduced cell performance. This conjugated copolymer design can be used in the development of advanced redox polymers for batteries.

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  • 2.
    Aderne, Rian E.
    et al.
    Pontifícia Universidade Católica do Rio de Janeiro – PUC-Rio, BRA.
    Borges, Bruno Gabriel A. L.
    Universidade Federal do Rio de Janeiro-UFRJ, BRA.
    Avila, Harold C.
    University of Atlantic, COL.
    von Kieseritzky, Fredrik
    Karolinska Institutet.
    Hellberg, Jonas
    Chemtron AB, Sweden.
    Koehler, Marlus
    Universidade Federal do Paraná-UFPR, BRA.
    Cremona, Marco
    Pontifícia Universidade Católica do Rio de Janeiro – PUC-Rio, BRA.
    Roman, Lucimara S.
    Universidade Federal do Paraná-UFPR, BRA.
    Araujo, Moyses C.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University.
    Rocco, Maria Luiza M.
    Universidade Federal do Rio de Janeiro-UFRJ, BRA.
    Marchiori, Cleber
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    On the energy gap determination of organic optoelectronic materials: the case of porphyrin derivatives2022In: Materials Advances, E-ISSN 2633-5409, no 3, p. 1791-1803Article in journal (Refereed)
    Abstract [en]

    The correct determination of the ionization potential (IP) and electron affinity (EA) as well as the energy gap is essential to properly characterize a series of key phenomena related to the applications of organic semiconductors. For example, energy offsets play an essential role in charge separation in organic photovoltaics. Yet there has been a lot of confusion involving the real physical meaning behind those quantities. Experimentally the energy gap can be measured by direct techniques such as UV-Vis absorption, or indirect techniques such as cyclic voltammetry (CV). Another spectroscopic method is the Reflection Electron Energy Loss Spectroscopy (REELS). Regarding data correlation, there is little consensus on how the REELS' energy gap can be interpreted in light of the energies obtained from other methodologies such as CV, UV-Vis, or photoemission. In addition, even data acquired using those traditional techniques has been misinterpreted or applied to derive conclusions beyond the limits imposed by the physics of the measurement. A similar situation also happens when different theoretical approaches are used to assess the energy gap or employed to explain outcomes from experiments. By using a set of porphyrin derivatives as model molecules, we discuss some key aspects of those important issues. The peculiar properties of these porphyrins demonstrate that even straightforward measurements or calculations performed in a group of very similar molecules need a careful interpretation of the outcomes. Differences up to 660 meV (similar to 190 meV) are found comparing REELS (electrochemical) measurements with UV-Vis energy gaps, for instance. From the theoretical point of view, a reasonable agreement with electrochemical measurements of the IP, EA, and the gap of the porphyrins is only obtained when the calculations involve the full thermodynamics of the redox processes. The purpose of this work is to shed light on the differences and similarities of those aforementioned characterization methods and provide some insight that might help one to develop a critical analysis of the different experimental and theoretical methodologies.

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  • 3.
    Araujo, Rafael B.
    et al.
    Uppsala universitet.
    Banerjee, Amitava
    Uppsala universitet.
    Panigrahi, Puspamitra
    Uppsala universitet.
    Yang, Li
    Uppsala universitet.
    Sjödin, Martin
    Uppsala universitet.
    Strömme, Maria
    Uppsala universitet.
    Araujo, C. Moyses
    Uppsala universitet.
    Ahuja, Rajeev
    Uppsala universitet.
    Assessing Electrochemical Properties of Polypyridine and Polythiophene for Prospective Application in Sustainable Organic Batteries2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 4, p. 3307-3314Article in journal (Refereed)
    Abstract [en]

    Conducting polymers are being considered promising candidates for sustainable organic batteries mainly due to their fast electron transport properties and high recyclability. In this work, key properties of polythiophene and polypyridine have been assessed through a combined theoretical and experimental study focusing on such applications. A theoretical protocol has been developed to calculate redox potentials in solution within the framework of the density functional theory and using continuous solvation models. Here, the evolution of the electrochemical properties of solvated oligomers as a function of the length of the chain is analyzed and then the polymer properties are estimated via linear regressions using ordinary least square. The predicted values were verified against our electrochemical experiments. This protocol can now be employed to screen a large database of compounds in order to identify organic electrodes with superior properties.

  • 4.
    Araujo, Rafael B.
    et al.
    Uppsala universitet.
    Banerjee, Amitava
    Uppsala universitet.
    Panigrahi, Puspamitra
    Uppsala universitet.
    Yang, Li
    Uppsala universitet.
    Strömme, Maria
    Uppsala universitet.
    Sjödin, Martin
    Uppsala universitet.
    Araujo, C. Moyses
    Uppsala universitet.
    Ahuja, Rajeev
    Uppsala universitet.
    Designing strategies to tune reduction potential of organic molecules for sustainable high capacity batteries application2017In: Journal of Materials Chemistry A, ISSN 2050-7488, E-ISSN 2050-7496, Vol. 5, no 9, p. 4430-4454Article in journal (Refereed)
    Abstract [en]

    Organic compounds evolve as a promising alternative to the currently used inorganic materials in rechargeable batteries due to their low-cost, environmentally friendliness and flexibility. One of the strategies to reach acceptable energy densities and to deal with the high solubility of known organic compounds is to combine small redox active molecules, acting as capacity carrying centres, with conducting polymers. Following this strategy, it is important to achieve redox matching between the chosen molecule and the polymer backbone. Here, a synergetic approach combining theory and experiment has been employed to investigate this strategy. The framework of density functional theory connected with the reaction field method has been applied to predict the formal potential of 137 molecules and identify promising candidates for the referent application. The effects of including different ring types, e.g. fused rings or bonded rings, heteroatoms, [small pi] bonds, as well as carboxyl groups on the formal potential, has been rationalized. Finally, we have identified a number of molecules with acceptable theoretical capacities that show redox matching with thiophene-based conducting polymers which, hence, are suggested as pendent groups for the development of conducting redox polymer based electrode materials.

  • 5.
    Benatto, Leandro
    et al.
    Federal University of Paraná, BRA.
    Marchiori, Cleber
    Uppsala universitet.
    Araujo, Carlos Moyses
    Uppsala universitet.
    Koehler, Marlus
    Federal University of Paraná, BRA.
    Molecular origin of efficient hole transfer from non-fullerene acceptors: insights from first-principles calculations2019In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 7, no 39, p. 12180-12193Article in journal (Refereed)
    Abstract [en]

    Due to the strong exciton binding energy (E-b) of organic materials, the energy offset between donor (D) and acceptor (A) materials is essential to promote charge generation in organic solar cells (OSCs). Yet an efficient exciton dissociation from non-fullerene acceptors (NFAs) began to be observed in D/A blends even at very low driving force for hole transfer (Delta H-h). The mechanism behind this efficient photoinduced hole transfer (PHT) remains unclear since current estimates from calculations of isolated molecules indicate that E-b > Delta H-h. Here we rationalize these discrepancies using density functional theory (DFT), the total Gibbs free energy method and the extended Huckel theory (EHT). First, we employed DFT to calculate E-b for NFAs of three representative groups (perylene diimide derivatives, indacenodithiophene and subphthalocyanines) as well as for fullerene acceptors (FAs). Considering isolated molecules in the calculations, we verified that E-b for NFAs is lower than for FAs but still higher than the experimental Delta H-h in which efficient PHT has been observed. Finding the molecular geometry of the excited state, we also obtain that the structural relaxation after photoexcitation tends to further decrease (increase) E-b for NFAs (FAs). This effect helps explain the delayed charge generation measured in some NFA systems. However, this effect is still not large enough for a significant decrease in E-b. We then applied EHT to quantify the decrease of E-b induced by energy levels coupling between stacked molecules in a model aggregate. We then estimated the number of stacked molecules so that E-b approaches Delta H-h's. We found that small NFA aggregates, involving around 5 molecules, are already large enough to explain the experiments. Our results are justified by the low energy barrier to the generation of delocalized states in these systems (especially for the hole delocalization). Therefore, they indicate that molecular systems with certain characteristics can achieve efficient molecular orbital delocalization, which is a key factor to allow an efficient exciton dissociation in low-driving-force systems. These theoretical findings provide a sound explanation to very recent observations in OSCs.

  • 6.
    Carvalho, Rodrigo P.
    et al.
    Uppsala Universitet.
    Alhanash, Mirna
    Uppsala Universitet; Chalmers tekniska högskola.
    Marchiori, Cleber
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Brandell, Daniel
    Uppsala universitet.
    Araujo, C. Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala universitet.
    Exploring Metastable Phases During Lithiation of Organic Battery Electrode Materials2022In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, no 2, article id e202200354Article in journal (Refereed)
    Abstract [en]

    In this work, the Li-ion insertion mechanism in organic electrode materials is investigated through the lens of atomic-scale models based on first-principles theory. Starting with a structural analysis, the interplay of density functional theory with evolutionary and potential-mapping algorithms is used to resolve the crystal structure of the different (de)lithiated phases. These methods elucidate different lithiation reaction pathways and help to explore the formation of metastable phases and predict one- or multi-electron reactions, which are still poorly understood for organic intercalation electrodes. The cathode material dilithium 2,5-oxyterephthalate (operating at 2.6 V vs. Li/Li+) is investigated in depth as a case study, owing to its rich redox chemistry. When compared with recent experimental results, it is demonstrated that metastable phases with peculiar ring-ring molecular interactions are more likely to be controlling the redox reactions thermodynamics and consequently the battery voltage.

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  • 7.
    Carvalho, Rodrigo P.
    et al.
    Uppsala University, Sweden.
    Brandell, Daniel
    Uppsala University, Sweden.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University, Sweden.
    An evolutionary-driven AI model discovering redox-stable organic electrode materials for alkali-ion batteries2023In: Energy Storage Materials, ISSN 2405-8289, E-ISSN 2405-8297, Vol. 61, article id 102865Article in journal (Refereed)
    Abstract [en]

    Data-driven approaches have been revolutionizing materials science and materials discovery in the past years. Especially when coupled with other computational physics methods, they can be applied in complex high-throughput schemes to discover novel materials, e.g. for batteries. In this direction, the present work provides a robust AI-driven framework, to accelerate the discovery of novel organic-based materials for Li-, Na- and K-ion batteries. This platform is able to predict the open-circuit voltage of the respective battery and provide an initial assessment of the materials redox stability. The model was employed to screen 45 million small molecules in the search for novel high-potential cathodes, resulting in a proposed shortlist of 3202, 689 and 702 novel compounds for Li-, Na- and K-ion batteries, respectively, considering only the redox stable candidates. 

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  • 8.
    Carvalho, Rodrigo P
    et al.
    Uppsala university.
    Marchiori, Cleber
    Uppsala universitet.
    Araujo, Moyses
    Uppsala universitet.
    Brandell, Daniel
    Uppsala university.
    Atomic-scale Modelling of Redox-active Organic Molecules and Polymers for Energy Applications2020In: Redox Polymers for Energy and Nanomedicine / [ed] Nerea Casado, David Mecerreyes, Royal Society of Chemistry, 2020, p. 93-136Chapter in book (Other academic)
  • 9.
    Carvalho, Rodrigo P.
    et al.
    Uppsala University.
    Marchiori, Cleber
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Brandell, Daniel
    Uppsala University.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University.
    Artificial intelligence driven in-silico discovery of novel organic lithium-ion battery cathodes2022In: Energy Storage Materials, ISSN 2405-8289, E-ISSN 2405-8297, Vol. 44, p. 313-325Article in journal (Refereed)
    Abstract [en]

    Organic electrode materials (OEMs) combine key sustainability and versatility properties with the potential to enable the realisation of the next generation of truly green battery technologies. However, for OEMs to become a competitive alternative, challenging issues related to energy density, rate capability and cycling stability need to be overcome. In this work, we have developed and applied an alternative yet systematic methodology to accelerate the discovery of suitable cathode-active OEMs by interplaying artificial intelligence (AI) and quantum mechanics. This AI-kernel has allowed a high-throughput screening of a huge library of organic molecules, leading to the discovery of 459 novel promising OEMs with candidates offering the potential to achieve theoretical energy densities superior to 1000 W h kg(1). Moreover, the machinery accurately identified common molecular functionalities that lead to such higher-voltage electrodes and pointed out an interesting donor-accepter-like effect that may drive the future design of cathode-active OEMs.

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  • 10.
    Carvalho, Rodrigo P.
    et al.
    Uppsala University .
    Marchiori, Cleber
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Brandell, Daniel
    Uppsala University .
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University.
    Understanding the lithiation limits of high-capacity organic battery anodes by atomic charge derivative analysis2022In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 157, no 18, article id 181101Article in journal (Refereed)
    Abstract [en]

    The superlithiation of organic anodes is a promising approach for developing the next generation of sustainable Li-ion batteries with high capacity. However, the lack of fundamental understanding hinders its faster development. Here, a systematic study of the lithiation processes in a set of dicarboxylate-based materials is carried out within the density functional theory formalism. It is demonstrated that a combined analysis of the Li insertion reaction thermodynamics and the conjugated-moiety charge derivative enables establishing the experimentally observed maximum storage, thus allowing an assessment of the structure-function relationships also.

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  • 11.
    Carvalho, Rodrigo P.
    et al.
    Uppsala University.
    Marchiori, Cleber F. N.
    Uppsala University.
    Oltean, Viorica-Alina
    Uppsala University.
    Renault, Steven
    University Nantes, FRA.
    Willhammar, Tom
    Stockholm University.
    Gomez, Cesar Pay
    Uppsala University.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University.
    Brandell, Daniel
    Uppsala University.
    Structure-property relationships in organic battery anode materials: exploring redox reactions in crystalline Na- and Li-benzene diacrylate using combined crystallography and density functional theory calculations2021In: Materials Advances, E-ISSN 2633-5409, Vol. 2, no 3, p. 1024-1034Article in journal (Refereed)
    Abstract [en]

    Organic-based materials are potential candidates for a new generation of sustainable and environmentally friendly battery technologies, but insights into the structural, kinetic and thermodynamic properties of how these compounds lithiate or sodiate are currently missing. In this regard, benzenediacrylates (BDAs) are here investigated for application as low-potential electrodes in Na-ion and Li-ion batteries. Aided by a joint effort of theoretical and experimental frameworks, we unveil the structural, electronic and electrochemical properties of the Na(2)BDA and Li(2)BDA compounds. The crystal structure of these systems in their different sodiated and lithiated phases have been predicted by an evolutionary algorithm interplayed with density functional theory calculations. Due to difficulties in obtaining useful single crystals for the BDA salts, other methods have been explored in combination with the computational approach. While the predicted structure of the pristine Na(2)BDA compound has been experimentally confirmed through the 3D Electron Diffraction (3DED) technique, the hydrated version of Li(2)BDA is analysed through single crystal X-ray diffraction. The calculated cell voltages for the sodiation (0.63 V vs. Na/Na+) and lithiation (1.12 V vs. Li/Li+) processes display excellent quantitative agreement with experimental findings. These results validate the developed theoretical methodology. Moreover, fundamental aspects of the electronic structures and their relationship with the reaction thermodynamics are discussed. The results suggest a possible disproportionation between the sodiated phases of Na(2)BDA, supporting a two-electron process, and also unveil major differences for the two employed cations: Na+ and Li+.

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  • 12.
    Chen, Qiaonan
    et al.
    Siyuan Laboratory, Guangzhou Key Laboratory of Vacuum Coating Technologies and New Energy Materials, CHN; Chalmers University of Technology, SWE.
    Han, Yung Hee
    Korea Advanced Institute of Science and Technology (KAIST), South Korea.
    Franco, Leandro R.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Marchiori, Cleber F. N.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Genene, Zewdneh
    Chalmers University of Technology.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University.
    Lee, Jin-Woo
    Korea Advanced Institute of Science and Technology (KAIST), South Korea.
    Phan, Tan Ngoc-Lan
    Korea Advanced Institute of Science and Technology (KAIST), South Korea.
    Wu, Jingnan
    Chalmers University of Technology; Aalborg University, DEN.
    Yu, Donghong
    Aalborg University, DEN; Sino-Danish Center for Education and Research, DEN.
    Kim, Dong Jun
    Korea Advanced Institute of Science and Technology (KAIST), South Korea.
    Kim, Taek-Soo
    Korea Advanced Institute of Science and Technology (KAIST), South Korea.
    Hou, Lintao
    Jinan University, CHN.
    Kim, Bumjoon J.
    Korea Advanced Institute of Science and Technology (KAIST), South Korea.
    Wang, Ergang
    Chalmers University of Technology; Zhengzhou University, CHN.
    Effects of Flexible Conjugation-Break Spacers of Non-Conjugated Polymer Acceptors on Photovoltaic and Mechanical Properties of All-Polymer Solar Cells2022In: Nano-Micro Letters, ISSN 2150-5551, Vol. 14, no 1, article id 164Article in journal (Refereed)
    Abstract [en]

    Highlights: A series of non-conjugated acceptor polymers with flexible conjugation-break spacers (FCBSs) of different lengths were synthesized.The effect of FCBSs length on solubility of the acceptor polymers, and their photovoltaic and mechanical properties in all-polymer solar cells were explored.This work provides useful guidelines for the design of semiconducting polymers by introducing FCBS with proper length, which can giantly improved properties that are not possible to be achieved by the state-of-the-art fully conjugated polymers. Abstract: All-polymer solar cells (all-PSCs) possess attractive merits including superior thermal stability and mechanical flexibility for large-area roll-to-roll processing. Introducing flexible conjugation-break spacers (FCBSs) into backbones of polymer donor (PD) or polymer acceptor (PA) has been demonstrated as an efficient approach to enhance both the photovoltaic (PV) and mechanical properties of the all-PSCs. However, length dependency of FCBS on certain all-PSC related properties has not been systematically explored. In this regard, we report a series of new non-conjugated PAs by incorporating FCBS with various lengths (2, 4, and 8 carbon atoms in thioalkyl segments). Unlike common studies on so-called side-chain engineering, where longer side chains would lead to better solubility of those resulting polymers, in this work, we observe that the solubilities and the resulting photovoltaic/mechanical properties are optimized by a proper FCBS length (i.e., C2) in PA named PYTS-C2. Its all-PSC achieves a high efficiency of 11.37%, and excellent mechanical robustness with a crack onset strain of 12.39%, significantly superior to those of the other PAs. These results firstly demonstrate the effects of FCBS lengths on the PV performance and mechanical properties of the all-PSCs, providing an effective strategy to fine-tune the structures of PAs for highly efficient and mechanically robust PSCs.

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  • 13.
    Choi, Young Won
    et al.
    Royal Institute Technology, Sweden.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University.
    Lizarraga, Raquel
    Royal Institute Technology, Sweden.
    Amorphisation-induced electrochemical stability of solid-electrolytes in Li-metal batteries: The case of Li3ClO2022In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 521, article id 230916Article in journal (Refereed)
    Abstract [en]

    Energy storage technologies that can meet the unprecedented demands of a sustainable energy system based on intermittent energy sources require new battery materials. In recent years, new superionic conducting glasses have been discovered that have captured the attention of the community due to their potential use as solid electrolytes for all-solid-state Li-ion batteries. New research is needed to understand the correlations between the non-crystalline structure of glasses and their advanced properties. Here we investigate the structural properties, the electronic structure and the electrochemical stability against Li metal of the high ionic conducting Li3ClO glass. We use the stochastic quenching method based on first principles theory to model the amorphous structure of the glass. We characterise the structure by means of radial distribution functions, angle distributions functions, bond lengths and coordination numbers. Our calculations of the electronic structure of Li3ClO for both phases, crystalline and amorphous, demonstrate that both materials are good insulators. We assess the electrochemical stability of the electrolyte against Li metal electrode and in particular we analyse the role of amorphisation. Our results show that crystalline Li3ClO is not stable against Li metal electrode and that the glass can be made stable if less oxygen is supplied, for instance, by producing an substoichiometric glass.

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  • 14.
    Damas, Giane B.
    et al.
    Uppsala University; Linköping University.
    Costa, Luciano T.
    Fluminense Federal University, Brazil.
    Ahuja, Rajeev
    Uppsala University.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University.
    Understanding carbon dioxide capture on metal-organic frameworks from first-principles theory: The case of MIL-53(X), with X = Fe3+, Al3+, and Cu2+2021In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 155, no 2, article id 024701Article in journal (Refereed)
    Abstract [en]

    Metal-organic frameworks (MOFs) constitute a class of three-dimensional porous materials that have shown applicability for carbon dioxide capture at low pressures, which is particularly advantageous in dealing with the well-known environmental problem related to the carbon dioxide emissions into the atmosphere. In this work, the effect of changing the metallic center in the inorganic counterpart of MIL-53 (X), where X = Fe3+, Al3+, and Cu2+, has been assessed over the ability of the porous material to adsorb carbon dioxide by means of first-principles theory. In general, the non-spin polarized computational method has led to adsorption energies in fair agreement with the experimental outcomes, where the carbon dioxide stabilizes at the pore center through long-range interactions via oxygen atoms with the axial hydroxyl groups in the inorganic counterpart. However, spin-polarization effects in connection with the Hubbard corrections, on Fe 3d and Cu 3d states, were needed to properly describe the metal orbital occupancy in the open-shell systems (Fe- and Cu-based MOFs). This methodology gave rise to a coherent high-spin configuration, with five unpaired electrons, for Fe atoms leading to a better agreement with the experimental results. Within the GGA+U level of theory, the binding energy for the Cu-based MOF is found to be E-b = -35.85 kJ/mol, which is within the desirable values for gas capture applications. Moreover, it has been verified that the adsorption energetics is dominated by the gas-framework and internal weak interactions.

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  • 15.
    Damas, Giane B.
    et al.
    Uppsala University ;Linköping University.
    Ivashchenko, Dmytro A.
    University Lyon, FRA.
    Rivalta, Ivan
    University Lyon, FR;University Bologna, ITA.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University.
    Carbon dioxide reduction mechanism on Ru-based electrocatalysts [Ru(bpy)(2)(CO)(2)](2+): insights from first-principles theory2021In: Sustainable Energy & Fuels, E-ISSN 2398-4902, Vol. 5, no 23, p. 6066-6076Article in journal (Refereed)
    Abstract [en]

    Solar fuel production through the so-called artificial photosynthesis has attracted a great deal of attention to the development of a new world energy matrix that is renewable and environmentally friendly. This process is characterized by light absorption with enough photon energy to generate conduction electrons, which drive the carbon dioxide reduction to produce organic fuels. It is also common to couple Ru-complex electrocatalysts to form a more efficient and selective hybrid system for this application. In this work, we have undertaken a thorough investigation of the redox reaction mechanism of Ru-based electrocatalysts by means of density functional theory (DFT) methods under the experimental conditions that have been previously reported. More specifically, we have studied the electrochemistry and catalytic activity of the [Ru(bpy)(2)(CO)(2)](2+) coordination complex. Our theoretical assessment supports the following catalytic cycle: (i) [Ru(bpy)(2)(CO)(2)](2+) is transformed into [Ru(bpy)(2)(CO)](0) upon two-electron reduction and CO release; (ii) [Ru(bpy)(2)(CO)](0) is protonated to form the [Ru(bpy)(2)(CO)H](+) hydride complex; (iii) CO2 is activated by the hydride complex through an electrophilic addition to form the [Ru(bpy)(2)(CO)(OCHO)](+) intermediate; (iv) the resulting formic acid ligand is released in solution; and, finally, (v) the CO ligand is reattached to the complex to recover the initial [Ru(bpy)(2)(CO)(2)](2+) catalyst.

  • 16.
    Damas, Giane B.
    et al.
    Uppsala universitet, Materialteori.
    Miranda, Caetano
    Institute of Physics, University of São Paulo, São Paulo 05508-090, Brazil.
    Sgarbi, Ricardo
    Institute of Chemistry, University of São Paulo, São Carlos 13560-970, Brazil.
    Portela, James
    Institute of Chemistry, University of São Paulo, São Carlos 13560-970, Brazil.
    Camilo, Mariana R.
    Institute of Chemistry, University of São Paulo, São Carlos 13560-970, Brazil.
    Araujo, Carlos Moyses
    Uppsala universitet.
    On the Mechanism of Carbon Dioxide Reduction on Sn-Based Electrodes: Insights into the Role of Oxide Surfaces2019In: Catalysts, E-ISSN 2073-4344, Vol. 9, no 8, article id 636Article in journal (Refereed)
    Abstract [en]

    The electrochemical reduction of carbon dioxide into carbon monoxide, hydrocarbons and formic acid has offered an interesting alternative for a sustainable energy scenario. In this context, Sn-based electrodes have attracted a great deal of attention because they present low price and toxicity, as well as high faradaic efficiency (FE) for formic acid (or formate) production at relatively low overpotentials. In this work, we investigate the role of tin oxide surfaces on Sn-based electrodes for carbon dioxide reduction into formate by means of experimental and theoretical methods. Cyclic voltammetry measurements of Sn-based electrodes, with different initial degree of oxidation, result in similar onset potentials for the CO2 reduction to formate, ca. −0.8 to −0.9 V vs. reversible hydrogen electrode (RHE), with faradaic efficiencies of about 90–92% at −1.25 V (vs. RHE). These results indicate that under in-situ conditions, the electrode surfaces might converge to very similar structures, with partially reduced or metastable Sn oxides, which serve as active sites for the CO2 reduction. The high faradaic efficiencies of the Sn electrodes brought by the etching/air exposition procedure is ascribed to the formation of a Sn oxide layer with optimized thickness, which is persistent under in situ conditions. Such oxide layer enables the CO2 “activation”, also favoring the electron transfer during the CO2 reduction reaction due to its better electric conductivity. In order to elucidate the reaction mechanism, we have performed density functional theory calculations on different slab models starting from the bulk SnO and Sn6O4(OH)4 compounds with focus on the formation of -OH groups at the water-oxide interface. We have found that the insertion of CO2 into the Sn-OH bond is thermodynamically favorable, leading to the stabilization of the tin-carbonate species, which is subsequently reduced to produce formic acid through a proton-coupled electron transfer process. The calculated potential for CO2 reduction (E = −1.09 V vs. RHE) displays good agreement with the experimental findings and, therefore, support the CO2 insertion onto Sn-oxide as a plausible mechanism for the CO2 reduction in the potential domain where metastable oxides are still present on the Sn surface. These results not only rationalize a number of literature divergent reports but also provide a guideline for the design of efficient CO2 reduction electrocatalysts.

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  • 17.
    Damas, Giane
    et al.
    Uppsala universitet.
    Marchiori, Cleber
    Uppsala universitet.
    Araujo, Carlos Moyses
    Uppsala universitet.
    Tailoring the Electron-Rich Moiety in Benzothiadiazole-Based Polymers for an Efficient Photocatalytic Hydrogen Evolution Reaction2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 42, p. 25531-25542Article in journal (Refereed)
    Abstract [en]

    Polymeric materials containing an extended π-conjugated backbone have shown a wide range of applicability including photocatalytic activity for the hydrogen evolution reaction (HER). The latter requires highly efficient materials with optimal light absorption and thermodynamic driving force for charge transfer processes, properties that are tailored by linking chemical units with distinct electron affinity to form a donor−acceptor architecture. Here, this concept is explored by means of ab initio theory in benzothiadiazole-based polymers with varying electron-rich moieties, viz., fluorene (PFO), cyclopentadithiophene (CPT), methoxybenzodithiophene (O-BzT), thiophenebenzodithiophene (T-BzT), and thiophene (T, VT)and thienethiophene (TT, VTT)-based units. All materials exhibit a red-shifted absorption spectrum with respect to the reference polymer (PFO-DT-BT) while keeping the catalytic power for hydrogen production almost unchanged. In particular, a displacement ofΔλ = 167 nm in the first absorption maximum has been achieved upon combination of chemical units with high donating character in CPT-VTT-BT. Furthermore, the exciton binding energies (Eb) have been systematically investigated to unveil the effects of geometry relaxation, environment polarity, and finite temperature contributions to the free energy. For instance, we show a significant change in Eb when going from the gas phase (Eb = 1.43−1.85 eV) to the solvent environment (Eb = 0.29−0.54 eV in 1-bromooctane with ε = 5.02). Furthermore, we have found a linear correlation between the lowering of exciton binding energies and the increasing of the ratio between donor and acceptor contributions to the HOMO orbital. This is a consequence of increased donating ability and enhanced spatial separation of electron−hole pairs, which weakens their interaction. Finally, our findings reveal that the donor unit plays a crucial role in key properties that govern the photocatalytic activity of donor−acceptor polymers contributing to the development of a practical guideline to design more efficient photocatalysts for the HER. This goes through a proper combination of electron-rich moieties to tune the optical gap, favor thermodynamic driving force for charge transfer, and lower exciton binding energies.

  • 18.
    Damas, Giane
    et al.
    Uppsala universitet.
    Marchiori, Cleber F. N.
    Uppsala universitet.
    Araujo, Carlos Moyses
    Uppsala universitet.
    On the Design of Donor Acceptor Conjugated Polymers for Photocatalytic Hydrogen Evolution Reaction: First-Principles Theory-Based Assessment2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 47, p. 26876-26888Article in journal (Refereed)
    Abstract [en]

    A set of fluorene-based polymers with a donor acceptor architecture has been investigated as a potential candidate for photocatalytic hydrogen evolution reaction. A design protocol has been employed based on first -principles theory and focusing on the following properties: (i) broad absorption spectrum to promote a higher number of photogenerated electron hole pairs, (ii) suitable redox potentials, and (iii) appropriate reaction thermodynamics using the hydrogen -binding energy as a descriptor. We have found that the polymers containing a fused -ring acceptor formed by benzo(triazole-thiadiazole) or benzo(triazole-selenodiazole) units display a suitable combination of such properties and stand out as potential candidates. In particular, PFO-DSeBTrT (poly (9,9'-dioctylfluorene)-2,7-diyl-alt-(4,7-bis(thien-2y1)-2-dodecyl-benzo-(1,2c:4,5c')-1,2,3-triazole-2,1,3-selenodiazole)) has an absorption maximum at around 950 nm for the highest occupied molecular orbital lowest unoccupied molecular orbital transition, covering a wider range of solar emission spectrum, and a reduction catalytic power of 0.78 eV. It also displays a calculated hydrogen -binding free energy of Delta G(H) = 0.02 eV, which is lower in absolute value than Furthermore, the results and trends analysis provide guidance for the rational design of novel photo-electrocatalysts. that of Pt (Delta G(H) approximate to -0.10 eV).

  • 19.
    Damas, Giane
    et al.
    Uppsala universitet.
    von Kieseritzky, Fredrik
    Arubedo AB.
    Hellberg, Jonas
    Arubedo AB.
    Marchiori, Cleber
    Uppsala universitet.
    Araujo, Carlos Moyses
    Uppsala universitet.
    Symmetric Small-Molecules With Acceptor-Donor-Acceptor Architecture for Efficient Visible-Light Driven Hydrogen Production: Optical and Thermodynamic Aspects2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 51, p. 30799-30808Article in journal (Refereed)
    Abstract [en]

    Small-molecules (SM) have attracted a great deal of attention in the field of solar energy conversion due to their unique propertiescompared to polymers, such as well-defined molecular weight and lack of regio-isomeric impurities. Furthermore, these materials can be synthesized in a variety of configurational architectures, representing an opportunity for tailoring chemical and optical properties that could lead to a better photocatalytic efficiency for hydrogen generation. Here, we evaluate by means of density functional theory (DFT) and time-dependent DFT methods a set of small-molecules with A-D-A architecture (A-acceptor; D- donor) based on well-known building blocks like thiophene (T), cyclopentadithiophene (CPT) and benzothiadiazole (BT) as potential candidates for photocatalytic hydrogen evolution reaction (HER). We also propose i) the replacement of the thiophene unit by 3,4-ethylenedioxythiophene (EDOT) to form with CPT unit an extended donor core ii) an additional acceptor unit, the 1,3,4-thiadiazole (Tz), in the extremities and iii) insertion of the difluoromethoxy (DFM) as substituent in the BT unit. Our outcomes reveal that these materials have a broad absorption spectrum with λ= 318-719 nm, being the most intense absorption peak originated from an electronic transition with charge-transfer nature, as the spatial distribution of LUMO is concentrated on the acceptor units for all materials. Moreover, these small-molecules not only present catalytic power or thermodynamic driving force to carry out the chemical reactions involved in the process of hydrogen production, but can be coupled in cooperative photocatalytic systems to promote intramolecular charge transfer that is expected to boost the overall photocatalytic efficiency of these materials.

  • 20.
    Ebadi, Mahsa
    et al.
    Uppsala universitet.
    Brandell, Daniel
    Uppsala universitet.
    Araujo, Carlos Moyses
    Uppsala universitet.
    Electrolyte decomposition on Li-metal surfaces from first-principles theory2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, no 20, p. 1-10, article id 204701Article in journal (Refereed)
    Abstract [en]

    Animportant feature in Li batteries is the formation of a solid electrolyte interphase (SEI) on the surface of the anode. This film can have a profound effect on the stability and the performance of the device. In this work, we have employed density functional theory combined with implicit solvation models to study the inner layer of SEI formation from the reduction of common organic carbonate electrolyte solvents (ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate) on a Li metal anode surface. Their stability and electronic structure on the Li surface have been investigated. It is found that the CO producing route is energetically more favorable for ethylene and propylene carbonate decomposition. For the two linear solvents, dimethyl and diethyl carbonates, no significant differences are observed between the two considered reduction pathways. Bader charge analyses indicate that 2 e(-) reductions take place in the decomposition of all studied solvents. The density of states calculations demonstrate correlations between the degrees of hybridization between the oxygen of adsorbed solvents and the upper Li atoms on the surface with the trend of the solvent adsorption energies.

  • 21.
    Ebadi, Mahsa
    et al.
    Uppsala universitet.
    Costa, Luciano T.
    Fluminense Federal University, BRA.
    Araujo, C. Moyses
    Uppsala universitet, Materialteori.
    Brandell, Daniel
    Uppsala universitet.
    Modelling the Polymer Electrolyte/Li-Metal Interface by Molecular Dynamics simulations2017In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 234, p. 43-51Article in journal (Refereed)
    Abstract [en]

    Solid polymer electrolytes are considered promising candidates for application in Li-metal batteries due to their comparatively high mechanical strength, which can prevent dendrite formation. In this study, we have performed Molecular Dynamics simulations to investigate structural and dynamical properties of a common polymer electrolyte, poly(ethylene oxide) (PEO) doped with LiTFSI salt in the presence of a Li metal surface. Both a physical (solid wall) and a chemical (slab) model of the Li (100) surface have been applied, and the results are also compared with a model of the bulk electrolyte. The average coordination numbers for oxygen atoms around the Li ions are ca. 6 for all investigated systems. However, the calculated Radial Distribution Functions (RDFs) for Li+-(OPEO) and Li+-(OTFSI) show sharper peaks for the Li slab model, indicating a more well-defined coordination sphere for Li+ in this system. This is clearly a surface effect, since the RDF for Li+ in the interface region exhibits sharper peaks than in the bulk region of the same system. The simulations also display a high accumulation of TFSI anions and Li+ cations close to interface regions. This also leads to slower dynamics of the ionic transport in the systems, which have a Li-metal surface present, as seen from the calculated mean-square-displacement functions. The accumulation of ions close to the surface is thus likely to induce a polarization close to the electrode.

  • 22.
    Ebadi, Mahsa
    et al.
    Uppsala universitet.
    Eriksson, Therese
    Uppsala universitet.
    Mandal, Prithwiraj
    Uppsala universitet.
    Costa, Luciano T.
    Universidade Federal Fluminense, BRA.
    Araujo, Carlos Moyses
    Uppsala universitet.
    Mindemark, Jonas
    Uppsala universitet.
    Brandell, Daniel
    Uppsala universitet.
    Restricted Ion Transport by Plasticizing Side Chains in Polycarbonate-Based Solid Electrolytes2020In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 53, no 3, p. 764-774Article in journal (Refereed)
    Abstract [en]

    Increasing the ionic conductivity has for decades been an overriding goal in the development of solid polymer electrolytes. According to fundamental theories on ion transport mechanisms in polymers, the ionic conductivity is strongly correlated to free volume and segmental mobility of the polymer for the conventional transport processes. Therefore, incorporating plasticizing side chains onto the main chain of the polymer host often appears as a clear-cut strategy to improve the ionic conductivity of the system through lowering of the glass transition temperature (T-g) This intended correlation between Tg and ionic conductivity is, however, not consistently observed in practice. The aim of this study is therefore to elucidate this interplay between segmental mobility and polymer structure in polymer electrolyte systems comprising plasticizing side chains. To this end, we utilize the synthetic versatility of the ion-conductive poly(trimethylene carbonate) (PTMC) platform. Two types of host polymers with side chains added to a PTMC backbone are employed, and the resulting electrolytes are investigated together with the side chain-free analogue both by experiment and with molecular dynamics (MD) simulations. The results show that while added side chains do indeed lead to a lower Tg, the total ionic conductivity is highest in the host matrix without side chains. It was seen in the MD simulations that while side chains promote ionic mobility associated with the polymer chain, the more efficient interchain hopping transport mechanism occurs with a higher probability in the system without side chains. This is connected to a significantly higher solvation site diversity for the Li+ ions in the side-chain-free system, providing better conduction paths. These results strongly indicate that the side chains in fact restrict the mobility of the Li+ ions in the polymer hosts.

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  • 23.
    Ebadi, Mahsa
    et al.
    Uppsala universitet.
    Lacey, Matthew
    Uppsala universitet.
    Brandell, Daniel
    Uppsala universitet.
    Araujo, Carlos Moyses
    Uppsala universitet.
    Density Functional Theory Modeling the Interfacial Chemistry of the LiNO3 Additive for Lithium-Sulfur Batteries by Means of Simulated Photoelectron Spectroscopy2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 42, p. 23324-23332Article in journal (Refereed)
    Abstract [en]

    Lithium-sulfur (Li-S) batteries are considered candidates for next-generation energy storage systems due to their high theoretical specific energy. There exist, however, some shortcomings of these batteries, not least the solubility of intermediate polysulfides into the electrolyte generating a so-called "redox shuttle", which gives rise to self-discharge. LiNO3 is therefore frequently used as an electrolyte additive to help suppress this mechanism, but the exact nature of the LiNO3 functionality is still unclear. Here, density functional theory calculations are used to investigate the electronic structure of LiNO3 and a number of likely species (N-2, N2O, LiNO2, Li3N, and Li2N2O2) resulting from the reduction of this additive on the surface of Li metal anode. The N is X-ray photoelectron spectroscopy core level binding energies of these molecules on the surface are calculated in order to compare the results with experimentally reported values. The core level shifts (CLS) of the binding energies are studied to identify possible factors responsible for the position of the peaks. Moreover, solid phases of (cubic) c-Li3N and (hexagonal) alpha-Li3N on the surface of Li metal are considered. The N is binding energies for the bulk phases of Li3N and at the Li3N/Li interfaces display higher values as compared to the Li3N molecule, indicating a clear correlation between the coordination number and the CLS of the solid phases of Li3N.

  • 24.
    Ebadi, Mahsa
    et al.
    Uppsala universitet.
    Marchiori, Cleber
    Uppsala universitet.
    Mindemark, Jonas
    Uppsala universitet.
    Brandell, Daniel
    Uppsala universitet.
    Araujo, Carlos Moyses
    Uppsala universitet, Materialteori.
    Assessing structure and stability of polymer/lithium-metal interfaces from first-principles calculations2019In: Journal of Materials Chemistry A, ISSN 2050-7488, E-ISSN 2050-7496, Vol. 7, no 14, p. 8394-8404Article in journal (Refereed)
    Abstract [en]

    Solid polymer electrolytes (SPEs) are promising candidates for Li metal battery applications, but the interface between these two categories of materials has so far been studied only to a limited degree. A better understanding of interfacial phenomena, primarily polymer degradation, is essential for improving battery performance. The aim of this study is to get insights into atomistic surface interaction and the early stages of solid electrolyte interphase formation between ionically conductive SPE host polymers and the Li metal electrode. A range of SPE candidates are studied, representative of major host material classes: polyethers, polyalcohols, polyesters, polycarbonates, polyamines and polynitriles. Density functional theory (DFT) calculations are carried out to study the stability and the electronic structure of such polymer/Li interfaces. The adsorption energies indicated a stronger adhesion to Li metal of polymers with ester/carbonate and nitrile functional groups. Together with a higher charge redistribution, a higher reactivity of these polymers is predicted as compared to the other electrolyte hosts. Products such as alkoxides and CO are obtained from the degradation of ester- and carbonate-based polymers by AIMD simulations, in agreement with experimental studies. Analogous to low-molecular-weight organic carbonates, decomposition pathways through C-carbonyl-O-ethereal and C-ethereal-O-ethereal bond cleavage can be assumed, with carbonate-containing fragments being thermodynamically favorable.

  • 25.
    Ebadi, Mahsa
    et al.
    Uppsala universitet.
    Nasser, Antoine
    Uppsala universitet.
    Carboni, Marco
    Uppsala universitet.
    Younesi, Reza
    Uppsala universitet.
    Marchiori, Cleber
    Uppsala universitet.
    Brandell, Daniel
    Uppsala universitet.
    Araujo, Carlos Moyses
    Uppsala universitet, Materialteori.
    Insights into the Li-Metal/Organic Carbonate Interfacial Chemistry by Combined First-Principles Theory and X-ray Photoelectron Spectroscopy2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 1, p. 347-355Article in journal (Refereed)
    Abstract [en]

    X-ray photoelectron spectroscopy (XPS) is a widely used technique to study surfaces and interfaces. In complex chemical systems, however, interpretation of the XPS results and peak assignments is not straightforward. This is not least true for Li-batteries, where XPS yet remains a standard technique for interface characterization. In this work, a combined density functional theory (DFT) and experimental XPS study is carried out to obtain the C 1s and O 1s core-level binding energies of organic carbonate molecules on the surface of Li metal. Decomposition of organic carbonates is frequently encountered in electrochemical cells employing this electrode, contributing to the build up of a complex solid electrolyte interphase (SEI). The goal in this current study is to identify the XPS fingerprints of the formed compounds, degradation pathways, and thereby the early formation stages of the SEI. The contribution of partial atomic charges on the core-ionized atoms and the electrostatic potential due to the surrounding atoms on the core-level binding energies, which is decisive for interpretation of the XPS spectra, are addressed based on the DFT calculations. The results display strong correlations between these two terms and the binding energies, whereas electrostatic potential is found to be the dominating factor. The organic carbonate molecules, decomposed at the surface of the Li metal, are considered based on two different decomposition pathways. The trends of calculated binding energies for products from ethereal carbon-ethereal oxygen bond cleavage in the organic carbonates are better supported when compared to the experimental XPS results.

  • 26.
    Espinosa-Garcia, W. F.
    et al.
    Universidad de San Buenaventura-Medellín, Facultad de Ingenierías, Grupo de Investigación en Modelamiento y Simulación Computacional; Universidad de Antioquia UdeA, Instituto de Física.
    Osorio-Guillen, J. M.
    Universidad de Antioquia UdeA, Instituto de Física.
    Araujo, Carlos Moyses
    Uppsala universitet, Materialteori.
    Dimension-dependent band alignment and excitonic effects in graphitic carbon nitride: a many-body perturbation and time-dependent density functional theory study2017In: RSC Advances, E-ISSN 2046-2069, Vol. 7, no 71, p. 44997-45002Article in journal (Refereed)
    Abstract [en]

    First-principles many-body theory and time-dependent density functional theory were used to study the dimension effects on the band alignment and optical properties of s-triazine and graphitic C3N4. The inclusion of quasiparticle corrections is very important to describe the quantum confinement and the enhancement of the electron-electron (e-e) interaction. The calculated quasiparticle gaps range from 4.0 eV (monolayer) to 3.21 eV (tetralayer). The position of the valence band maxima is found to be almost constant, whereas the conduction band minima show a strong quantum confinement effect with a variation of similar to 0.7 eV respective to the bulk structure. The calculated frequency-dependent imaginary part of the dielectric function using the Bethe-Salpeter equation shows prominent excitonic effects, where there is a strong redistribution of the spectral weight to lower photon energies in the ultraviolet frequencies where the major part of the absorption occurs. On the other hand, a less intense excitonic absorption in the visible region is due to light polarization perpendicular to the surface plane. In contrast, time-dependent density functional theory also shows a redistribution of the spectral weight in the ultraviolet but it fails to describe the excitonic features in the visible region.

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  • 27.
    Espinosa-Garcia, W. F.
    et al.
    La Universidad de San Buenaventura, COL ;The University of Antioquia, COL.
    Perez-Walton, S.
    ITM, Fac Ingn, COL.
    Osorio-Guillen, J. M.
    The University of Antioquia, COL.
    Araujo, Carlos Moyses
    Uppsala universitet, Materialteori.
    The electronic and optical properties of the sulvanite compounds: a many-body perturbation and time-dependent density functional theory study2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 3, article id 035502Article in journal (Refereed)
    Abstract [en]

    We have studied, by means of first-principles calculations, the electronic and optical properties of the sulvanite family: Cu3MX4 (M = V, Nb, Ta and X = S, Se), which, due to its broad range of gaps and chemical stability, have emerged as promising materials for technological applications such as photovoltaics and transparent conductivity. To address the reliability of those properties we have used semi-local and hybrid functionals (PBEsol, HSE06), many-body perturbation theory (G(0)W(0) approximation and Bethe-Salpeter equation), and time-dependent density functional theory (revised bootstrap kernel) to calculate the quasi-particle dispersion relation, band gaps, the imaginary part of the macroscopic dielectric function and the absorption coefficient. The calculated valence band maximum and the conduction band minimum are located at the R and X-points, respectively. The calculated gaps using PBEsol are between 0.81 and 1.88 eV, with HSE06 into 1.73 and 2.94 eV, whereas the G(0)W(0) values fall into the 1.91-3.19 eV range. The calculated dielectric functions and absorption coefficients show that all these compounds present continuous excitonic features when the Bethe-Salpeter equation is used. Contrarily, the revised bootstrap kernel is incapable of describing the excitonic spectra. The calculated optical spectra show that Cu3VS4 and Cu3MSe4 have good absorption in the visible, whereas Cu3NbS4 and Cu3TaS4 have it on the near ultraviolet.

  • 28.
    Franco, Leandro R.
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Universidade de São Paulo, BRA.
    Figueiredo Toledo, Kalil Cristhian
    Universidade de São Paulo, BRA.
    Matias, Tiago Araujo
    Universidade de São Paulo, BRA.
    Benavides, Paola Andrea
    Universidade de São Paulo, BRA.
    Cezar, Henrique Musseli
    Universidade de São Paulo, BRA.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University.
    Coutinho, Kaline
    Universidade de São Paulo, BRA.
    Araki, Koiti
    Universidade de São Paulo, BRA.
    Unraveling the acid-base characterization and solvent effects on the structural and electronic properties of a bis-bidentate bridging ligand2022In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 24, no 17, p. 10222-10240Article in journal (Refereed)
    Abstract [en]

    Understanding the interactions and the solvent effects on the distribution of several species in equilibrium and how it can influence the 1H-NMR properties, spectroscopy (UV-vis absorption), and the acid–base equilibria can be especially challenging. This is the case of a bis-bidentate bridging ligand bis(2-pyridyl)-benzo-bis(imidazole), where the two pyridyl and four imidazolyl nitrogen atoms can be protonated in different ways, depending on the solvent, generating many isomeric/tautomeric species. Herein, we report a combined theoretical–experimental approach based on a sequential quantum mechanics/molecular mechanics procedure that was successfully applied to describe in detail the acid–base characterization and its effects on the electronic properties of such a molecule in solution. The calculated free-energies allowed the identification of the main species present in solution as a function of the solvent polarity, and its effects on the magnetic shielding of protons (1H-NMR chemical shifts), the UV-vis absorption spectra, and the acid–base equilibrium constants (pKas) in aqueous solution. Three acid–base equilibrium constants were experimentally/theoretically determined (pKa1 = 1.3/1.2, pKa2 = 2.1/2.2 and pKa5 = 10.1/11.3) involving mono-deprotonated and mono-protonated cis and trans species. Interestingly, other processes with pKa3 = 3.7 and pKa4 = 6.0 were also experimentally determined and assigned to the protonation and deprotonation of dimeric species. The dimerization of the most stable neutral species was investigated by Monte Carlo simulations and its electronic effects were considered for the elucidation of the UV-vis absorption bands, revealing transitions mainly with the charge-transfer characteristic and involving both the monomeric species and the dimeric species. The good matching of the theoretical and experimental results provides an atomistic insight into the solvent effects on the electronic properties of this bis-bidentate bridging ligand.

  • 29.
    Franco, Leandro R.
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Marchiori, Cleber
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University, Sweden.
    Unveiling the impact of exchange-correlation functionals on the description of key electronic properties of non-fullerene acceptors in organic photovoltaics2023In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 159, no 20, article id 204110Article in journal (Refereed)
    Abstract [en]

    Non-fullerene electron acceptors have emerged as promising alternatives to traditional electron-acceptors in the active layers of organic photovoltaics. This is due to their tunable energy levels, optical response in the visible light spectrum, high electron mobility, and photochemical stability. In this study, the electronic properties of two representative non-fullerene acceptors, ITIC and Y5, have been calculated within the framework of density functional theory using a range of hybrid and non-hybrid density functionals. Screened range-separated hybrid (SRSH) approaches were also tested. The results are analyzed in light of the previously reported experimental outcomes. Specifically, we have calculated the oxidation and reduction potentials, fundamental and optical gaps, the highest occupied molecular orbital and lowest unoccupied molecular orbital energies, and exciton binding energies. Additionally, we have investigated the effects of the medium dielectric constant on these properties employing a universal implicit solvent model. It was found that hybrid functionals generally perform poorly in predicting oxidation potentials, while non-hybrid functionals tend to overestimate reduction potentials. The inclusion of a large Hartree-Fock contribution to the global or long range was identified as the source of inaccuracy for many hybrid functionals in predicting both redox potentials and the fundamental and optical gaps. Corroborating with the available literature, ∼50% of all tested functionals predicted very small exciton binding energies, within the range of ±0.1 eV, that become even smaller by increasing the dielectric constant of the material. Finally, the OHSE2PBE and tHCTHhyb functionals and the optimal tuning SRSH approach emerged as the best-performing methods, with good accuracy in the description of the electronic properties of interest. 

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  • 30.
    Franco, Leandro R.
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). University of São Paulo, Brazil.
    Toledo, Kalil Cristhian Figueiredo
    University of São Paulo, Brazil.
    Matias, Tiago Araujo
    University of São Paulo, Brazil.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University, Sweden.
    Araki, Koiti
    University of São Paulo, Brazil.
    Coutinho, Kaline
    University of São Paulo, Brazil.
    Theoretical investigation of solvent and oxidation/deprotonation effects on the electronic structure of a mononuclear Ru-aqua-polypyridine complex in aqueous solution2023In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 25, no 36, p. 24475-24494Article in journal (Refereed)
    Abstract [en]

    Mononuclear polypyridine ruthenium (Ru) complexes can catalyze various reactions, including water splitting, and can also serve as photosensitizers in solar cells. Despite recent progress in their synthesis, accurately modeling their physicochemical properties, particularly in solution, remains challenging. Herein, we conduct a theoretical investigation of the structural and electronic properties of a mononuclear Ru-aqua polypyridine complex in aqueous solution, considering five of its possible oxidation/protonation states species: [RuII(H2O)(py)(bpy)2]2+, [RuII(OH)(py)(bpy)2]+, [RuIII(H2O)(py)(bpy)2]3+, [RuIII(OH)(py)(bpy)2]2+ and [RuIV(O)(py)(bpy)2]2+, where py = pyridine and bpy = 2,2 & PRIME;-bipyridine. At first, we investigate the impact of proton-coupled and non-coupled electron transfer reactions on the geometry and electronic structure of the complexes in vacuum and in solution, using an implicit solvent model. Then, using a sequential multiscale approach that combines quantum mechanics and molecular mechanics (S-QM/MM), we examine the explicit solvent effects on the electronic excitations of the complexes, and compare them with the experimental results. The complexes were synthesized, and their absorption spectra measured in aqueous solution. To accurately describe the QM interactions between the metal center and the aqueous ligand in the MM simulations, we developed new force field parameters for the Ru atom. We analyze the solvent structure around the complexes and account for its explicit influence on the polarization and electronic excitations of the complexes. Notably, accounting for the explicit solvent polarization effects of the first solvation shells is essential to correctly describe the energy of the electronic transitions, and the explicit treatment of the hydrogen bonds at the QM level in the excitation calculations improves the accuracy of the description of the metal-to-ligand charge-transfer bands. Transition density matrix analysis is used to characterize all electronic transitions in the visible and ultraviolet ranges according to their charge-transfer (CT) character. This study elucidates the electronic structure of those ruthenium polypyridyl complexes in aqueous solution and underscores the importance of precisely describing solvent effects, which can be achieved employing the S-QM/MM method. Ru-aqua complex in water, showcasing Ru atom, coordinated water, and hydrogen bonds on left; UV-Vis spectrum and comparison to experiment on right. QM/MM approach emphasized.

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  • 31.
    González-Moya, Johan R
    et al.
    Universida de Federal de Pernambuco, BRA; Centro de Tecnologias Estratégicas do Nordeste, BRA.
    Garcia-Basabe, Yunier
    Universida de Federal de Rio de Janeiro, BRA; Universida de Federal da Integração Latino-Americana, BRA.
    Rocco, Maria Luiza M
    Universida de Federal de Rio de Janeiro, BRA.
    Pereira, Marcelo B
    Universida de Federal do Rio Grande do Sul, BRA.
    Princival, Jefferson L
    Universida de Federal de Pernambuco, BRA.
    Almeida, Luciano C
    Universida de Federal de Pernambuco, BRA.
    Araujo, C Moyses
    Uppsala University.
    David, Denis G F
    Universidade Federal da Bahia, BRA.
    da Silva, Antonio Ferreira
    Universidade Federal da Bahia, BRA.
    Machado,, Giovanna
    Universidade Federal de Pernambuco, BRA; Centro de Tecnologias Estratégicas do Nordeste, BRA.
    Effects of the large distribution of CdS quantum dot sizes on the charge transfer interactions into TiO2 nanotubes for photocatalytic hydrogen generation2016In: Nanotechnology, ISSN 0957-4484, Vol. 27, no 28, article id 285401Article in journal (Refereed)
    Abstract [en]

    Hydrogen fuels generated by water splitting using a photocatalyst and solar irradiation are currently gaining the strength to diversify the world energy matrix in a green way. CdS quantum dots have revealed a hydrogen generation improvement when added to TiO2 materials under visible-light irradiation. In the present paper, we investigated the performance of TiO2 nanotubes coupled with CdS quantum dots, by a molecular bifunctional linker, on photocatalytic hydrogen generation. TiO2 nanotubes were obtained by anodization of Ti foil, followed by annealing to crystallize the nanotubes into the anatase phase. Afterwards, the samples were sensitized with CdS quantum dots via an in situ hydrothermal route using 3-mercaptopropionic acid as the capping agent. This sensitization technique permits high loading and uniform distribution of CdS quantum dots onto TiO2 nanotubes. The XPS depth profile showed that CdS concentration remains almost unchanged (homogeneous), while the concentration relative to the sulfate anion decreases by more than 80% with respect to the initial value after ~100 nm in depth. The presence of sulfate anions is due to the oxidation of sulfide and occurs in greater proportion in the material surface. This protection for air oxidation inside the nanotubular matrix seemingly protected the CdS for photocorrosion in sacrificial solution leading to good stability properties proved by long duration, stable photocurrent measurements. The effect of the size and the distribution of sizes of CdS quantum dots attached to TiO2 nanotubes on the photocatalytic hydrogen generation were investigated. The experimental results showed three different behaviors when the reaction time of CdS synthesis was increased in the sensitized samples, i.e. similar, deactivation and activation effects on the hydrogen production with regard to TiO2 nanotubes. The deactivation effect was related to two populations of sizes of CdS, where the population with a shorter band gap acts as a trap for the electrons photogenerated by the population with a larger band gap. Electron transfer from CdS quantum dots to TiO2 semiconductor nanotubes was proven by the results of UPS measurements combined with optical band gap measurements. This property facilitates an improvement of the visible-light hydrogen evolution rate from zero, for TiO2 nanotubes, to approximately 0.3 μmol cm–2 h–1 for TiO2 nanotubes sensitized with CdS quantum dots.

  • 32. Guimaraes, Robson R
    et al.
    Gon\c calves, Josue M
    Björneholm, Olle
    Araujo, C Moyses
    de Brito, Arnaldo Naves
    Araki, Koiti
    Single-Atom Electrocatalysts for Water Splitting2020In: Methods for Electrocatalysis / [ed] Inamuddin, Satyanarayana, Boddula, Asiri, Abdullah M., Cham: Springer, 2020, p. 67-111Chapter in book (Other academic)
  • 33.
    Jalan, Ishita
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Marchiori, Cleber
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Genene, Zewdneh
    Chalmers University of Technology, Sweden.
    Johansson, André
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Wang, Ergang
    Chalmers University of Technology, Sweden.
    van Stam, Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Donor-acceptor polymer complex formation in solution confirmed by spectroscopy and atomic-scale modelling2023In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 11, no 27, p. 9316-9326Article in journal (Refereed)
    Abstract [en]

    In all-polymer solar cells, high performance is attributed to the fine-grained morphology of the film in the active layer. However, the mechanism by which this fine-grained morphology is achieved remains unknown. Polymeric non-fullerene acceptors have the potential to restrict the self-aggregation, typical of non-fullerene small molecule acceptors. Here we employed a blend of the polymeric acceptor PF5-Y5 and the donor polymer PBDB-T to investigate the balance between molecular interactions in solution. Temperature-dependent absorption spectra show evidence of temperature-induced disaggregation of both donor and acceptor polymers, where the donor polymer disaggregation depends on the solvent polarity. Concentration-dependent fluorescence spectra of blend solutions display blue-shifted acceptor emission upon dilution, similar to that observed in acceptor solutions, and a decreased tendency for charge transfer from donor to acceptor upon dilution. Excitation spectra of dilute blend solutions contain an increased contribution to the long-wavelength acceptor emission, as compared to pure acceptor solutions, from a chromophore that absorbs in a region where the donor does not absorb. These observations can be explained by donor-acceptor complexation in dilute blend solutions, that is stabilized in more polar solvents. Moreover, the near IR-region of the absorption spectrum could be matched with the calculated electronic excitations of donor-acceptor complexes of PBDB-T and PF5-Y5 oligomers. The results corroborate that the interaction between segments of the donor and acceptor polymer chains favours the formation of donor-acceptor charge transfer complexes, stabilized by hybridization of the molecular orbitals, which reduces the electronic energy. The proposed donor-acceptor complex formation competes with the donor and acceptor self-aggregation and is influenced by the solvent environment. These pre-formed donor-acceptor complexes in low-concentration solutions can be expected to have important consequences on the film morphology of all-polymer blends. The results from this joint experimental-theoretical spectroscopy study provide insights that can guide the design of compatible donor and acceptor polymers for future high-performance organic solar cells.

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  • 34.
    Jin, Wentao
    et al.
    China, CHN.
    Chen, Guangde
    China, CHN.
    Duan, Xiangyang
    China, CHN.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University.
    Jia, Xubo
    China, CHN.
    Yin, Yuan
    China, CHN.
    Wu, Yelong
    China, CHN.
    Absolute surface energies of wurtzite (10 1 over bar 1) surfaces and the instability of the cation-adsorbed surfaces of II-VI semiconductors2021In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 119, no 20, p. 1-6, article id 201603Article in journal (Refereed)
    Abstract [en]

    We have investigated the wurtzite (10 1 over bar 1) planes of five semiconductors, AlN, GaN, GaAs, ZnO, and ZnS. The absolute surface energies are obtained by using a series of wedge nanowire structures. A cation-adsorbed surface reconstruction, (1 x 1)X (X is the electropositive element of the semiconductor) adlayer, is found to have dramatically low energy under the cation-rich condition for AlN and GaN. A p electron draining mechanism is proposed to explain these results. We also developed a framework to analyze the stabilization mechanism of the unneutral surfaces. It suggests that the cation-adsorbed surfaces of II-VI semiconductors should be more unstable than the anion-adsorbed surfaces.

  • 35.
    Khan, Ziyauddin
    et al.
    Linköping University, Sweden.
    Martinelli, Anna
    Chalmers University of Technology, Sweden.
    Franco, Leandro R.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Kumar, Divyaratan
    Linköping University, Sweden.
    Idström, Alexander
    Chalmers University of Technology, Sweden.
    Evenäs, Lars
    Chalmers University of Technology, Sweden.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University, Sweden.
    Crispin, Xavier
    Linköping University, Sweden.
    Mass Transport in “Water-in-Polymer Salt” Electrolytes2023In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 35, p. 6382-6395Article in journal (Refereed)
    Abstract [en]

    “Water-in-polymer salt” electrolytes (WiPSEs) based on potassium polyacrylate (PAAK) belong to a new family of “water-in-salt” electrolytes that is envisioned as a potential solution for large-scale supercapacitors to balance the electric grid at short time scales. The WiPSEs display a broad electrochemical stability window up to 3 V, yet they are nonflammable and provide high ionic conductivity (100 mS/cm) as required in high-power devices. However, the transport of matter in PAAK-based WiPSEs has not been studied. In this work, we have extensively characterized PAAK by spectroscopic methods such as Raman spectroscopy and NMR diffusometry to determine the state of water and elucidate the mechanism of ionic transport as well as its interplay with water and polymer chain dynamics, which reveals that a significant proportion of the transport in WiPSEs is attributed to hydrated cations. The results are further supported by molecular dynamics (MD) simulations. Finally, the potential of WiPSEs based on PAAK is demonstrated in an activated carbon-based supercapacitor operating up to 2 V with reasonable self-discharge. This proof of concept shows promise for low-cost and large-scale supercapacitors.

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  • 36.
    Kozdra, Melania
    et al.
    Uppsala University, Sweden.
    Brandell, Daniel
    Uppsala University, Sweden.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University, Sweden.
    Mace, Amber
    Uppsala University, Sweden.
    The sensitive aspects of modelling polymer-ceramic composite solid-state electrolytes using molecular dynamics simulations2024In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 26, no 7, p. 6216-6227Article in journal (Refereed)
    Abstract [en]

    Solid-state composite electrolytes have arisen as one of the most promising materials classes for next-generation Li-ion battery technology. These composites mix ceramic and solid-polymer ion conductors with the aim of combining the advantages of each material. The ion-transport mechanisms within such materials, however, remain elusive. This knowledge gap can to a large part be attributed to difficulties in studying processes at the ceramic-polymer interface, which are expected to play a major role in the overall ion transport through the electrolyte. Computational efforts have the potential of providing significant insight into these processes. One of the main challenges to overcome is then to understand how a sufficiently robust model can be constructed in order to provide reliable results. To this end, a series of molecular dynamics simulations are here carried out with a variation of certain structural (surface termination and polymer length) and pair potential (van der Waals parameters and partial charges) models of the Li7La3Zr2O12 (LLZO) poly(ethylene oxide) (PEO) system, in order to test how sensitive the outcome is to each variation. The study shows that the static and dynamic properties of Li-ion are significantly affected by van der Waals parameters as well as the surface terminations, while the thickness of the interfacial region - where the structure-dynamic properties are different as compared to the bulk-like regime - is the same irrespective of the simulation setup. 

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  • 37.
    Lanzilotto, Valeria
    et al.
    Uppsala universitet.
    Silva, Jose Luis
    Uppsala universitet.
    Zhang, Teng
    Uppsala universitet.
    Stredansky, Matus
    The University of Trieste, ITA; IOM, TASC laboratory, ITA .
    Grazioli, Cesare
    Instituto di Struttura della Materia (ISM), CNR, ITA .
    Simonov, Konstantin
    Uppsala universitet.
    Giangrisostomi, Erika
    Helmholtz-Zentrum Berlin, DEU.
    Ovsyannikov, Ruslan
    Helmholtz-Zentrum Berlin, DEU.
    De Simone, Monica
    IOM, TASC laboratory, ITA .
    Coreno, Marcello
    Instituto di Struttura della Materia (ISM), CNR, ITA .
    Araujo, Carlos Moyses
    Uppsala universitet.
    Brena, Barbara
    Uppsala universitet.
    Puglia, Carla
    Uppsala universitet.
    Spectroscopic Fingerprints of Intermolecular H-Bonding Interactions in Carbon Nitride Model Compounds2018In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 53, p. 14198-14206Article in journal (Refereed)
    Abstract [en]

    The effect of intermolecular H-bonding interactions on the local electronic structure of N-containing functional groups (amino group and pyridine-like N) that are characteristic of polymeric carbon nitride materials p-CN(H), a new class of metal-free organophotocatalysts, was investigated. Specifically, the melamine molecule, a building block of p-CN(H), was characterized by X-ray photoelectron (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The molecule was studied as a noninteracting system in the gas phase and in the solid state within a H-bonded network. With the support of DFT simulations of the spectra, it was found that the H-bonds mainly affect the N1s level of the amino group, leaving the N1s level of the pyridine-like N mostly unperturbed. This is responsible for a reduction of the chemical shift between the two XPS N1s levels relative to free melamine. Consequently, N K-edge NEXAFS resonances involving the amino N1s level also shift to lower photon energies. Moreover, the solid-state absorption spectra showed significant modification/quenching of resonances related to transitions from the amino N1s level to sigma* orbitals involving the NH2 termini.

  • 38.
    Liu, Huanji
    et al.
    Sichuan University, CHN.
    Zhu, Juncheng
    University of Science & Technology of China Hefei, CHN.
    Tian, Dan
    Nanjing Forestry University, CHN.
    Carvalho, Rodrigo
    Uppsala universitet.
    Shi, Zhicheng
    Sichuan University, CHN.
    Cai, Zhao
    Huazhong University of Science and Technology, CHN.
    Chang, Xinghua
    Central South University, CHN.
    Araujo, Carlos Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala Universitet.
    Zhou, Yu
    Central South University, CHN.
    Zhu, Jiliang
    Sichuan University, CHN.
    3D Lattice-Matching Layered Hydroxide Heterostructure with Improved Interfacial Charge Transfer and Ion Diffusion for High Energy Density Supercapacitor2021In: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 8, no 14, p. 1-11, article id 2100429Article in journal (Refereed)
    Abstract [en]

    The electrochemical charge storage mostly relies on the electrical properties of complex interfaces and electrode materials as well as the dynamic ions diffusion in the electrolytes. Nickel-cobalt layered double hydroxides (LDHs) with tunable chemical composition are promising for electrochemical supercapacitors, where the theoretical performance could be up to 3000 F g(-1). However, the experimental performances of NiCo-LDHs are still limited by low charge transfer rate and slow dynamic ions diffusion. Here, a 3D lattice matching Ni0.85Co0.15(OH)(2)@alpha-Co(OH)(2) heterostructure is epitaxially grown. The experimental results and theoretical calculation confirm that such a 3D heterostructure could improve charge transfer abilities and accelerated ions diffusion. The specific capacitance of 2480 F g(-1) and retained 71% of the initial capacitance at high current density of 30 A g(-1) have been achieved by optimal Co(OH)(2) amount of 20 mg (NCC-20). Asymmetric button devices and soft-pack devices have been demonstrated with exceptional energy densities of 69.2 and 65.7 Wh kg(-1) at power densities of 0.79 and 0.78 kW kg(-1), and maintained 88% and 80% initial capacitance under 10 000 cycles, respectively. The general design principles clearly demonstrate the importance of electrochemical interface and dynamic process, paving the way to push forward the application capability of electrochemical devices.

  • 39.
    Marchiori, Cleber F.N.
    et al.
    Uppsala universitet.
    Brandell, Daniel
    Uppsala universitet.
    Araujo, Carlos Moyses
    Uppsala universitet, Materialteori.
    Predicting Structure and Electrochemistry of Dilithium Thiophene-2,5-Dicarboxylate Electrodes by Density Functional Theory and Evolutionary Algorithms2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 8, p. 4691-4700Article in journal (Refereed)
    Abstract [en]

    Organic electroactive materials are promising candidates to be TUC used as lithium insertion electrodes in the next generation of environmentally friendly battery technologies. In this work, evolutionary algorithms at interplay with density functional theory calculations have been employed to predict the crystal structure for both delithiated and lithiated phases of dilithium thiophene dicarboxylate (Li2TDC). On the basis of the resulting crystals, electronic structure modifications and voltage profiles for the lithiation process have been calculated. The obtained structure for the delithiated phase showed a well-defined salt layer intercalating the organic components, forming a so-called lithium organic framework (LOF). Upon lithiation, new structures appear which deviate from the LOF as a consequence of the reduction of the S atoms, which coordinate with the additional Li ions. The calculated average potential of similar to 1.00 V vs Li/Li+ is found to be in good agreement with experimental findings. An additional study at the molecular level has also been conducted aiming at gaining insight into the importance of the crystallographic environment on the structural and thermodynamics properties. This strategy is suitable for an initial assessment of the electrochemical process that underlies the lithiation mechanism of electrode materials. Moreover, the employed evolutionary algorithm emerges as a promising tool to predict crystal structures during lithiation, which are otherwise difficult to resolve experimentally.

  • 40.
    Marchiori, Cleber F.N.
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Damas, Giane B.
    Linköpings universitet.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala universitet.
    Tuning the photocatalytic properties of porphyrins for hydrogen evolution reaction: An in-silico design strategy2022In: Journal of Power Sources Advances, E-ISSN 2666-2485, Vol. 15, article id 100090Article in journal (Refereed)
    Abstract [en]

    Porphyrins constitute a class of attractive materials for harvesting sunlight and promote chemical reactions following their natural activity for the photosynthetic process in plants. In this work, we employ an in-silico design strategy to propose novel porphyrin-based materials as photocatalysts for hydrogen evolution reaction (HER). More specifically, a set of meso-substituted porphyrins with donor-acceptor architecture are evaluated within the density functional theory (DFT) framework, according to these screening criteria: i) broad absorption spectrum in the ultraviolet–visible (UV–Vis) and near infrared (NIR) range, ii) suitable redox potentials to drive the uphill reaction that lead to molecular hydrogen formation, iii) low exciton binding free energy (Eb), and iv) low hydrogen binding free energy (ΔGH), a quantity that should present low HER overpotentials, ideally ΔGH = 0. The outcomes indicate that the Se-containing compound, where the donor ligands are attached to the porphyrin core by the spacer, outstands as the most promising candidate that is presented in this work. It displays a broad absorption in the visible and NIR regions to up to 1000 nm, suitable catalytic power, low Eb (in special in high dielectric constant environment, such as water) and the lowest ΔGH = +0.082 eV. This is comparable, in absolute values, to the value exhibited by platinum (ΔGH = −0.10 eV), one of the most efficient catalysts for HER.

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  • 41.
    Marchiori, Cleber
    et al.
    Uppsala universitet.
    Pereira de Carvalho, Rodrigo
    Uppsala universitet.
    Ebadi, Mahsa
    Uppsala universitet.
    Brandell, Daniel
    Uppsala universitet.
    Araujo, Moyses
    Uppsala universitet.
    Understanding the Electrochemical Stability Window of Polymer Electrolytes in Solid-State Batteries from Atomic-Scale Modeling: The Role of Li-Ion Salts2020In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 32, no 17, p. 7237-7246Article in journal (Refereed)
    Abstract [en]

    After decades of development in Li-ion batteries, solid polymer electrolytes (SPEs) are currently experiencing a renaissance as a promising category of materials to be used in all-solid-state batteries. However, a fundamental understanding of their electrochemical properties in the battery environment is still lacking, which in turn limits the implementation of this prospective solution. With the aim of bridging this knowledge gap, we have assessed, through first-principles thermodynamics calculations based on atomic-scale modeling, the electrochemistry of a range of relevant polymer electrolyte hosts in their pristine form and also when doped with commonly used Li-ion salts. A significant change of the electrochemical stability window upon formation of the polymer/salt complexes was found. The mechanisms of the reduction and oxidation reactions are unveiled and correlated to the electronic structures and molecular structural relaxations. In the reduction process, the salt anions control the potentials due to bond cleavage that stabilize the reduced state. In the oxidation process, the mechanism is different with the charge being stabilized either on the polymer or on the salt anion depending on the complex formed. This assessment of the electrochemical stability of the polymer/salt complexes could serve as a guide for electrolyte design in SPE-based all-solid-state batteries.

  • 42.
    Mirsakiyeva, Amina
    et al.
    Uppsala universitet.
    Ebadi, Mahsa
    Uppsala universitet.
    Araujo, Carlos Moyses
    Uppsala universitet.
    Brandell, Daniel
    Uppsala universitet.
    Broqvist, Peter
    Uppsala universitet.
    Kullgren, Jolla
    Uppsala universitet.
    Initial Steps in PEO Decomposition on a Li Metal Electrode2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 37, p. 22851-22857Article in journal (Refereed)
    Abstract [en]

    Poly(ethylene oxide) (PEO) is the most widely used compound as a solid-state (solvent-free) polymer electrolyte for Li batteries, mainly due to its low glass transition temperature (T-g) and ability to dissolve Li salts. It is also frequently suggested that its cathodic stability renders it possible to operate with Li metal anodes in the design of high energy density storage devices. However, little is still known about the true interfacial chemistry between Li metal and PEO and how these two materials interact with each other. We are here exploring this relationship by the means of density functional theory (DFT)-based modeling. Using bulk structures and isolated PEO chains, we have found that there is a strong thermodynamic driving force to oxidize Li metal into lithium oxide (Li2O) when PEO is decomposed into C2H4 and H-2, irrespectively of the PEO oligomer length. Explicit modeling of PEO on a Li(100) surface reveals that all steps in the decomposition are exothermic and that the PEO/Li metal system should have a layer of Li2O between the polymer electrolyte and the metal surface. These insights and the computational strategy adopted here could be highly useful to better tailor polymer electrolytes with favorable interfacial properties.

  • 43.
    Osorio-Guillen, J. M.
    et al.
    University of Antioquia, COL.
    Espinosa-Garcia, W. F.
    University of Antioquia, COL.;La Universidad de San Buenaventura, COL..
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala universitet, Materialteori.
    Assessing photocatalytic power of g-C3N4 for solar fuel production: A first-principles study involving quasi-particle theory and dispersive forces2015In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 143, no 9, article id 094705Article in journal (Refereed)
    Abstract [en]

    First-principles quasi-particle theory has been employed to assess catalytic power of graphitic carbon nitride, g-C3N4, for solar fuel production. A comparative study between g-h-triazine and g-h-heptazine has been carried out taking also into account van der Waals dispersive forces. The band edge potentials have been calculated using a recently developed approach where quasi-particle effects are taken into account through the OW approximation First, it was found that the description of ground state properties such as cohesive and surface formation energies requires the proper treatment of dispersive interaction. Furthermore, through the analysis of calculated band-edge potentials, it is shown that g-h-triazine has high reductive power reaching the potential to reduce CO2 to formic acid, coplanar g-h-heptazine displays the highest thermodynamics force toward H2O/O-2 oxidation reaction, and corrugated g-h-heptazine exhibits a good capacity for both reactions. This rigorous theoretical study shows a route to further improve the catalytic performance of g-C3N4. (C) 2015 AIP Publishing LLC.

  • 44.
    Pati, Palas Baran
    et al.
    Uppsala universitet, Fysikalisk kemi.
    Damas, Giane
    Uppsala universitet, Materialteori.
    Tian, Lei
    Uppsala universitet, Fysikalisk kemi.
    Fernandes, Daniel L. A.
    Uppsala universitet, Fysikalisk kemi.
    Zhang, Lei
    Uppsala universitet, Fysikalisk kemi.
    Bayrak Pehlivan, Ilknur
    Uppsala universitet, Fasta tillståndets fysik.
    Edvinsson, Tomas
    Uppsala universitet, Fasta tillståndets fysik.
    Araujo, Carlos Moyses
    Uppsala universitet, Materialteori.
    Tian, Haining
    Uppsala universitet, Fysikalisk kemi.
    An experimental and theoretical study of an efficient polymer nano-photocatalyst for hydrogen evolution2017In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 10, no 6, p. 1372-1376Article in journal (Refereed)
    Abstract [en]

    In this work, we report a highly efficient organic polymer nano-photocatalyst for light driven proton reduction. The system renders an initial rate of hydrogen evolution up to 50 +/- 0.5 mmol g(-1) h(-1), which is the fastest rate among all other reported organic photocatalysts. We also experimentally and theoretically prove that the nitrogen centre of the benzothiadiazole unit plays a crucial role in the photocatalysis and that the Pdots structure holds a close to ideal geometry to enhance the photocatalysis.

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  • 45.
    Pavliuk, Mariia V.
    et al.
    Uppsala universitet.
    Alvarez, Sol Gutierrez
    Uppsala universitet.
    Hattori, Yocefu
    Uppsala universitet.
    Messing, Maria E.
    Lund Universitet.
    Czapla-Masztafiak, Joanna
    Polish Academy of Sciences, POL.
    Szlachetko, Jakub
    Polish Academy of Sciences, POL.
    Silva, Jose Luis
    Uppsala universitet .
    Araujo, Carlos Moyses
    Uppsala universitet.
    Fernandes, Daniel L. A.
    Uppsala universitet,.
    Lu, Li
    Kiely, Christopher J.
    Lehigh University, USA .
    Abdellah, Mohamed
    Uppsala universitet.
    Nordlander, Peter
    Rice University, USA.
    Sá, Jacinto
    Uppsala universitet.
    Hydrated Electron Generation by Excitation of Copper Localized Surface Plasmon Resonance2019In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 8, p. 1743-1749Article in journal (Refereed)
    Abstract [en]

    Hydrated electrons are important in radiation chemistry and charge transfer reactions, with applications that include chemical damage of DNA, catalysis, and signaling. Conventionally, hydrated electrons are produced by pulsed radiolysis, sonolysis, two-ultraviolet-photon laser excitation of liquid water, or photodetachment of suitable electron donors. Here we report a method for the generation of hydrated electrons via single-visible-photon excitation of localized surface plasmon resonances (LSPRs) of supported sub-3 nm copper nanoparticles in contact with water. Only excitations at the LSPR maximum resulted in the formation of hydrated electrons, suggesting that plasmon excitation plays a crucial role in promoting electron transfer from the nanoparticle into the solution. The reactivity of the hydrated electrons was confirmed via proton reduction and concomitant H-2 evolution in the presence of a Ru/TiO2 catalyst.

  • 46.
    Pereira de Carvalho, Rodrigo
    et al.
    Uppsala universitet, Materialteori.
    Marchiori, Cleber
    Uppsala universitet, Strukturkemi.
    Brandell, Daniel
    Uppsala universitet, Strukturkemi.
    Araujo, Carlos Moyses
    Uppsala universitet, Materialteori.
    Tuning the Electrochemical Properties of Organic Battery Cathode Materials: Insights from Evolutionary Algorithm DFT Calculations2020In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 13, no 9, p. 2402-2409Article in journal (Refereed)
    Abstract [en]

    Several forms of organic materials have arisen as promising candidates for future active electrode materials for Li-ion and post-Li-ion batteries, owing to a series of key features that encompasses sustainability, accessibility, and tunable electrochemical properties by molecular modifications. In this context, a series of organic electrode materials (OEMs) are investigated to further understand their thermodynamic and electronic properties. Through an evolutionary algorithm approach combined with first-principles calculations, the crystal structure of lithiated and delithiated phases of these OEMs and their respective NO2-substituted analogues are predicted. This framework allows a first assessment of their electrochemical and electronic properties and further understanding on the effects of the nitro group in the substituted compounds. NO2 is found to strongly affect structural and thermodynamic aspects during the electrochemical reaction with the reducing equivalents (Li++e(-)), changing the OEM's character from a low-potential anode to a high-potential cathode by creating a localization of the additional electrons, thus resulting in a better-defined redox-active center and leading to a shift in the potential from 0.92 V to 2.66 V vs. Li/Li+.

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  • 47.
    Prasad, Suraj
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Marchiori, Cleber
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Genene, Zewdneh
    Chalmers University of Technology, Sweden.
    Ericsson, Leif
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Wang, Ergang
    Chalmers University of Technology, Sweden.
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Photostability of Y-type electron acceptor molecules and related copolymer2023In: Proceedings Volume 12660, Organic, Hybrid, and Perovskite Photovoltaics XXIV; / [ed] Gang Li, Natalie Stingelin, Ana Flávia Nogueira, Thuc-Quyen Nguyen, Ellen Moons, Barry P. Rand, SPIE - The International Society for Optics and Photonics, 2023, Vol. 12660Conference paper (Refereed)
    Abstract [en]

    The lifetime of organic solar cells critically depends on the photochemical stability of the materials. To shed light on the photostability of novel Y-series electron acceptors, we investigate the evolution of optical properties and composition during one-sun illumination in ambient atmosphere of thin films of the small-molecule acceptor Y5 and its copolymers PF5-Y5 and PYT. We employ UV-vis, Fourier-transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS), to assess changes in these properties as a function of illumination time. UV-Vis spectra show that PF5-Y5 undergoes rapid photobleaching, while the Y5 spectrum remains essentially unaffected even after 30 hours of exposure. The absorption spectrum of PYT, which contains a different co-mer than PF5-Y5, is only weakly affected. XPS C1s spectra of the PF5- Y5 film show a decreasing main peak and the development of a new component after 30 hours exposure, while the Y5 film surface composition remained intact. The photodegradation products of PF5-Y5 are characterized by the presence of new carbonyl groups, emerging as absorption bands in the FTIR spectra, while such spectral changes are absent for the Y5 film, indicating that Y5 is resistant to photooxidation, while PF5-Y5 undergoes photochemical reactions. The faster photodegradation of PF5-Y5 compared to Y5 and PYT raises the question about the role of the copolymer’s BDT moiety in the photooxidation. These new insights on the dependence of the photostability of acceptor molecules on their molecular structure are expected to contribute to the design of stable acceptor copolymers for organic solar cells with long operational lifetimes. 

  • 48.
    Renault, Stéven
    et al.
    Uppsala universitet.
    Oltean, Viorica Alina
    Uppsala universitet.
    Araujo, C. Moyses
    Uppsala universitet.
    Grigoriev, Anton
    Uppsala universitet.
    Edström, Kristina
    Uppsala universitet.
    Brandell, Daniel
    Uppsala universitet.
    Superlithiation of Organic Electrode Materials: The Case of Dilithium Benzenedipropiolate2016In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 28, no 6, p. 1920-1926Article in journal (Refereed)
    Abstract [en]

    Dilithium benzenedipropiolate was prepared and investigated as a potential negative electrode material for secondary lithium-ion batteries. In addition to the expected reduction of its carbonyls, this material can reduce and reversibly oxidize its unsaturated carbon–carbon bonds leading to a Li/C ratio of 1/1 and a specific capacity as high as 1363 mAh g–1: the highest ever reported for a lithium carboxylate. Density functional theory calculations suggest that the lithiation is preferential on the propiolate carbons.

  • 49. Renault, Stéven
    et al.
    Oltean, Viorica Alina
    Araujo, Moyses
    Grigoriev, Anton
    Edström, Kristina
    Brandell, Daniel
    Dilithium Benzenedipropiolate: a Superlithiated Organic Electrode Material2016Conference paper (Refereed)
  • 50. Renault, Stéven
    et al.
    Oltean, Viorica Alina
    Araujo, Moyses
    Grigoriev, Anton
    Edström, Kristina
    Brandell, Daniel
    Superlithiation of Dilithium Benzenedipropiolate: Stability and Reversibility with Liquid or Solid Electrolytes2016Conference paper (Refereed)
12 1 - 50 of 66
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