| 1. |
- de Araujo, L. O., et al.
(author)
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A new CBD-CC-E spectral similarity scale for optimizing computer-simulated UV–vis spectra
- 2021
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In: Computational and Theoretical Chemistry. - : Elsevier. - 2210-271X .- 2210-2728. ; 1197
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Journal article (peer-reviewed)abstract
- A new CBD-CC-E spectral similarity scale is proposed to optimize computer-simulated UV–vis spectra. The scale was tested using the S1←S0 spectrum of the dithienyl-diketopyrrolopyrrole molecule (DPP2T), an important building block for manufacturing materials for optoelectronic applications. Our results indicate that the spectrum calculated at M06/6-311++G(d,p) level was the one that best reproduced the intensity and shape features of the experimental spectrum, while CAM-B3LYP/6-311++G(d,p) was the one that best reproduced the energy. The CBD-CC-E scale makes the comparison between computer-simulated and experimental spectra statistically based, allowing a systematic and automated choice of the theory level whose calculated spectrum best reproduces the shape, intensity or energy of the experimental UV–vis spectrum.
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| 2. |
- Aderne, Rian E., et al.
(author)
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On the energy gap determination of organic optoelectronic materials : the case of porphyrin derivatives
- 2022
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In: Materials Advances. - : Royal Society of Chemistry. - 2633-5409. ; :3, s. 1791-1803
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Journal article (peer-reviewed)abstract
- 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.
(author)
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Designing strategies to tune reduction potential of organic molecules for sustainable high capacity batteries application
- 2017
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In: Journal of Materials Chemistry A. - 2050-7488 .- 2050-7496. ; 5:9, s. 4430-4454
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
- Pereira de Carvalho, Rodrigo, et al.
(author)
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Exploring Metastable Phases During Lithiation of Organic Battery Electrode Materials
- 2022
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In: ChemSusChem. - : John Wiley & Sons. - 1864-5631 .- 1864-564X. ; :2
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Journal article (peer-reviewed)abstract
- 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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| 5. |
- Scalon, Lucas, et al.
(author)
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Assessing the Donor-Acceptor Nature and the Electrochemical Stability of a Fluorene-Diketopyrrolopyrrole-Thiophene-Based Copolymer
- 2021
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In: ACS Applied Polymer Materials. - : American Chemical Society (ACS). - 2637-6105. ; 3:8, s. 4223-4233
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Journal article (peer-reviewed)abstract
- Organic dyes have been studied for applications in large-area, flexible, cheap, and efficient organic electronic devices. Among them, diketopyrrolopyrrole (DPP) has gained attention thanks to its planar structure, photochemical and thermal stability, and easy processability. Also, the electron-withdrawing nature of DPP makes its application attractive in the synthesis of donor-acceptor (D-A) copolymers, with appealing features such as the tunable energy levels and photophysical and electrochemical properties. Inspired by these exciting characteristics, a copolymer was developed based on DPP, thiophene, and fluorene (PFDPP2T). Photophysical and electrochemical studies using both experimental and theoretical approaches were performed aiming to understand the properties of this material, such as, for instance, the D-A characteristic and the outstanding electrochemical stability upon oxidation that enables more than 400 cycles of p-doping. The outcomes unveil fundamental aspects of this class of copolymers, reinforcing their suitability for photo-electrochemical and optoelectronic applications.
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| 6. |
- Zhang, Chao, et al.
(author)
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2023 Roadmap on molecular modelling of electrochemical energy materials
- 2023
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In: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 2515-7655. ; 5:4
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Journal article (peer-reviewed)abstract
- New materials for electrochemical energy storage and conversion are the key to the electrification and sustainable development of our modern societies. Molecular modelling based on the principles of quantum mechanics and statistical mechanics as well as empowered by machine learning techniques can help us to understand, control and design electrochemical energy materials at atomistic precision. Therefore, this roadmap, which is a collection of authoritative opinions, serves as a gateway for both the experts and the beginners to have a quick overview of the current status and corresponding challenges in molecular modelling of electrochemical energy materials for batteries, supercapacitors, CO2 reduction reaction, and fuel cell applications.
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| 7. |
- Axelsson, Martin, et al.
(author)
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Small Organic Molecule Based on Benzothiadiazole for Electrocatalytic Hydrogen Production
- 2021
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:50, s. 21229-21233
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Journal article (peer-reviewed)abstract
- A small organic molecule 2,1,3-benzothiadiazole-4, 7-dicarbonitrile (BTDN) is assessed for electrocatalytic hydrogen evolution on glassy carbon electrode and shows a hydrogen production Faradaic efficiency of 82% in the presence of salicylic acid. The key catalytic intermediates of reduced species BTDN-. and protonated intermediates are characterized or hypothesized by using various spectroscopic methods and density functional theory (DFT)-based calculations. With the experimental and theoretical results, a catalytic mechanism of BTDN for electrocatalytic H-2 evolution is proposed.
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| 8. |
- Ebadi, Mahsa, et al.
(author)
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Modelling the Polymer Electrolyte/Li-Metal Interface by Molecular Dynamics simulations
- 2017
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In: Electrochimica Acta. - : Pergamon-Elsevier. - 0013-4686 .- 1873-3859. ; 234, s. 43-51
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Journal article (peer-reviewed)abstract
- 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.
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| 9. |
- Jin, Wentao, et al.
(author)
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Absolute surface energies of wurtzite (101‾1) surfaces and the instability of the cation-adsorbed surfaces of II-VI semiconductors
- 2021
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In: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 119:20
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Journal article (peer-reviewed)abstract
- We have investigated the wurtzite (101‾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 × 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.
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| 10. |
- Sousa, O. M., et al.
(author)
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Charging behavior of ZnMn2O4 and LiMn2O4 in a zinc- and lithium-ion battery : an ab initio study
- 2024
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In: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 2515-7655. ; 6:2
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Journal article (peer-reviewed)abstract
- In the field of sustainable energy storage systems, zinc-ion batteries (ZIB) employing aqueous electrolytes have emerged as viable successors to the widely used lithium-ion batteries, attributed to their cost-effectiveness, environmental friendliness, and intrinsic safety features. Despite these advantages, the performance of ZIBs is significantly hindered by the scarcity of suitable cathode materials, positioning manganese zinc oxide (ZnMn2O4) as a potential solution. In this study, we describe the ZnMn2O4 (ZMO) compound focusing on its properties variations during Zn extraction and potential battery applications. For the sake of comparison, we also analyze the same properties of the LiMn2O4 in its tetragonal phase (TLMO), for the first time, motivated by a recent discovery that the substitution of Zn ions by Li in ZMO forms isostructural TLMO compound at room temperature. The study was conducted within the density functional theory (DFT) framework, where the structural, electronic, magnetic, electrochemical, and spectroscopic properties of ZMO and TLMO are investigated under various conditions. Although both systems crystallize in tetragonal structures, they demonstrate distinct electronic and magnetic properties due to different oxidation states of the Mn. Computationally optimized lattice parameters align closely with experimental values. The TLMO exhibits a narrower band gap compared to ZMO, indicating enhanced electrical conductivity. In addition, TLMO presented a lower diffusion energy barrier than ZMO, indicating better ionic conductivity. To evaluate the potential application of these materials in battery technologies, we further explored their volume changes during charging/discharging cycles, simulating Zn or Li ions extraction. TLMO underwent a significant volume contraction of 5.8% upon complete Li removal, while ZMO experienced a more pronounced contraction of 12.5% with full Zn removal. By adjusting ion extraction levels, it is possible to reduce these contractions, thereby approaching more viable battery applications. Voltage profiles, constructed from DFT-based simulation results, unveiled an average voltage of 4.05 V for TLMO, closely matching experimental values. Furthermore, spectroscopy results provide insights into the electronic transitions and validate the computational findings, consolidating our understanding of the intrinsic properties of ZMO and TLMO.
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