Showing papers in "Physical Chemistry Chemical Physics in 2018"
TL;DR: A type-II band alignment and a large built-in electric field are formed at the MoS2/ZnO interface, which ensure the enhanced separation of the photogenerated electron-hole pairs, indicating that it has potential for application in photovoltaic and photocatalytic devices.
Abstract: Previous investigations [H. L. Zhuang and R. G. Hennig, J. Phys. Chem. C, 2013, 117, 20440-20445; J. Kang, S. Tongay, J. Zhou, J. Li and J. Wu, Appl. Phys. Lett., 2013, 102, 012111] demonstrated that molybdenum disulfide (MoS2) is a potential photocatalyst for water splitting. However, the photogenerated electron-hole pairs in MoS2 remain in the same spatial regions, resulting in a high rate of recombination. Using first-principles calculations, we designed a MoS2-based heterostructure by stacking MoS2 on two-dimensional zinc oxide (ZnO) and investigated its structural, electronic, and optical properties. The interaction at the MoS2/ZnO interface was found to be dominated by van der Waals (vdW) forces. The energy levels of both water oxidation and reduction lie within the bandgap of the MoS2/ZnO vdW heterostructure, which guarantee their occurrence for water splitting. Moreover, a type-II band alignment and a large built-in electric field are formed at the MoS2/ZnO interface, which ensure the enhanced separation of the photogenerated electron-hole pairs. In addition, strong optical absorption in the visible region was also found in the MoS2/ZnO vdW heterostructure, indicating that it has potential for application in photovoltaic and photocatalytic devices.
275 citations
TL;DR: This work develops a multiphysics model for gas diffusion electrodes for CO2 reduction and used it to investigate the interplay between species transport and electrochemical reaction kinetics, and demonstrates how the local environment near the catalyst layer affects cell performance.
Abstract: CO2 reduction conducted in electrochemical cells with planar electrodes immersed in an aqueous electrolyte is severely limited by mass transport across the hydrodynamic boundary layer. This limitation can be minimized by use of vapor-fed, gas-diffusion electrodes (GDEs), enabling current densities that are almost two orders of magnitude greater at the same applied cathode overpotential than what is achievable with planar electrodes in an aqueous electrolyte. The addition of porous cathode layers, however, introduces a number of parameters that need to be tuned in order to optimize the performance of the GDE cell. In this work, we develop a multiphysics model for gas diffusion electrodes for CO2 reduction and used it to investigate the interplay between species transport and electrochemical reaction kinetics. The model demonstrates how the local environment near the catalyst layer, which is a function of the operating conditions, affects cell performance. We also examine the effects of catalyst layer hydrophobicity, loading, porosity, and electrolyte flowrate to help guide experimental design of vapor-fed CO2 reduction cells.
254 citations
TL;DR: A comprehensive review including characterization methods, the effects of chemical composition of the ionic liquids on the thermal, electrochemical, and radiolytic stabilities of ions, respectively, and the thermal stability of some special types of ionic fluids are discussed.
Abstract: Research on ionic liquids has achieved rapid progress in the last several decades. Stability is a prerequisite for the application of ionic liquids. Ionic liquids may be used at elevated temperature, as electrolytes, or under irradiation. Therefore, the thermal, electrochemical, and radiolytic stabilities of ionic liquids are important and need to be known before their usage. Many research papers and some reviews on the stabilities of ionic liquids have been published. However, new results are continuously being published and a comprehensive review and perspective on this topic are still urgently needed. In this perspective, we intend to provide a comprehensive review including characterization methods, the effects of chemical composition of the ionic liquids on the thermal, electrochemical, and radiolytic stabilities of ionic liquids, respectively. Moreover, the thermal stability of some special types of ionic liquids such as poly(ionic liquids) and mixed ionic liquids, and the thermal and electrochemical stabilities of protic ionic liquids are discussed too. For thermal stability, the interactions between ions are less important than the individual anions and cations. The decomposition temperature is mainly determined by the less-stable ion, usually the anion. For electrochemical stability, the electrochemical window is determined by both the cation and anion. The less stable ion could influence the stability by interaction between the generated species from the decomposition with the more stable ion (opposite ion). This perspective is helpful for people to avoid using unstable ionic liquids and choose suitable ionic liquids.
232 citations
TL;DR: The results show that the ff03 force field performs the best, but the predictions given by the tested force fields are comparable, implying that the MM/GBSA predictions are not very sensitive to force fields.
Abstract: Entropy effects play an important role in drug–target interactions, but the entropic contribution to ligand-binding affinity is often neglected by end-point binding free energy calculation methods, such as MM/GBSA and MM/PBSA, due to the expensive computational cost of normal mode analysis (NMA). Here, we systematically investigated entropy effects on the prediction power of MM/GBSA and MM/PBSA using >1500 protein–ligand systems and six representative AMBER force fields. Two computationally efficient methods, including NMA based on truncated structures and the interaction entropy approach, were used to estimate the entropic contributions to ligand–target binding free energies. In terms of the overall accuracy, we found that, for the minimized structures, in most cases the inclusion of the conformational entropies predicted by truncated NMA (enthalpynmode_min_9A) compromises the overall accuracy of MM/GBSA and MM/PBSA compared with the enthalpies calculated based on the minimized structures (enthalpymin). However, for the MD trajectories, the binding free energies can be improved by the inclusion of the conformation entropies predicted by either truncated-NMA for a relatively high dielectric constant (ein = 4) or the interaction entropy method for ein = 1–4. In terms of reproducing the absolute binding free energies, the binding free energies estimated by including the truncated-NMA entropies based on the MD trajectories (ΔGnmode_md_9A) give the lowest average absolute deviations against the experimental data among all the tested strategies for both MM/GBSA and MM/PBSA. Although the inclusion of the truncated NMA based on the MD trajectories (ΔGnmode_md_9A) for a relatively high dielectric constant gave the overall best result and the lowest average absolute deviations against the experimental data (for the ff03 force field), it needs too much computational time. Alternatively, considering that the interaction entropy method does not incur any additional computational cost and can give comparable (at high dielectric constant, ein = 4) or even better (at low dielectric constant, ein = 1–2) results than the truncated-NMA entropy (ΔGnmode_md_9A), the interaction entropy approach is recommended to estimate the entropic component for MM/GBSA and MM/PBSA based on MD trajectories, especially for a diverse dataset. Furthermore, we compared the predictions of MM/GBSA with six different AMBER force fields. The results show that the ff03 force field (ff03 for proteins and gaff with AM1-BCC charges for ligands) performs the best, but the predictions given by the tested force fields are comparable, implying that the MM/GBSA predictions are not very sensitive to force fields.
209 citations
TL;DR: The synergetic effects between Ti3C2 and Pt were fundamentally investigated, indicating that the specific transfer of electrons not only contributed to the inhibited recombination of charge carriers but also resulted in good stability of heterostructured photocatalysts.
Abstract: Co-catalyst loading provides an effective way to enhance the efficiency of photocatalysts for solar hydrogen production. From a sustainability point of view, it has immense scientific and technological values to explore more efficient co-catalytic systems by using multi-cocatalysts, because of potential synergetic effects between different components. Herein, the feasibility of using Ti3C2 MXene nanoparticles and Pt nanoclusters as dual co-catalysts to enhance the photoactivity of g-C3N4 for H2 production was investigated. Due to the improved electrical conductivity and increased reactive sites for photoreduction reactions, Ti3C2 and Pt co-modified photocatalysts exhibited a high photocatalytic hydrogen production activity of 5.1 mmol h-1 g-1. Compared to g-C3N4/Ti3C2 and g-C3N4/Pt, the 3- and 5-fold increased photoactivity demonstrated great potential of Ti3C2 MXene nanoparticles to construct high-performance photocatalysts. The synergetic effects between Ti3C2 and Pt were fundamentally investigated, indicating that the specific transfer of electrons not only contributed to the inhibited recombination of charge carriers but also resulted in good stability of heterostructured photocatalysts. Our results have demonstrated an approach worthy for the design and fabrication of high-efficiency heterostructures with superior photoactivity for hydrogen energy production.
163 citations
TL;DR: The single Mo atom embedded into the MoS2 nanosheet was found to be the most active catalyst for NRR with an onset potential of -0.53 V, in which the hydrogenation of the adsorbed N2* to N2H* is the potential-determining step.
Abstract: The electrochemical reduction of N2 to NH3 (NRR) under ambient conditions is significant for sustainable agriculture. Here, by means of density functional theory (DFT) computations, the potential of a series of single transition metal (TM) atoms embedded into a MoS2 monolayer with an S-vacancy (TM/MoS2) as electrocatalysts for NRR was systematically investigated. Our DFT results revealed that among all these considered candidate catalysts, the single Mo atom embedded into the MoS2 nanosheet was found to be the most active catalyst for NRR with an onset potential of -0.53 V, in which the hydrogenation of the adsorbed N2* to N2H* is the potential-determining step. The high stabilization of the N2H* species is responsible for the superior performance of the embedded Mo atom for the NRR, which is well consistent with its d-band center. Our findings may facilitate the further design of single-atom electrocatalysts with high efficiency for NH3 synthesis at room temperature.
151 citations
TL;DR: In this article, the authors performed extensive electronic structure and phonon calculations, and determined the force constants, bond strengths, and static exfoliation energies of MAX phases to MXenes for 82 different experimentally synthesized crystalline MAX phases.
Abstract: Chemical exfoliation of MAX phases into two-dimensional (2D) MXenes can be considered as a major breakthrough in the synthesis of novel 2D systems. To gain insight into the exfoliation possibility of MAX phases and to identify which MAX phases are promising candidates for successful exfoliation into 2D MXenes, we perform extensive electronic structure and phonon calculations, and determine the force constants, bond strengths, and static exfoliation energies of MAX phases to MXenes for 82 different experimentally synthesized crystalline MAX phases. Our results show a clear correlation between the force constants and the bond strengths. As the total force constant of an "A" atom contributed from the neighboring atoms is smaller, the exfoliation energy becomes smaller, thus making exfoliation easier. We propose 37 MAX phases for successful exfoliation into 2D Ti2C, Ti3C2, Ti4C3, Ti5C4, Ti2N, Zr2C, Hf2C, V2C, V3C2, V4C3, Nb2C, Nb5C4, Ta2C, Ta5C4, Cr2C, Cr2N, and Mo2C MXenes. In addition, we explore the effect of charge injection on MAX phases. We find that the injected charges, both electrons and holes, are mainly received by the transition metals. This is due to the electronic property of MAX phases that the states near the Fermi energy are mainly dominated by d orbitals of the transition metals. For negatively charged MAX phases, the electrons injected cause swelling of the structure and elongation of the bond distances along the c axis, which hence weakens the binding. For positively charged MAX phases, on the other hand, the bonds become shorter and stronger. Therefore, we predict that the electron injection by electrochemistry or gating techniques can significantly facilitate the exfoliation possibility of MAX phases to 2D MXenes.
149 citations
TL;DR: Development of the NBFIX (Non-Bonded FIX) corrections to the AMBER and CHARMM force fields is reviewed and their implications for MD simulations of electrolyte solutions, dense DNA systems, Holliday junctions, protein folding, and lipid bilayer membranes are discussed.
Abstract: In contrast to ordinary polymers, the vast majority of biological macromolecules adopt highly ordered three-dimensional structures that define their functions. The key to folding of a biopolymer into a unique 3D structure or to an assembly of several biopolymers into a functional unit is a delicate balance between the attractive and repulsive forces that also makes such self-assembly reversible under physiological conditions. The all-atom molecular dynamics (MD) method has emerged as a powerful tool for studies of individual biomolecules and their functional assemblies, encompassing systems of ever increasing complexity. However, advances in parallel computing technology have outpaced the development of the underlying theoretical models-the molecular force fields, pushing the MD method into an untested territory. Recent tests of the MD method have found the most commonly used molecular force fields to be out of balance, overestimating attractive interactions between charged and hydrophobic groups, which can promote artificial aggregation in MD simulations of multi-component protein, nucleic acid, and lipid systems. One route towards improving the force fields is through the NBFIX corrections method, in which the intermolecular forces are calibrated against experimentally measured quantities such as osmotic pressure by making atom pair-specific adjustments to the non-bonded interactions. In this article, we review development of the NBFIX (Non-Bonded FIX) corrections to the AMBER and CHARMM force fields and discuss their implications for MD simulations of electrolyte solutions, dense DNA systems, Holliday junctions, protein folding, and lipid bilayer membranes.
147 citations
TL;DR: It is demonstrated that through cation mixing of MA and FA in perovskites the formation of these defects can be substantially suppressed and result in reduced carrier lifetimes and low open circuit voltages in FAPbI3-based photovoltaic devices.
Abstract: As an alternative to methylammonium lead triiodide (MAPbI3), formamidinium lead triiodide (FAPbI3) perovskites have recently attracted significant attention because of their higher stability and smaller band gaps. Here, based on first-principles calculations, we investigate systematically the intrinsic defects in FAPbI3. While methylammonium (MA)-related defects MAI and IMA in MAPbI3 have high formation energies, we found that formamidinium (FA)-related defects VFA, FAI and IFA in FAPbI3 have much lower formation energies. Antisites FAI and IFA create deep levels in the band gap, and they can act as recombination centers and result in reduced carrier lifetimes and low open circuit voltages in FAPbI3-based photovoltaic devices. We further demonstrate that through cation mixing of MA and FA in perovskites the formation of these defects can be substantially suppressed.
146 citations
TL;DR: This study proposed a universal method starting from the diffuse-reflection spectrum for calculating the J-O parameters of RE3+-doped powdered samples via an auto-combustion-assisted fluoridation technique and deduced that the proposedJ-O calculation route was practicable.
Abstract: It is difficult to calculate the Judd-Ofelt (J-O) parameters for trivalent rare earth (RE)-doped powders due to the unavailable absorption spectrum that is necessarily used in the conventional J-O calculation procedure. In this study, a universal method starting from the diffuse-reflection spectrum for calculating the J-O parameters of RE3+-doped powdered samples was proposed. In this proposed method, by taking the Kubelka-Munk function into account, the absorption cross-section spectrum was derived from the diffuse-reflection spectrum in the RE3+-doped powdered sample using the connection between the absorption cross section and the radiative transition rate of RE3+. Then, the J-O parameters might be calculated from the absorption cross-section spectrum via the traditional J-O calculation technique. The NaYF4:Er3+/Yb3+ and NaYF4:Er3+ phosphors were prepared via an auto-combustion-assisted fluoridation technique, and the J-O calculation was carried out for the obtained samples. The obtained J-O parameters were compared with those reported in the literature and also verified by comparing the calculated radiative transition lifetimes with the experimental values. Finally, it was deduced that the proposed J-O calculation route was practicable.
141 citations
TL;DR: Density functional theory calculations (DFT) showed that the effectiveness of the inhibitive actions of the studied compounds correlates well with their electron donating ability, whilst Monte Carlo simulations revealed that the extent and favourability of adsorption of inhibitor molecules on the carbon steel surface establish their corrosion inhibition performances.
Abstract: Three new organic compounds primarily based on 8-hydroxyquinoline have been successfully synthesized and characterized via different spectroscopic methods (FTIR, 1H, and 13C NMR). The synthesized compounds, namely 5-propoxymethyl-8-hydroxyquinoline (PMHQ), 5-methoxymethyl-8-hydroxyquinoline (MMHQ) and 5-hydroxymethyl-8-hydroxyquinoline (HMHQ), were evaluated as corrosion inhibitors for carbon steel in 1 M HCl solution using electrochemical impedance spectroscopy, potentiodynamic polarization and weight loss measurements at 298 K. Electrochemical measurements confirmed that the newly synthesized 5-alkoxymethyl-8-hydroxyquinoline derivatives are mixed type corrosion inhibitors and confirmed maximum protection efficiencies of 94, 89 and 81% for PMHQ, MMHQ, and HMHQ, respectively, at the optimum concentration of 10−3 M. The EIS spectra confirmed a slightly depressed semi-circle profile with a single time constant in Bode diagrams for the three organic compounds over the whole concentration and temperature ranges studied. The adsorption of PMHQ, MMHQ, and HMHQ on the carbon steel surface followed the Langmuir adsorption isotherm. In addition, the kinetic and thermodynamic parameters for carbon steel corrosion and inhibitor adsorption, respectively, were determined and discussed. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses supported the formation of a protective film on carbon steel in the presence of PMHQ, MMHQ, and HMHQ. Density functional theory calculations (DFT) showed that the effectiveness of the inhibitive actions of the studied compounds correlates well with their electron donating ability, whilst Monte Carlo simulations revealed that the extent and favourability of adsorption of inhibitor molecules on the carbon steel surface establish their corrosion inhibition performances.
TL;DR: In this article, the phonon transport and lattice thermal conductivity of transition metal Dichalcogenide (TMD) monolayers were investigated using first-principles calculations and the linearized phonon Boltzmann equation within the single-mode relaxation time approximation (RTA).
Abstract: Transition Metal Dichalcogenide (TMD) monolayers are very widely studied due to their unique physical properties. Recently, Janus TMD monolayer MoSSe, with a sandwiched S-Mo-Se structure, has been synthesized by replacing the top S atomic layer in MoS2 with Se atoms. In this work, we systematically investigate the phonon transport and lattice thermal conductivity (κL) in MoSSe monolayers using first-principles calculations and the linearized phonon Boltzmann equation within the single-mode relaxation time approximation (RTA). The calculated results show that the κL of MoSSe monolayers is much lower than that of MoS2 monolayers, and higher than that of MoSe2 monolayers. The corresponding thermal sheet conductance of MoSSe monolayers is 342.50 W K-1 at room temperature. This can be understood by studying the phonon group velocities and lifetimes. Compared to MoS2 monolayers, the smaller group velocities and shorter phonon lifetimes of MoSSe monolayers give rise to a lower κL. The larger group velocities of MoSSe compared to those of MoSe2 monolayers are the main reason for the higher κL. The elastic properties of MoS2, MoSSe and MoSe2 monolayers are also calculated, and the order of the Young's modulus is identical to that of the κL. The calculated results show that isotope scattering leads to a 5.8% reduction of the κL. The size effects on the κL are also considered, and are usually used in device implementation. When the characteristic length of the MoSSe monolayer is about 110 nm, the κL reduces to half. These results may offer perspectives on thermal management of MoSSe monolayers, for applications in thermoelectrics, thermal circuits and nanoelectronics, and may motivate further theoretical or experimental efforts to investigate thermal transport in Janus TMD monolayers.
TL;DR: Three universally attractive factors, polarization, dispersion and charge transfer, together with permanent electrostatics, which is usually attractive, drive halogen bonding, against Pauli repulsion.
Abstract: The halogen bond is a class of non-covalent interaction that has attracted considerable attention recently. A widespread theory for describing them is the σ-hole concept, which predicts that the strength of the interaction is proportional to the size of the σ-hole, a region of positive electrostatic potential opposite a σ bond. Previous work shows that in the case of CX3I, with X equal to F, Cl, Br, and I, the σ-hole trend is exactly opposite to the trend in binding energy with common electron pair donors. Using energy decomposition analysis (EDA) applied to a potential energy scan as well as the recent adiabatic EDA technique, we show that the observed trend is a result of charge transfer. Therefore a picture of the halogen bond that excludes charge transfer cannot be complete, and permanent and induced electrostatics do not always provide the dominant stabilizing contributions to halogen bonds. Overall, three universally attractive factors, polarization, dispersion and charge transfer, together with permanent electrostatics, which is usually attractive, drive halogen bonding, against Pauli repulsion.
TL;DR: This work designs a new class of NRR electrocatalysts based on a single transition metal (TM) atom supported on the experimentally feasible two-dimensional C2N monolayer (TM@C2N), and opens a new avenue for optimizing the TM catalytic performance for the NRR with the lowest number of metal atoms on porous low-dimensional materials.
Abstract: The nitrogen reduction reaction (NRR) under ambient conditions using renewable energy is a green and sustainable strategy for the synthesis of NH3, which is one of the most important chemicals and carbon-free carriers. Thus, the search for low-cost, highly efficient, and stable NRR electrocatalysts is critical to achieve this goal. Herein, using comprehensive density functional theory (DFT) computations, we design a new class of NRR electrocatalysts based on a single transition metal (TM) atom supported on the experimentally feasible two-dimensional C2N monolayer (TM@C2N). Based on the computed free energies of each elementary pathway, Mo@C2N is predicted to exhibit the best catalytic activity among the TM@C2N, in which the proton-coupled electron transfer of the NH2* species to NH3(g) is the potential-determining step. Especially, the computed onset potential of the NRR on Mo@C2N is −0.17 V, which is even lower than that for the well-established stepped Ru(0001) surface (−0.43 V). Furthermore, the NRR catalytic performance of these TM@C2N can be well explained by their adsorption strength with N2H* species. Our findings open a new avenue for optimizing the TM catalytic performance for the NRR with the lowest number of metal atoms on porous low-dimensional materials.
TL;DR: It is demonstrated that CH3 NH3PbI3 devices do not require any residual PbI2 for a high performance and a comparison of solar cell parameters of devices prepared using CH3NH3P bI3 samples having different Pbi2 contents reveals a strong influence on the current density-voltage hysteresis as well as storage stability.
Abstract: We report a systematic investigation on the role of excess PbI2 content in CH3NH3PbI3 perovskite film properties, solar cell parameters and device storage stability. We used the CH3NH3I vapor assisted method for the preparation of PbI2-free CH3NH3PbI3 films under a N2 atmosphere. These pristine CH3NH3PbI3 films were annealed at 165 °C for different time intervals in a N2 atmosphere to generate additional PbI2 in these films. From XRD measurements, the excess of PbI2 was quantified. Detailed characterization using scanning electron microscopy, X-ray diffraction, UV-Visible and photoluminescence for continuous aging of CH3NH3PbI3 films under ambient condition (50% humidity) is carried out for understanding the influence of different PbI2 contents on degradation of the CH3NH3PbI3 films. We find that the rate of degradation of CH3NH3PbI3 is accelerated due to the amount of PbI2 present in the film. A comparison of solar cell parameters of devices prepared using CH3NH3PbI3 samples having different PbI2 contents reveals a strong influence on the current density–voltage hysteresis as well as storage stability. We demonstrate that CH3NH3PbI3 devices do not require any residual PbI2 for a high performance. Moreover, a small amount of excess PbI2, which improves the initial performance of the devices slightly, has undesirable effects on the CH3NH3PbI3 film stability as well as on device hysteresis and stability.
TL;DR: This work focuses on the novel and promising optoelectronic properties of organic cocrystals based on charge transfer interactions, and briefly discusses the outlook for the future development of these multicomponent crystalline materials.
Abstract: Organic cocrystals, formed by a combination of electron-rich donors and electron-poor acceptors, play an important role in tailoring the optoelectronic properties of molecular materials. Charge transfer interactions in cocrystals not only endow them with an ordered three-dimensional (3D) supramolecular network in different constituent units, but also render them ideal scaffolds to control the intermolecular interactions in multicomponent solids. In this perspective, we firstly introduce preparation methods, molecular packing modes and charge transfer in organic cocrystals. Then, we focus on the novel and promising optoelectronic properties of organic cocrystals based on charge transfer interactions. Finally, we briefly discuss the outlook for the future development of these multicomponent crystalline materials.
TL;DR: The state-of-the-art density functional theory calculations suggest that the 2D JTMD monolayers are promising for nanoelectronic, optoelectronics, and photocatalytic applications.
Abstract: Atomically thin Janus transition metal dichalcogenides (JTMDs) with an asymmetric structure have emerged as a new class of intriguing two-dimensional (2D) semiconductor materials. Using state-of-the-art density functional theory (DFT) calculations, we systematically investigate the structural, electronic, and optical properties of JTMD monolayers and heterostructures. Our calculated results indicate that the JTMD monolayers suffer from a bending strain but present high thermodynamic stability. All of them are semiconductors with a band-gap range from 1.37 to 1.96 eV. They possess pronounced optical absorption in the visible-light region and cover a large range of carrier mobilities from 28 to 606 cm2 V−1 s−1, indicating strong anisotropic characteristics. Significantly, some monolayer JTMDs (e.g., WSSe and WSeTe) exhibit superior mobilities than conventional TMD monolayers, such as MoS2. Moreover, the absolute band-edge positions of the JTMD monolayers are higher than the water redox potential, and most JTMD heterostructures have a type-II band alignment that contributes to the separation of carriers. Our work suggests that the 2D JTMD monolayers are promising for nanoelectronic, optoelectronic, and photocatalytic applications.
TL;DR: Modification methods to optimize the performance of key VFB materials and investigations of models and simulations of VFBs will be discussed, and the available ideas and approaches will be provided to direct further improvements in the power density and energy density of V FB systems.
Abstract: Vanadium flow batteries (VFBs) have received increasing attention due to their attractive features for large-scale energy storage applications. However, the relatively high cost and severe polarization of VFB energy storage systems at high current densities restrict their utilization in practical industrial applications. Optimization of the performance of key VFB materials, including electrodes, electrolytes and membranes, can realize simultaneous minimization of polarization and capacity decay. The power density and energy density of VFBs are thus simultaneously enhanced. Moreover, relevant theoretical mechanisms and foundations based on virtual investigations of VFB models and simulations can guide these optimizations. The improved power density and energy density can reduce the cost of VFB energy storage systems, accelerating their successful industrialization. In this perspective, modification methods to optimize the performance of key VFB materials and investigations of models and simulations of VFBs will be discussed. Therefore, the available ideas and approaches will be provided to direct further improvements in the power density and energy density of VFB systems.
TL;DR: The findings of this study may further facilitate the rational design of more potent but less toxic multi-target antidepressant drugs.
Abstract: Amitifadine, the only drug ever clinically tested in Phase 3 for treating depression, is a triple reuptake inhibitor (TRI) that simultaneously interacts with human monoamine transporters (MATs) including hSERT, hNET and hDAT. This novel multi-target strategy improves drug efficacy and reduces the toxic side effects of drugs. However, the binding modes accounting for amitifadine's polypharmacological mode of action are still elusive, and extensive exploration of the amitifadine–target interactions between amitifadine and MATs is urgently needed. In this study, a total of 0.63 μs molecular dynamics (MD) simulations with an explicit solvent as well as endpoint binding free energy (BFE) calculation were carried out. MD simulation results identified a shared binding mode involving eleven key residues at the S1 site of MATs for the binding of amitifadine, and the results of the BFE calculations were in good agreement with experimental reports. Moreover, by analyzing the per-residue energy contribution variation at the S1 site of three MATs and additional cross-mutagenesis simulations, the variation in the inhibition ratio of amitifadine between hSERT and two other MATs was discovered to mainly come from non-conserved residues (Y95, I172 and T439 in hNET and Y95, I172, A169 and T439 in hDAT). As the rational inhibition ratio of multi-target drugs among various therapeutic targets was found to be the key to their safety and tolerance, the findings of this study may further facilitate the rational design of more potent but less toxic multi-target antidepressant drugs.
TL;DR: Transference numbers thus clearly deviate from apparent transference numbers estimated from diffusion coefficients, as an effect of a vehicular transport mechanism, which has important implications for the mechanism of Li mass transport in Li ion batteries as the drift of charged clusters has to be overcompensated by diffusive mass transport of neutral, Li-containing aggregates.
Abstract: The electrophoretic mobilities μ of all ion species in the lithium salt/ionic liquid mixtures LiTFSA/EmimTFSA and LiBF4/EmimBF4 are determined by 1H, 19F and 7Li electrophoretic NMR. The average drift direction of Li is identical to that of the anions TFSA- or BF4-. This proves a correlated ion motion of Li with the anions in negatively charged Li-containing clusters in both systems. The effective charge of these clusters is determined as -1, or -2 in the system with TFSA or BF4, respectively, pointing at the existence of [Li(TFSA)2]- or [Li(BF4)3]2-. This behavior is described by a negative effective transference number of Li, resulting in a negative contribution of Li ions to the overall conductivity. Li effective transference numbers are in the range of -0.04 to -0.02, depending on Li salt concentration and anion type. Transference numbers thus clearly deviate from apparent transference numbers estimated from diffusion coefficients, as an effect of a vehicular transport mechanism. This has important implications for the mechanism of Li mass transport in Li ion batteries as the drift of charged clusters has to be overcompensated by diffusive mass transport of neutral, Li-containing aggregates.
TL;DR: These issues can be fully explained in coulombic terms, electrostatics and polarization (which include electronic correlation and dispersion) in the context of noncovalent interactions.
Abstract: Since quantum mechanical calculations do not typically lend themselves to chemical interpretation, analyses of bonding interactions depend largely upon models (the octet rule, resonance theory, charge transfer, etc.). This sometimes leads to a blurring of the distinction between mathematical modelling and physical reality. The issue of polarization vs. charge transfer is an example; energy decomposition analysis is another. The Hellmann–Feynman theorem at least partially bridges the gap between quantum mechanics and conceptual chemistry. It proceeds rigorously from the Schrodinger equation to demonstrating that the forces exerted upon the nuclei in molecules, complexes, etc., are entirely classically coulombic attractions with the electrons and repulsions with the other nuclei. In this paper, we discuss these issues in the context of noncovalent interactions. These can be fully explained in coulombic terms, electrostatics and polarization (which include electronic correlation and dispersion).
TL;DR: This work uses Bayesian statistics using the nested-sampling algorithm to compare and rank multiple models of ergodic diffusion as well as to assess their optimal parameters for in silico-generated and real time-series, and presents first model-ranking results in application to experimental data of tracer diffusion in polymer-based hydrogels.
Abstract: We employ Bayesian statistics using the nested-sampling algorithm to compare and rank multiple models of ergodic diffusion (including anomalous diffusion) as well as to assess their optimal parameters for in silico-generated and real time-series We focus on the recently-introduced model of Brownian motion with "diffusing diffusivity"-giving rise to widely-observed non-Gaussian displacement statistics-and its comparison to Brownian and fractional Brownian motion, also for the time-series with some measurement noise We conduct this model-assessment analysis using Bayesian statistics and the nested-sampling algorithm on the level of individual particle trajectories We evaluate relative model probabilities and compute best-parameter sets for each diffusion model, comparing the estimated parameters to the true ones We test the performance of the nested-sampling algorithm and its predictive power both for computer-generated (idealised) trajectories as well as for real single-particle-tracking trajectories Our approach delivers new important insight into the objective selection of the most suitable stochastic model for a given time-series We also present first model-ranking results in application to experimental data of tracer diffusion in polymer-based hydrogels
TL;DR: The central aim of this paper is the detailed investigation of the relationship between defect interactions at the microscopic level and the macroscopic oxygen ion conductivity in the bulk of doped ceria, and by combining ab initio density functional theory (DFT) with Kinetic Monte Carlo (KMC) simulations, the oxygen ions conductivity is predicted as a function of the doping concentration.
Abstract: Materials with high oxygen ion conductivity and low electronic conductivity are required for electrolytes in solid oxide fuel cells (SOFC) and high-temperature electrolysis (SOEC) A potential candidate for the electrolytes, which separate oxidation and reduction processes, is rare-earth doped ceria The prediction of the ionic conductivity of the electrolytes and a better understanding of the underlying atomistic mechanisms provide an important contribution to the future of sustainable and efficient energy conversion and storage The central aim of this paper is the detailed investigation of the relationship between defect interactions at the microscopic level and the macroscopic oxygen ion conductivity in the bulk of doped ceria By combining ab initio density functional theory (DFT) with Kinetic Monte Carlo (KMC) simulations, the oxygen ion conductivity is predicted as a function of the doping concentration Migration barriers are analyzed for energy contributions, which are caused by the interactions of dopants and vacancies with the migrating oxygen vacancy We clearly distinguish between energy contributions that are either uniform for forward and backward jumps or favor one migration direction over the reverse direction If the presence of a dopant changes the migration energy identically for forward and backward jumps, the resulting energy contribution is referred to as blocking If the change in migration energy due to doping is different for forward and backward jumps of a specific ionic configuration, the resulting energy contributions are referred to as trapping The influence of both effects on the ionic conductivity is analyzed: blocking determines the dopant fraction where the ionic conductivity exhibits the maximum Trapping limits the maximum ionic conductivity value In this way, a deeper understanding of the underlying mechanisms determining the influence of dopants on the ionic conductivity is obtained and the ionic conductivity is predicted more accurately The detailed results and insights obtained here for doped ceria can be generalized and applied to other ion conductors that are important for SOFCs and SOECs as well as solid state batteries
TL;DR: Combining UPS and UV-Vis spectroscopies in order to get the full description of the electronic band alignment of powder samples, TiO2 rutile and anatase provides a better insight into the properties of a powdered material which can differ from single crystal model systems.
Abstract: An accurate experimental determination of electronic structures in semi-conductor nanopowders is a challenging task. We propose here to combine UPS and UV-Vis spectroscopies in order to get the full description of the electronic band alignment of powder samples, TiO2 rutile and anatase. For UPS measurements, two preparation methods, namely the dropping method and electrophoretic deposition, were used to prepare layers of titania powders on a conducting substrate, ITO or Ag. Both methods lead to comparable results, with a quantitative description of the energy levels from the valence band. Combining these results with the UV-Vis spectra of the same powders enables the determination of the absolute position of the valence band maximum and the conduction band minimum. Combined UPS-UV-Vis spectroscopy provides a better insight into the properties of a powdered material which can differ from single crystal model systems. It can also be used to predict the electronic transfer in mixed phase systems during photocatalytic processes.
TL;DR: A 2D fluid dynamics model for the interaction between a plasma jet and liquid water indicates that the formed reactive species originate from either the gas phase (with further solvation) or are formed at the liquid interface.
Abstract: The interaction between cold atmospheric pressure plasma and liquids is receiving increasing attention for various applications. In particular, the use of plasma-treated liquids (PTL) for biomedical applications is of growing importance, in particular for sterilization and cancer treatment. However, insight into the underlying mechanisms of plasma–liquid interactions is still scarce. Here, we present a 2D fluid dynamics model for the interaction between a plasma jet and liquid water. Our results indicate that the formed reactive species originate from either the gas phase (with further solvation) or are formed at the liquid interface. A clear increase in the aqueous density of H2O2, HNO2/NO2− and NO3− is observed as a function of time, while the densities of O3, HO2/O2− and ONOOH/ONOO− are found to quickly reach a maximum due to chemical reactions in solution. The trends observed in our model correlate well with experimental observations from the literature.
TL;DR: The ZnWO4 nanocrystals obtained at 160 °C exhibited excellent photodegradation of Rhodamine under ultraviolet light irradiation, which was found to be related to the surface energy and the types of clusters formed on the surface of the catalyst.
Abstract: The present joint experimental and theoretical work provides in-depth understanding on the morphology and structural, electronic, and optical properties of ZnWO4 nanocrystals. Monoclinic ZnWO4 nanocrystals were prepared at three different temperatures (140, 150, and 160 °C) by a microwave hydrothermal method. Then, the samples were investigated by X-ray diffraction with Rietveld refinement analysis, field-emission scanning electron microscopy, transmission electronic microscopy, micro-Raman and Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, and photoluminescence measurements. First-principles theoretical calculations within the framework of density functional theory were employed to provide information at the atomic level. The band structure diagram, density of states, Raman and infrared spectra were calculated to understand the effect of structural order-disorder on the properties of ZnWO4. The effects of the synthesis temperature on the above properties were rationalized. The band structure revealed direct allowed transitions between the VB and CB and the experimental results in the ultraviolet-visible region were consistent with the theoretical results. Moreover, the surface calculations allowed the association of the surface energy stabilization with the temperature used in the synthesis of the ZnWO4 nanocrystals. The photoluminescence properties of the ZnWO4 nanocrystals prepared at 140, 150, and 160 °C were attributed to oxygen vacancies in the [WO6] and [ZnO6] clusters, causing a red shift of the spectra. The ZnWO4 nanocrystals obtained at 160 °C exhibited excellent photodegradation of Rhodamine under ultraviolet light irradiation, which was found to be related to the surface energy and the types of clusters formed on the surface of the catalyst.
TL;DR: The chemical structure of the hydrogen bond acceptor (HBA) in a DES clearly controls the dipolarity/polarizability afforded by the DES and a substitution of the HBD was found to play an important role in solvatochromic probe behaviour for all the studied systems.
Abstract: Deep eutectic solvents (DESs) constitute a new class of ionic solvents that has been developing at a fast pace in recent years. Since these solvents are commonly suggested as green alternatives to organic solvents, it is important to understand their physical properties. In particular, polarity plays an important role in solvation phenomena. In this work, the polarity of different families of DESs was studied through solvatochromic responses of UV-vis absorption probes. Kamlet–Taft α, β, π* and ETN parameters were evaluated using different solvatochromic probes, as 2,6-dichloro-4-(2,4,6-triphenyl-N-pyridino)-phenolate (Reichardt's betaine dye 33), 4-nitroaniline, and N,N-diethyl-4-nitroaniline for several families of DESs based on cholinium chloride, DL-menthol and a quaternary ammonium salt ([N4444]Cl). In addition, a study to understand the difference in polarity properties between DESs and the corresponding ILs, namely ILs based on cholinium cation and carboxylic acids as anions ([Ch][Lev], [Ch][Gly] and [Ch][Mal]), was carried out. The chemical structure of the hydrogen bond acceptor (HBA) in a DES clearly controls the dipolarity/polarizability afforded by the DES. Moreover, Kamlet–Taft parameters do not vary much within the family, but they differ among families based on different HBA, either for DESs containing salts ([Ch]Cl or [N4444]Cl) or neutral compounds (DL-menthol). A substitution of the HBD was also found to play an important role in solvatochromic probe behaviour for all the studied systems.
TL;DR: This review has reviewed the recent developments in oil/water separation by using superwetting porous materials, mainly focusing on natural materials and shows how to use superwettability of the natural materials to separate different mixtures of water and oil.
Abstract: The frequency of oil spills and the increasing amount of oily sewage not only cause serious water pollution as well as a lot of ecological problems but also result in huge economic losses To address such problems, developing advanced technologies and materials for achieving efficient oil/water separation is a critical way and emerging as a hot research topic nowadays Herein, we have reviewed the recent developments in oil/water separation by using superwetting porous materials, mainly focusing on natural materials By using natural materials as examples, we show how to use superwetting porous materials to separate different mixtures of water and oil, including the inherent superwettability of the natural materials, separating method/process, and separation mechanism Natural superwetting materials are usually low-cost and eco-friendly, and can be easily obtained, so oil/water separation based on natural materials has great promise to address the above-mentioned globally recognized oil contamination challenge In addition, these natural examples seem more attractive to the general researcher who is new to this field as well as the expert and even the public, since natural materials look more interesting than artificial complex materials We believe our review will help beginners better understand the significance, application value, mechanism and principle of oil/water separation by superwetting porous materials
TL;DR: Using density functional theory, this work investigated systematically the electronic properties and Schottky barrier modulation in a multilayer graphene/bilayer-GaSe heterostructure by varying the interlayer spacing and by applying an external electric field.
Abstract: In this work, using density functional theory we investigated systematically the electronic properties and Schottky barrier modulation in a multilayer graphene/bilayer-GaSe heterostructure by varying the interlayer spacing and by applying an external electric field. At the equilibrium state, the graphene is bound to bilayer-GaSe by a weak van der Waals interaction with the interlayer distance d of 3.40 A with the binding energy per carbon atom of -37.71 meV. The projected band structure of the graphene/bilayer-GaSe heterostructure appears as a combination of each band structure of graphene and bilayer-GaSe. Moreover, a tiny band gap of about 10 meV is opened at the Dirac point in the graphene/bilayer-GaSe heterostructure due to the sublattice symmetry breaking. The band gap opening in graphene makes it suitable for potential applications in nanoelectronic and optoelectronic devices. The graphene/bilayer-GaSe heterostructure forms an n-type Schottky contact with the Schottky barrier height of 0.72 eV at the equilibrium interlayer spacing. Furthermore, a transformation from the n-type to p-type Schottky contact could be performed by decreasing the interlayer distance or by applying an electric field. This transformation is observed when the interlayer distance is smaller than 3.30 A, or when the applied positive external electric field is larger than 0.0125 V A-1. These results are very important for designing new electronic Schottky devices based on graphene and other 2D semiconductors such as a graphene/bilayer-GaSe heterostructure.
TL;DR: This study successfully synthesized porous 2D sponge-like Ni/derivative heterostructures composed of Ni, NiO and Ni(OH)2 through a controllable hydrogen reduction method, demonstrating a fresh exploration of designing novel electromagnetic wave absorbing materials.
Abstract: One of the major hurdles of Ni-based microwave absorbing materials is the preparation of two-dimensional (2D) Ni flakes that can improve magnetic anisotropy to tune complex permeability. In this study, we successfully synthesized porous 2D sponge-like Ni/derivative heterostructures composed of Ni, NiO and Ni(OH)2 through a controllable hydrogen reduction method. Thanks to the larger grain size of the Ni/derivative heterostructure prepared at 600 °C (Ni-600) under hydrogen flow, good magnetic properties and high magnetic loss could be obtained, which is beneficial for the enhancement of microwave absorption properties. For the Ni-600 samples, the minimal reflection loss (RL) is −37.3 dB at 7.1 GHz and the effective bandwidth (RL < −10 dB, 90% microwave dissipation) could be tuned in the range of 4.5–18.0 GHz with the thickness of 1.5–4.5 mm. High attenuation ability, including dielectric loss and magnetic loss, and good impedance matching are the requirements for excellent microwave absorption properties. In addition, the porous 2D heterostructure flake structure also significantly contributes to microwave absorption. Multiple reflections and scattering caused by the porous flakes, interfacial polarizations in the heterostructures, tunable impedance matching in the porous structure, strong natural resonance induced by the 2D flakes and plentiful micro-capacitors in the separate flakes account for the enhanced microwave absorption performance. This study demonstrates a fresh exploration of designing novel electromagnetic wave absorbing materials.