查看更多>>摘要：Quaternary halide double perovskites exhibit a range of electronic properties,making them candidates for a variety of applications,notably in optoelectronics.The determination of the band gap of these materials has proved difficult and large discrepancies are found in results reported in the literature.In this work,we use first-principles methods to study the electronic structure of cesium chloride double perovskites Cs2B'B"Cl6,with B'= Ag,Na and B"= Bi,In.We employ the DFT-1/2 approximate quasiparticle method to determine the electronic structure of these materials.This approach is an accurate and computationally efficient alternative to more expensive techniques,like hybrid functionals and GW quasiparticle calculations,opening an avenue to study more complex systems,as heterostructures,interfaces,and defects.
查看更多>>摘要：Using nonadiabatic molecular dynamics combined with the time-domain density functional theory,we have explored the influence of selenide vacancy and passivation of anions with different radii on the nonradiative charge trapping and recombination in monolayer InSe.Our results reveal that electron-hole recombination for pristine InSe occurs within several nanoseconds due to the weak nonadiabatic(NA) coupling.Selenide vacancy generates three trap states within the band gap,enhances the NA coupling,and provides new channels for charge carrier relaxation,resulting in the significantly decreased charge carrier recombination time.Passivating the selenide vacancy with anions(O~(2-),S~(2-),and Te~(2-)) can eliminate the trap states within the band gap and extend the charge carrier lifetimes because of the decreased NA coupling.Meanwhile,the passivation effect of anions is dramatically dependent on the type of anions,and S2-is more suitable for repairing selenide vacancy than O~(2-) and Te~(2-) because S~(2-) and Se~(2-) have much closer radii.This study provides an atomistic mechanism of the effects of selenide vacancy and anion passivation on the performance of InSe thin-film solar cells and suggests that the choice of anions with a suitable radius is valuable for prolonging the excited-state lifetime.
查看更多>>摘要：Solar conversions of water to hydrogen and carbon dioxide to hydrocarbon fuels are the two attractive options to reduce global warming and generation of sustainable energy.The mission for utilization of the sunlight to the maximum extent for these purposes has provided motivation to find efficient materials.In the present study,we have systematically investigated the electronic structure of Co-doped TiO2 with anatase crystal structure to explain the experimentally observed photocatalytic activity and to explore the limiting factors.The present study revealed the preferred charge state for Co to achieve the best photoconversion efficiency.We have also investigated the role of lattice defects in the photoactivity of Co-doped TiO2.Motivated by experimental observation,we have investigated the role of codoping of B/N/V into Co-doped TiO2.For this purpose,we have employed a more reliable hybrid density functional.To further enhance the photoactivity,we have proposed codoping with(F/Sb/Nb/Ta/Cr/Mo/W) into Co-doped TiO2.We have checked the feasibility of doping by calculating the defect formation energy.Interestingly,codoping with(F/Sb/V/Nb/Ta) successfully overcomes the limitations of Co-doped TiO2.Finally,eligibility of these materials toward water splitting and CO2 conversion is checked by aligning the band edges with respect to water and CO,redox levels.By considering all these factors,the present study was carried out to find out the best choice of the dopant pair to enhance the photocatalytic activity for TiO2 under sunlight.
查看更多>>摘要：In this study,we prepared singie-walled carbon nanotube electrodes for lithium-air batteries(LABs) to investigate the structural changes of the electrodes during the discharge-charge cycle coupled with the precipitation and decomposition of Li oxide.Wide-angle X-ray scattering(WAXS) and small-angle X-ray scattering(SAXS) were used for the structural analysis.A new test cell was designed and fabricated to perform these measurements under operando conditions.From the results of the WAXS measurements during discharge tests,diffraction peaks indicating crystalline oxides and a broad peak indicating amorphous components were observed.The intensities of these peaks increased rapidly in the later stages of the discharge.Moreover,the WAXS measurements showed that the peak of the amorphous component preferentially disappears during the charging process.Furthermore,the nanoscale structural changes associated with the precipitation and decomposition of Li oxide were analyzed using SAXS.The results suggest that the electrode expansion caused electrolyte depletion in the electrode.The post-test electrode thickness was also analyzed,and the results support interpreting the data obtained from WAXS and SAXS.We think that the structural analysis approach and the pore formation discovered in this study will enable LABs to be used more effectively in the future.
查看更多>>摘要：Polymer-based electrolytes would be ideal for all-solid-state Li metal batteries due to the superior processability of polymers and their ability to make good interfaces with electrode materials.However,polymer electrolytes have lower room temperature Li~+ conductivities than desired.Composite solid electrolytes(CSEs) containing both polymer and ceramic filler have far greater conductivity than the polymer alone,and it is believed this is due to conduction paths along the polymer-ceramic interface.A strategy often pursued for increasing conductivity has been to engineer the filler with a high aspect ratio shape,such as nanorods or interconnected nanofibers.In this work we employ a multiscale hollow spherical filler,which is not directional but achieves similar conductivity to those with fibrous morphologies.The hollow spherical shape avoids agglomeration and provides continuous Li~+ transfer channels.We fabricated multiscale hollow spherical ceramic Li_(1.3)Al_(0.3)Ti_(17)(PO4)3(LATP) nanoparticles for use in a poly(ethylene oxide)(PEO) matrix.This network also provided structural support and enhanced the mechanical properties of the polymer matrix,which is important for a battery electrolyte.The resulting CSE membrane had room temperature ionic conductivity of 1.64 × 10~(-4) S/cm.Li/Li symmetric cells using this CSE showed no short circuits for 500 h cycling at a current density 0.1 mA cm~(-2).Control cells using standard LATP powder showed higher overpotential and dendrite failure,as did the polymer membrane with no LATP.
查看更多>>摘要：Due to the high cost and limited availability of lithium,Mg-based batteries are currently being investigated as a promising alternative.A critical component in these batteries is the electrolyte,with all-solid-state ones that show superior safety features but must guarantee adequate ionic conductivity to be viable for applications.In this work,a metal borohydride ammonia borane complex,Mg(BH4)2(NH3BH3)2,was theoretically investigated using state-of-the-art ab initio methods based on density functional theory(DFT) approaches and software for the modeling of battery materials.Several features of this compound were first characterized,including its crystal structure and topology,vibrational properties,and infrared and Raman spectra.Theoretical results were compared with experiments showing excellent agreement,thus properly setting the ground for ionic transport analysis.Magnesium ion migration was then investigated by performing climbing image nudged elastic band(CI-NEB) calculations.The most promising migration path occurs along the c-axis and presents two transition states with a calculated migration barrier(including weak van der Waals interactions) in the range of 0.550-0.668 eV.The topological analysis suggests repulsive interactions between Mg and B atoms.It has been confirmed that defect formation energy plays an essential role in correctly evaluating the activation energy for ion migration,as shown by comparing calculated and experimental results for this system.Assuming the formation of Frenkel pairs as the dominant mechanism,the calculated defect formation energy is 1.05 eV(per single defect),which combined with the migration barrier gives a value of the activation energy for migration in the range of 1.60-1.71 eV.The present findings confirm that the activation energy for ion migration in solid-state electrolytes can be reliably estimated by DFT-based methods.
查看更多>>摘要：Interfacial engineering is significantly important for achieving the high performance of perovskite solar cells.Exploring and developing universally efficient methods and strategies for interlayer optimization are greatly demanded by perovskite solar cells to reduce photovoltaic losses.By introducing small-molecule F4-TCNQ and conjugated polyelectrolyte PFN-Br as dopants,the performance regulation of inverted perovskite solar cells was systematically investigated.The results demonstrate the great effectiveness of F4-TCNQ to improve the V_(OC)(from 0.959 to 1.032 V) and PFN-Br to enhance the current density(from 21.50 to 24.41 mA/cm~2) of devices,as their ability to passivate defects,optimize energy-level alignment,and promote charge extraction.The synergistic/bifacial modification accomplished simultaneous enhancement of the parameters,thus improving the efficiency.The basic morphology and optical property of perovskite films were characterized to understand the performance parameters.This work provides a simple effective method for interface modification to reduce photovoltaic loss in perovskite solar cells and demonstrates the promising potential of bifacial modification to enhance the device performance.
查看更多>>摘要：The thick electrode design is preferential in high-energy lithium-ion batteries(LIBs) systems.However,the sluggish ionic transport in homogeneous porous thick electrodes severely limits the areal capacity at high charging/discharging rates.The hierarchical porous design is a promising approach to mitigate kinetic limitations because it can distribute mass effectively in natural systems.In this study,the effects of bimodal microscale pores are fully investigated in thick electrodes from both architectural and electrochemical perspectives.Notably,by introduction of the bimodal microscale porous structure,the rate capability improves remarkably in thick electrodes with a low porosity(39%).By combining experimental results with simulations,this work presents a rational design guideline for preparing thick electrodes with a porosity at the commercial level,as well as simultaneous high energy and power densities,which brings new insights into the advanced electrode architecture design in scalable high-energy and high-power energy storage systems for practical applications.
查看更多>>摘要：Controlling the surface composition of colloidal nanoparticles is still a challenging yet mandatory prerequisite in catalytic studies to investigate composition-activity trends,active sites,and reaction mechanisms without superposition of particle size or morphology effects.Laser post-processing of colloidal nanoparticles has been employed previously to create defects in oxide nanoparticles,while the possibility of laser-based cation doping of colloidal nanoparticles without affecting their size remains mostly unaccounted for.Consequently,at the example of doping iron into colloidal Co3O4 spinel nanoparticles,we developed a pulse-by-pulse laser cation doping method to provide a catalyst series with a gradually modified surface composition but maintained extrinsic properties such as phase,size,and surface area for catalytic studies.Laser pulse number-resolved doping series were prepared at a laser intensity chosen to selectively heat the Co3O4-NPs to roughly 1000 K and enable cation diffusion of surface-adsorbed Fe~(3+) into the Co3O4 lattice.The combination of bulk-sensitive X-ray fluorescence and surface-sensitive X-ray photoelectron spectroscopy was used to confirm the surface enrichment of the Fe-dopant.X-ray diffraction,magnetometry,and Mossbauer spectroscopy revealed an increasing interaction between Fe and the antiferromagnetic Co3O4 with arising number of applied laser pulses,in line with a herein proposed laser-induced surface doping of the colloidal Co3O4 nanoparticles with Fe.Using Fick's second law,the thermal diffusion-related doping depth was estimated to be roughly 2 nm after 4 laser pulses.At the example of gas-phase 2-propanol oxidation and liquid-phase oxygen evolution reaction,the activity of the laser-doped catalysts is in good agreement with previous activity observations on binary iron-cobalt oxides.The catalytic activity was found to linearly increase with the calculated doping depth in both reactions,while only catalysts processed with at least one laser pulse were catalytically stable,highlighting the presented method in providing comparable,active,and stable gradual catalyst doping series for future catalytic studies.
查看更多>>摘要：Identifying and characterizing active surface phases are critical for understanding([the behavior of oxidation catalysts.In this study,we investigated the catalytic activity of Ir(l00) and an IrOj(110) film for the complete oxidation of methane at pressures near 1 Torr and characterized the surface activity using ambient pressure X-ray photoelectron spectroscopy(AP-XPS) measurements and density functional theory(DFT) calculations.Our results show that IrO2(110) is highly active for catalytic CH4 oxidation in CH4-rich mixtures(~90% CH4) and moderate temperature(650 K),whereas the Ir(l00) surface is inactive at the same conditions.AP-XPS shows that the Ir(l00) surface remains metallic when immersed in the CH4-rich mixture at temperatures up to 650 K but becomes nearly saturated with chemisorbed O atoms.According to DFT,CH4 activation is facile on clean Ir(l00),but activation via H transfer to a chemisorbed O atom has a significantly higher energy barrier.The DFT calculations further predict that the dissociative chemisorption of O2 is more efficient than CH4 dissociation on Ir(l00) and generates high O coverages even in CH4-enriched reactant mixtures.As a result,the preferential adsorption of oxygen effectively poisons Ir(l00) toward initial CH4 activation,rendering this surface inactive for catalytic CH4 oxidation.Our results clarify the fundamental origins of the catalytic activity of Ir(l00) and IrO2(ll0) toward CH4 oxidation and provide insights about reaction conditions that can enhance the activity of Ir catalysts for this chemistry.
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