The main challenge in lithium sulphur (Li-S) batteries is the shuttling of lithium polysulphides ... more The main challenge in lithium sulphur (Li-S) batteries is the shuttling of lithium polysulphides (LiPSs) caused by the rapid LiPSs migration to the anode and the slow reaction kinetics in the chain of LiPSs conversion. In this study, we explore 1T-MoS2 as a cathode host for Li-S batteries by examining the affinity of 1T-MoS2 substrates (pristine 1T-MoS2, defected 1T-MoS2 with one and two S vacancies) toward LiPSs and their electrocatalytic effects. Density functional theory (DFT) simulations are used to determine the adsorption energy of LiPSs to these substrates, the Gibbs free energy profiles for the reaction chain, and the preferred pathways and activation energies for the slow reaction stage from Li2S4 to Li2S. The obtained information highlights the potential benefit of a combination of 1T-MoS2 regions, without or with one and two sulphur vacancies, for an improved Li-S battery performance. The recommendation is implemented in a Li-S battery with areas of pristine 1T-MoS2 and s...
To support the development of hydrogen production by high temperature electrolysis using solid ox... more To support the development of hydrogen production by high temperature electrolysis using solid oxide electrolysis cells (SOECs), the effects of operating conditions on the performance of the SOECs were investigated using a one-dimensional model of a cathode-supported planar SOEC stack. Among all the operating parameters, temperature is the most influential factor on the performance of an SOEC, in both cell voltage and operation mode (i.e. endothermic, thermoneutral and exothermic). Current density is another influential factor, in both cell voltage and operation mode. For the conditions used in this study it is recommended that the SOEC be operated at 1073 K and with an average current density of 10000 A m-2 , as this results in the stack operating at almost constant temperature along the cell length. Both the steam molar fraction at the inlet and the steam utilisation factor have little influence on the cell voltage of the SOEC but their influence on the temperature distribution cannot be neglected. Changes in the operating parameters of the SOEC can result in a transition between endothermic and exothermic operation modes, calling for careful temperature control. The introduction of air into the anode stream appears to be a promising approach to ensure small temperature variations along the cell.
Correction for ‘A revised mechanistic model for sodium insertion in hard carbons’ by Heather Au e... more Correction for ‘A revised mechanistic model for sodium insertion in hard carbons’ by Heather Au et al., Energy Environ. Sci., 2020, 13, 3469–3479, DOI: 10.1039/D0EE01363C.
Experimental and computational study of the electrode evolutions in a bismuth-potassium battery r... more Experimental and computational study of the electrode evolutions in a bismuth-potassium battery reveals that the voltage plateau variation results from intermediate phases and structural collapse.
In the search for post lithium ion batteries (LIBs), sodium ion batteries (NIBs) are gaining trac... more In the search for post lithium ion batteries (LIBs), sodium ion batteries (NIBs) are gaining traction, but fundamental understanding of the atomic scale interactions at the anode electrolyte interfaces in NIBs remains poorly understood. In moving from LIBs, the LIB anode material graphite was found to be unsuitable for NIBs. Instead, hard carbon anode materials have arisen as one of the most promising electrode materials for sodium ion batteries (NIBs), which are also suitable for use with carbonate based electrolyte solvents. Hard carbons are complex amorphous carbon structures with randomly orientated, defective, and curved graphene nanosheets, and turbostratically stacked graphitic layers. This complex structure leads to a plethora of carbon structural motifs being present in the anode, leading to a large number of potential morphologies having to be taken into account when investigating the anode electrolyte interface. In this study, we use ab initio molecular dynamics to invest...
High capacity electrode materials are the key for high energy density Li-ion batteries (LIB) to m... more High capacity electrode materials are the key for high energy density Li-ion batteries (LIB) to meet the requirement of the increased driving range of electric vehicles. Here we report the synthesis of a novel anode material, Bi 2 MoO 6 /palm-carbon composite, via a simple hydrothermal method. The composite shows higher reversible capacity and better cycling performance, compared to pure Bi 2 MoO 6 . In 0-3 V, a potential window of 100 mA/g current density, the LIB cells based on Bi 2 MoO 6 /palm-carbon composite show retention reversible capacity of 664 mAh•g -1 after 200 cycles. Electrochemical testing and ab initio density functional theory calculations are used to study the fundamental mechanism of Li ion incorporation into the materials. These studies confirm that Li ions incorporate into Bi 2 MoO 6 via insertion to the interstitial sites in the MoO 6 -layer, and the presence of palm-carbon improves the electronic conductivity, and thus enhanced the performance of the composite materials.
Recently, molecular dynamics (MD) simulations have been utilized to investigate the barrier prope... more Recently, molecular dynamics (MD) simulations have been utilized to investigate the barrier properties of human skin stratum corneum (SC) lipid bilayers. Different MD methods and force fields have been utilized, with predicted permeabilities varying by few orders of magnitude. In this work, we compare constrained MD simulations with restrained MD simulations to obtain the potential of the mean force and the diffusion coefficient profile for the case of a water molecule permeating across an SC lipid bilayer. Corresponding permeabilities of the simulated lipid bilayer are calculated via the inhomogeneous solubility diffusion model. Results show that both methods perform similarly, but restrained MD simulations have proven to be the more robust approach for predicting the potential of the mean force profile. Critical to both methods are the sampling of the whole trans-bilayer axis and the following symmetrization process. Re-analysis of the previously reported free energy profiles showed that some of the discrepancies in the reported permeability values is due to misquotation of units, while some are due to the inaccurately obtained potential of the mean force. By using the existing microscopic geometrical models via the intercellular lipid pathway, the permeation through the whole SC is predicted from the MD simulation results, and the predicted barrier properties have been compared to experimental data from the literature with good agreement.
The solvation effect enables the amorphous P4SSe2 compound to deliver excellent electrochemical p... more The solvation effect enables the amorphous P4SSe2 compound to deliver excellent electrochemical performance as an advanced anode for sodium-ion batteries in ether-based electrolytes.
Batteries that extend performance beyond the intrinsic limits of Li-ion batteries are among the m... more Batteries that extend performance beyond the intrinsic limits of Li-ion batteries are among the most important developments required to continue the revolution promised by electrochemical devices. Of these next-generation batteries, lithium sulfur (Li–S) chemistry is among the most commercially mature, with cells offering a substantial increase in gravimetric energy density, reduced costs and improved safety prospects. However, there remain outstanding issues to advance the commercial prospects of the technology and benefit from the economies of scale felt by Li-ion cells, including improving both the rate performance and longevity of cells. To address these challenges, the Faraday Institution, the UK’s independent institute for electrochemical energy storage science and technology, launched the Lithium Sulfur Technology Accelerator (LiSTAR) programme in October 2019. This Roadmap, authored by researchers and partners of the LiSTAR programme, is intended to highlight the outstanding...
The performance of metal-ion batteries at low temperatures and their fast charge/discharge rates ... more The performance of metal-ion batteries at low temperatures and their fast charge/discharge rates are determined mainly by the electrolyte (ion) transport. Accurate transport properties must be evaluated for designing and/or optimization of lithium-ion and other metal-ion batteries. In this review, we report and discuss experimental and atomistic computational studies on ion transport, in particular, ion diffusion/dynamics, transference number, and ionic conductivity. Although a large number of studies focusing on lithium-ion transport in organic liquids have been performed, only a few experimental studies have been conducted in the organic liquid electrolyte phase for other alkali metals that are used in batteries (such as sodium, potassium, magnesium, etc.). Atomistic computer simulations can play a primary role and predict ion transport in organic liquids. However, to date, atomistic force fields and models have not been explored and developed exhaustively to simulate such organic...
Journal of Chemical Information and Modeling, 2021
Liquid-liquid extraction (LLE) is an important technique to separate aromatics from aliphatics si... more Liquid-liquid extraction (LLE) is an important technique to separate aromatics from aliphatics since these compounds have very similar boiling points and cannot be separated by distillation. Ionic liquids (ILs) are considered as potential extractants to extract aromatics from aliphatics. In this paper, molecular dynamics (MD) simulations were used to predict the extraction property (i.e., capacity and selectivity) of ILs for the LLE of aromatics from aliphatics. The extraction properties of seven different ILs including [C2mim][Tf2N], [C2mim][TFO], [C2mim][SCN], [C2mim][DCA], [C2mim][TCM], [C4mim][Tf2N], and [C8mim][Tf2N] were investigated. Results show that ILs with shorter alkyl chain cations and [Tf2N]- anion exhibit better extraction efficiency than other ILs, which is in agreement with previously reported experimental data on the extraction of toluene from aliphatics and further validated the reliability of the proposed model. The binding energies between ILs and organic molecules were calculated by the density functional theory, which help explain the different extraction behaviors of different ILs. The symmetry-adapted perturbation theory analysis was performed to further understand the interaction mechanisms between ILs and organics. Our study shows that the [Tf2N]- anion also has the best extraction capability for heavier aromatics (o-xylene, m-xylene, and p-xylene) from common aliphatics (heptane and octane). The MD modeling approach can be a low-cost in silico tool for the high-throughput fast screening of ILs for the LLE of aromatics from aliphatics.
complements to Li whose resources are rapidly declining with increasing energy demands. [5] For t... more complements to Li whose resources are rapidly declining with increasing energy demands. [5] For the next-generation batteries to emerge, optimization of the anode material needs to be achieved. Hard carbons (HCs) are promising alkali ion metal battery anodes, [6,7] and have been successfully synthesized from biomass, making this anode material interesting from a sustainability and circular economy perspective. [8] Currently, HC anodes are limited by their poor rate capability, irreversible capacity loss, and insufficient voltage. [7,9] To improve the HC anode performance, atomic scale structural understanding is essential. HCs are complex nanoporous disordered nongraphitizable materials consisting of randomly oriented, curved, and defective graphene nanosheets (sometimes also referred to as fullerenic) with varying interlayer distances. [7,10,11] The structure consists of sp 2-hybridized carbons in a hexagonal pattern, with pentagons, defects, and sp 3-hybridized carbons interspersed throughout the structure. [11-14] A variety of defects have been shown to exist in the graphenic sheets such as carbon vacancies and heteroatom defects. [11,14,15] High-resolution transmission electron spectroscopy images of HC structures show curved regions that are randomly interlinked, with rumpling leading to the formation of a domed surface. [16] These curved regions are interpreted as randomly stacked graphene layers arching as a result of strain or packing, with highly defective and disordered structures. [16-20] Metal ions can store at defects both at basal plane and edge sites, within pores, and in between the turbostratically stacked expanded graphitic layers. [7,21-23] During electrochemical cycling, the increased capacity observed for HC anodes is attributed to surface defects, adsorption at basal plane defects, metal deposition in pores, and bond formation with heteroatoms. [6,10,22] The surface adsorption contributing to metal ion storage and the voltage profile is dependent on the HC surface, which is in contact with the electrolyte. [9,10,23,24] The HC surface can vary greatly between different HCs. These differences are attributed to the synthetic method and the presence of defects and heteroatoms. [9,10,14,23,25,26] Furthermore, cross-linking of the sp 2-hybridized carbon layers through sp 3-hybridized carbon atoms has been observed in HC materials from their Raman spectra. [1,6,24] Deciphering the interplay between these motifs is challenging but vital in developing an understanding of HC as an anode material. HCs from different precursors have been shown to have markedly different structures and heteroatom contents. [6,7,22,27] Hard carbon anodes have shown significant promise for next-generation battery technologies. These nanoporous carbon materials are highly complex and vary in structure depending on synthesis method, precursors, and pyrolysis temperature. Structurally, hard carbons are shown to consist of disordered planar and curved motifs, which have a dramatic impact on anode performance. Here, the impact of position on defect formation energy is explored through density functional theory simulations, employing a mixed planar bulk and curved surface model. At defect sites close to the surface, a dramatic decrease (≥ ≥50%) in defect formation energy is observed for all defects except the nitrogen substitutional defect. These results confirm the experimentally observed enhanced defect concentration at surfaces. Previous studies have shown that defects have a marked impact on metal storage. This work explores the interplay between position and defect type for lithium, sodium, and potassium adsorption. Regardless of defect location, it is found that the energetic contributions to the metal adsorption energies are principally dictated by the defect type and carbon interlayer distance.
Abstract This work reports the preparation of nanocrystalline Ni-Gd0.1Ce0.9O1.95 (NiO-GDC) anode ... more Abstract This work reports the preparation of nanocrystalline Ni-Gd0.1Ce0.9O1.95 (NiO-GDC) anode powders using a novel single-step co-precipitation synthesis method (carboxylate route) based on ammonium tartrate as a low-cost green precipitant. The thermogravimetric analysis (TGA) of the synthesised powder showed the complete calcination/crystallisation of the resultant precipitates to take place at 500 °C. The prepared NiO-GDC powder was coated on a GDC electrolyte disc and co-sintered at 1300 °C. A mixture of La0.6Sr0.4Co0.2Fe0.8O3−δ and GDC was used as the cathode material and subsequently coated onto the anode-electrolyte bilayer, resulting in the fabrication of a NiO-GDC|GDC|La0.6Sr0.4Co0.2Fe0.8O3−δ-GDC cell. The crystallite size of both NiO and CeO2 phases were estimated using the X-ray powder diffraction (XRD) profiles and were calculated to be ∼14 nm. Applied H2 temperature-programmed reduction (H2-TPR) analysis indicated a synergetic effect among different anode composites' constituents, where an intense interaction between the dispersed NiO nanocrystalline particles and the GDC crystallite phase had weakened the metal-oxygen bonds in the synthesised anode composites, resulting in a strikingly high catalytic activity at temperatures as low as 300 °C. The electrochemical impedance spectroscopy (EIS) and the electrochemical performance of the fabricated cells were measured over a broad range of operating temperatures (500–750 °C) and H2/Ar-ratios of the anode fuel (e.g. 100%–15%). Quantitative analysis from the EIS data and the application of the distribution of relaxation times (DRT) method allowed for the estimation of the activation energies of the anodic high and intermediate frequency processes that were 0.45 eV and 0.76 eV, respectively. This is the first report of a NiO-GDC synthesis, where a considerable improvement in activation energy is observed at the low-temperature region. Such low activation energies were later associated with the adsorption/desorption process of water molecules at the surface of NiO-GDC composite, indicating a high activity towards hydrogen oxidation.
Abstract The δ-MnO2 nanowires are fabricated and chemically bonded with the carbon black that has... more Abstract The δ-MnO2 nanowires are fabricated and chemically bonded with the carbon black that has appropriate amounts of oxygen containing functional groups. These short δ-MnO2 nanowires are (006) crystal plane-dominated and the hybrid (δ-MnO2 nanowires/carbon black) exhibits enhanced electrocatalytic activity towards oxygen reduction reaction (ORR). The half-wave potential (0.82 V (vs. RHE)) and limiting-current density (5.47 mA cm−2) of the hybrid in alkaline medium are close to those of 20 wt% Pt/C, respectively. The hybrid is used as cathodic catalyst in a Zn-air battery cell, which displays a peak power density of 138.0 mW cm−2, comparable to that using Pt/C catalyst (142.8 mW cm−2). This excellent catalytic performance is attributed to the unique microstructure of the hybrid that accelerates the kinetics of ORR. Furthermore, the ORR catalytic mechanism is also systematically analysed based on the microstructural characterization and electrochemical response.
Sodium filling inside hard carbon pores demonstrates increasingly metallic character with increas... more Sodium filling inside hard carbon pores demonstrates increasingly metallic character with increasing pore size.
Abstract Carbon nanofiber (CNF) papers have been widely used in many renewable energy systems, an... more Abstract Carbon nanofiber (CNF) papers have been widely used in many renewable energy systems, and the development of its catalytic function is of great significance and a major challenge. In this work, we pioneer a time- and cost-efficient strategy for the preparation of large-area flexible CNF films with uniformly distributed diatomic FeN3-CoN3 sites (Fe1Co1-CNF). Due to the excellent compatibility and similar functionality of the pre-designed ZnFeCo-NC precursors (ZnFeCo-pre) with the electrospun polymer polyacrylonitrile (PAN), the mixture of ZnFeCo-pre and PAN can be co-electrospun and subject to a standard CNF fabrication process. The resulting Fe1Co1-CNF exhibits excellent bifunctional catalytic performance for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), attributing to the abundant dual catalytic FeN3-CoN3 sites which are mutually beneficial for attaining optimal electronic properties for the adsorption/desorption of reaction intermediates. The assembled liquid-electrolyte ZAB provides a high specific power of 201.7 mW cm−2 and excellent cycling stability. More importantly, due to the good mechanical strength and flexibility of Fe1Co1-CNF, portable ZAB with exceptional shape deformability and stability can be demonstrated, in which Fe1Co1-CNF utility as an integrated free-standing membrane electrode. These findings provide a facile strategy for manufacturing flexible multi-functional catalytic electrodes with high production.
CO2/CH4 separation using ionic liquids (ILs) encapsulated metal-organic frameworks (MOFs), especi... more CO2/CH4 separation using ionic liquids (ILs) encapsulated metal-organic frameworks (MOFs), especially ZIF-8, has shown promise as a new technique for separating CO2 from CH4. However, the mechanisms behind the high CO2/CH4 selectivity of the method remains indistinct. Here we report the progress of understanding the mechanisms from examining the ZIF-8 aperture configuration variation using DFT and MD simulations. The results indicate that the pristine aperture configuration exhibits the best separation performance, and the addition of ILs prevents the apertures from large swing (i.e. configuration variation). Subsequently, the effect of IL viscosity on the layout variation was investigated. MD simulations also show that the pristine aperture configuration is more stabilized by ILs with large viscosity (0-87Cp). Further increase of IL viscosity above 87Cp did not result in noticeable changes in the aperture stability.
Two-dimensional nanoporous graphene (NPG) with uniformly distributed nanopores has been synthesiz... more Two-dimensional nanoporous graphene (NPG) with uniformly distributed nanopores has been synthesized recently and shown remarkable electronic, mechanical, thermal, and optical properties with potential applications in several fields [Science 360, 199 (2018)]. Here, we explore the potential application of NPG as an anode material for Li, Na, K, Mg and Ca ion batteries. We use density functional theory calculations to study structural properties, defect formation energies, metal binding energies, charge analysis, and electronic structures of NPG monolayers. Pristine NPG can bind effectively K + cations, but cannot bind the other metal cations sufficiently strongly, which is a prerequisite of an efficient anode material. However, upon substitution with oxygen-rich functional groups (e.g., O, OH, COOH) and doping with heteroatoms (B, N, P, S), the metal binding ability of NPG is significantly enhanced. Of the considered systems, S-doped NPG (S-NPG) binds the metal cations most strongly with binding energies of-3.87 (Li),-3.28 (Na),-3.37 (K),-3.68 (Mg), and-4.97 (Ca) eV, followed by P-NPG, O-NPG, B-NPG, and N-NPG. Of the substituted NPG systems, O substituted NPG exhibits the strongest metal binding with binding energies of-3.30 (Li),-2.62 (Na),-2.89 (K),-1.67 (Mg) and-3.40 eV (Ca). Bader charge analysis and Roby-Gould bond indices show that a significant amount of charge is transferred from the metal cations to the functionalized NPG monolayers. Electronic properties were studied by density of states plots and all the systems were found to be metallic upon the introduction of metal cations. These results suggest that functionalized NPG could be used as a global anode material for Li, Na, K, Mg, and Ca ion batteries.
Hard carbons are among the most promising materials for alkali-ion metal anodes. These materials ... more Hard carbons are among the most promising materials for alkali-ion metal anodes. These materials have a highly complex structure and understanding the metal storage and migration within these structures is of utmost importance for the development of next-generation battery technologies. The effect of different carbon structural motifs on Li, Na, and K storage and diffusion are probed using density functional theory based on experimental characterizations of hard carbon samples. Two carbon structural models-the planar graphitic layer model and the cylindrical pore model-are constructed guided by small-angle X-ray scattering and transmission electron microscopy characterization. The planar graphitic layers with interlayer distance <6.5 Å are beneficial for metal storage, but do not have significant contribution to rapid metal diffusion. Fast diffusion is shown to take place in planar graphitic layers with interlayer distance >6.5 Å, when the graphitic layer separation becomes so wide that there is negligible interaction between the two graphitic layers. The cylindrical pore model, reflecting the curved morphology, does not increase metal storage, but significantly lowers the metal migration barriers. Hence, the curved carbon morphologies are shown to have great importance for battery cycling. These findings provide an atomic-scale picture of the metal storage and diffusion in these materials.
The main challenge in lithium sulphur (Li-S) batteries is the shuttling of lithium polysulphides ... more The main challenge in lithium sulphur (Li-S) batteries is the shuttling of lithium polysulphides (LiPSs) caused by the rapid LiPSs migration to the anode and the slow reaction kinetics in the chain of LiPSs conversion. In this study, we explore 1T-MoS2 as a cathode host for Li-S batteries by examining the affinity of 1T-MoS2 substrates (pristine 1T-MoS2, defected 1T-MoS2 with one and two S vacancies) toward LiPSs and their electrocatalytic effects. Density functional theory (DFT) simulations are used to determine the adsorption energy of LiPSs to these substrates, the Gibbs free energy profiles for the reaction chain, and the preferred pathways and activation energies for the slow reaction stage from Li2S4 to Li2S. The obtained information highlights the potential benefit of a combination of 1T-MoS2 regions, without or with one and two sulphur vacancies, for an improved Li-S battery performance. The recommendation is implemented in a Li-S battery with areas of pristine 1T-MoS2 and s...
To support the development of hydrogen production by high temperature electrolysis using solid ox... more To support the development of hydrogen production by high temperature electrolysis using solid oxide electrolysis cells (SOECs), the effects of operating conditions on the performance of the SOECs were investigated using a one-dimensional model of a cathode-supported planar SOEC stack. Among all the operating parameters, temperature is the most influential factor on the performance of an SOEC, in both cell voltage and operation mode (i.e. endothermic, thermoneutral and exothermic). Current density is another influential factor, in both cell voltage and operation mode. For the conditions used in this study it is recommended that the SOEC be operated at 1073 K and with an average current density of 10000 A m-2 , as this results in the stack operating at almost constant temperature along the cell length. Both the steam molar fraction at the inlet and the steam utilisation factor have little influence on the cell voltage of the SOEC but their influence on the temperature distribution cannot be neglected. Changes in the operating parameters of the SOEC can result in a transition between endothermic and exothermic operation modes, calling for careful temperature control. The introduction of air into the anode stream appears to be a promising approach to ensure small temperature variations along the cell.
Correction for ‘A revised mechanistic model for sodium insertion in hard carbons’ by Heather Au e... more Correction for ‘A revised mechanistic model for sodium insertion in hard carbons’ by Heather Au et al., Energy Environ. Sci., 2020, 13, 3469–3479, DOI: 10.1039/D0EE01363C.
Experimental and computational study of the electrode evolutions in a bismuth-potassium battery r... more Experimental and computational study of the electrode evolutions in a bismuth-potassium battery reveals that the voltage plateau variation results from intermediate phases and structural collapse.
In the search for post lithium ion batteries (LIBs), sodium ion batteries (NIBs) are gaining trac... more In the search for post lithium ion batteries (LIBs), sodium ion batteries (NIBs) are gaining traction, but fundamental understanding of the atomic scale interactions at the anode electrolyte interfaces in NIBs remains poorly understood. In moving from LIBs, the LIB anode material graphite was found to be unsuitable for NIBs. Instead, hard carbon anode materials have arisen as one of the most promising electrode materials for sodium ion batteries (NIBs), which are also suitable for use with carbonate based electrolyte solvents. Hard carbons are complex amorphous carbon structures with randomly orientated, defective, and curved graphene nanosheets, and turbostratically stacked graphitic layers. This complex structure leads to a plethora of carbon structural motifs being present in the anode, leading to a large number of potential morphologies having to be taken into account when investigating the anode electrolyte interface. In this study, we use ab initio molecular dynamics to invest...
High capacity electrode materials are the key for high energy density Li-ion batteries (LIB) to m... more High capacity electrode materials are the key for high energy density Li-ion batteries (LIB) to meet the requirement of the increased driving range of electric vehicles. Here we report the synthesis of a novel anode material, Bi 2 MoO 6 /palm-carbon composite, via a simple hydrothermal method. The composite shows higher reversible capacity and better cycling performance, compared to pure Bi 2 MoO 6 . In 0-3 V, a potential window of 100 mA/g current density, the LIB cells based on Bi 2 MoO 6 /palm-carbon composite show retention reversible capacity of 664 mAh•g -1 after 200 cycles. Electrochemical testing and ab initio density functional theory calculations are used to study the fundamental mechanism of Li ion incorporation into the materials. These studies confirm that Li ions incorporate into Bi 2 MoO 6 via insertion to the interstitial sites in the MoO 6 -layer, and the presence of palm-carbon improves the electronic conductivity, and thus enhanced the performance of the composite materials.
Recently, molecular dynamics (MD) simulations have been utilized to investigate the barrier prope... more Recently, molecular dynamics (MD) simulations have been utilized to investigate the barrier properties of human skin stratum corneum (SC) lipid bilayers. Different MD methods and force fields have been utilized, with predicted permeabilities varying by few orders of magnitude. In this work, we compare constrained MD simulations with restrained MD simulations to obtain the potential of the mean force and the diffusion coefficient profile for the case of a water molecule permeating across an SC lipid bilayer. Corresponding permeabilities of the simulated lipid bilayer are calculated via the inhomogeneous solubility diffusion model. Results show that both methods perform similarly, but restrained MD simulations have proven to be the more robust approach for predicting the potential of the mean force profile. Critical to both methods are the sampling of the whole trans-bilayer axis and the following symmetrization process. Re-analysis of the previously reported free energy profiles showed that some of the discrepancies in the reported permeability values is due to misquotation of units, while some are due to the inaccurately obtained potential of the mean force. By using the existing microscopic geometrical models via the intercellular lipid pathway, the permeation through the whole SC is predicted from the MD simulation results, and the predicted barrier properties have been compared to experimental data from the literature with good agreement.
The solvation effect enables the amorphous P4SSe2 compound to deliver excellent electrochemical p... more The solvation effect enables the amorphous P4SSe2 compound to deliver excellent electrochemical performance as an advanced anode for sodium-ion batteries in ether-based electrolytes.
Batteries that extend performance beyond the intrinsic limits of Li-ion batteries are among the m... more Batteries that extend performance beyond the intrinsic limits of Li-ion batteries are among the most important developments required to continue the revolution promised by electrochemical devices. Of these next-generation batteries, lithium sulfur (Li–S) chemistry is among the most commercially mature, with cells offering a substantial increase in gravimetric energy density, reduced costs and improved safety prospects. However, there remain outstanding issues to advance the commercial prospects of the technology and benefit from the economies of scale felt by Li-ion cells, including improving both the rate performance and longevity of cells. To address these challenges, the Faraday Institution, the UK’s independent institute for electrochemical energy storage science and technology, launched the Lithium Sulfur Technology Accelerator (LiSTAR) programme in October 2019. This Roadmap, authored by researchers and partners of the LiSTAR programme, is intended to highlight the outstanding...
The performance of metal-ion batteries at low temperatures and their fast charge/discharge rates ... more The performance of metal-ion batteries at low temperatures and their fast charge/discharge rates are determined mainly by the electrolyte (ion) transport. Accurate transport properties must be evaluated for designing and/or optimization of lithium-ion and other metal-ion batteries. In this review, we report and discuss experimental and atomistic computational studies on ion transport, in particular, ion diffusion/dynamics, transference number, and ionic conductivity. Although a large number of studies focusing on lithium-ion transport in organic liquids have been performed, only a few experimental studies have been conducted in the organic liquid electrolyte phase for other alkali metals that are used in batteries (such as sodium, potassium, magnesium, etc.). Atomistic computer simulations can play a primary role and predict ion transport in organic liquids. However, to date, atomistic force fields and models have not been explored and developed exhaustively to simulate such organic...
Journal of Chemical Information and Modeling, 2021
Liquid-liquid extraction (LLE) is an important technique to separate aromatics from aliphatics si... more Liquid-liquid extraction (LLE) is an important technique to separate aromatics from aliphatics since these compounds have very similar boiling points and cannot be separated by distillation. Ionic liquids (ILs) are considered as potential extractants to extract aromatics from aliphatics. In this paper, molecular dynamics (MD) simulations were used to predict the extraction property (i.e., capacity and selectivity) of ILs for the LLE of aromatics from aliphatics. The extraction properties of seven different ILs including [C2mim][Tf2N], [C2mim][TFO], [C2mim][SCN], [C2mim][DCA], [C2mim][TCM], [C4mim][Tf2N], and [C8mim][Tf2N] were investigated. Results show that ILs with shorter alkyl chain cations and [Tf2N]- anion exhibit better extraction efficiency than other ILs, which is in agreement with previously reported experimental data on the extraction of toluene from aliphatics and further validated the reliability of the proposed model. The binding energies between ILs and organic molecules were calculated by the density functional theory, which help explain the different extraction behaviors of different ILs. The symmetry-adapted perturbation theory analysis was performed to further understand the interaction mechanisms between ILs and organics. Our study shows that the [Tf2N]- anion also has the best extraction capability for heavier aromatics (o-xylene, m-xylene, and p-xylene) from common aliphatics (heptane and octane). The MD modeling approach can be a low-cost in silico tool for the high-throughput fast screening of ILs for the LLE of aromatics from aliphatics.
complements to Li whose resources are rapidly declining with increasing energy demands. [5] For t... more complements to Li whose resources are rapidly declining with increasing energy demands. [5] For the next-generation batteries to emerge, optimization of the anode material needs to be achieved. Hard carbons (HCs) are promising alkali ion metal battery anodes, [6,7] and have been successfully synthesized from biomass, making this anode material interesting from a sustainability and circular economy perspective. [8] Currently, HC anodes are limited by their poor rate capability, irreversible capacity loss, and insufficient voltage. [7,9] To improve the HC anode performance, atomic scale structural understanding is essential. HCs are complex nanoporous disordered nongraphitizable materials consisting of randomly oriented, curved, and defective graphene nanosheets (sometimes also referred to as fullerenic) with varying interlayer distances. [7,10,11] The structure consists of sp 2-hybridized carbons in a hexagonal pattern, with pentagons, defects, and sp 3-hybridized carbons interspersed throughout the structure. [11-14] A variety of defects have been shown to exist in the graphenic sheets such as carbon vacancies and heteroatom defects. [11,14,15] High-resolution transmission electron spectroscopy images of HC structures show curved regions that are randomly interlinked, with rumpling leading to the formation of a domed surface. [16] These curved regions are interpreted as randomly stacked graphene layers arching as a result of strain or packing, with highly defective and disordered structures. [16-20] Metal ions can store at defects both at basal plane and edge sites, within pores, and in between the turbostratically stacked expanded graphitic layers. [7,21-23] During electrochemical cycling, the increased capacity observed for HC anodes is attributed to surface defects, adsorption at basal plane defects, metal deposition in pores, and bond formation with heteroatoms. [6,10,22] The surface adsorption contributing to metal ion storage and the voltage profile is dependent on the HC surface, which is in contact with the electrolyte. [9,10,23,24] The HC surface can vary greatly between different HCs. These differences are attributed to the synthetic method and the presence of defects and heteroatoms. [9,10,14,23,25,26] Furthermore, cross-linking of the sp 2-hybridized carbon layers through sp 3-hybridized carbon atoms has been observed in HC materials from their Raman spectra. [1,6,24] Deciphering the interplay between these motifs is challenging but vital in developing an understanding of HC as an anode material. HCs from different precursors have been shown to have markedly different structures and heteroatom contents. [6,7,22,27] Hard carbon anodes have shown significant promise for next-generation battery technologies. These nanoporous carbon materials are highly complex and vary in structure depending on synthesis method, precursors, and pyrolysis temperature. Structurally, hard carbons are shown to consist of disordered planar and curved motifs, which have a dramatic impact on anode performance. Here, the impact of position on defect formation energy is explored through density functional theory simulations, employing a mixed planar bulk and curved surface model. At defect sites close to the surface, a dramatic decrease (≥ ≥50%) in defect formation energy is observed for all defects except the nitrogen substitutional defect. These results confirm the experimentally observed enhanced defect concentration at surfaces. Previous studies have shown that defects have a marked impact on metal storage. This work explores the interplay between position and defect type for lithium, sodium, and potassium adsorption. Regardless of defect location, it is found that the energetic contributions to the metal adsorption energies are principally dictated by the defect type and carbon interlayer distance.
Abstract This work reports the preparation of nanocrystalline Ni-Gd0.1Ce0.9O1.95 (NiO-GDC) anode ... more Abstract This work reports the preparation of nanocrystalline Ni-Gd0.1Ce0.9O1.95 (NiO-GDC) anode powders using a novel single-step co-precipitation synthesis method (carboxylate route) based on ammonium tartrate as a low-cost green precipitant. The thermogravimetric analysis (TGA) of the synthesised powder showed the complete calcination/crystallisation of the resultant precipitates to take place at 500 °C. The prepared NiO-GDC powder was coated on a GDC electrolyte disc and co-sintered at 1300 °C. A mixture of La0.6Sr0.4Co0.2Fe0.8O3−δ and GDC was used as the cathode material and subsequently coated onto the anode-electrolyte bilayer, resulting in the fabrication of a NiO-GDC|GDC|La0.6Sr0.4Co0.2Fe0.8O3−δ-GDC cell. The crystallite size of both NiO and CeO2 phases were estimated using the X-ray powder diffraction (XRD) profiles and were calculated to be ∼14 nm. Applied H2 temperature-programmed reduction (H2-TPR) analysis indicated a synergetic effect among different anode composites' constituents, where an intense interaction between the dispersed NiO nanocrystalline particles and the GDC crystallite phase had weakened the metal-oxygen bonds in the synthesised anode composites, resulting in a strikingly high catalytic activity at temperatures as low as 300 °C. The electrochemical impedance spectroscopy (EIS) and the electrochemical performance of the fabricated cells were measured over a broad range of operating temperatures (500–750 °C) and H2/Ar-ratios of the anode fuel (e.g. 100%–15%). Quantitative analysis from the EIS data and the application of the distribution of relaxation times (DRT) method allowed for the estimation of the activation energies of the anodic high and intermediate frequency processes that were 0.45 eV and 0.76 eV, respectively. This is the first report of a NiO-GDC synthesis, where a considerable improvement in activation energy is observed at the low-temperature region. Such low activation energies were later associated with the adsorption/desorption process of water molecules at the surface of NiO-GDC composite, indicating a high activity towards hydrogen oxidation.
Abstract The δ-MnO2 nanowires are fabricated and chemically bonded with the carbon black that has... more Abstract The δ-MnO2 nanowires are fabricated and chemically bonded with the carbon black that has appropriate amounts of oxygen containing functional groups. These short δ-MnO2 nanowires are (006) crystal plane-dominated and the hybrid (δ-MnO2 nanowires/carbon black) exhibits enhanced electrocatalytic activity towards oxygen reduction reaction (ORR). The half-wave potential (0.82 V (vs. RHE)) and limiting-current density (5.47 mA cm−2) of the hybrid in alkaline medium are close to those of 20 wt% Pt/C, respectively. The hybrid is used as cathodic catalyst in a Zn-air battery cell, which displays a peak power density of 138.0 mW cm−2, comparable to that using Pt/C catalyst (142.8 mW cm−2). This excellent catalytic performance is attributed to the unique microstructure of the hybrid that accelerates the kinetics of ORR. Furthermore, the ORR catalytic mechanism is also systematically analysed based on the microstructural characterization and electrochemical response.
Sodium filling inside hard carbon pores demonstrates increasingly metallic character with increas... more Sodium filling inside hard carbon pores demonstrates increasingly metallic character with increasing pore size.
Abstract Carbon nanofiber (CNF) papers have been widely used in many renewable energy systems, an... more Abstract Carbon nanofiber (CNF) papers have been widely used in many renewable energy systems, and the development of its catalytic function is of great significance and a major challenge. In this work, we pioneer a time- and cost-efficient strategy for the preparation of large-area flexible CNF films with uniformly distributed diatomic FeN3-CoN3 sites (Fe1Co1-CNF). Due to the excellent compatibility and similar functionality of the pre-designed ZnFeCo-NC precursors (ZnFeCo-pre) with the electrospun polymer polyacrylonitrile (PAN), the mixture of ZnFeCo-pre and PAN can be co-electrospun and subject to a standard CNF fabrication process. The resulting Fe1Co1-CNF exhibits excellent bifunctional catalytic performance for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), attributing to the abundant dual catalytic FeN3-CoN3 sites which are mutually beneficial for attaining optimal electronic properties for the adsorption/desorption of reaction intermediates. The assembled liquid-electrolyte ZAB provides a high specific power of 201.7 mW cm−2 and excellent cycling stability. More importantly, due to the good mechanical strength and flexibility of Fe1Co1-CNF, portable ZAB with exceptional shape deformability and stability can be demonstrated, in which Fe1Co1-CNF utility as an integrated free-standing membrane electrode. These findings provide a facile strategy for manufacturing flexible multi-functional catalytic electrodes with high production.
CO2/CH4 separation using ionic liquids (ILs) encapsulated metal-organic frameworks (MOFs), especi... more CO2/CH4 separation using ionic liquids (ILs) encapsulated metal-organic frameworks (MOFs), especially ZIF-8, has shown promise as a new technique for separating CO2 from CH4. However, the mechanisms behind the high CO2/CH4 selectivity of the method remains indistinct. Here we report the progress of understanding the mechanisms from examining the ZIF-8 aperture configuration variation using DFT and MD simulations. The results indicate that the pristine aperture configuration exhibits the best separation performance, and the addition of ILs prevents the apertures from large swing (i.e. configuration variation). Subsequently, the effect of IL viscosity on the layout variation was investigated. MD simulations also show that the pristine aperture configuration is more stabilized by ILs with large viscosity (0-87Cp). Further increase of IL viscosity above 87Cp did not result in noticeable changes in the aperture stability.
Two-dimensional nanoporous graphene (NPG) with uniformly distributed nanopores has been synthesiz... more Two-dimensional nanoporous graphene (NPG) with uniformly distributed nanopores has been synthesized recently and shown remarkable electronic, mechanical, thermal, and optical properties with potential applications in several fields [Science 360, 199 (2018)]. Here, we explore the potential application of NPG as an anode material for Li, Na, K, Mg and Ca ion batteries. We use density functional theory calculations to study structural properties, defect formation energies, metal binding energies, charge analysis, and electronic structures of NPG monolayers. Pristine NPG can bind effectively K + cations, but cannot bind the other metal cations sufficiently strongly, which is a prerequisite of an efficient anode material. However, upon substitution with oxygen-rich functional groups (e.g., O, OH, COOH) and doping with heteroatoms (B, N, P, S), the metal binding ability of NPG is significantly enhanced. Of the considered systems, S-doped NPG (S-NPG) binds the metal cations most strongly with binding energies of-3.87 (Li),-3.28 (Na),-3.37 (K),-3.68 (Mg), and-4.97 (Ca) eV, followed by P-NPG, O-NPG, B-NPG, and N-NPG. Of the substituted NPG systems, O substituted NPG exhibits the strongest metal binding with binding energies of-3.30 (Li),-2.62 (Na),-2.89 (K),-1.67 (Mg) and-3.40 eV (Ca). Bader charge analysis and Roby-Gould bond indices show that a significant amount of charge is transferred from the metal cations to the functionalized NPG monolayers. Electronic properties were studied by density of states plots and all the systems were found to be metallic upon the introduction of metal cations. These results suggest that functionalized NPG could be used as a global anode material for Li, Na, K, Mg, and Ca ion batteries.
Hard carbons are among the most promising materials for alkali-ion metal anodes. These materials ... more Hard carbons are among the most promising materials for alkali-ion metal anodes. These materials have a highly complex structure and understanding the metal storage and migration within these structures is of utmost importance for the development of next-generation battery technologies. The effect of different carbon structural motifs on Li, Na, and K storage and diffusion are probed using density functional theory based on experimental characterizations of hard carbon samples. Two carbon structural models-the planar graphitic layer model and the cylindrical pore model-are constructed guided by small-angle X-ray scattering and transmission electron microscopy characterization. The planar graphitic layers with interlayer distance <6.5 Å are beneficial for metal storage, but do not have significant contribution to rapid metal diffusion. Fast diffusion is shown to take place in planar graphitic layers with interlayer distance >6.5 Å, when the graphitic layer separation becomes so wide that there is negligible interaction between the two graphitic layers. The cylindrical pore model, reflecting the curved morphology, does not increase metal storage, but significantly lowers the metal migration barriers. Hence, the curved carbon morphologies are shown to have great importance for battery cycling. These findings provide an atomic-scale picture of the metal storage and diffusion in these materials.
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