Decomposition Barrier Research Articles

Monolayers APS3 (A = Cr, Co) as cathode hosts for lithium/sodium-sulfur batteries with enhanced electrochemical performance

Metal-sulfur batteries (M–S batteries, M = Li, Na), because of their high energy density and low cost, are expected to become the next-generation energy storage systems. However, their commercial applications are impeded by the poor conductivity of polysulfides, the “shuttle effect” of soluble M2Sn (n = 4, 6, 8), and the slow reaction kinetics. In this work, we perform first-principles calculations to find that the two-dimensional APS3 (A = Cr, Co) monolayers are effective sulfur host materials for high-performance M–S batteries. The metallic electronic structures of APS3 can accelerate electron transfer in reaction processes. The shuttle effect is inhibited by moderate binding strength between APS3 and M2Sn. Remarkably, APS3, as a bifunctional electrocatalyst, can greatly reduce the rate-limiting step of sulfur reduction reaction (SRR) and the decomposition barriers of Li2S/Na2S. We further explored the effect of strain engineering on the catalytic activity of APS3 for SRR and found that the battery performance can be regulated by varying the applied strains ranging from −2 % to 5 %. These findings provide a new direction for the design of highly efficient catalysts for M–S batteries.

Relay-Type Catalysis by a Dual-Metal Single-Atom System in a Waste Biomass Derivative Host for High-Rate and Durable Li-S Batteries.

An environmental-friendly and sustainable carbon-based host is one of the most competitive strategies for achieving high loading and practicality of Li-S batteries. However, the polysulfide conversion reaction kinetics is still limited by the nonuniform or monofunctional catalyst configuration in the carbon host. In this work, we propose a catalysis mode based on "relay-type" co-operation by adjacent dual-metal single atoms for high-rate and durable Li-S batteries. A discarded sericin fabric-derived porous N-doped carbon with a stacked schistose structure is prepared as the high-loading sulfur (84 wt %) host by a facile ionothermal method, which further enables the uniform anchoring of Fe/Co dual-metal single atoms. This multifunctional host enables superior lithiophilic-sulfiphilic and electrocatalytic capabilities contributed by the "relay-type" single-atom modulation effects on different conversion stages of liquid polysulfides and solid Li2S2/Li2S, leading to the suppression of the "shuttle effect", alleviation of nucleation and decomposition barriers of Li2Sx, and acceleration of polysulfide conversion kinetics. The corresponding Li-S batteries exhibit a high specific capacity of 1399.0 mA h g-1, high-rate performance up to 10 C, and excellent cycling stability over 1000 cycles. They can also endure the high sulfur loading of 8.5 mg cm-2 and the lean electrolyte condition and yield an areal capacity as high as 8.6 mA h cm-2. This work evidentially demonstrates the potential of waste biomass reutilization coupled with the design of a single-atom system for practical Li-S batteries with high energy density.

Engineering atomic Fe sites with asymmetrical nitrogen/sulfur coordination for stable and boosted sulfur conversion

Introducing nonmetallic heteroatoms into the conventional metal-N-C configuration is thought to be an effective strategy to regulate the coordinated chemistry environment of atomic metal centers and further improve the sulfur electrochemistry behavior in lithium-sulfur batteries. Nevertheless, the modulation of heteroatoms junction states (doped or coordinated) in carbocycle is rarely explored. Herein, based on the stable pre-coordination of Fe3+ and terminal sulfhydryl/amino groups in cysteine, an asymmetrical Fe-N3S1 coordination structure in cysteine-derived graphene (Fe/CG) is rationally designed and prepared. The intervention of S atom at the first-coordination shell of Fe centers could induce the distorted spatial coordination structure, which greatly reduces the Li2S decomposition barrier. Moreover, the bonded S atom increases the d-band center (Ɛda) of Fe and pronouncedly activates the surrounding atoms, enhancing the electronic conductivity and reaction activity/affinity of Fe/CG, which was evidenced through theoretical calculations. The serial electro-kinetic analysis further confirms the bidirectional catalytic effect of Li2S redox conversions on Fe/CG. Consequently, the S@Fe/CG cathodes exhibit outstanding cycling stability (718.8 mAh g−1 after 500 cycles at 1 C with a decay of 0.037 % per cycle) and rate performance (639 mAh g−1 at 4 C). This work provides a new perspective to regulate the local chemistry environment of metal centers via coordination engineering.

Uncovering the discharge structure evolution and electrochemical performance of sulfur cathode host 2D-Fe0.89M0.11S2 (M = Ti, V)

The sulfur cathode host materials with excellent electronic conductivity and catalytic performance are the key to highly efficient Li-S redox chemistry for the lithium‑sulfur batteries (LSBs). Although 2D-FeS2 as sulfur cathode host shows high theoretical capacity and flat voltage plateaus, the Li-S redox chemical reaction mechanism is still unclear. By using the first-principles calculations, the formation energy, working voltage, theoretical capacity, electronic conductivity, adsorption performance, electrocatalytic mechanism, Li+ diffusion and Li2S decomposition barrier of 2D-FeS2 and M (M = Ti, V) doped 2D-FeS2 are investigated to evaluate its physicochemical properties. 2D-Fe0.89M0.11S2 is thermodynamically stable due to its low lattice distortion, formation energy and mixing enthalpy. The charging voltage of 2D-Fe0.89Ti0.11S2 is better than that of 2D-Fe0.89V0.11S2, but the charging voltage step is reversed. The electrical conductivity of 2D-Fe0.89M0.11S2 is superior to 2D-FeS2. The closer the highest molecule occupied orbitals is to the Fermi level, the lower the discharge voltage will be. 2D-Fe0.89V0.11S2 and its discharge structure 2D-Li2Fe0.89V0.11S2 improve the efficiency of catalytic reduction of Li2S4. 2D-Fe0.89V0.11S2 has low Li+ diffusion and decomposition barrier of Li2S, which has potential application value in promoting the Li-S redox chemistry. This work deepens the understanding of the doping strategy and provides theoretical guidance for the design and development of sulfur cathode host to improve the Li-S redox chemistry.

Reconfiguration of the charge density difference of nitrogen-doped graphene by covalently bonded Cu-N4 active sites boosting thermodynamics and performance in aprotic Li-CO2 battery

The slow kinetics of the CO2 reduction and evolution reactions in the Li-CO2 battery result in a high overpotential, low energy efficiency and undesired life. Exploring the durable electrocatalysts with high activity for CO2 reduction and evolution processes in aprotic Li-CO2 batteries is of great significance for CO2 capture and utilization. Herein, single-atom copper uniformly anchored on nitrogen-doped graphene (SA-Cu-NG) was demonstrated as a durable catalyst for the rechargeable Li-CO2 battery. The resulting Li-CO2 battery shows a remarkable specific capacity of 29033 mAh g−1 at 100 mA g−1, an ultra-long life up to 538 cycles (over 2730 h), and a low overpotential of 1.47 V (1000 mA g−1), outperforming the reported Li-CO2 batteries. The X-ray absorption fine structure analysis of SA-Cu-NG unravels that the covalent effect between Cu and N, which exists in the form of Cu-N4 in nitrogen-doped graphene. Further, it is theoretically elucidated that the covalent effect of Cu-N4 leads to the reconfiguration of the charge density difference on nitrogen-doped graphene, thereby improving the adsorption of CO2 and weakening the decomposition barrier of the discharge products on the surface single-atom copper, thus optimizing the nucleation decomposition process. In conclusion, the exceptional performances of Li-CO2 battery are attributed to the superior catalytic activity on Cu-N4 sites and the excellent electronic conductivity of nitrogen-doped graphene, activating the reversible process of discharge product formation and decomposition.

Theoretical study on K poisoning resistance of M-doped Ce/TiO2 (001) surface (M=Cu, Co, Zr, Sb, Mo, Nb, W)

Enhancing the resistance of SCR (Selective Catalytic Reduction) catalyst to K poisoning can be effectively achieved through modification. This study investigated the impact of transition metal modification on improving the ability of Ce/TiO2 (CT) catalysts to resist K poisoning by DFT (Density functional theory) calculations. Mo-, Nb-, and W-doping could effectively suppress the adsorption of K. Ov (oxygen vacancy) formation and hydrogenation reactions were both facilitated due to the modification of Cu, Co and Sb. The Cu-doping had a significant contribution to the adsorption of NH3 and NO, and showed the best resistance to K poisoning in the adsorption of reactive species. Additionally, Cu-doping decreased the energy barriers for NH3 dehydrogenation, NH2NO generation and decomposition, and NO2 formation on CT catalyst, and weakened the inhibition effect of K on the above elementary reactions. Consequently, this provided an effective improvement in the k-poisoning tolerance of the CT catalysts.

Niobium Boride/Graphene Directing High-Performance Lithium-Sulfur Batteries Derived from Favorable Surface Passivation.

Efficient catalysts are needed to accelerate the conversion and suppress the shuttling of polysulfides (LiPSs) to promote the further development of lithium-sulfur (Li-S) batteries. Intermetallic niobium boride (NbB2) has indefinite potential due to superior catalytic activity. Nonetheless, the lack of a rational understanding of catalysis creates a challenge for the design of catalysts. Herein, a NbB2/reduced graphene oxide-modified PP separator (NbB2/rGO/PP) is rationally designed. Essential, an in-depth insight into the catalysis mechanism of NbB2 toward LiPSs is established based on experiments and multiperspective measurement characterization, ab initio molecular dynamics (AIMD), and density functional theory (DFT). It has been uncovered that the actual catalyst that interacts with LiPSs in NbB2 is the passivated surface with an oxide layer (O2-NbB2), which occurs through B-O-Li and Nb-O-Li bonds, rather than the clean NbB2 surface. And the decomposition barrier of Li2S is greatly reduced by a substantial margin, dropping from 3.390 to 0.93 and 0.85 eV on the Nb-O and B-O surfaces, respectively, with fast Li+ diffusivity. Consequently, the cell with NbB2/rGO/PP as a functional separator achieves a high discharge capacity of 873 mAh g-1 at 1C after 100 cycles. Moreover, the benefits of NbB2/rGO/PP can be effectively maintained even at a high sulfur loading of 7.06 mg cm-2 without significant reduction and with a low electrolyte/sulfur ratio of 8 μL mg-1s. This study enhances our understanding of the catalytic mechanism of Li-S systems and presents a promising approach for developing electrocatalysts that are resilient to poisoning.

Selecting non-metal doped FeS2 as efficient sulfur cathode host for enhanced Li-S redox chemistry.

Lithium-sulfur batteries (LSBs) are considered as the development direction of the new generation energy storage system due to their high energy density and low cost. The slow redox kinetics of sulfur and the shuttle effect of lithium polysulfide (LiPS) are considered to be the main obstacles to the practical application of LSBs. Transition-metal sulfide as the cathode host can improve the Li-S redox chemistry. However, there has been no investigation of the application of FeS2 host in Li-S redox chemistry. Applying the first-principles calculations, we investigated the formation energy, band gap, Li+ diffusion, adsorption energy, catalytic performance and Li2 S decomposition barrier of FeAx S2-x (A=N, P, O, Se; x=0, 0.125, 0.25, 0.375) to explore the Li-S redox chemistry and finally select excellent host material. FeA0.25 S1.75 (A=P, Se) has a low Li+ diffusion barrier and superior electronic conductivity. FeO0.25 S1.75 is more favorable for LiPS adsorption, followed by FeP0.25 S1.75 . FeP0.25 S1.75 (001) shows a low overpotential for the Li-S redox chemistry. In summary, FeP0.25 S1.75 has more application potential in LSBs due to its physical and chemical properties, followed by FeSe0.25 S1.75 . This work provides theoretical guidance for the design and selection of the sulfur cathode host materials in LSBs.

Synergistic promotion of electrocatalytic activities and multilevel descriptors in nitrogen-doped graphene supported dual-atom catalysts for lithium-sulfur batteries

Lithium-sulfur battery (LSB) is emerging as one of the most promising candidates in energy storage systems, but its performance is greatly limited by the polysulfide shuttle and sluggish reaction kinetics. Here, we focus on 18 dual-atom catalysts (DACs) supported by nitrogen-doped graphene with three types of metal coordination environment, namely M1M2Nx (M1, M2 = Fe, Co, Ni and x = 6 or 8), for sulfur redox by using first-principles calculations. Our results show that most DACs exhibit enhanced anchoring capacity toward polysulfides and superior electrocatalytic activity via a synergistic effect between the bimetallic sites. Among them, FeNiN8 presents balanced bifunctional catalytic activities with reduced Gibbs free energy change during the conversion of Li2S4 to Li2S (1.091 eV) and decomposition barrier of Li2S (1.330 eV) to boost reaction kinetics during charge-discharge cycling, surpassing single-atom counterparts. In particular, multilevel descriptors correlating the target catalytic properties with adsorption energies of key sulfur species, ICOHP of M-S atom pairs, and the fundamental geometric and electronic properties are identified to characterize the catalytic activities of DACs. Extended DACs to other 3d transition metals further demonstrate the effective design strategy and their broad application prospects in LSBs, which contributes to a deep understanding of the origin of catalytic activity of dual-atom sites.

Theoretical investigation of synergistically boosting the anchoring and electrochemical performance of lithiophilic/sulfiphilic transition metal carbides for lithium-sulfur batteries.

Lithium-sulfur (Li-S) battery is one of the most promising next-generation energy-storage systems with a high energy density and low cost. However, their commercial applications face several challenges, such as the shuttle effect caused by the soluble lithium polysulfide (LiPSs) intermediates and the sluggish sulfur redox reaction. In this article, we systematically investigated the anchoring and electrochemical performance of a series of transition metal carbides (TMCs: TiC, VC, ZrC, NbC, HfC, TaC) as cathode materials for Li-S batteries by theoretical calculations. The lithiophilic/sulfiphilic non-polar (001) surfaces of TMCs can offer moderate binding strength with LiPS intermediates, ensuring good performance of sulfur immobilization. These TMCs can also facilitate lithium diffusion, indicating the good rate performance of Li-S batteries. We also demonstrated that the studied TMCs can be classified into two classes according to their catalytic activity for Li2S decomposition which originated from their different electronic structural features. Furthermore, TiC, ZrC, and HfC exhibited excellent bifunctional electrochemical activity through reducing the Gibbs free energy for sulfur reduction reactions (SRRs) and lowering the barrier for Li2S decomposition which facilitates accelerating electrode kinetics and elevating utilization of sulfur. Our results offer a systematic approach to designing and screening non-polar materials for high-performance Li-S batteries, based on the rational electronic structure and lattice match strategy.

Vanadium niobium carbide (VNbCTx) bimetallic MXene derived V5S8-Nb2O5@MXene heterostructures for efficiently boosting the adsorption and catalytic performance of lithium polysulfide.

To alleviate the shuttle effect in lithium-sulfur (Li-S) batteries, the electrocatalytic conversion of polysulfides serves as a vital strategy. However, achieving a synergy that combines robust adsorption with high catalytic activity continues to pose significant challenges. Herein, a simple solid-state sintering method is employed to transform vanadium-niobium carbide MXene (VNbCTx) into a heterogeneous structure of V5S8-Nb2O5@VNbCTx MXene (denoted as V5S8-Nb2O5@MX). The Nb2O5 component immobilizes lithium polysulfides (LiPSs) at the electrode through its strong chemical affinity, while the V5S8 fraction serves as an outstanding electrochemical catalyst, enhancing the reaction kinetics of sulfur precipitation. Furthermore, the VNbCTx MXene precursor scaffold is preserved through the conversion and uniformly distributed throughout the composite, exhibiting excellent electrical conductivity. Thanks to the synergistic "capture-adsorption-catalysis" action on LiPSs, the V5S8-Nb2O5@MX composite effectively restrains the shuttle effect. The as-prepared Li-S battery demonstrates a significant increase in specific capacity, reaching 1508 mA h g-1 at 0.1C and maintaining a capacity decay of approximately 0.027% per cycle after 500 cycles at 1C and 766.1 mA h g-1 at 5C. Even under a high sulfur loading of 5.75 mg cm-2, the battery can maintain a specific capacity of 596.6 mA h g-1 and exhibit significant cycling stability after 100 cycles. DFT calculations indicate that the V5S8-Nb2O5@MX heterostructure exhibits a higher binding energy of 5.34 eV and a lower decomposition barrier energy of 0.68 eV, presenting potential advantages in accelerating the conversion reactions of LiPSs. Our research offers a straightforward approach for designing metal oxide-sulfide heterostructured catalysts that deliver superior performance and enhance the electrocatalytic conversion of LiPSs, clearing the path for high performance Li-S batteries.

Initial decomposition pathways of 1,1-diamino-2,2-dinitroethylene (α-FOX-7) in the condensed phase.

The initial decomposition pathways of α-FOX-7 in the condensed phase (crystal) were investigated via density functional theory. Calculations were carried out using three FOX-7 systems with increasing complexity from 1-layer (sheet) via 2-layer (surface) to 3-layer (bulk). The encapsulated environment of the central α-FOX-7 molecule, where decomposition takes place, is reconstructed by neighbouring molecules following a crystal structure. A minimal number of neighbouring molecules that have an impact on the energetics of decomposition are identified among all surrounding molecules. The results show that the presence of intermolecular hydrogen bonds due to the encapsulated environment in the condensed phase decreases the sensitivity of α-FOX-7, i.e. it increases the barrier of decomposition, but it does not alter the initial decomposition pathways of the reaction compared to the gas phase. Moreover, increasing the complexity of the system from a single gas phase molecule via sheet and surface to bulk increases the decomposition barriers. The calculations reveal a remarkable agreement with experimental data [A. M. Turner, Y. Luo, J. H. Marks, R. Sun, J. T. Lechner, T. M. Klapötke and R. I. Kaiser, Exploring the Photochemistry of Solid 1, 1-Diamino-2, 2-Dinitroethylene (FOX-7) Spanning Simple Bon Ruptures, Nitro-to-Nitrite Isomerization, and Nonadiabatic Dynamics, J. Phys. Chem. A, 2022, 126, 29, 4747-4761] and suggest that the initial decomposition of α-FOX-7 likely takes place at the surface of the crystal.

Theoretical insights into single-atom catalysts for improved charging and discharging kinetics of Na-S and Na-Se batteries.

Dissolution of poly-sulfide/selenides (p-S/Ses) intermediates into electrolytes, commonly known as the shuttle effect, has posed a significant challenge in the development of more efficient and reliable Na-S/Se batteries. Single-atom catalysts (SACs) play a crucial role in mitigating the shuttling of Na-pS/Ses and in promoting Na2S/Se redox processes at the cathode. In this work, single transition metal atoms Co, Fe, Ir, Ni, Pd, Pt, and Rh supported in nitrogen-deficient graphitic carbon nitride (rg-C3N4) are investigated to explore the charging and discharging kinetics of Na-S and Na-Se batteries using Density Functional Theory calculations. We find that SAs adsorbed on reduced g-C3N4 monolayers are substantially more effective in trapping higher-order Na2Xn than pristine g-C3N4 surfaces. Moreover, our ab initio molecular dynamics calculations indicate that the structure of X8 (X = S, Se) remains almost intact when adsorbed on Fe, Co, Ir, Ni, Pt, and Rh SACs, suggesting that there is no significant S or Se poisoning in these cases. Additionally, SACs reduce the free energies of the rate-determining step during discharge and present a lower decomposition barrier of Na2X during charging of Na-X electrode. The underlying mechanisms behind this fast kinetics are thoroughly examined using charge transfer, bonding strength, and d-band center analysis. Our work demonstrates an effective strategy for designing single-atom catalysts and offers solutions to the performance constraints caused by the shuttle effect in sodium-sulfur and sodium-selenium batteries.

High energy barrier hydroxyl radical dissociation mechanism of a low shock sensitivity dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50) explosive.

As a representative of the new generation of high-energy explosives, TKX-50 has attracted widespread attention due to its remarkably low sensitivity toward shock. However, the reported decomposition barriers of TKX-50 (∼37 kcal mol-1) are comparable to those of commonly used explosives. The mechanism of its low shock sensitivity remains unclear. In this study, using an ab initio molecular dynamics method combined with a multiscale shock simulation technique and transition state calculations (at the B2PLYP-D3/Def2TZVP level), we discovered an unconventional reaction pathway of TKX-50 under shock, and its rate-controlling step is the dissociation of the hydroxyl radical (OH) from the anion ring after proton transfer, followed by ring rupture and the production of H2O and N2. The barrier for this OH dissociation reaction is as high as 51.9 kcal mol-1. In contrast, under thermal stimuli, TKX-50 prefers to open rings directly after proton transfer without losing the OH. The corresponding barrier is 35.4 kcal mol-1, which is in good agreement with previous studies. The reason for the unconventional reaction pathway of TKX-50 under shock may be the suppression of anion ring opening in thermal decomposition by steric hindrance upon shock compression. In addition, the dominant N2 generation pathway under shock releases less energy than pyrolysis which further explains the low shock sensitivity of TKX-50. This study comprehensively elucidates the different reaction mechanisms of TKX-50 under thermal and shock conditions and proposes a crucial reaction pathway leading to its low shock sensitivity. These findings will contribute to the understanding and application of tetrazole anionic energetic salts.

Ferromagnetic single atom doped boron phosphide monolayers as effective electrocatalysts for Lithium-Sulfur batteries

Ferromagnetic single atom doped BP monolayers are proposed as electrocatalysts for lithium-sulfur batteries. Based on first-principles calculations, it is found that Fe-BP and Ni-BP monolayers exhibit higher electronic conductivity, and their adsorption ability for lithium polysulfides are significantly enhanced compared to the bare BP monolayer, which could effectively suppress the shuttling effect. Besides, the Fe-BP monolayer shows the lowest energy barrier for both sulfur reduction reaction and Li2S decomposition, with a low Li+ diffusion energy barrier of 0.25 eV. Based on these results, Fe-BP monolayer is suggested as a promising single-atom electrocatalyst for sulfur redox reactions which will show fast charge–discharge kinetics and long cycle life in lithium-sulfur batteries.

Importance of hydrogen bonding in base-catalyzed transesterification reactions with vicinal diols

The transesterification reaction kinetics of 2-(benzoyloxy)ethyl benzoate with various alcohols (ethylene glycol, 1,3-propanediol, 1-butanol, propylene glycol and 1,2-butylene glycol) using various cyclic amidine catalysts were investigated. For transesterification with excess glycol (glycolysis), the rate was nearly zero order in diester and glycol concentration, which is substantially different from classical transesterification kinetics with mono-alcohols. The measured kinetic parameters during glycolysis are consistent with a reaction path that is kinetically limited by the decomposition of the reaction intermediate formed from the alkoxide and diester. The DFT-calculated reaction energy and activation barrier for decomposition of this intermediate reveal a critical role of intramolecular hydrogen-bond stabilization made possible by the vicinal –OH of the glycol that effectively increases the concentration of the intermediate during reaction resulting in acceleration of the overall transesterification rate. These findings indicate the nature of both the alcohol solvent and the catalyst influence transesterification rate, and results suggest they are also important in the deconstruction of carbonyl-containing condensation polymers.

Strain effects on the adsorption behavior of PtS2 monolayer as anchoring material for lithium-sulfur batteries: A DFT study

The practical implement of lithium-sulfur batteries is significantly impeded by low electronic conductivity of anchoring substrate and the shuttle effect. To address these issues, we employed density functional theory (DFT) to investigate the behavior of lithium polysulfides (LiPSs) adsorbed on PtS2 monolayers in lithium-sulfur batteries. The results demonstrate a moderate binding strength between PtS2 monolayers and LiPSs, effectively suppressing the shuttle effect. Furthermore, the bandgap of PtS2 monolayers decreased remarkably during the lithiation, accompanied with semiconductor-metal transition, leading to a significant improvement in conductivity. The diffusion barriers and decomposition barrier of the adsorbed of Li2S clusters on PtS2 monolayer were calculated to assess the delithiation reaction kinetics. These values are comparable to those observed in other two-dimension (2D) materials, indicating the potential for rapid charge/discharge in Li-S batteries. Especially we considered the impact of strain arise from volume expansion on binding energy and diffusion processes. Our results indicate that under strain, the PtS2 substrate can still effectively anchor LiPSs while facilitating their diffusion. Through a series of calculations, we can conclude that the PtS2 monolayer holds promise as the anchoring material for Li–S batteries.

Remarkable low-temperature dehydration kinetics of rare-earth-ion-doped Ca(OH)2 for thermochemical energy storage

Thermochemical energy storage based on dehydration-hydration of Ca(OH)2/CaO reversible reaction is considered a promising strategy to address the intermittency of solar thermal energy due to its extremely high storage density, possibility of seasonal heat storage, and low cost. However, conventionally-used Ca(OH)2 particles suffer from instabilities and poor multi-cycle performance at high temperature, which limits their applications. Here, we propose rare-earth-ion-doped Ca(OH)2 materials for thermochemical energy storage at reduced dehydration temperature through extensive DFT computational screening. Rare-earth elements, Sc, Y, La, Gd and Lu, -doped Ca(OH)2 exhibit lower decomposition barrier in comparison to the Ca(OH)2 without doping. The Sc-doped Ca(OH)2 shows the significantly reduced onset temperature of ∼326 °C, which is 50 °C lower than that of the pure Ca(OH)2. Importantly, more than 3-fold increase in the dehydration rate and excellent stability during multi-cycles of the compositions at 320 °C is reached by the doping of Sc or Y into Ca(OH)2. The working performance makes this material a practical alternative to realize stable high-density solar thermal energy storage.

Full Potential Catalysis of Co0.4Ni1.6P-V/CNT with Phosphorus Vacancies for Li2S1-2 Deposition/Decomposition and S8/Li2Sn (3 ≤ n ≤ 8) Conversion in Li-S Batteries.

The slow kinetics of polysulfide conversions hinders the commercial progress of Li-S batteries. The introduction of high-efficiency catalysts accelerates heterogeneous reactions and enhances the utilization of S. The full potential of the Co0.4Ni1.6P-V/CNT-modified separator catalyzes the all-process reactions of the S electrode and increases the rates and cycling lives of the batteries. The two-site synergistic effect of Co0.4Ni1.6P-V/CNT regulates the catalytic activity, and the phosphorus vacancies enrich the active sites. The higher electron density at the Co and Ni double sites increases chemisorption of the Co0.4Ni1.6P-V/CNT on Li2Sn (1 ≤ n ≤ 4), stretches and breaks the Li-S and Ni-S bonds during Li2S decomposition, and reduces the energy barrier for Li2S decomposition. The cyclic voltammograms of the asymmetric batteries demonstrated that Co0.4Ni1.6P-V/CNT also catalyzed the Li2Sn ⇌ S8 (3 ≤ n ≤ 8) reaction, realizing the full catalytic potential of the Li-S batteries. Increased Li+ diffusion/migration in the Co0.4Ni1.6P-V/CNT-modified separator ensured fast electrochemical reactions. The excellent catalytic effect of Co0.4Ni1.6P-V/CNT provided smaller polarization and superior rate performance, which led to high discharge specific capacities of 1511.9, 1172.6, 1006.0, 881.0, and 785.7 mA h g-1 at current densities of 0.1, 0.2, 0.5, 1, and 2 mA cm-2 with sulfur loadings of 7.98 mg cm-2, respectively. This approach involving simple crystal modulation and introduction of defects provides a new way to achieve the full catalytic potential of Li-S batteries.

Ultra-thin WS2 decorated Co-based Metal‒organic framework derived materials for synergistic electrocatalysis towards pH-Universal hydrogen evolution reaction

Rational designing of a WS2-based hybrid material is extremely important to resolve low-edge sites and poor conductivity of bare WS2, but it is still challenging to construct applicable structures. In this study, an electrocatalyst with ultra-thin WS2 nanosheets homogeneously decorated on Co–N-co-doped carbon hollow nanocages (WS2-3/Co–N–CN-750) is developed, which has favorable hydrogen evolution reaction (HER) activity and stability. The performance of WS2-3/Co–N–CN-750 is significantly improved due to the collective synergy of the specific micro-morphology, interfacial structure, and electronic property. The hybridization of WS2 and Co9S8 can optimize the electronic structure, reduce hydrogen adsorption energy, slash the decomposition barrier of H2O, and accelerate the electron transfer to WS2. Furthermore, the marginal sites of WS2 are significantly increased by optimizing the aggregation growth of WS2. Besides, the precipitation of appropriate Co particles and the Co-based metal-organic framework (Co-MOF) lay a solid foundation for the favorable conductivity of the hybrid material. However, samples after stability tests reveal that cobalt sulfide is corroded and transformed in a locally strong alkali condition. This study highlights the synergies of multicomponent hybridization and provides insights into the stability of congeneric materials.