Charge Self-Regulation of Metallic Heterostructure Ni2 P@Co9 S8 for Alkaline Water Electrolysis with Ultralow Overpotential at Large Current Density.

Designing cost-effective alkaline water-splitting electrocatalysts is essential for large-scale hydrogen production. However, nonprecious catalysts face challenges in achieving high activity and durability at a large current density. An effective strategy for designing high-performance electrocatalysts is regulating the active electronic states near the Fermi-level, which can improve the intrinsic activity and increase the number of active sites. As a proof-of-concept, it proposes a one-step self-assembly approach to fabricate a novel metallic heterostructure based on nickel phosphide and cobalt sulfide (Ni2 P@Co9 S8 ) composite. The charge transfer between active Ni sites of Ni2 P and Co─Co bonds of Co9 S8 efficiently enhances the active electronic states of Ni sites, and consequently, Ni2 P@Co9 S8 exhibits remarkably low overpotentials of 188 and 253 mV to reach the current density of 100 mA cm-2 for the hydrogen evolution reaction and oxygen evolution reaction, respectively. This leads to the Ni2 P@Co9 S8 incorporated water electrolyzer possessing an ultralow cell voltage of 1.66 V@100 mA cm-2 with ≈100% retention over 100 h, surpassing the commercial Pt/C║RuO2 catalyst (1.9 V@100 mA cm-2 ). This work provides a promising methodology to boost the activity of overall water splitting with ultralow overpotentials at large current density by shedding light on the charge self-regulation of metallic heterostructure.

Engineering Cf /ZrB2 -SiC-Y2 O3 for Thermal Structures of Hypersonic Vehicles with Excellent Long-Term Ultrahigh Temperature Ablation Resistance.

Ultrahigh temperature ceramic matrix composites (UHTCMCs) are critical for the development of high Mach reusable hypersonic vehicles. Although various materials are utilized as the thermal components of hypersonic vehicles, it is still challenging to meet the ultrahigh temperature ablation-resistant and reusability. Herein, the Y2 O3 reinforced Cf /ZrB2 -SiC composites are designed, which demonstrates near-zero damage under long-term ablation at temperatures up to 2500 °C for ten cycles. Notably, the linear ablation rate of the composites (0.33 µm s-1 ) is over 24 times better than that of the conventional Cf /C-ZrC at 2500 °C (8.0 µm s-1 ). Moreover, the long-term multi-cycle ablation mechanisms of the composites are investigated with the assistance of DFT calculations. Especially, the size effect and the content of the Zr-based crystals in the oxide layer fundamentally affect the stability of the oxide layer and the ablation properties. The ideal component and structure of the oxide layer for multi-cycle ablation condition are put forward, which can be obtained by controlling the Y2 O3 /ZrB2 mole ratio and establishing Y-Si-O - t-Zr0.9 Y0.1 O1.95 core-shell nano structure. This work proposes a new strategy for improving the long-term multi-cycle ablation resistance of UHTCMCs.

Modulating the Catalytic Properties of Bimetallic Atomic Catalysts: Role of Dangling Bonds and Charging.

Bimetallic atomic catalysts (BACs) exhibit great potential in CO2 electroreduction. However, modulation and improvement of their catalytic performance are still challenging. To address these issues, an intrinsic descriptor ψ based on the valence properties of active centers was used. The role of the dangling bonds and charging in modulating the catalytic properties of BACs called M1 M2 -N6 -G (M1 =Ru and Fe) was studied. It was shown that linear relationships between the adsorption energy of the C-species are broken under the effect of the dangling bonds and that they are restored with charging. However, charging has minor effects on the adsorption of the O-species. These findings enable screening promising BACs for CH3 OH production. This research provides effective schemes for modulating the properties of catalysts, which is beneficial to enriching high-performance catalysts for various reactions.

Trinitroaromatic Salts as High-Energy-Density Organic Cathode Materials for Li-Ion Batteries.

Even though organic molecules with designed structures can be assembled into high-capacity electrode materials, only limited functional groups such as -C═O and -C═N- could be designed as high-voltage cathode materials with enough high capacity. Here, we propose a common chemical raw material, trinitroaromatic salt, to have promising potential to develop organic cathode materials with high discharge voltage and capacity through a strong delocalization effect between -NO2 and aromatic ring. Our first-principles calculations show that electrochemical reactions of trinitroaromatic potassium salt C6H2(NO2)3OK are a 6-electron charge-transfer process, providing a high discharge capacity of 606 mAh g-1 and two voltage plateaus of 2.40 and 1.97 V. Electronic structure analysis indicates that the discharge process from C6H2(NO2)3OK to C6H2(NO2Li2)3OK stabilizes oxidized [C6]n+ to achieve a stable conjugated structure through electron delocalization from -NO2 to [C6]n+. The ordered layer structure C6H2(NO2)3OK can provide large spatial pore channels for Li-ion transport, achieving a high ion diffusion coefficient of 3.41 × 10-6 cm2 s-1.

Charge self-regulation in 1T'''-MoS2 structure with rich S vacancies for enhanced hydrogen evolution activity.

Active electronic states in transition metal dichalcogenides are able to prompt hydrogen evolution by improving hydrogen absorption. However, the development of thermodynamically stable hexagonal 2H-MoS2 as hydrogen evolution catalyst is likely to be shadowed by its limited active electronic state. Herein, the charge self-regulation effect mediated by tuning Mo-Mo bonds and S vacancies is revealed in metastable trigonal MoS2 (1T'''-MoS2) structure, which is favarable for the generation of active electronic states to boost the hydrogen evolution reaction activity. The optimal 1T'''-MoS2 sample exhibits a low overpotential of 158 mV at 10 mA cm-2 and a Tafel slope of 74.5 mV dec-1 in acidic conditions, which are far exceeding the 2H-MoS2 counterpart (369 mV and 137 mV dec-1). Theoretical modeling indicates that the boosted performance is attributed to the formation of massive active electronic states induced by the charge self-regulation effect of Mo-Mo bonds in defective 1T'''-MoS2 with rich S vacancies.

Bamboo-Based Biomaterials for Cell Transportation and Bone Integration.

The construction of hierarchical porous structure in biomaterials is of great significance for improving nutrient transport and biological performance. However, it is still challenging to design porous bone substitutes with high strength and biological properties, which limits their clinical applications in load-bearing bone regeneration. Herein, based on hierarchical porous structure of renewable bamboo, the mineralized calcium phosphate/bamboo composite scaffolds with high strength and excellent transport performance are successfully prepared in combination of biotemplated approach and biomimetic mineralization. The mineralized biomaterials have simultaneously achieved high mechanical strength and low modulus, similar to those of cortical bone. Furthermore, the mineralized biomaterials exhibit good liquid transport capacity and can transport cells along anti-gravity direction. Based on density functional theory (DFT) calculations, the mineralized calcium phosphate reveals the optimal H2 O adsorption energy (-0.651 eV) and low diffusion energy barrier (0.743 eV), which is conducive to enhance hydrophilicity and liquid transport performance. Moreover, owing to the synergistic effect of the porous structure of biotemplate and bioactive mineralized components, the mineralized biomaterials possess enhanced bone integration and osteoconduction properties. The present study shed light on deeper understanding of mineralized biosourced materials, offering a strategy of combining green chemistry with tissue engineering to prepare eco-friendly biomaterials.

Engineering Metallic Heterostructure Based on Ni3 N and 2M-MoS2 for Alkaline Water Electrolysis with Industry-Compatible Current Density and Stability.

Alkaline water electrolysis is commercially desirable to realize large-scale hydrogen production. Although nonprecious catalysts exhibit high electrocatalytic activity at low current density (10-50 mA cm-2 ), it is still challenging to achieve industrially required current density over 500 mA cm-2  due to inefficient electron transport and competitive adsorption between hydroxyl and water. Herein, the authors design a novel metallic heterostructure based on nickel nitride and monoclinic molybdenum disulfide (Ni3 N@2M-MoS2 ) for extraordinary water electrolysis. The Ni3 N@2M-MoS2  composite with heterointerface provides two kinds of separated reaction sites to overcome the steric hindrance of competitive hydroxyl/water adsorption. The kinetically decoupled hydroxyl/water adsorption/dissociation and metallic conductivity of Ni3 N@2M-MoS2  enable hydrogen production from Ni3 N and oxygen evolution from the heterointerface at large current density. The metallic heterostructure is proved to be imperative for the stabilization and activation of Ni3 N@2M-MoS2 , which can efficiently regulate the active electronic states of Ni/N atoms around the Fermi-level through the charge transfer between the active atoms of Ni3 N and MoMo bonds of 2M-MoS2  to boost overall water splitting. The Ni3 N@2M-MoS2  incorporated water electrolyzer requires ultralow cell voltage of 1.644 V@1000 mA cm-2  with ≈100% retention over 300 h, far exceeding the commercial Pt/C║RuO2 (2.41 V@1000 mA cm-2 , 100 h, 58.2%).

Assembling organic-inorganic building blocks for high-capacity electrode design.

Metal-organic electrode materials have exhibited extraordinary promise for green and sustainable electrochemical energy storage devices, but usually suffer from low specific capacity, and poor cycling stability and rate capability because of limited active sites at organic functional groups. To address this issue, activating transition metals and carbon conjugate rings has become significantly effective to make transferred electrons dispersed in the whole molecule. In this work, we demonstrate that assembling inorganic-organic building blocks into "local" composite metal-organic materials could synergistically activate transition metal ions and carbon conjugate rings to operate cationic and anionic redox, respectively. Based on first-principles calculations, the composite inorganic-organic material FeF3(4,4'-bpy) generates 8-electron transfer redox processes of Fe3+ + 2e-→ Fe+ and 2 -C[double bond, length as m-dash]N- + 2e-→ 2 (-C-N-)- and 4 -C[double bond, length as m-dash]C- + 4e-→ 4 (-C-C-)-, achieving a high specific capacity of 796.7 mA h g-1, maintaining structural stability, and reducing the band gap. The strongly electronegative F-ions in inorganic structure [FeF4]2- play an important role in making highly oxidized Fe3+ through forming a strong ligand field and electrochemically activating -C[double bond, length as m-dash]C-via electrostatic interaction with Li+. In addition, electrochemical measurements also reveal that the central metal Fe, and -C[double bond, length as m-dash]C and -C[double bond, length as m-dash]N bonds of the FeF3(4,4'-bpy) electrode are the active sites for Li-ion storage to deliver a high reversible capacity (793.1 mA h g-1 at 50 mA g-1) and excellent rate capability, which are echoes of the DFT calculations. Through this design principle, we found a series of high-capacity metal organic electrode materials such as MnF3(4,4'-bpy) (799.6 mA h g-1) and VF3(4,4'-bpy) (811.7 mA h g-1).

Manipulation on active electronic states of metastable phase ß-NiMoO4 for large current density hydrogen evolution.

Non-noble transition metal oxides are abundant in nature. However, they are widely regarded as catalytically inert for hydrogen evolution reaction (HER) due to their scarce active electronic states near the Fermi-level. How to largely improve the HER activity of these kinds of materials remains a great challenge. Herein, as a proof-of-concept, we design a non-solvent strategy to achieve phosphate substitution and the subsequent crystal phase stabilization of metastable ß-NiMoO4. Phosphate substitution is proved to be imperative for the stabilization and activation of ß-NiMoO4, which can efficiently generate the active electronic states and promote the intrinsic HER activity. As a result, phosphate substituted ß-NiMoO4 exhibits the optimal hydrogen adsorption free energy (-0.046 eV) and ultralow overpotential of -23 mV at 10 mA cm-2 in 1 M KOH for HER. Especially, it maintains long-term stability for 200 h at the large current density of 1000 mA cm-2 with an overpotential of only -210 mV. This work provides a route for activating transition metal oxides for HER by stabilizing the metastable phase with abundant active electronic states.

Identifying Metallic Transition-Metal Dichalcogenides for Hydrogen Evolution through Multilevel High-Throughput Calculations and Machine Learning.

High-performance electrocatalysts not only exhibit high catalytic activity but also have sufficient thermodynamic stability and electronic conductivity. Although metallic 1T-phase MoS2 and WS2 have been successfully identified to have high activity for hydrogen evolution reaction, designing more extensive metallic transition-metal dichalcogenides (TMDs) faces a large challenge because of the lack of a full understanding of electronic and composition attributes related to catalytic activity. In this work, we carried out systematic high-throughput calculation screening for all possible existing two-dimensional TMD (2D-TMD) materials to obtain high-performance hydrogen evolution reaction (HER) electrocatalysts by using a few important criteria, such as zero band gap, highest thermodynamic stability among available phases, low vacancy formation energy, and approximately zero hydrogen adsorption energy. A series of materials-perfect monolayer VS2 and NiS2, transition-metal ion vacancy (TM-vacancy) ZrTe2 and PdTe2, chalcogenide ion vacancy (X-vacancy) MnS2, CrSe2, TiTe2, and VSe2-have been identified to have catalytic activity comparable with that of Pt(111). More importantly, electronic structural analysis indicates active electrons induced by defects are mostly delocalized in the nearest-neighbor and next-nearest neighbor range, rather than a single-atom active site. Combined with the machine learning method, the HER-catalytic activity of metallic phase 2D-TMD materials can be described quantitatively with local electronegativity (0.195·LEf + 0.205·LEs) and valence electron number (Vtmx), where the descriptor is ΔGH* = 0.093 - (0.195·LEf + 0.205·LEs) - 0.15·Vtmx.

Partial-Single-Atom, Partial-Nanoparticle Composites Enhance Water Dissociation for Hydrogen Evolution.

The development of an efficient electrocatalyst toward the hydrogen evolution reaction (HER) is of significant importance in transforming renewable electricity to pure and clean hydrogen by water splitting. However, the construction of an active electrocatalyst with multiple sites that can promote the dissociation of water molecules still remains a great challenge. Herein, a partial-single-atom, partial-nanoparticle composite consisting of nanosized ruthenium (Ru) nanoparticles (NPs) and individual Ru atoms as an energy-efficient HER catalyst in alkaline medium is reported. The formation of this unique composite mainly results from the dispersion of Ru NPs to small-size NPs and single atoms (SAs) on the Fe/N codoped carbon (Fe-N-C) substrate due to the thermodynamic stability. The optimal catalyst exhibits an outstanding HER activity with an ultralow overpotential (9 mV) at 10 mA cm-2 (η 10), a high turnover frequency (8.9 H2 s-1 at 50 mV overpotential), and nearly 100% Faraday efficiency, outperforming the state-of-the-art commercial Pt/C and other reported HER electrocatalysts in alkaline condition. Both experimental and theoretical calculations reveal that the coexistence of Ru NPs and SAs can improve the hydride coupling and water dissociation kinetics, thus synergistically enhancing alkaline hydrogen evolution performance.

Liquid-Phase Assisted Engineering of Highly Strong SiC Composite Reinforced by Multiwalled Carbon Nanotubes.

Despite the ultrahigh intrinsic strength of multiwalled carbon nanotube (MWCNT), the strengthening effect on ceramic matrix composite remains far from expectation mainly due to the weak load transfer between the reinforcement and ceramic matrix. With the assistance of the in situ pullout test, it is revealed that the liquid-phase sintering (LPS) can serve as a novel strategy to achieve effective load transfer in MWCNT reinforced ceramic matrix composites. The YAlO3 formed liquid phase during spark plasma sintering of SiC composite greatly facilitates radical elastic deformation of MWCNT, leading to highly increased interfacial shear strength (IFSS) as well as interlayer shear resistance (ISR) of nested walls. The liquid phase with superior wettability can even penetrate into the defects of MWCNT, which further increases the ISR of MWCNT. Moreover, the first-principles calculation indicates that the oxygen terminated YAlO3 phase displays much stronger bonding compared with SiC matrix, which is also responsible for the large IFSS in the composite. As a result, as high as 30% improvement of bending strength is achieved in the composite with only 3 wt% MWCNT in comparison to the monolithic ceramic, manifesting the unprecedented strengthening effect of MWCNT assisted by LPS.

Dual-Metal Interbonding as the Chemical Facilitator for Single-Atom Dispersions.

Atomically dispersed catalysts, with maximized atom utilization of expensive metal components and relatively stable ligand structures, offer high reactivity and selectivity. However, the formation of atomic-scale metals without aggregation remains a formidable challenge due to thermodynamic stabilization driving forces. Here, a top-down process is presented that starts from iron nanoparticles, using dual-metal interbonds (RhFe bonding) as a chemical facilitator to spontaneously convert Fe nanoparticles to single atoms at low temperatures. The presence of RhFe bonding between adjacent Fe and Rh single atoms contributes to the thermodynamic stability, which facilitates the stripping of a single Fe atom from the Fe nanoparticles, leading to the stabilized single atom. The dual single-atom Rh-Fe catalyst renders excellent electrocatalytic performance for the hydrogen evolution reaction in an acidic electrolyte. This discovery of dual-metal interbonding as a chemical facilitator paves a novel route for atomic dispersion of chemical metals and the design of efficient catalysts at the atomic scale.

Theoretical Study of Fast Calculation of Damping Loss Factors for Rubber Polymers.

Rubber polymers as acoustic damping materials are widely used in industrial sectors. However, there is still no theoretical method to rapidly predict the damping properties of rubber polymers. Here we propose a theoretical method for the fast calculation of damping loss factors in rubber polymers. Molecular dynamics simulations were employed to construct the optimal configuration of internal polymer chains with density as the descriptor in order to calculate the mechanical properties and thus the damping loss factors. The acceptable difference between the calculated and experimental damping loss factors shows that the proposed method is efficient to predict the intrinsic damping properties of rubber polymers. Through studying the relationship among composition, microstructure, and the damping property, we found that the carbon-carbon skeletal chains with lateral methyl groups produce high damping properties.

Feasibility of N2 Reduction on the V Anchored 1T-MoS2 Monolayer: A Density Functional Theory Study.

The front cover artwork is provided by the groups of Prof. BeiBei, Xiao and Lei, Yang (Jiangsu University of Science and Technology, China) as well as Dr. ErHong, Song (Shanghai Institute of Ceramics, Chinese Academy of Sciences, China). The image shows that the environmental-friendly N2 -to-NH3 conversion is achieved by the V decorated MoS2 monolayer with the 1T atomic configuration, featured by the effective electrocatalysis in combination with the good electronic conductivity. Read the full text of the Article at 10.1002/cphc.202000147.

Enhanced performance of in-plane transition metal dichalcogenides monolayers by configuring local atomic structures.

The intrinsic activity of in-plane chalcogen atoms plays a significant role in the catalytic performance of transition metal dichalcogenides (TMDs). A rational modulation of the local configurations is essential to activating the in-plane chalcogen atoms but restricted by the high energy barrier to break the in-plane TM-X (X = chalcogen) bonds. Here, we theoretically design and experimentally realize the tuning of local configurations. The electron transfer capacity of local configurations is used to screen suitable TMDs materials for hydrogen evolution reaction (HER). Among various configurations, the triangular-shape cobalt atom cluster with a central sulfur vacancy (3CoMo-VS) renders the distinct electrocatalytic performance of MoS2 with much reduced overpotential and Tafel slope. The present study sheds light on deeper understanding of atomic-scale local configuration in TMDs and a methodology to boost the intrinsic activity of chalcogen atoms.

Feasibility of N2 Reduction on the V Anchored 1T-MoS2 Monolayer: A Density Functional Theory Study.

Developing efficient electrocatalysts for nitrogen reduction reaction (NRR) at ambient conditions is crucial for NH3 synthesis. In this manuscript, the NRR performance of the transition metal anchored MoS2 monolayer with 1T atomic structure (1T-MoS2 ) is systematically evaluated by density functional theory computations. Our results reveal that the V decorated 1T-MoS2 exhibits the outstanding catalytic activity toward NRR via distal mechanism where the corresponding onset potential is 0.66 V, being superior to the commercial Ru material. Furthermore, the powerful binding energy between the V atom and the 1T-MoS2 provides the good resistance against clustering of the V dopant, indicating its stability. Overall, this work provides a potential alternative for the application of NH3 synthesis.

Auto-optimizing Hydrogen Evolution Catalytic Activity of ReS2 through Intrinsic Charge Engineering.

Optimizing active electronic states responding to catalysis is of paramount importance for developing high-activity catalysts because thermodynamics itself may not favor forming an optimal electronic state. Setting the monolayer transition metal dichalcogenide (TMD) ReS2 as a model for the hydrogen evolution reaction (HER), we uncover that intrinsic charge engineering has an auto-optimizing effect on enhancing catalytic activity through regulating active electronic states. The experimental and theoretical results show that intrinsic charge compensation from S to Re-Re bonds could manipulate the active electronic states, allowing hydrogen to absorb the active sites neither strongly nor weakly. Two types of S sites exhibit the optimal hydrogen adsorption free energies (Δ GH*) of 0.016 and 0.061 eV, which are the closest to zero corresponding to the highest HER activity. This auto-optimization via charge engineering is further demonstrated by higher turnover frequency per sulfur atom of 1-10 s-1 and lower overpotential of -147 mV at 10 mA cm-2 than those of other TMDs through multiscale activation and optimization. This work opens an avenue in designing extensive active catalysts through intrinsic charge engineering strategy.

In-situ liquid cell transmission electron microscopy investigation on oriented attachment of gold nanoparticles.

Inside a liquid solution, oriented attachment (OA) is now recognized to be as important a pathway to crystal growth as other, more conventional growth mechanisms. However, the driving force that controls the occurrence of OA is still poorly understood. Here, using in-situ liquid cell transmission electron microscopy, we demonstrate the ligand-controlled OA of citrate-stabilized gold nanoparticles at atomic resolution. Our data reveal that particle pairs rotate randomly at a separation distance greater than twice the layer thickness of adsorbed ligands. In contrast, when the particles get closer, their ligands overlap and guide the rotation into a directional mode until they share a common {111} orientation, when a sudden contact occurs accompanied by the simultaneous expulsion of the ligands on this surface. First-principle calculations confirm that the lower ligand binding energy on {111} surfaces is the intrinsic reason for the preferential attachment at this facet, rather than on other low-index facets.