Stabilizing and Activating Metastable Nickel Nanocrystals for Highly Efficient Hydrogen Evolution Electrocatalysis

Phase Engineering and Dispersion Stabilization of Cobalt toward Enhanced Hydrogen Evolution

Phase engineering is promising to increase the intrinsic activity of the catalyst toward hydrogen evolution reaction (HER). However, the polymorphism interface is unstable due to the presence of metastable phases. Herein, phase engineering and dispersion stabilization are applied simultaneously to boost the HER activity of cobalt without sacrificing the stability. A fast and facile approach (plasma cathodic electro deposition) is developed to prepare cobalt film with a hetero-phase structure. The polymorphs of cobalt are realized through reduced stacking fault energy due to the doping of Mo, and the high temperature treatment resulted from the plasma discharge. Meanwhile, homogeneously dispersed oxide/carbide nanoparticles are produced from the reaction of plasma-induced oxygen/carbon atoms with electro-deposited metal. The existence of rich polymorphism interface and oxide/carbide help to facilitate H2 production by the tuning of electronic structure and the increase of active sites. Furthermore, oxide/carbide dispersoid effectively prevents the phase transition through a pinning effect on the grain boundary. As-prepared Co-hybrid/CoO_MoC exhibits both high HER activity and robust stability (44 mV at 10 mA cm-2, Tafel slope of 53.2 mV dec-1, no degradation after 100 h test). The work reported here provides an alternate approach to the design of advanced HER catalysts for real application.

Partially oxidized inter-doped RuNi alloy aerogel for the hydrogen evolution reaction in both alkaline and acidic media

A facile reduction and doping process is employed with the supercritical ethanol drying method to form RuNi alloy aerogels. The optimized heterostructure comprising RuNi metal, RuO2, and NiO phases is synthesized through partial oxidation. When applied to the surface of Ni foam, the multiphase aerogels form a morphology of highly porous 0D colloidal aerogel networks on the surface. RuNi alloy-Ni foam oxidized at 350 °C (RuNi-350@NF) has an overpotential of 89 and 61 mV in 1 M KOH and 0.5 M H2SO4 media at 50 mA cm-2, as well as satisfactory long-term stability. Additionally, the Tafel slopes in alkaline and acidic media are found to be 34 and 30.9 mV dec-1, respectively. Furthermore, it exhibits long-term stability (35 h) in alkaline and acidic media at high current densities of 50 mA cm-2, respectively. This study presents a novel strategy for developing exceptionally efficient and free-standing 3D porous aerogel electrocatalysts with potential applications in hydrogen production.

Lattice Strain Engineering on Metal-Organic Frameworks by Ligand Doping to Boost the Electrocatalytic Biomass Valorization

As an efficient and environmental-friendly strategy, electrocatalytic oxidation can realize biomass lignin valorization by cleaving its aryl ether bonds to produce value-added chemicals. However, the complex and polymerized structure of lignin presents challenges in terms of reactant adsorption on the catalyst surface, which hinders further refinement. Herein, NiCo-based metal-organic frameworks (MOFs) are employed as the electrocatalyst to enhance the adsorption of reactant molecules through π-π interaction. More importantly, lattice strain is introduced into the MOFs via curved ligand doping, which enables tuning of the d-band center of metal active sites to align with the reaction intermediates, leading to stronger adsorption and higher electrocatalytic activity toward bond cleavage within lignin model compounds and native lignin. When 2'-phenoxyacetophenone is utilized as the model compound, high yields of phenol (76.3%) and acetophenone (21.7%) are achieved, and the conversion rate of the reactants reaches 97%. Following pre-oxidation of extracted poplar lignin, >10 kinds of phenolic compounds are received using the as-designed MOFs electrocatalyst, providing ≈12.48% of the monomer, including guaiacol, vanillin, eugenol, etc., and p-hydroxybenzoic acid dominates all the products. This work presents a promising and deliberately designed electrocatalyst for realizing lignin valorization, making significant strides for the sustainability of this biomass resource.

Synthesis of Ni decorated MoOx nanorod catalysts for efficient overall urea-water splitting

Substituting slow oxygen evolution reaction (OER) with thermodynamically favorable urea oxidation reaction (UOR) is considered as one of the feasible strategies for achieving energy-saving hydrogen production. Herein, a uniform layer of NiMoO4 nanorods was grown on nickel foam by a hydrothermal method. Then, a series of Ni-MoOx/NF-X nanorod catalysts comprising Ni/NiO and MoOx (MoO2/MoO3) were prepared through regulating annealing atmosphere and reduction temperature. The optimized Ni-MoOx/NF-3 with a large accessible specific area can act as a bifunctional catalyst for electrocatalytic anodic UOR and cathodic hydrogen evolution reaction (HER). At a current density of 100 mA cm-2, the introduction of urea can significantly reduce the overpotential of Ni-MoOx/NF-3 by 210 mV compared to OER. In addition, Ni-MoOx/NF-3 has a higher intrinsic activity than other catalysts. It only requires -0.21 and 1.38 V to reach 100 mA cm-2 in HER and UOR, respectively. Such an excellent performance can be attributed to the synergistic function between Ni and MoOx. The presence of metallic Ni and reduced MoOx in pairs is beneficial for improving the electrical conductivity and modulating the electronic structure, resulting in enhancing the electrocatalytic performance. When assembling Ni-MoOx/NF-3 into an overall urea-water splitting system, it can achieve energy-saving hydrogen production and effective removal of urea-rich wastewater.

Core-Shell Design of Metastable Phase Catalyst Enables Highly-Performance Selective Hydrogenation

Highly selective semihydrogenation of alkynes to alkenes is a highly important reaction for catalytic industry. Developing non-noble metal based catalysts with platinum group metal-like activity and selectivity is extremely crucial yet challenging. Metastable phase catalysts provide a potential candidate to realize high activity, yet the control of selectivity remains an open question. Here, this work first reports a metastable phase core-shell: face-centered cubic (fcc) phase Ag (10 at%) core-metastable hexagonal closest packed (hcp) phase Ni (90 at%) shell catalyst, which represents high conversion rate, high selectivity, and remarkable universality for the semihydrogenation of phenylacetylene and its derivatives. More impressively, a turnover frequency (TOF) value of 8241.8 h-1 is achieved, much higher than those of stable phase catalysts and reported platinum group metal based catalysts. Mechanistic investigation reveals that the surface of hcp Ni becomes more oxidized due to electron transfer from hcp Ni shell to fcc Ag core, which decreases the adsorption capacity of styrene on the metastable phase Ni surface, thus preventing full hydrogenation. This work has gained crucial research significance for the design of high performance metastable phase catalysts.

Strain and Surface Engineering of Multicomponent Metallic Nanomaterials with Unconventional Phases

Multicomponent metallic nanomaterials with unconventional phases show great prospects in electrochemical energy storage and conversion, owing to unique crystal structures and abundant structural effects. In this review, we emphasize the progress in the strain and surface engineering of these novel nanomaterials. We start with a brief introduction of the structural configurations of these materials, based on the interaction types between the components. Next, the fundamentals of strain, strain effect in relevant metallic nanomaterials with unconventional phases, and their formation mechanisms are discussed. Then the progress in surface engineering of these multicomponent metallic nanomaterials is demonstrated from the aspects of morphology control, crystallinity control, surface modification, and surface reconstruction. Moreover, the applications of the strain- and surface-engineered unconventional nanomaterials mainly in electrocatalysis are also introduced, where in addition to the catalytic performance, the structure-performance correlations are highlighted. Finally, the challenges and opportunities in this promising field are prospected.

Three-dimensional ordered macroporous molybdenum doped NiCoP honeycomb electrode for two-step water electrolysis

Two-step alkaline water electrolysis is considered a safe and efficient method for producing hydrogen from renewable energy. Reversal of the current polarity in a bifunctional electrocatalyst used as a gas evolution electrode (GEE) in two-step water electrolysis can generate H₂/O₂ at different times and in different spaces. The design of a bifunctional electrocatalyst with high durability and excellent activity is imperative to achieving continuous, safe, and pure H₂ generation via two-step alkaline water electrolysis. Here, we present for the first time a novel 3D Mo-doped NiCo phosphide honeycomb electrocatalyst that was grown on nickel foam (3D Mo-NiCoP/NF) and fabricated using polystyrene as a template. The electrocatalyst exhibited extremely low overpotentials in both the hydrogen evolution reaction (HER; 117 mV at 10 mA/cm²) and the oxygen evolution reaction (OER; 344 mV at 100 mA/cm²). As a bifunctional electrocatalyst for two-step alkaline water electrolysis, the device had a 1.784 V cell voltage at 10 mA/cm², 95% decoupling efficiency, and ∼83% energy conversion efficiency. Taken together, the use of 3D Mo-NiCoP/NF as a GEE reduced the complexity and lowered the cost of the electrolyzer. The latter could be used to construct highly competitive water-splitting systems for continuous H₂ production and green energy harvesting.

Homogeneous Metastable Hexagonal Phase Iridium Enhances Hydrogen Evolution Catalysis

Catalytic reactions are surface-sensitive processes. Fabrication of homogeneous metastable metals can be used to promote phase-dependent catalytic performance; however, this has been a challenging task. Herein, homogeneous metastable hexagonal close-packed (hcp) Ir is epitaxially grown onto metastable phase hcp Ni, as demonstrated using spherical aberration electron microscopy. The as-fabricated metastable hcp Ir exhibits high intrinsic activity for the alkaline hydrogen evolution reaction (HER). In particular, metastable hcp Ir delivers a low overpotential of 17 mV at 10 mA cm-2 and presents a high specific activity of 8.55 mA cm-2 and a high turnover frequency of 38.26 s-1 at -0.07 V versus the reversible hydrogen electrode. Owing to its epitaxially grown structure, metastable hcp Ir is highly stable. Theoretical calculations reveal that metastable hcp Ir promotes H2 O adsorption and fast H2 O dissociation, which contributes to its remarkable HER activity. Findings can elucidate the crystal phase-controlled synthesis of advanced noble metal nanomaterials for the fundamental catalytic applications.

Unconventional Phase Synergies with Doping Engineering Over Ni Electrocatalyst Featuring Regulated Electronic State for Accelerated Urea Oxidation

Exploring high-performing Ni-based electrocatalysts for the urea oxidation reaction (UOR) is crucial for developing urea-related energy technologies yet remains a daunting challenge. In this study, a synergistic anomalous hcp phase and heteroatom doping engineering over metallic Ni are found to enhance the UOR. A metal-organic framework-mediated approach is proposed to construct Ni nanoparticles (NPs) with designated crystal phase embedded in N-doped carbon (fcc-Ni/NC and hcp-Ni/NC). Significant crystal phase-dependent catalytic activity for the UOR is observed; hcp-Ni/NC, featuring unusual hcp phase, outperforms fcc-Ni/NC with conventional fcc phase. Moreover, incorporating foreign Mn species in hcp-Ni/NC can further dramatically promote UOR, making it among the best UOR catalysts reported to date. From experimental results and DFT calculations, the specific nanoarchitecture, involving an anomalous hcp phase together with Mn doping engineering, endows hcp-MnNi/NC with abundant exposed active sites, facile charge transfer, and more significantly, optimized electronic state, giving rise to enriched Ni³⁺ active species and oxygen vacancies on the catalyst surface during electrocatalysis. These features collectively contribute to the enhanced UOR activity. This work highlights a potent design strategy to develop advanced catalysts with regulated electronic state through synergistic crystal phase and doping engineering.

Conversion between Metavalent and Covalent Bond in Metastable Superlattices Composed of 2D and 3D Sublayers

Reversible conversion over multimillion times in bond types between metavalent and covalent bonds becomes one of the most promising bases for universal memory. As the conversions have been found in metastable states, an extended category of crystal structures from stable states via redistribution of vacancies, research on kinetic behavior of the vacancies is highly in demand. However, it remains lacking due to difficulties with experimental analysis. Herein, the direct observation of the evolution of chemical states of vacancies clarifies the behavior by combining analysis on charge density distribution, electrical conductivity, and crystal structures. Site-switching of vacancies of Sb₂Te₃ gradually occurs with diverged energy barriers owing to their own activation code: the accumulation of vacancies triggers spontaneous gliding along atomic planes to relieve electrostatic repulsion. Studies on the behavior can be further applied to multiphase superlattices composed of Sb₂Te₃ (2D) and GeTe (3D) sublayers, which represent superior memory performances, but their operating mechanisms were still under debate due to their complexity. The site-switching is favorable (suppressed) when Te-Te bonds are formed as physisorption (chemisorption) over the interface between Sb₂Te₃ (2D) and GeTe (3D) sublayers driven by configurational entropic gain (electrostatic enthalpic loss). Depending on the type of interfaces between sublayers, phases of the superlattices are classified into metastable and stable states, where the conversion could only be achieved in the metastable state. From this comprehensive understanding on the operating mechanism via kinetic behaviors of vacancies and the metastability, further studies toward vacancy engineering are expected in versatile materials.

Spontaneous Seed Formation during Electrodeposition Drives Epitaxial Growth of Metastable Bismuth Selenide Microcrystals

Materials with metastable phases can exhibit vastly different properties from their thermodynamically favored counterparts. Methods to synthesize metastable phases without the need for high-temperature or high-pressure conditions would facilitate their widespread use. We report on the electrochemical growth of microcrystals of bismuth selenide, Bi₂Se₃, in the metastable orthorhombic phase at room temperature in aqueous solution. Rather than direct epitaxy with the growth substrate, the spontaneous formation of a seed layer containing nanocrystals of cubic BiSe enforces the metastable phase. We first used single-crystal silicon substrates with a range of resistivities and different orientations to identify the conditions needed to produce the metastable phase. When the applied potential during electrochemical growth is positive of the reduction potential of Bi³⁺, an initial, Bi-rich seed layer forms. Electron microscopy imaging and diffraction reveal that the seed layer consists of nanocrystals of cubic BiSe embedded within an amorphous matrix of Bi and Se. Using density functional theory calculations, we show that epitaxial matching between cubic BiSe and orthorhombic Bi₂Se₃ can help stabilize the metastable orthorhombic phase over the thermodynamically stable rhombohedral phase. The spontaneous formation of the seed layer enables us to grow orthorhombic Bi₂Se₃ on a variety of substrates including single-crystal silicon with different orientations, polycrystalline fluorine-doped tin oxide, and polycrystalline gold. The ability to stabilize the metastable phase through room-temperature electrodeposition in aqueous solution without requiring a single-crystal substrate broadens the range of applications for this semiconductor in optoelectronic and electrochemical devices.

Methane plasma-mediated phase engineering of Ni nanosheets for alkaline hydrogen evolution

Engineering of the crystal structures of metallic nanomaterials is an alternative avenue to control the size and shape of nanocatalysts. However, the phase-controlled synthesis of Ni nanocatalysts is challenging because of its low reduction potential under mild conditions. We developed a room-temperature CH₄ plasma conversion of Ni(OH)₂ nanosheets to hexagonal close packed (hcp) Ni while maintaining a pristine shape. Increasing the temperature resulted in the formation of face-centered cubic (fcc) Ni. The hcp Ni nanosheets exhibited an overpotential of 85 mV at 10 mA cm^-2 for an electrocatalytic hydrogen evolution reaction (HER) in alkaline solution, which was superior to that of the fcc (122 mV) counterpart. Density-functional-theory calculations demonstrated that during the HER, the d-band center of hcp Ni was closer to the Fermi level, which aided the formation of H₂ molecules. This work could facilitate the synthesis of other metastable metals and metallic alloys with high efficiency for various applications.

Monoatomic Platinum-Embedded Hexagonal Close-Packed Nickel Anisotropic Superstructures as Highly Efficient Hydrogen Evolution Catalyst

The rational design of platinum (Pt) based nanostructures with specific crystal structure plays a significant role in their diverse applications. Herein, the anisotropic superstructures (ASs) of monoatomic Pt-embedded hexagonal close-packed nickel (hcp Ni) nanosheets were successfully synthesized for efficient hydrogen evolution in which an unusual dissociation-diffusion-desorption mechanism played a crucial role. The overpotential for the Pt/Ni ASs to reach the specific current density (10 mA cm^-2) is 28.0 mV, which is much lower than that of conventional Pt/C catalyst (71.0 mV). Moreover, at the overpotential of 100 mV, the mass activity of 30.2 A mg_Pt^-1 for the Pt/Ni ASs is 1060% greater than that in conventional Pt/C catalyst (2.6 A mg_Pt^-1). This work provides a new approach to synthesize highly anisotropic superstructures embedded with monoatomic noble metals to boost their hopeful applications in catalytic applications.

Kinetic 2D Crystals via Topochemical Approach

The designing of novel materials is a fascinating and innovative pathway in materials science. Particularly, novel layered compounds have tremendous influence in various research fields. Advanced fundamental studies covering various aspects, including reactants and synthetic methods, are required to obtain novel layered materials with unique physical and chemical properties. Among the promising synthetic techniques, topochemical approaches have afforded the platform for widening the extent of novel 2D materials. Notably, the synthesis of binary layered materials is considered as a major scientific breakthrough after the synthesis of graphene as they exhibit a wide spectrum of material properties with varied potential applicability. In this review, a comprehensive overview of the progress in the development of metastable layered compounds is presented. The various metastable layered compounds synthesized from layered ternary bulk materials through topochemical approaches are listed, followed by the descriptions of their mechanisms, structural analyses, characterizations, and potential applications. Finally, an essential research direction concerning the synthesis of new materials is indicated, wherein the possible application of topochemical approaches in unprecedented areas is explored.

Compressive Strain in N-Doped Palladium/Amorphous-Cobalt (II) Interface Facilitates Alkaline Hydrogen Evolution

The development of palladium-based catalysts for alkaline hydrogen evolution reaction (HER) is highly desired for renewable hydrogen energy systems, yet still challenging due to the strong palladium-hydrogen bond. Herein, the bottleneck is largely overcome by constructing a nitridation-induced compressively strained-interface N-doped palladium/amorphous cobalt (II) interface (N-Pd/A-Co(II)), which dramatically boosts HER performance in alkaline condition. The optimized catalyst with the compressive strain of 2.7% exhibits the higher activity with an overpotential of only 58 mV to achieve the current density of 10 mA cm^-2 , much better than those of pure Pd (327 mV), and the state-of-art Pt/C (78 mV). Notably, it also shows excellent stability with negligible decline during a 30 h stability test. Detailed analyses reveal that the strong absorption of H_ads on Pd can be efficiently reduced via the compressively strained N-doped Pd. And the amorphous Co(II) component accelerates the water dissociation. Consequently, the cooperative effect between the compressed N-doped Pd and amorphous Co(II) creates the impressive HER performance in alkaline condition, highlighting the importance of the functional interface to develop efficient electrocatalysts for HER and beyond.

Iridium metallene oxide for acidic oxygen evolution catalysis

Exploring new materials is essential in the field of material science. Especially, searching for optimal materials with utmost atomic utilization, ideal activities and desirable stability for catalytic applications requires smart design of materials' structures. Herein, we report iridium metallene oxide: 1 T phase-iridium dioxide (IrO2) by a synthetic strategy combining mechanochemistry and thermal treatment in a strong alkaline medium. This material demonstrates high activity for oxygen evolution reaction with a low overpotential of 197 millivolt in acidic electrolyte at 10 milliamperes per geometric square centimeter (mA cmgeo-2). Together, it achieves high turnover frequencies of 4.2 sUPD-1 (3.0 sBET-1) at 1.50 V vs. reversible hydrogen electrode. Furthermore, 1T-IrO2 also shows little degradation after 126 hours chronopotentiometry measurement under the high current density of 250 mA cmgeo-2 in proton exchange membrane device. Theoretical calculations reveal that the active site of Ir in 1T-IrO2 provides an optimal free energy uphill in *OH formation, leading to the enhanced performance. The discovery of this 1T-metallene oxide material will provide new opportunities for catalysis and other applications.

Manipulation on active electronic states of metastable phase β-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 β-NiMoO₄. Phosphate substitution is proved to be imperative for the stabilization and activation of β-NiMoO₄, which can efficiently generate the active electronic states and promote the intrinsic HER activity. As a result, phosphate substituted β-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.

Non-noble transition metal oxides are common yet typically poor hydrogen evolution catalysts due to scarce active electronic states. This work provides a route for achieving hydrogen evolution at high current densities by stabilizing a metastable NiMoO₄ phase with abundant active electronic states.

Low-cost and multi-level structured NiFeMn alloy@NiFeMn oxyhydroxide electrocatalysts for highly efficient overall water splitting

NiFeMn alloy@NiFeMn oxyhydroxide was fabricated by electrodeposition, which reveals exceptional electrocatalytic property toward overall water splitting owing to the extraordinary multi-level structure.

Closest Packing Polymorphism Interfaced Metastable Transition Metal for Efficient Hydrogen Evolution

Metastable materials are promising because of their catalytic properties, high-energy structure, and unique electronic environment. However, the unstable nature inherited from the metastability hinders further performance improvement and practical applications of these materials. Herein, this limitation is successfully addressed by constructing an in situ polymorphism interface (inf) between the metastable hexagonal-close-packed (hcp) phase and its stable counterpart (face-centered cubic, fcc) in cobalt-nickel (CoNi) alloy. Calculations reveal that the interfacial synergism derived from the hcp and fcc phases lowers the formation energy and enhances stability. Consequently, the optimized CoNi-inf exhibits an exceptionally low potential of 72 mV at 10 mA cm^-2 and a Tafel slope of 57 mV dec^-1 for the hydrogen evolution reaction (HER) in 1.0 m KOH. Furthermore, it is superior to most state-of-the-art non-noble-metal-based HER catalysts. No noticeable activity decay or structural changes are observed even over 14 h of catalysis. The computational simulation further rationalizes that the interface of CoNi-inf with a suitable d-band center provides uniform sites for hydrogen adsorption, leading to a distinguished HER catalytic activity. This work, therefore, presents a new route for designing metastable catalysts for potential energy conversion.

Faceted Branched Nickel Nanoparticles with Tunable Branch Length for High-Activity Electrocatalytic Oxidation of Biomass

Controlling the formation of nanosized branched nanoparticles with high uniformity is one of the major challenges in synthesizing nanocatalysts with improved activity and stability. Using a cubic-core hexagonal-branch mechanism to form highly monodisperse branched nanoparticles, we vary the length of the nickel branches. Lengthening the nickel branches, with their high coverage of active facets, is shown to improve activity for electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF), as an example for biomass conversion.

Implanting Ni-O-VOx sites into Cu-doped Ni for low-overpotential alkaline hydrogen evolution

Nickel-based catalysts are most commonly used in industrial alkaline water electrolysis. However, it remains a great challenge to address the sluggish reaction kinetics and severe deactivation problems of hydrogen evolution reaction (HER). Here, we show a Cu-doped Ni catalyst implanted with Ni-O-VOx sites (Ni(Cu)VOx) for alkaline HER. The optimal Ni(Cu)VOx electrode exhibits a near-zero onset overpotential and low overpotential of 21 mV to deliver –10 mA cm⁻², which is comparable to benchmark Pt/C catalyst. Evidence for the formation of Ni-O-VOx sites in Ni(Cu)VOx is established by systematic X-ray absorption spectroscopy studies. The VOx can cause a substantial dampening of Ni lattice and create an enlarged electrochemically active surface area. First-principles calculations support that the Ni-O-VOx sites are superactive and can promote the charge redistribution from Ni to VOx, which greatly weakens the H-adsorption and H₂ release free energy over Ni. This endows the Ni(Cu)VOx electrode high HER activity and long-term durability.

Producing H₂ from water using electricity and earth-abundant elements is necessary for worldwide renewable fuel production, yet most electrocatalysts have sluggish activities or poor stabilities. Here, authors show vanadium oxide modified copper-doped nickel to enable active and durable H₂ evolution.

Geometric Structure and Electronic Polarization Synergistically Boost Hydrogen Evolution Kinetics in Alkaline Medium

Efficient electrocatalysts for the hydrogen evolution reaction (HER) are significant for the utilization of hydrogen as a fuel, particularly under alkaline conditions. However, the sluggish kinetics of HER remains a challenge. Here we demonstrate an efficient HER catalyst comprising Ru and AgCl nanoparticles anchored on Ag nanowires (Ru/AgCl@Ag), which delivers a low overpotential of 12 mV at 10 mA cm^-2 and a Tafel slope of 38 mV decade^-1. A high mass activity of 214 mA mg^-1 at an overpotential of 25 mV and a long-term durability in 1.0 M KOH are observed. In combination with computational simulations, we find that the high electronegativity of chlorine in AgCl and d-band electrons from Ru synergistically destabilize the water molecule and modulate H adsorption/desorption on the surface of Ru/AgCl@Ag, respectively. This work opens a promising avenue for the facile design and application of highly active and stable composite electrocatalysts toward water splitting.

P-Functionalized and O-deficient TiOn/VOm nanoparticles grown on Ni foam as an electrode for supercapacitors: epitaxial grown heterojunction and visible-light-driven photoresponse

P-TiOn-VOm nanowires were grown on nickel foam (NF) via a one-pot hydrothermal method and by further vapor deposition/phosphorization method. It was found that low valence states of titanium oxide and deficient-oxygen coexist in P-TiOn-VOm/NF. Furthermore, (TiO1.25)3.07 (denoted as TiOn) and VO (denoted as VOm) possess similar structures and matched facets, and their epitaxial growth leads to the formation of TiOn/VOm heterostructure with a formation energy of -1.59 eV. P-TiOn-VOm/NF possesses good electron conductivity and electrons can be transferred from Ti to V centers, as evidenced by the DFT calculations and the XPS spectra. As a result, the specific capacity of P-TiOn-VOm/NF can reach 785 C g-1 at 1 A g-1 in the potential range of 0-0.55 V vs. Hg/HgO, which is much larger than those of VOm/NF, P-VOm/NF, and P-TiO2-VOm/NF. On the other hand, the TiOn/VOm heterostructure also favors the separation and transfer of photoinduced electrons and holes, and P-TiOn-VOm/NF exhibits visible-light-driven photoresponse. Under visible light illumination, the specific capacity of P-TiOn-VOm/NF is increased by 6.2% relative to that in the dark. Furthermore, the P-TiOn-VOm/NF//activated carbon (AC) asymmetric supercapacitor (ASC) shows an energy density of 37.2 W h kg-1 at a power density of 1 kW kg-1 and excellent cycling performance with 93.6% capacity retention after 10 000 cycles at 5 A g-1, which is comparable to and even superior to those of titanium oxides and vanadium oxides. A promising achievement has been proposed to improve the energy storage performance of P-TiOn-VOm through P-functionalization and O-deficiency in this work.

Se-Incorporation Stabilizes and Activates Metastable MoS2 for Efficient and Cost-Effective Water Gas Shift Reaction

Although the water gas shift (WGS) reaction has sparked intensive attention for the production of high-purity hydrogen, the design of cost-efficient catalysts with noble metal-like performance still remains a great challenge. Here, we successfully overcome this obstacle by using Se-incorporated MoS₂ with a 1T phase. Combining the optimized electronic structure, additional active sites from edge sites, and a sulfur vacancy based on the 1T phase, as well as the high surface ratio from the highly open structure, the optimal MoS_1.75Se_0.25 exhibits superior activity and stability compared to the conventional 2H-phase MoS₂, with poor activity, large sulfur loss, and rapid inactivation. The hydrogen production of MoS_1.75Se_0.25 is 942 μmol, which is 1.9 times higher than MoS₂ (504 μmol) and 2.8 times higher than MoSe₂ (337 μmol). Furthermore, due to the lattice stabilization via Se-incorporation, MoS_1.75Se_0.25 exhibited excellent long-term stability without obvious change in more than 10 reaction rounds. Our results demonstrate a pathway to design efficient and cost-efficient catalysts for WGS.