Surface Composition Dependent Ligand Effect in Tuning the Activity of Nickel–Copper Bimetallic Electrocatalysts toward Hydrogen Evolution in Alkaline

Non-metallic surface-modified X-Cu (X = F, Cl, Br) metal catalysts for all-pH hydrogen evolution reaction with high performance

Producing hydrogen through water electrolysis represents a clean and sustainable solution that is crucial in addressing the energy crisis. Nonetheless, the slow process of water electrolysis leads to large different kinetics for hydrogen evolution reaction (HER) under different pH solutions. Here, we designed surface modified metallic X-Cu catalysts (X = F, Cl, Br) with different non-metallic elements on nickel foam (NF) using an electrochemical deposition method, which realizes high performance for all-pH range. In 1.0 M KOH, 1.0 M phosphate-buffered saline (PBS), and 0.5 M H2SO4 media, F-Cu catalyst reaches 10 mA cm-2 with overpotentials of 56 mV, 110 mV, and 197 mV, respectively. Theoretical calculations disclose that the surface modification of F atom leads to redistribution of electrons, causing an upward shift of Cu's d-band center and enhanced adsorption ability for H2O and H intermediates (H*). This work offers novel perspectives for designing Cu-based catalysts with high HER performance, making them applicable across all-pH conditions.

Porous Silicon-Supported Catalytic Materials for Energy Conversion and Storage

Porous silicon (Si) has a tetrahedral structure similar to that of sp3-hybridized carbon atoms in a typical diamond structure, which affords it unique chemical and physical properties including an adjustable intrinsic bandgap, a high-speed carrier transfer efficiency. It has shown great potential in photocatalysis, rechargeable batteries, solar cells, detectors, and electrocatalysis. This review introduces various porous Si-supported electrocatalysts and analyzes the reasons why porous Si is used as a new carrier/active sites from the perspectives of its molecular structure, electronic properties, synthesis methods, etc. The electrochemical applications of porous Si-based electrocatalysts in energy conversion reactions such as hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, and total water decomposition together with lithium-ion battery and supercapacitor in energy storage are summarized. The challenges and future research directions for porous Si are also discussed. This review aims to deepen the understanding of porous Si and promote the development and applications of this new type of Si material.

Hierarchical Selenium-Doped Nickel-Cobalt Hybrids on Carbon Paper for the Overall Water-Splitting Electrocatalytic System

Designing and constructing hierarchically structured materials with heterogeneous compositions is the key to developing an effective catalyst for overall water-splitting applications. Herein, we report the fabrication of hollow-structured selenium-doped nickel-cobalt hybrids on carbon paper as a self-supported electrode (denoted as Se-Ni|Co/CP, where Ni|Co hybrids consist of nickel-cobalt alloy-incorporated nickel-cobalt oxide). The procedure involves direct growth of zeolitic imidazolate framework-67 (ZIF-67) on bimetal-based nickel-cobalt hydroxide (NiCoOH) electrodeposited on CP, followed by selenous etching and pyrolysis to obtain the final Se-Ni|Co/CP electrocatalytic system. The optimized Se-Ni|Co/CP [Se-Ni1|Co9/CP(0.3)] exhibits remarkable performance in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), displaying a current density of 10 mA cm-2 at small overpotentials of 105 mV for HER and 235 mV for OER. Furthermore, it allows an alkali electrolyzer to achieve a current density of 10 mA cm-2 at a cell voltage of only 1.51 V. The outstanding catalytic activity of Se-Ni|Co/CP is ascribed to the high intrinsic activity of the bimetallic catalyst, efficient interfaces, and charge transport facilitated by the heterogeneous component, the hollow structure inherited from the metal-organic frameworks (MOF)-derived material providing ample porosity and active sites, and structural robustness achieved through self-supported construction.

Band Engineering of Mn-P Alloy Enables HER-suppressed Aqueous Manganese Ion Batteries

Aqueous manganese ion batteries hold potential for stationary storage applications owing to their merits in cost, energy density, and environmental sustainability. However, the formidable challenge is the instability of metallic manganese (Mn) anodes in aqueous electrolytes due to severe hydrogen evolution reaction (HER), which is more serious than the commonly studied Zn metal anodes. Moreover, the mechanism of HER side reactions has remained unclear. Herein, we design a series of Mn-P alloying anodes by precisely regulating their energy band structures to mitigate the HER issue. It is found that the serious HER primarily originates from the spontaneous Mn-H2O reaction driven by the excessively high HOMO energy level of Mn, rather than electrocatalytic water splitting. Owing to a reduced HOMO energy level and enhanced electron escape work function, the MnP anode achieves an evidently enhanced cycle durability (over 1000 hours at a high current density of 5 mA cm-2). The MnP||AgVO full cell with an N/P ratio of 4 exhibits better rate capability and extended cycle life (7000 cycles) with minimal capacity degradation than the cell using metallic Mn anode (less than 100 cycles). This study provides a practical approach for developing highly durable aqueous Mn ion batteries.

Structurally Asymmetric Ni-O-Mn Node in Metal-Organic Layers on Carbon Nitride Support for CO2 Photoreduction

The Jahn-Teller (J-T) effect-induced lattice distortion presents an advantageous approach to tailor the electronic structure and CO2 adsorption properties of catalytic centers, consequently conferring desirable photocatalytic CO2 reduction activity and selectivity. Nevertheless, achieving precise J-T distortion control over catalytic sites to enhance CO2 adsorption/activation and target-product desorption remains a formidable challenge. In this work, we successfully induced J-T lattice distortion in neighboring Ni sites by exchanging high-spin Mn2+ into Ni-O-Ni nodes. EXAFS results and DFT simulations revealed that the highly asymmetric Ni-O-Mn nodes induced structural contraction (shortened Ni-O bonds) in the adjacent Ni-O lattice. The magnetic hysteresis loop (M-H) confirmed that the introduction of Mn2+ increased the number of spin electrons, thereby increasing the magnetization intensity. The spin mismatch between photogenerated electrons and holes suppressed charge recombination. Significantly, the d orbitals of the Ni sites in the Ni-O-Mn nodes exhibited strong orbital hybridization with the p orbitals of CO2, as evidenced by the enhanced d-p orbital overlap, facilitating rapid CO2 adsorption and activation. Consequently, the sample featuring lattice-mismatched Ni-O-Mn nodes exhibited an 8.79-fold enhancement in CO production rate compared to the Ni-O-Ni nodes, in the absence of cocatalysts and sacrificial reagents.

Achievements and Challenges in Surfactants-Assisted Synthesis of MOFs-Derived Transition Metal-Nitrogen-Carbon as a Highly Efficient Electrocatalyst for ORR, OER, and HER

Metal-organic frameworks (MOFs) are excellent precursors for preparing transition metal and nitrogen co-doped carbon catalysts, which have been widely utilized in the field of electrocatalysis since their initial development. However, the original MOFs derived catalysts have been greatly limited in their development and application due to their disadvantages such as metal atom aggregation, structural collapse, and narrow pore channels. Recently, surfactants-assisted MOFs derived catalysts have attracted much attention from researchers due to their advantages such as hierarchical porous structure, increased specific surface area, and many exposed active sites. This review mainly focuses on the synthesis methods of surfactants-assisted MOFs derived catalysts and comprehensively introduces the action of surfactants in MOFs derived materials and the structure-activity relationship between the catalysts and the oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction performance. Apparently, the aims of this review not only introduce the status of surfactants-assisted MOFs derived catalysts in the field of electrocatalysis but also contribute to the rational design and synthesis of MOFs derived catalysts for fuel cells, metal-air cells, and electrolysis of water toward hydrogen production.

Alkaline Hydrogen Evolution Reaction Electrocatalysts for Anion Exchange Membrane Water Electrolyzers: Progress and Perspective

For the aim of achieving the carbon-free energy scenario, green hydrogen (H2) with non-CO2 emission and high energy density is regarded as a potential alternative to traditional fossil fuels. Over the last decades, significant breakthroughs have been realized on the alkaline hydrogen evolution reaction (HER), which is a fundamental advancement and efficient process to generate high-purity H2 in the laboratory. Based on this, the development of the practical industry-oriented anion exchange membrane water electrolyzer (AEMWE) is on the rise, showing competitiveness with the incumbent megawatt-scale H2 production technologies. Still, great challenges lie in exploring the electrocatalysts with remarkable activity and stability for alkaline HER, as well as bridging the gap of performance difference between the three-electrode cell and AEMWE devices. In this perspective, we systematically discuss the in-depth mechanisms for activating alkaline HER electrocatalysts, including electronic modification, defect construction, morphology control, synergistic function, field effect, etc. In addition, the current status of AEMWE is reviewed, and the underlying bottlenecks that impede the application of HER electrocatalysts in AEMWE are summarized. Finally, we share our thoughts regarding the future development directions of electrocatalysts toward both alkaline HER and AEMWE, in the hope of advancing the commercialization of water electrolysis technology for green H2 production.

Insights into the pH effect on hydrogen electrocatalysis

Hydrogen electrocatalytic reactions, including the hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR), play a crucial role in a wide range of energy conversion and storage technologies. However, the HER and HOR display anomalous non-Nernstian pH dependent kinetics, showing two to three orders of magnitude sluggish kinetics in alkaline media compared to that in acidic media. Fundamental understanding of the origins of the intrinsic pH effect has attracted substantial interest from the electrocatalysis community. More critically, a fundamental molecular level understanding of this effect is still debatable, but is essential for developing active, stable, and affordable fuel cells and water electrolysis technologies. Against this backdrop, in this review, we provide a comprehensive overview of the intrinsic pH effect on hydrogen electrocatalysis, covering the experimental observations, underlying principles, and strategies for catalyst design. We discuss the strengths and shortcomings of various activity descriptors, including hydrogen binding energy (HBE) theory, bifunctional theory, potential of zero free charge (pzfc) theory, 2B theory and other theories, across different electrolytes and catalyst surfaces, and outline their interrelations where possible. Additionally, we highlight the design principles and research progress in improving the alkaline HER/HOR kinetics by catalyst design and electrolyte optimization employing the aforementioned theories. Finally, the remaining controversies about the pH effects on HER/HOR kinetics as well as the challenges and possible research directions in this field are also put forward. This review aims to provide researchers with a comprehensive understanding of the intrinsic pH effect and inspire the development of more cost-effective and durable alkaline water electrolyzers (AWEs) and anion exchange membrane fuel cells (AMFCs) for a sustainable energy future.

Interpretable Data-Driven Descriptors for Establishing the Structure-Activity Relationship of Metal-Organic Frameworks Toward Oxygen Evolution Reaction

The development of readily accessible and interpretable descriptors is pivotal yet challenging in the rational design of metal-organic framework (MOF) catalysts. This study presents a straightforward and physically interpretable activity descriptor for the oxygen evolution reaction (OER), derived from a dataset of bimetallic Ni-based MOFs. Through an artificial-intelligence (AI) data-mining subgroup discovery (SGD) approach, a combination of the d-band center and number of missing electrons in eg states of Ni, as well as the first ionization energy and number of electrons in eg states of the substituents, is revealed as a gene of a superior OER catalyst. The found descriptor, obtained from the AI analysis of a dataset of MOFs containing 3-5d transition metals and 13 organic linkers, has been demonstrated to facilitate in-depth understanding of structure-activity relationship at the molecular orbital level. The descriptor is validated experimentally for 11 Ni-based MOFs. Combining SGD with physical insights and experimental verification, our work offers a highly efficient approach for screening MOF-based OER catalysts, simultaneously providing comprehensive understanding of the catalytic mechanism.

Enhancement of acidic hydrogen evolution reaction efficiency through Cu/Ni-doped MFI-type protozeolite layered nanoclusters

We have prepared a highly active and stable copper-doped nickel electrocatalyst. Cu/Ni-doped MFI-type protozeolite layered nanoclusters electrodes have a large electrochemically active surface area (ECSA) and good HER activity, as well as excellent durability. The addition of Cu greatly increases hydrogen evolution reaction (HER) activity under acidic conditions. At the same time, the in situ grown Cu2+1O provides some activity, and in addition, the interface constructed between Cu and Ni further generates sufficient electrochemically active surface area. The activated Cu/Ni-doped MFI-type layered nanoclusters required only a 385 mV overpotential to generate 10 mA cm-2, demonstrating efficient and stable activity with potential practical applications.

Design and fabrication of intermetallic NiCo electrocatalysts for the alkaline HER

The design and fabrication of highly efficient electrocatalysts are crucial for reducing energy consumption, improving hydrogen production rates, and prolonging the service life of alkaline electrolyzers. In this study, intermetallic L10-NiCo electrocatalysts were designed using DFT calculations and fabricated through a one-step solid-state reaction method. The DFT calculations indicated that L10-NiCo presented a lower H adsorption Gibbs free energy and a moderate H2O dissociation barrier compared to the commonly used Ni catalyst and disordered NiCo alloy. Increasing the solid-state reaction temperature facilitated the formation of intermetallic L10-NiCo. Electrocatalytic tests for the alkaline HER demonstrated that the ECSA of L10-NiCo nanoparticles increased to 2.3 times, the overpotential decreased by 19%, the electrocatalytic activity increased to 1.5 times, and the stability improved to 2.2 times compared to those of the Ni nanoparticles. This research provides insights into the design and fabrication of highly efficient catalytic electrodes for alkaline electrolyzers.

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.

In Situ Electrochemical Rapid Induction of Highly Active γ-NiOOH Species for Industrial Anion Exchange Membrane Water Electrolyzer

Limited by the strong oxidation environment and sluggish reconstruction process in oxygen evolution reaction (OER), designing rapid self-reconstruction with high activity and stability electrocatalysts is crucial to promoting anion exchange membrane (AEM) water electrolyzer. Herein, trace Fe/S-modified Ni oxyhydroxide (Fe/S-NiOOH/NF) nanowires are constructed via a simple in situ electrochemical oxidation strategy based on precipitation-dissolution equilibrium. In situ characterization techniques reveal that the successful introduction of Fe and S leads to lattice disorder and boosts favorable hydroxyl capture, accelerating the formation of highly active γ-NiOOH. The Density Functional Theory (DFT) calculations have also verified that the incorporation of Fe and S optimizes the electrons redistribution and the d-band center, decreasing the energy barrier of the rate-determining step (*O→*OOH). Benefited from the unique electronic structure and intermediate adsorption, the Fe/S-NiOOH/NF catalyst only requires the overpotential of 345 mV to reach the industrial current density of 1000 mA cm-2 for 120 h. Meanwhile, assembled AEM water electrolyzer (Fe/S-NiOOH//Pt/C-60 °C) can deliver 1000 mA cm-2 at a cell voltage of 2.24 V, operating at the average energy efficiency of 71% for 100 h. In summary, this work presents a rapid self-reconstruction strategy for high-performance AEM electrocatalysts for future hydrogen economy.

Turning copper into an efficient and stable CO evolution catalyst beyond noble metals

Using renewable electricity to convert CO2 into CO offers a sustainable route to produce a versatile intermediate to synthesize various chemicals and fuels. For economic CO2-to-CO conversion at scale, however, there exists a trade-off between selectivity and activity, necessitating the delicate design of efficient catalysts to hit the sweet spot. We demonstrate here that copper co-alloyed with isolated antimony and palladium atoms can efficiently activate and convert CO2 molecules into CO. This trimetallic single-atom alloy catalyst (Cu92Sb5Pd3) achieves an outstanding CO selectivity of 100% (±1.5%) at -402 mA cm-2 and a high activity up to -1 A cm-2 in a neutral electrolyte, surpassing numerous state-of-the-art noble metal catalysts. Moreover, it exhibits long-term stability over 528 h at -100 mA cm-2 with an FECO above 95%. Operando spectroscopy and theoretical simulation provide explicit evidence for the charge redistribution between Sb/Pd additions and Cu base, demonstrating that Sb and Pd single atoms synergistically shift the electronic structure of Cu for CO production and suppress hydrogen evolution. Additionally, the collaborative interactions enhance the overall stability of the catalyst. These results showcase that Sb/Pd-doped Cu can steadily carry out efficient CO2 electrolysis under mild conditions, challenging the monopoly of noble metals in large-scale CO2-to-CO conversion.

Advancing electrocatalytic reactions through mapping key intermediates to active sites via descriptors

Descriptors play a crucial role in electrocatalysis as they can provide valuable insights into the electrochemical performance of energy conversion and storage processes. They allow for the understanding of different catalytic activities and enable the prediction of better catalysts without relying on the time-consuming trial-and-error approaches. Hence, this comprehensive review focuses on highlighting the significant advancements in commonly used descriptors for critical electrocatalytic reactions. First, the fundamental reaction processes and key intermediates involved in several electrocatalytic reactions are summarized. Subsequently, three types of descriptors are classified and introduced based on different reactions and catalysts. These include d-band center descriptors, readily accessible intrinsic property descriptors, and spin-related descriptors, all of which contribute to a profound understanding of catalytic behavior. Furthermore, multi-type descriptors that collectively determine the catalytic performance are also summarized. Finally, we discuss the future of descriptors, envisioning their potential to integrate multiple factors, broaden application scopes, and synergize with artificial intelligence for more efficient catalyst design and discovery.

Electrocatalytic Properties of Quasi-2D Oxides LaSrMn0.5M0.5O4 (M = Co, Ni, Cu, and Zn) for Hydrogen and Oxygen Evolution Reactions

Designing cost-effective and highly efficient electrocatalysts for water splitting is a significant challenge. We have systematically investigated a series of quasi-2D oxides, LaSrMn0.5M0.5O4 (M = Co, Ni, Cu, Zn), to enhance the electrocatalytic properties of the two half-reactions of water-splitting, namely oxygen and hydrogen evolution reactions (OER and HER). The four materials are isostructural, as confirmed by Rietveld refinements with X-ray diffraction. The oxygen contents and metal valence states were determined by iodometric titrations and X-ray photoelectron spectroscopy. Electrical conductivity measurements in a wide range of temperatures revealed semiconducting behavior for all four materials. Electrocatalytic properties were studied for both half-reactions of water-splitting, namely, oxygen-evolution and hydrogen-evolution reactions (OER and HER). For the four materials, the trends in both OER and HER were the same, which also matched the trend in electrical conductivities. Among them, LaSrMn0.5Co0.5O4 showed the best bifunctional electrocatalytic activity for both OER and HER, which may be attributed to its higher electrical conductivity and favorable electron configuration.

Interfacial engineering of Ni-Co-Mn@Ni nanosheet-nanocone arrays as high performance non-noble metal electrocatalysts for hydrogen generation

The electrochemical hydrogen production from water splitting is a promising strategy for obtaining new energy sources and replacing fossil fuels. In this study, nickel nanocones were first deposited on a nickel foam substrate using a direct current method. Then, a nickel-cobalt-manganese ternary alloy with a nanosheet morphology was deposited on the nanocones using a cyclic voltammetry method with different cycles and sweep rates. The results show that the sample synthesized in 3 cycles with a sweep rate of 10 mV s-1 exhibits the best electrocatalytic activity and requires -81, -121, and -214 mV overpotentials to reach 10, 20 and 100 mA cm-2 current densities, respectively. Electrochemical impedance spectroscopy studies also improved the HER performance with the lowest charge transfer resistance among all of the synthesized electrodes. This study introduces an effective and facile method for the fabrication of highly active and stable electrocatalysts.

Bimetallic Cu@Ru Core-Shell Structures with Ligand Effects for Endo-Exogenous Stimulation-Mediated Dynamic Oncotherapy

Dynamic therapies, which induce reactive oxygen species (ROS) production in situ through endogenous and exogenous stimulation, are emerging as attractive options for tumor treatment. However, the complexity of the tumor substantially limits the efficacy of individual stimulus-triggered dynamic therapy. Herein, bimetallic copper and ruthenium (Cu@Ru) core-shell nanoparticles are applied for endo-exogenous stimulation-triggered dynamic therapy. The electronic structure of Cu@Ru is regulated through the ligand effects to improve the adsorption level for small molecules, such as water and oxygen. The core-shell heterojunction interface can rapidly separate electron-hole pairs generated by ultrasound and light stimulation, which initiate reactions with adsorbed small molecules, thus enhancing ROS generation. This synergistically complements tumor treatment together with ROS from endogenous stimulation. In vitro and in vivo experiments demonstrate that Cu@Ru nanoparticles can induce tumor cell apoptosis and ferroptosis through generated ROS. This study provides a new paradigm for endo-exogenous stimulation-based synergistic tumor treatment.

Solidophobic Surface for Electrochemical Extraction of High-Valued Mg(OH)2 Coupled with H2 Production from Seawater

A significant challenge in direct seawater electrolysis is the rapid deactivation of the cathode due to the large scaling of Mg(OH)2. Herein, we synthesized a Pt-coated highly disordered NiCu alloy (Pt-NiCu alloy) electrode with superior solidophobic behavior, enabling stable hydrogen generation (100 mA cm-2, >1000 h durability) and simultaneous production of Mg(OH)2 (>99.0% purity) in electrolyte enriched with Mg2+ and Ca2+. The unconventional solidophobic property primarily stems from the high surface energy of the NiCu alloy substrate, which facilitates the adsorption of surface water and thereby compels the bulk formation of Mg(OH)2 via homogeneous nucleation. The discovery of this solidophobic electrode will revolutionarily simplify the existing techniques for seawater electrolysis and increase the economic viability for seawater electrolysis.

Stabilizing Lattice Oxygen through Mn Doping in NiCo2O4-δ Spinel Electrocatalysts for Efficient and Durable Acid Oxygen Evolution

Design the electrocatalysts without noble metal is still a challenge for oxygen evolution reaction (OER) in acid media. Herein, we reported the manganese (Mn) doping method to decrease the concentration of oxygen vacancy (VO) and form the Mn-O structure adjacent octahedral sites in spinel NiCo2O4-δ (NiMn1.5Co3O4-δ), which highly enhanced the activity and stability of spinel NiCo2O4-δ with a low overpotential (η) of 280 mV at j=10 mA cm-2 and long-term stability of 80 h in acid media. The isotopic labelling experiment based on differential electrochemical mass spectrometry (DEMS) clearly demonstrated the lattice oxygen in NiMn1.5Co3O4-δ is more stable due to strong Mn-O bond and shows synergetic adsorbate evolution mechanism (SAEM) for acid OER. Density functional theory (DFT) calculations reveal highly increased oxygen vacancy formation energy (EVO) of NiCo2O4-δ after Mn doping. More importantly, the highly hydrogen bonding between Mn-O and *OOH adsorbed on adjacent Co octahedral sites promote the formation of *OO from *OOH due to the greatly enhanced charge density of O in Mn substituted sites.

Synchronous Regulation of D-Band Centers in Zn Substrates and Weakening Pauli Repulsion of Zn Ions Using the Ascorbic Acid Additive for Reversible Zinc Anodes

The advanced aqueous zinc-ion batteries (AZIBs) are still challenging due to the harmful reactions including hydrogen evolution and corrosion. Here, a natural small molecule acid vitamin C (Vc) as an aqueous electrolyte additive has been selectively identified. The small molecule Vc can adjust the d band center of Zn substrate which fixes the active H+ so that the hydrogen evolution reaction (HER) is restrained. Simultaneously, it could also fine-tune the solvation structure of Zn ions due to the enhanced electrostatics and reduced Pauli repulsion verified by energy decomposition analysis (EDA). Hence, the cell retains an ultra-long cycle performance of over 1300 cycles and a superior Coulombic efficiency (CE) of 99.5 %. The prepared full cells display increased rate capability, cycle lifetime, and self-discharge suppression. Our results shed light on the mechanistic principle of electrolyte additives on the performance improvement of ZIBs, which is anticipated to render a new round of studies.

Atomic reconstruction for realizing stable solar-driven reversible hydrogen storage of magnesium hydride

Reversible solid-state hydrogen storage of magnesium hydride, traditionally driven by external heating, is constrained by massive energy input and low systematic energy density. Herein, a single phase of Mg2Ni(Cu) alloy is designed via atomic reconstruction to achieve the ideal integration of photothermal and catalytic effects for stable solar-driven hydrogen storage of MgH2. With the intra/inter-band transitions of Mg2Ni(Cu) and its hydrogenated state, over 85% absorption in the entire spectrum is achieved, resulting in the temperature up to 261.8 °C under 2.6 W cm-2. Moreover, the hydrogen storage reaction of Mg2Ni(Cu) is thermodynamically and kinetically favored, and the imbalanced distribution of the light-induced hot electrons within CuNi and Mg2Ni(Cu) facilitates the weakening of Mg-H bonds of MgH2, enhancing the "hydrogen pump" effect of Mg2Ni(Cu)/Mg2Ni(Cu)H4. The reversible generation of Mg2Ni(Cu) upon repeated dehydrogenation process enables the continuous integration of photothermal and catalytic roles stably, ensuring the direct action of localized heat on the catalytic sites without any heat loss, thereby achieving a 6.1 wt.% H2 reversible capacity with 95% retention under 3.5 W cm-2.

Electrocatalytic Activation in ReSe2-VSe2 Alloy Nanosheets to Boost Water-Splitting Hydrogen Evolution Reaction

It is challenging to control the electronic structure of 2D transition metal dichalcogenides (TMD) for extended applications in renewable energy devices. Here, ReSe2-VSe2 (Re1- xVxSe2) alloy nanosheets over the whole composition range via a colloidal reaction is synthesized. Increasing x makes the nanosheets more metallic and induces a 1T″-to-1T phase transition at x = 0.5-0.6. Compared to the MoSe2-VSe2 and WSe2-VSe2 alloy nanosheets, ReSe2 and VSe2 are mixed more homogeneously at the atomic scale. The alloy nanosheets at x = 0.1-0.7 exhibit an enhanced electrocatalytic activity toward acidic hydrogen evolution reaction (HER). In situ X-ray absorption fine structure measurements reveal that alloying caused the Re and V atoms to be synergically more active in the HER. Gibbs free energy (ΔGH*) and density of state calculations confirm that alloying and Se vacancies effectively activate the metal sites toward HER. The composition dependence of HER performance is explained by homogenous atomic mixing with the increased Se vacancies. The study provides a strategy for designing new TMD alloy nanosheets with enhanced catalytic activity.

Temporally Decoupled Ammonia Splitting by a Zn-NH3 Battery with an Ammonia Oxidation/Hydrogen Evolution Bifunctional Electrocatalyst as a Cathode

Ammonia splitting to hydrogen is a decisive route for hydrogen economy but is seriously limited by the complex device and low efficiency. Here, we design and propose a new rechargeable Zn-NH3 battery based on temporally decoupled ammonia splitting to achieve efficient NH3-to-H2 conversion. In this system, ammonia is oxidized into nitrogen during cathodic charging (2NH3 + 6OH- → N2 + 6H2O + 6e-) with external electrical energy conversion and storage, while during cathodic discharging, water is reduced to hydrogen (2H2O + 2e- → H2 + 2OH-) with electrical energy generation. In this loop, continuous and efficient H2 production without separation and purification is achieved. With the help of the ammonia oxidation reaction (AOR) and hydrogen evolution reaction (HER) bifunctional catalyst of Mo2C/NiCu@C, a rechargeable Zn-NH3 battery is realized that exhibits a high NH3-to-H2 FE of 91.6% with outstanding durability for 900 cycles (300 h) at 20 mA/cm2, enabling efficient and continuous NH3-to-H2 conversion.

Thermally Enhanced Relay Electrocatalysis of Nitrate-to-Ammonia Reduction over Single-Atom-Alloy Oxides

The electrochemical nitrate reduction reaction (NO3RR) holds promise for converting nitrogenous pollutants to valuable ammonia products. However, conventional electrocatalysis faces challenges in effectively driving the complex eight-electron and nine-proton transfer process of the NO3RR while also competing with the hydrogen evolution reaction. In this study, we present the thermally enhanced electrocatalysis of nitrate-to-ammonia conversion over nickel-modified copper oxide single-atom alloy oxide nanowires. The catalyst demonstrates improved ammonia production performance with a Faradaic efficiency of approximately 80% and a yield rate of 9.7 mg h-1 cm-2 at +0.1 V versus a reversible hydrogen electrode at elevated cell temperatures. In addition, this thermally enhanced electrocatalysis system displays impressive stability, interference resistance, and favorable energy consumption and greenhouse gas emissions for the simulated industrial wastewater treatment. Complementary in situ analyses confirm that the significantly superior relay of active hydrogen species formed at Ni sites facilitates the thermal-field-coupled electrocatalysis of Cu surface-adsorbed *NOx hydrogenation. Theoretical calculations further support the thermodynamic and kinetic feasibility of the relay catalysis mechanism for the NO3RR over the Ni1Cu model catalyst. This study introduces a conceptual thermal-electrochemistry approach for the synergistic regulation of complex catalytic processes, highlighting the potential of multifield-coupled catalysis to advance sustainable-energy-powered chemical synthesis technologies.

Computational chemistry for water-splitting electrocatalysis

Electrocatalytic water splitting driven by renewable electricity has attracted great interest in recent years for producing hydrogen with high-purity. However, the practical applications of this technology are limited by the development of electrocatalysts with high activity, low cost, and long durability. In the search for new electrocatalysts, computational chemistry has made outstanding contributions by providing fundamental laws that govern the electron behavior and enabling predictions of electrocatalyst performance. This review delves into theoretical studies on electrochemical water-splitting processes. Firstly, we introduce the fundamentals of electrochemical water electrolysis and subsequently discuss the current advancements in computational methods and models for electrocatalytic water splitting. Additionally, a comprehensive overview of benchmark descriptors is provided to aid in understanding intrinsic catalytic performance for water-splitting electrocatalysts. Finally, we critically evaluate the remaining challenges within this field.

Screening of transition metal and boron atoms co-doped graphdiyne catalysts for electrocatalytic urea synthesis

Electrocatalytic CN coupling using nitrogen (N2) and carbon dioxide (CO2) as precursors offers a promising alternative for urea production under mild conditions, compared to traditional synthesis approaches. However, the design and screening of extremely efficient electrocatalysts remains a significant challenge in this field. Hence, we propose a systematic approach to screen efficient double-atom catalysts (DACs) with both metal and boron active sites, employing density functional theory (DFT). A comprehensive evaluation of 27 potential catalysts were performed, taking into account their stability, co-adsorption of N2 and CO2, as well as the potential-determining step (PDS) involved urea formation. The calculated results show that co-doped graphdiyne with CrB and MnB double atoms (CrB@GDY and MnB@GDY) emerge as potential electrocatalysts for urea production, displaying thermodynamic energy barriers of 0.41 eV and 0.66 eV, respectively. More importantly, these two DACs can significantly suppress the ammonia (NH3) and C1 products formation. Furthermore, a catalytic activity relationship between the d-band centers of the DACs and urea production performance were established. This study not only forecasts two promising DACs for subsequent experimental work but also establishes a theoretical framework for the evaluation of DACs in electrocatalytic urea synthesis.

In Situ Regulating Cobalt/Iron Oxide-Oxyhydroxide Exchange by Dynamic Iron Incorporation for Robust Oxygen Evolution at Large Current Density

The key dilemma for green hydrogen production via electrocatalytic water splitting is the high overpotential required for anodic oxygen evolution reaction (OER). Co/Fe-based materials show superior catalytic OER activity to noble metal-based catalysts, but still lag far behind the state-of-the-art Ni/Fe-based catalysts probably due to undesirable side segregation of FeOOH with poor conductivity and unsatisfied structural durability under large current density. Here, a robust and durable OER catalyst affording current densities of 500 and 1000 mA cm-2 at extremely low overpotentials of 290 and 304 mV in base is reported. This catalyst evolves from amorphous bimetallic FeOOH/Co(OH)2 heterostructure microsheet arrays fabricated by a facile mechanical stirring strategy. Especially, in situ X-ray photoelectron spectroscopy (XPS) and Raman analysis decipher the rapid reconstruction of FeOOH/Co(OH)2 into dynamically stable Co1-x Fex OOH active phase through in situ iron incorporation into CoOOH, which perform as the real active sites accelerating the rate-determining step supported by density functional theory calculations. By coupling with MoNi4 /MoO2 cathode, the self-assembled alkaline electrolyzer can deliver 500 mA cm-2 at a low cell voltage of 1.613 V, better than commercial IrO2 (+) ||Pt/C(-) and most of reported transition metal-based electrolyzers. This work provides a feasible strategy for the exploration and design of industrial water-splitting catalysts for large-scale green hydrogen production.

Low-Cost Hydrogen Production from Alkaline/Seawater over a Single-Step Synthesis of Mo3 Se4 -NiSe Core-Shell Nanowire Arrays

The rational design and steering of earth-abundant, efficient, and stable electrocatalysts for hydrogen generation is highly desirable but challenging with catalysts free of platinum group metals (PGMs). Mass production of high-purity hydrogen fuel from seawater electrolysis presents a transformative technology for sustainable alternatives. Here, a heterostructure of molybdenum selenide-nickel selenide (Mo3 Se4 -NiSe) core-shell nanowire arrays constructed on nickel foam by a single-step in situ hydrothermal process is reported. This tiered structure provides improved intrinsic activity and high electrical conductivity for efficient charge transfer and endows excellent hydrogen evolution reaction (HER) activity in alkaline and natural seawater conditions. The Mo3 Se4 -NiSe freestanding electrodes require small overpotentials of 84.4 and 166 mV to reach a current density of 10 mA cm-2 in alkaline and natural seawater electrolytes, respectively. It maintains an impressive balance between electrocatalytic activity and stability. Experimental and theoretical calculations reveal that the Mo3 Se4 -NiSe interface provides abundant active sites for the HER process, which modulate the binding energies of adsorbed species and decrease the energetic barrier, providing a new route to design state-of-the-art, PGM-free catalysts for hydrogen production from alkaline and seawater electrolysis.

Ion-Sieve-Confined Synthesis of Size-Tunable Ru for Electrochemical Hydrogen Evolution

The controllable and low-cost synthesis of nanometal particles is highly desired in scientific and industrial research. Herein, size-tunable Ru nanoparticles were synthesized by using a novel ion-sieve-confined reduction method. The H2TiO3 ion-sieve was used to adsorb Ru3+ into the hydroxyl-enriched porous [TiO3]2- layers. The confined environment of the interlayer space facilitates Ru-Ru collision and bonding during annealing, achieving a precise reduction from Ru3+ to Ru0 without additional reductants. Owing to the confinement effect, Ru0 nanoparticles are uniformly embedded in the pores on the surface of the postannealed TiO2 matrix (Ru@TiO2). Ru@TiO2 exhibited a lower overpotential than Pt/C (57 vs 87 mV at 10 mA cm-2) for the HER in 0.1 M KOH solution. The confinement-induced reduction of metal ions was also preliminarily proved in ion-exchanged zeolites, which provides facile and abundant approaches for the size-controllable synthesis of nanometal catalysts with high catalytic activity.

Manipulation of Electron Spins with Oxygen Vacancy on Amorphous/Crystalline Composite-Type Catalyst

By substituting the oxygen evolution reaction (OER) with the anodic urea oxidation reaction (UOR), it not only reduces energy consumption for green hydrogen generation but also allows purification of urea-rich wastewater. Spin engineering of the d orbital and oxygen-containing adsorbates has been recognized as an effective pathway for enhancing the performance of electrocatalysts. In this work, we report the fabrication of a bifunctional electrocatalyst composed of amorphous RuO2-coated NiO ultrathin nanosheets (a-RuO2/NiO) with abundant amorphous/crystalline interfaces for hydrogen evolution reaction (HER) and UOR. Impressively, only 1.372 V of voltage is required to attain a current density of 10 mA cm-2 over a urea electrolyzer. The increased oxygen vacancies in a-RuO2/NiO by incorporation of amorphous RuO2 enhance the total magnetization and entail numerous spin-polarized electrons during the reaction, which speeds up the UOR reaction kinetics. The density functional theory study reveals that the amorphous/crystalline interfaces promote charge-carrier transfer, and the tailored d-band center endows the optimized adsorption of oxygen-generated intermediates. This kind of oxygen vacancy induced spin-polarized electrons toward boosting HER and UOR kinetics and provides a reliable reference for exploration of advanced electrocatalysts.

Orderly Nanodendritic Nickel Substitute for Raney Nickel Catalyst Improving Alkali Water Electrolyzer

The development of nonprecious metal catalysts to meet the activity-stability balance at industrial-grade large current densities remains a challenge toward practical alkali-water electrolysis. Here, this work develops an orderly nanodendritic nickel (ND-Ni) catalyst that consists of ultrafine nanograins in chain-like conformation, which shows both excellent activity and robust stability for large current density hydrogen evolution reaction (HER) in alkaline media, superior to currently applied Raney nickel (R-Ni) catalyst in commercial alkali-water electrolyzer (AWE). The ND-Ni catalyst featured by a three-dimensional (3D) interconnecting microporous structure endows with high specific surface area and excellent conductivity and hydrophilicity, which together afford superior charge/mass transport favorable to HER kinetics at high current densities. An actual AWE with ND-Ni catalyst demonstrates durable water splitting with 1.0 A cm-2 at 1.71 V under industrial conditions and renders a record-low power consumption of 3.95 kW h Nm-3 with an energy efficiency close to 90%. The hydrogen price per gallon of gasoline equivalent (GGE) is calculated to be ≈$0.95, which is less than the target of $2.0 per GGE by 2026 from the U.S. Department of Energy. The results suggest the feasibility of ND-Ni substitute for R-Ni catalyst in commercial AWE.

Metal Alloys-Structured Electrocatalysts: Metal-Metal Interactions, Coordination Microenvironments, and Structural Property-Reactivity Relationships

Metal alloys-structured electrocatalysts (MAECs) have made essential contributions to accelerating the practical applications of electrocatalytic devices in renewable energy systems. However, due to the complex atomic structures, varied electronic states, and abundant supports, precisely decoding the metal-metal interactions and structure-activity relationships of MAECs still confronts great challenges, which is critical to direct the future engineering and optimization of MAECs. Here, this timely review comprehensively summarizes the latest advances in creating the MAECs, including the metal-metal interactions, coordination microenvironments, and structure-activity relationships. First, the fundamental classification, design, characterization, and structural reconstruction of MAECs are outlined. Then, the electrocatalytic merits and modulation strategies of recent breakthroughs for noble and non-noble metal-structured MAECs are thoroughly discussed, such as solid solution alloys, intermetallic alloys, and single-atom alloys. Particularly, unique insights into the bond interactions, theoretical understanding, and operando techniques for mechanism disclosure are given. Thereafter, the current states of diverse MAECs with a unique focus on structural property-reactivity relationships, reaction pathways, and performance comparisons are discussed. Finally, the future challenges and perspectives for MAECs are systematically discussed. It is believed that this comprehensive review can offer a substantial impact on stimulating the widespread utilization of metal alloys-structured materials in electrocatalysis.

Spark plasma sintered catalytic nickel-copper alloy and carbon nanotube electrodes for the hydrogen evolution reaction

We report the proof-of-concept of spark plasma sintered (SPS) consolidated mesoporous composite catalytic electrodes based on nickel-copper alloys and carbon nanotubes for the electrocatalytic hydrogen evolution reaction (HER) in alkaline media. The optimized electrode (203 m2 g-1, 5 wt% Ni75Cu25) operated at -0.1 A cm-2 (current of -0.15 A) for 24 h with a stable overpotential of about 0.3 V. This newly described freestanding SPS approach allows the rational control of specific surface area, metal loading, and electrocatalytic performance, thus opening a new route to catalytic electrodes with controllable physical and catalytic properties.

Optimizing Pt-Based Alloy Electrocatalysts for Improved Hydrogen Evolution Performance in Alkaline Electrolytes: A Comprehensive Review

The splitting of water through electrocatalysis offers a sustainable method for the production of hydrogen. In alkaline electrolytes, the lack of protons forces water dissociation to occur before the hydrogen evolution reaction (HER). While pure Pt is the gold standard electrocatalyst in acidic electrolytes, since the 5d orbital in Pt is nearly fully occupied, when it overlaps with the molecular orbital of water, it generates a Pauli repulsion. As a result, the formation of a Pt-H* bond in an alkaline environment is difficult, which slows the HER and negates the benefits of using a pure Pt catalyst. To overcome this limitation, Pt can be alloyed with transition metals, such as Fe, Co, and Ni. This approach has the potential not only to enhance the performance but also to increase the Pt dispersion and decrease its usage, thus overall improving the catalyst's cost-effectiveness. The excellent water adsorption and dissociation ability of transition metals contributes to the generation of a proton-rich local environment near the Pt-based alloy that promotes HER. Significant progress has been achieved in comprehending the alkaline HER mechanism through the manipulation of the structure and composition of electrocatalysts based on the Pt alloy. The objective of this review is to analyze and condense the latest developments in the production of Pt-based alloy electrocatalysts for alkaline HER. It focuses on the modified performance of Pt-based alloys and clarifies the design principles and catalytic mechanism of the catalysts from both an experimental and theoretical perspective. This review also highlights some of the difficulties encountered during the HER and the opportunities for increasing the HER performance. Finally, guidance for the development of more efficient Pt-based alloy electrocatalysts is provided.

Single and double transition metal atoms doped graphdiyne for highly efficient electrocatalytic reduction of nitric oxide to ammonia

The electrocatalytic conversion of nitric oxide (NORR) to ammonia (NH3) represents a pivotal approach for sustainable energy transformation and efficient waste utilization. Designing highly effective catalysts to facilitate the conversion of NO into NH3 remains a formidable challenge. In this work, the density functional theory (DFT) is used to design NORR catalysts based on single and double transition metal (TM:Fe, Co, Ni and Cu) atoms supported by graphdiyne (TM@GDY). Among eight catalysts, the Cu2@GDY is selected as a the most stable NORR catalyst with high NH3 activity and selectivity. A pivotal discovery underscores that the NORR mechanism is thermodynamically constrained on single atom catalysts (SACs), while being governed by electrochemical processes on double atom catalysts (DACs), a distinction arising from the different d-band centers of these catalysts. Therefore, this work not only introduces an efficient NORR catalyst but also provides crucial insights into the fundamental parameters influencing NORR performance.

Grain Boundary Effects of Hierarchical Ni-Fe (Oxy)hydroxide Nanosheets in Water Oxidation

The robust and scalable oxygen evolution electrocatalysts that can deliver high current densities at low applied potential is a great challenge for the large-scale industrial application in hydrogen production. Here, the preparation of a grain-boundary-rich Ni-Fe (oxy)hydroxide catalyst on Ni foam is reported using a scalable coating approach followed by a chemical precipitating treatment. This facile method effectively assembles the hierarchical Ni-Fe (oxy)hydroxide nanosheet in the ultrasmall crystalline domains (<4 nm) with rich grain boundaries. The hierarchical nanosheet structure with the grain boundaries provides more accessible catalytic sites, facile charge, and mass transfer. Benefiting from the abundant grain boundaries in the hierarchical nanosheets, the as-prepared Ni-Fe (oxy)hydroxide electrodes deliver current densities of 500 and 1000 mA cm-2 at overpotentials of only 278 and 296 mV for the oxygen evolution reaction. The prepared electrode also exhibits long-term durability at a high current density in alkaline conditions.

Integrating PtCo nanoparticles on N, S doped pore carbon nanosheets as high-performance bifunctional catalysts for oxygen reduction and hydrogen evolution reactions

The development of low-Pt bifunctional electrocatalysts with excellent performance for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is critical for the advancement of the hydrogen economy. Here, we have integrated low-loading Pt and Co metals into N, S doped porous carbon nanosheets to obtain composite catalysts encapsulating PtCo alloy nanoparticles (PtCo2@Co9S8/N-CNS and PtCo2@N-CNS). The acquired PtCo nanoparticles, with dimensions of about 2.5 nm, are uniformly distributed and firmly anchored in N, S doped carbon nanosheets with large specific surface areas and rich pore structure, forming multiple active centers and effectively preventing the aggregation of metal nanoparticles. The PtCo2@Co9S8/N-CNS and PtCo2@N-CNS display high ORR catalytic mass activity of 1.65 A mgPt-1 and 1.01 A mgPt-1 in 0.1 M HClO4. The PtCo2@N-CNS catalyst exhibits excellent HER performance in 0.5 M H2SO4, with a mass activity (at 50 mV) 4.3 times higher than that of Pt/C. The PtCo2@Co9S8/N-CNS and PtCo2@N-CNS also exhibit stronger ORR and HER stability than Pt/C after accelerated durability tests. The superior catalytic activity performance of catalysts can be attributed to the synergistic effect of multiple active centers of PtCo, Co9S8 and Co-N in the catalysts. The confinement of PtCo nanoparticles by Co metal and N, S doped porous nanosheets derived from graphitic carbon nitride (g-C3N4) as the template, which can effectively prevent the corrosion and migration of the catalysts under acidic conditions, enhances the catalytic stability of the materials. This study provides a new perspective for the development of economical and efficient bifunctional low-Pt catalysts.

Lattice-Strain Engineering for Heterogenous Electrocatalytic Oxygen Evolution Reaction

The energy efficiency of metal-air batteries and water-splitting techniques is severely constrained by multiple electronic transfers in the heterogenous oxygen evolution reaction (OER), and the high overpotential induced by the sluggish kinetics has become an uppermost scientific challenge. Numerous attempts are devoted to enabling high activity, selectivity, and stability via tailoring the surface physicochemical properties of nanocatalysts. Lattice-strain engineering as a cutting-edge method for tuning the electronic and geometric configuration of metal sites plays a pivotal role in regulating the interaction of catalytic surfaces with adsorbate molecules. By defining the d-band center as a descriptor of the structure-activity relationship, the individual contribution of strain effects within state-of-the-art electrocatalysts can be systematically elucidated in the OER optimization mechanism. In this review, the fundamentals of the OER and the advancements of strain-catalysts are showcased and the innovative trigger strategies are enumerated, with particular emphasis on the feedback mechanism between the precise regulation of lattice-strain and optimal activity. Subsequently, the modulation of electrocatalysts with various attributes is categorized and the impediments encountered in the practicalization of strained effect are discussed, ending with an outlook on future research directions for this burgeoning field.

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.

Ordering-Dependent Hydrogen Evolution and Oxygen Reduction Electrocatalysis of High-Entropy Intermetallic Pt4 FeCoCuNi

Disordered solid-solution high-entropy alloys have attracted wide research attention as robust electrocatalysts. In comparison, ordered high-entropy intermetallics have been hardly explored and the effects of the degree of chemical ordering on catalytic activity remain unknown. In this study, a series of multicomponent intermetallic Pt4 FeCoCuNi nanoparticles with tunable ordering degrees is fabricated. The transformation mechanism of the multicomponent nanoparticles from disordered structure into ordered structure is revealed at the single-particle level, and it agrees with macroscopic analysis by selected-area electron diffraction and X-ray diffraction. The electrocatalytic performance of Pt4 FeCoCuNi nanoparticles correlates well with their crystal structure and electronic structure. It is found that increasing the degree of ordering promotes electrocatalytic performance. The highly ordered Pt4 FeCoCuNi achieves the highest mass activities toward both acidic oxygen reduction reaction (ORR) and alkaline hydrogen evolution reaction (HER) which are 18.9-fold and 5.6-fold higher than those of commercial Pt/C, respectively. The experiment also shows that this catalyst demonstrates better long-term stability than both partially ordered and disordered Pt4 FeCoCuNi as well as Pt/C when subject to both HER and ORR. This ordering-dependent structure-property relationship provides insight into the rational design of catalysts and stimulates the exploration of many other multicomponent intermetallic alloys.

Ultrathin Carbon Nitride Nanosheets Exfoliated and In Situ Modified with a Nickel Bis(Chelate) Complex for Boosting Photocatalytic Performances

Exfoliation and interfacial modification of two-dimensional (2D) polymeric carbon nitride (CN) are considerably vital for applications in photo/electrocatalysis fields. Here, a grinding-ultrasonic route was designed to construct nickel bis(chelate) complex (Ni(abt)₂, abt = 2-aminobenzenethiolate)-modified CN ultrathin nanosheets. Under the assistance of the shear force derived from the grinding process, Ni(abt)₂ was implanted into the interlamination of bulk CN, resulting in the formation of ultrathin CN (UCN) nanosheets. Simultaneously, Ni(abt)₂ molecules were anchored on the surfaces of as-formed UCN nanosheets due to the π-π stacking interaction. Interestingly, compared with single Ni(abt)₂ and UCN, the as-obtained Ni(abt)₂/UCN nanosheets exhibited excellent photocatalytic hydrogen evolution capability. A molecule-semiconductor internal electron transmission mechanism was suggested for explaining the separation and transfer of electron-hole pairs. Density functional theory (DFT) calculations demonstrated that the interface-induced electron redistribution tuned the electron density and hydrogen adsorption of the active centers, thus enhancing the photocatalytic performance of the hybrid catalyst. In addition, the as-obtained Ni(abt)₂/UCN nanosheets could also catalyze the reduction of nitroaromatics in the presence of NaBH₄. It was found that under the simulated sunlight irradiation, the conversion efficiency of nitroaromatic compounds to amino aromatic ones was up to 97.3%, far higher than that under the condition without light irradiation (51.7%), suggesting that the photocatalytic-produced hydrogen took part in the reduction of nitroaromatic compounds.

Engineering Amorphous/Crystalline Ru(OH)3/CoFe-Layered Double Hydroxide for Hydrogen Evolution at 1000 mA cm-2

For large-scale industrial applications, it is highly desirable to create effective, economical electrocatalysts with long-term stability for the hydrogen evolution reaction (HER) at a large current density. Herein, we report a unique motif with crystalline CoFe-layered hydroxide (CoFe-LDH) nanosheets enclosed by amorphous ruthenium hydroxide (a-Ru(OH)₃/CoFe-LDH) to realize the efficient hydrogen production at 1000 mA cm^-2, with a low overpotential of 178 mV in alkaline media. During the continuous HER process for 40 h at such a large current density, the potential remains almost constant with only slight fluctuations, indicating good long-term stability. The remarkable HER performance can be attributed to the charge redistribution caused by abundant oxygen vacancies in a-Ru(OH)₃/CoFe-LDH. The increased electron density of states lowers the charge-transfer resistance and promotes the formation and release of H₂ molecules. The water-splitting electrolyzer with a-Ru(OH)₃/CoFe-LDH as both an anode and a cathode in 1.0 M KOH demonstrates stable hydrogen production and a 100% faradic efficiency. The design strategy of interface engineering in this work will inspire the design of practical electrocatalysts for water splitting on an industrial scale.

Directed electron regulation promoted sandwich-like CoO@FeBTC/NF with p-n heterojunctions by gel electrodeposition for oxygen evolution reaction

Metal organic framework (MOF) is currently-one of the key catalysts for oxygen evolution reaction (OER), but its catalytic performance is severely limited by electronic configuration. In this study, cobalt oxide (CoO) on nickel foam (NF) was first prepared, which then wrapped it with FeBTC synthesized by ligating isophthalic acid (BTC) with iron ions by electrodeposition to obtain CoO@FeBTC/NF p-n heterojunction structure. The catalyst requires only 255 mV overpotential to reach a current density of 100 mA cm^-2, and can maintain 100 h long time stability at 500 mA cm^-2 high current density. The catalytic properties are mainly related to the strong induced modulation of electrons in FeBTC by holes in the p-type CoO, which results in stronger bonding and faster electron transfer between FeBTC and hydroxide. At the same time, the uncoordinated BTC at the solid-liquid interface ionizes acidic radicals which form hydrogen bonds with the hydroxyl radicals in solution, capturing them onto the catalyst surface for the catalytic reaction. In addition, CoO@FeBTC/NF also has strong application prospects in alkaline electrolyzers, which only needs 1.78 V to reach a current density of 1 A cm^-2, and it can maintain long-term stability for 12 h at this current. This study provides a new convenient and efficient approach for the control design of the electronic structure of MOF, leading to a more efficient electrocatalytic process.

3D Hierarchical-Architectured Nanoarray Electrode for Boosted and Sustained Urea Electro-Oxidation

Exploring active and durable Ni-based materials with optimized electronic and architectural engineering to promote the urea oxidation reaction (UOR) is pivotal for the urea-related technologies. Herein a 3D self-supported hierarchical-architectured nanoarray electrode (CC/MnNi@NC) is proposed in which 1D N-doped carbon nanotubes (N-CNTs) with 0D MnNi nanoparticles (NPs) encapsulation are intertwined into 2D nanosheet aligned on the carbon cloth for prominently boosted and sustained UOR electrocatalysis. From combined experimental and theoretical investigations, Mn-alloying can regulate Ni electronic state with downshift of the d-band center, facilitating active Ni³⁺ species generation and prompting the rate-determining step (*COO intermediate desorption). Meanwhile, the micro/nano-hierarchical nanoarray configuration with N-CNTs encapsulating MnNi NPs can not only endow strong operational durability against metal corrosion/agglomeration and enrich the density of active sites, but also accelerate electron transfer, and more intriguingly, promote mass transfer as a result of desirable superhydrophilic and quasi-superaerophobic characteristics. Therefore, with such elegant integration of 0D, 1D and 2D motifs into 3D micro/nano-hierarchical architecture, the resulting CC/MnNi@NC can deliver admirable UOR performance, favorably comparable to the best-performing UOR electrocatalysts reported thus far. This work opens a fresh prospect in developing advanced electrocatalysts via electronic manipulation coupled with architectural engineering for various energy conversion technologies.

Doping of Cr to Regulate the Valence State of Cu and Co Contributes to Efficient Water Splitting

Water electrolysis in alkaline media is the most promising technology for hydrogen production, but efficient electrocatalysts are required to reduce the overpotential in HER and OER processes. In this work, the multicomponent transition metal catalyst Cr-Cu/CoO_x was loaded on copper foam by electrodeposition and annealing, and the catalyst exhibited excellent electrochemical activity. The HER overpotential is 21 mV and the OER overpotential is 252 mV at a current density of 10 mA cm^-2. The overall water splitting voltage is 1.51 V, even better than the Pt/C//RuO₂ two-electrode system (1.61 V). The excellent performance of this catalyst is mainly derived from the close synergistic interaction among Cu, Co, and Cr. The doping of Cr modulates the valence states of Cu and Co at the active sites and improves the adsorption of various reaction intermediates. Density functional theory (DFT) calculations show that the doping of Cr can optimize the adsorption of the reaction intermediate H*. Meanwhile, the high-valent Cr and Co promote hydrolysis through strong adsorption with OH^-. The present work provides a reasonable strategy for designing low-cost transition metals as efficient catalysts for water electrolysis.

Composition-Tuned (MoWV)Se2 Ternary Alloy Nanosheets as Excellent Hydrogen Evolution Reaction Electrocatalysts

Ternary alloying of transition metal dichalcogenides (TMDs) has the potential for altering the electronic structure of materials to suit electrochemical applications. Herein, we synthesized (MoWV)Se₂ nanosheets at various compositions via a colloidal reaction. The mole fraction of V atoms (x_V) was successfully increased up to 0.8, producing a metallic phase that is highly durable against hydration. Furthermore, we synthesized (MoW)Se₂ nanosheets over the entire composition range. The atomic mixing of the ternary alloys is more random than that of the constitutional binary alloys, as supported by first-principles calculations. Compared to binary alloying, ternary alloying more effectively enhanced the electrocatalytic activity for acidic hydrogen evolution reaction (HER). The HER performance increased upon increasing x_V to 0.44, and thereafter, it declined at higher x_V primarily owing to surface oxidation. The analysis of Gibbs free energy for H adsorption revealed that ternary alloying strongly activates the basal plane for the HER. VSe₂ contains numerous sites favorable for H adsorption, facilitating the composition-dependent HER. These results provide a pioneering strategy for designing multicomponent TMD catalysts that maximize the advantages of each component.

Hydrogen evolution boosted by moderate Co3ZnC with current densities beyond 1000 mA cm-2

Co₃ZnC can efficiently boost the activity of Co@N, O co-doped carbons for hydrogen evolution. The results show that moderate Co₃ZnC plays key roles in achieving an appropriate weighted Co 3d band centre, enhancing charger transfer and thus optimizing the electrochemical active surface area. Thus, a low overpotential of ∼219 mV can drive a high current density of 1000 mA cm^-2 under the favourable condition of moderate Co₃ZnC.

A Petal-like Structured NiCuOOH-NF Electrode by a Sonochemical Combined with the Electrochemical Method for Ammonia Oxidation Reaction

Direct electrochemical oxidation, as an economical and efficient method, has recently received increasing attention for ammonia-nitrogen wastewater treatment. Developing a low-cost, efficient catalytic electrode is the key to solve the problem of sluggish ammonia oxidation reaction (AOR) kinetics. In this study, a three-dimensional (3D) Ni foam electrode coated with NiCuOOH petal-like cluster structures was prepared using a simple sonochemical method combined with a surface electrochemical reconstruction strategy. This structure has a large surface area and abundant NiCuOOH active sites, giving a good premise for extraordinary electrocatalytic activity of AOR. The results show that the maximum current density for AOR reaches 97.8 mA cm−2 at 0.60 V vs. saturated calomel electrode (SCE). Additionally, 96.53% of NH4+-N removal efficiency and 63.12% of TN removal efficiency were acquired in the electrolysis system based on the NiCuOOH-NF electrode, as well as a good stability for at least 24 h. It is a promising flow-through anode for the clean treatment of ammonia-nitrogen wastewater.