Surface reconstruction of RuO2/Co3O4 amorphous-crystalline heterointerface for efficient overall water splitting

Synergizing ternary CoMoW alloy with CeO2 for enhancing electrocatalytic hydrogen evolution

Integrating metal materials with metal oxides to construct a multi-component electrocatalyst represents an effective strategy to develop high-performance electrocatalysts for hydrogen evolution reaction (HER). In this work, we design and synthesize a synergistic heterogeneous electrocatalyst comprising of CoMoW ternary metal alloys and ceria (CeO2) nanosheet supported on nickel foam (NF) via a facile and fast electrodeposition method. The strong electronic interaction between CoMoW and CeO2 not only improves charge transfer but also promotes water dissociation and optimizes hydrogen adsorption capability, thereby improving the kinetics of HER. Benefiting from this properly designed interface, the optimized CoMoW-CeO2/NF delivered a low overpotential of only 35.25 mV at 10 mA cm-2 for HER, which is superior to many reported similar catalysts. This work offers an effective approach for the design and construction of high-performance heterogeneous electrocatalyst comprising of ternary alloys and metal oxides.

Phase-engineered metal boride nanobeads for highly efficient oxygen evolution

Non-precious metals with tailored phase structures show promise as oxygen evolution reaction (OER) catalysts due to their high inherent catalytic activity and extensive exposed active surface area. However, the mechanisms by which phase structures enhance catalytic performance remain unclear. Herein, we synthesized an amorphous cobalt boride (CoB) catalyst via a magnetic field-assisted method, yielding uniform nanoparticles that self-assemble into a nanobead structure. This material undergoes heat treatment to transition from an amorphous phase to a crystalline phase. The catalyst demonstrated exceptional OER activity and long-term stability in an alkaline electrolyte, requiring only 350 mV overpotential at 10 mA cm-2. The amorphous CoB demonstrates remarkable durability by maintaining stable operation for 100 h under harsh conditions characterized by high alkalinity and elevated temperature without any observable performance degradation. We demonstrate that electrochemical activation of an amorphous catalyst can unveil active sites within the bulk material, leveraging the short-range order characteristic of amorphous structures. This process significantly amplifies the active site density, consequently enhancing the electrocatalytic performance of the amorphous catalyst in the oxygen evolution reaction within water oxidation. Furthermore, in situ Raman spectroscopy reveals that amorphous CoB rapid self-reconstruction upon electrochemical activation, leading to the formation of a metal (oxy)hydroxide active layer. This study offers valuable insights into the design of high-efficiency OER catalysts by elucidating the mechanisms underlying amorphous and crystalline materials.

Quenching induced Cu and F co-doping multi-dimensional Co3O4 with modulated electronic structures and rich oxygen vacancy as excellent oxygen evolution reaction electrocatalyst

The development of highly efficient non-precious electrocatalysts for the oxygen evolution reaction (OER) remains a significant challenge. In this work, we introduce a highly effective OER electrocatalyst, Cu-F-Co3O4, synthesized by doping copper (Cu) and fluorine (F) into Co3O4 using a quenching method. Both experimental and theoretical calculations reveal that Cu and F incorporation significantly shifts the d-band center closer to the Fermi level, creates abundant oxygen vacancies, and facilitates the reconstruction of the catalyst to form the CuCo2O4-yFy/CuO heterojunction. This structural modification enhances the OER performance of the catalyst. Additionally, the multi-dimensional architecture exposes more active sites and accelerates mass and charge transfer kinetics. The optimal catalyst, Cu-F-Co3O4-0.7, demonstrates a low overpotential of 290 mV at 10 mA·cm-2, along with remarkable stability exceeding 100 h, significantly outperforming both pristine Co3O4 and benchmark RuO2 electrocatalysts. These findings offer new insights into activating surface reconstruction in spinel oxides by engineering both anion and cation defects for water oxidation.

Electrochemically reconstructable CuMn-bimetal-based metal-organic framework encapsulated Co3O4 composite for selective methanol electrooxidation

In this work, a CuMn-bimetal-based metal-organic framework (MOF) encapsulated Co3O4 composite (CuMn-MOF@Co3O4) with a three-dimensionmal hierarchical structure formed by interwoven nanosheets was in-situ grown on nickel foam (NF) through a three-step fabrication method for the electrochemical methanol oxidation reaction(MOR). The characterizations revealed the phase transformation of CuMn-MOF during the electrochemical activation generated abundant hydroxides/hydroxyoxides (Cu(OH)2, Mn(OH)2, MOOH), which provided optimal architecture and real active sites for MOR. At the same time, the combination of Co3O4 with the generated CuMn(OH)x effectively enhanced the synergistic interactions between them, greatly hindering high-valent hydroxides formation, lowering methanol and intermediate adsorption energy barriers, thereby ensuring highly selective electrooxidation of methanol to formate with high activity. As a result, the electrochemically reconstructable CuMn-MOF@Co3O4 composite exhibited excellent performance, achieving a high MOR current density of 500 mA cm-2 at 1.41 V vs. RHE, with a Faradaic efficiency (FE) of near 100 % and long-term stability. Moreover, in a two-electrode electrolysis system with MeOH-water solution, only 1.60 V of cell voltage was required to maintain a current density of 100 mA cm-2 for MOR-HER, which significantly reduced energy consumption compared to the conventional OER-HER system. It opens a novel avenue for the design of advanced electrochemically reconstructable MOF-based composites for elecrooxidation process.

Noble metal confined in defect-enriched NiCoO2 with synergistic effects for boosting alkaline electrocatalytic oxygen evolution

Achieving a balance between catalytic activity and economic benefit is crucial for water-splitting reactions, which can be addressed by low loading and high dispersion of noble metals on catalytic supports. However, preventing the thermodynamic-driven agglomeration of noble metals during reaction remains a formidable challenge. Herein, we demonstrate a novel oxygen vacancy confinement strategy to enhance the activity and stability of noble metals in defect-rich M/NiCoO2 (M = Ru, Pd, Pt and Ag) catalysts. The oxygen vacancies in the support NiCoO2 facilitate electron delocalization and enhance conductivity, promoting the dispersion of noble metals to prevent aggregation. Moreover, the strong interaction between noble metal atoms and oxygen vacancies ensures a better structural integrity during catalytic processes. Interestingly, the hybrid M/NiCoO2-x catalysts (e.g. Ru/NiCoO2-x) exhibit superior catalytic activities (235 mV) and stability (with activity retention above 98 % after 100 h) compared to the non-confined Ru@NiCoO2 (275 mV, with activity decay of 60 % after 100 h). Further DFT calculations and experimental results indicate that the noble metal atoms confined by oxygen vacancies are electron-deficient, fostering stronger binding with reactive oxygen intermediates. This synergistic effect consequently reduces the energy barrier of the rate-determining step in oxygen evolution reaction, thus accelerating the overall reaction kinetics. This work provides a general strategy for the design of noble metal catalysts that achieve a synergistic balance of high activity and robust stability.

Constructing Palladium-Based Crystalline@Amorphous Core-Shell Heterojunctions for Efficient Formic Acid Oxidation

Constructing crystalline@amorphous heterostructures allows nanomaterials to maintain high electrical conductivity of crystalline structures while acquiring abundant active sites from amorphous structure. This emerging strategy has attracted considerable attention in electrochemical and photoelectrochemistry applications. However, achieving crystalline@amorphous heterostructures based on palladium (Pd) remains challenging due to the difficulties in balancing the transformation between these two phases. Here, a feasible strategy is developed to manufacture Pd-based crystalline@amorphous core-shell structures through non-metallic element doping. The obtained core-shell structures exhibit outstanding catalytic performance for formic acid oxidation (FAO) with mass activity of up to 2.503 A mg-1 Pd. Detailed theoretical and experimental analyses reveal that the construction of crystalline@amorphous core-shell structures increase surface active sites, lowers the oxidation energy barrier, and enhances the selectivity of the direct pathway, thereby effectively facilitating the FAO process. This work demonstrates the feasibility of constructing efficient FAO catalysts using crystalline@amorphous core-shell structures and provides a new platform for achieving platinum-group metals (PGMs) based crystalline-amorphous heterostructures.

V-O-Ru Heterogeneous Interphase Reversible Reconstruction Endowing Zn0.85V10O24·7.4H2O/0.65RuO2 Cathode Robust H+/Zn2+ Storage

Intercalation-type layered vanadium oxides have been widely explored as cathode materials for aqueous zinc-ion batteries (AZIBs). However, attaining both high power density and superior stability remains a formidable challenge. Herein, layered vanadium oxides are pre-intercalated with Zn2+ to form Zn0.85V10O24·7.4H2O (ZVO), which is then combined with RuO2 nanoparticles to construct a ZVO/RuO2 heterostructure featuring interphase V─O─Ru bonds. ZVO/RuO2 heterostructure exhibits a dynamic stable coupling at the interphase via V─O─Ru chemical bonds reconstruction during discharging/charging processes. The dynamically reversible reconstruction of interphase V─O─Ru bonds provides a fast electron transfer channel between RuO2 and ZVO cathode, as demonstrated by ex situ X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations, making RuO2 an additional electron acceptor and donor, and accelerating the migration of H+/Zn2+ in layered ZVO cathode. Therefore, an ultra-high capacity (411 mAh g-1 at 0.5 A g-1, 225 mAh g-1 at 20 A g-1) and long cycling stability (a retention of 92.2% at 20 A g-1 over 20000 cycles) performances are achieved. This interphase reversible reconstruction route provides a promising approach to achieving excellent cycling stability in cathode materials.

Vacancy Engineering in the First Coordination Shell of Single-Atom Catalysts for Enhanced Hydrogen and Oxygen Evolution Reactions

Modulating the coordination environment of active centers has been proven to be an effective strategy for tuning the activity and selectivity of single-atom catalysts (SACs). However, most current research primarily focuses on altering non-metallic elements coordinating with the single metal atom. In this study, a novel approach is presented by introducing various vacancies into the first coordination shell of single-atom doped boron-carbon-nitride (BCN) catalysts, systematically evaluating their hydrogen evolution (HER) and oxygen evolution (OER) reactions performances. Results indicate that the introduction of vacancy defects enhances the stability of M-BXCYNZ structures. Furthermore, adjusting the coordinating atoms around metal sites modulates charge distribution, influencing the binding propensity of intermediates on the adsorption sites and promoting synergistic effects between metal and nonmetal, thereby altering catalytic activity. Specifically, among 147 M-BXCYNZ and M-BXCYNZ-vacancy structures, 17 catalysts with excellent HER performance have been identified. Notably, C-vacancy modulated Ni-BC2N exhibits an OER overpotential of only 0.36V, suggesting that Ni-BC2N-C1 may serve as an efficient multifunctional electrocatalyst for water-splitting reactions. This work employs vacancy engineering to precisely modulate the first coordination shell of single-atom catalysts, not only screening out efficient HER/OER electrocatalysts but also providing guidance for the development of potential BCN-based multifunctional electrocatalysts.

Interface Engineering of RuO2/Ni-Co3O4 Heterostructures for enhanced acidic oxygen evolution reaction

RuO2 has been recognized as a standard electrocatalyst for acidic oxygen evolution reaction (OER). Nonetheless, its high cost and limited durability are still ongoing challenges. Herein, a RuO2/Ni-Co3O4 heterostructure confining a heterointerface (between RuO2 and Ni-doped Co3O4) is constructed to realize enhanced OER performance. Specifically, RuO2/Ni-Co3O4 containing a low Ru content (2.7 ± 0.3 wt%) achieves an overpotential of 186 mV at a current density of 10 mA cm-2 with a long-run stability (≥1300 h). Also, it exhibits a mass activity of 1202.29 mA mgRu-1 at an overpotential of 250 mV, exceeding commercial RuO2. The results disclose an optimum electron transfer at the heterointerface, wherein Ni doping improves the adsorption energy of oxygen-containing intermediates, thereby facilitating OER. This study presents an effective approach for designing highly active and stable OER electrocatalysts.

Rational Design of Transition-Metal-Based Catalysts for the Electrochemical 5-Hydroxymethylfurfural Reduction Reaction

The electrochemical reduction reaction (HMFRR) of 5-hydroxymethylfurfural (HMF) has emerged as a promising avenue for the utilization and refinement of the biomass-derived platform molecule HMF into high-value chemicals, addressing energy sustainability challenges. Transition metal electrocatalysts (TMCs) have recently garnered attention as promising candidates for catalyzing HMFRR, capitalizing on the presence of vacant d orbitals and unpaired d electrons. TMCs play a pivotal role in facilitating the generation of intermediates through interactions with HMF, thereby lowering the activation energy of intricate reactions and significantly augmenting the catalytic reaction rate. In the absence of comprehensive and guiding reviews in this domain, this paper aims to comprehensively summarize the key advancements in the design of transition metal catalysts for HMFRR. It elucidates the mechanisms and pH dependency of various products generated during the electrochemical reduction of HMF, with a specific emphasis on the bond-cleavage angle. Additionally, it offers a detailed introduction to typical in-situ characterization techniques. Finally, the review explores engineering strategies and principles to enhance HMFRR activity using TMCs, particularly focusing on multiphase interface control, crystal face control, and defect engineering control. This review introduces novel concepts to guide the design of HMFRR electrocatalysts, especially TMCs, thus promoting advancements in biomass conversion.

Constructing heterogeneous interface between Co3O4 and RuO2 with enhanced electronic regulation for efficient oxygen evolution reaction at large current density

Exploring effective strategies for developing new high-efficiency catalysts for water splitting is essential for advancing hydrogen energy technology. Herein, Co3O4/RuO2 heterojunction interface is construct through ion exchange reaction and pyrolysis. The as-synthesized Co3O4/RuO2-4 exhibits outstanding oxygen evolution reaction (OER) activity at the current density of 100 mA cm-2 with a low overpotential of 276 mV, and remarkable stability (maintaining activity for 60 h at 100 mA cm-2). Experimental results and theoretical calculations reveal that the electrons around the heterogeneous interface transferred from RuO2 to Co3O4, resulting in electron redistribution and optimization of energy barriers for OER intermediates. This unique composite catalyst structure offers a new potential for designing efficient oxygen electrocatalysts at large current density.

Advancing overall water splitting via phase-engineered amorphous/crystalline interface: A novel strategy to accelerate proton-coupled electron transfer

Traditional phase engineering enhances conductivity or activity by fully converting electrocatalytic materials into either a crystalline or an amorphous state, but this approach often faces limitations. Thus, a practical solution entails balancing the dynamic attributes of both phases to maximize an electrocatalyst's functionality is urgently needed. Herein, in this work, Co/Co2C crystals have been assembled on the amorphous N, S co-doped porous carbon (NSPC) through hydrothermal and calcination processes. The stable biphase structure and amorphous/crystalline (A/C) interface enhance conductivity and intrinsic activity. Moreover, the adsorption ability of water molecules and intermediates is improved significantly attributed to the rich oxygen-containing groups, unsaturated bonds, and defect sites of NSPC, which accelerates proton-coupled electron transfer (PCET) and overall water splitting. Consequently, A/C-Co/Co2C/NSPC (Co/Co2C/NSPC with amorphous/crystalline interface) exhibits outstanding behavior for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), requiring the overpotential of 240.0 mV and 70.0 mV to achieve 10 mA cm-2. Moreover, an electrolyzer assembled by A/C-Co/Co2C/NSPC-3 (anode) and A/C-Co/Co2C/NSPC-2 (cathode) demonstrates a low drive voltage of 1.54 V during overall water splitting process. Overall, this work has pioneered the coexistence of crystalline/amorphous phases in electrocatalysts and provided new insights into phase engineering.

High-Nuclear Co-Added Polyoxometalate-Based Chain: Electrocatalytic Oxygen Production

A high-nuclear Co-added polyoxometalate (CoAP) was synthesized via a hydrothermal reaction: H14.5K9Na7.5-{[Co8(μ2-OH)(μ3-OH)2(H2O)2(Co(H2O)GeW6O26)(B-α-GeW9O34)2][BO(OH)2][Co12(μ2-OH)(μ3-OH)5(H2O)3(Co(H2O)GeW6O26)(GeW6O26)(B-α-GeW9O34)]}·46H2O (1). The polyoxoanion of 1 contains a large Co20 cluster gathered by lacunary GeW6O26 and GeW9O34 subunits. 1 represents a one-dimensional (1D) chain formed by adjacent polyoxoanions coupling through a CoO6 double bridge, showing the first example of a high-nuclear CoAP-based inorganic chain. 1 served as an efficient electrocatalyst in oxygen evolution reactions (OERs).

Heteronuclear Dual Metal Atom Electrocatalysts for Water-Splitting Reactions

Hydrogen is considered a promising substitute for traditional fossil fuels because of its widespread sources, high calorific value of combustion, and zero carbon emissions. Electrocatalytic water-splitting to produce hydrogen is also deemed to be an ideal approach; however, it is a challenge to make highly efficient and low-cost electrocatalysts. Single-atom catalysts (SACs) are considered the most promising candidate to replace traditional noble metal catalysts. Compared with SACs, dual-atom catalysts (DACs) are capable of greater attraction, including higher metal loading, more versatile active sites, and excellent catalytic activity. In this review, several general synthetic strategies and structural characterization methods of DACs are introduced, and recent experimental advances in water-splitting reactions are discussed. The authors hope that this review provides insights and inspiration to researchers regarding DACs in electrocatalytic water-splitting.