Vertically Aligned Oxygenated-CoS2–MoS2 Heteronanosheet Architecture from Polyoxometalate for Efficient and Stable Overall Water Splitting

Laser-Induced Preparation of Anderson-Type Polyoxometalate-Derived Sulfide/Oxide Electrocatalysts for Electrochemical Water Oxidation

Developing cost-effective and high-active electrocatalysts is vital to enhance the electrocatalytic performance for oxygen evolution reaction (OER). However, traditional pyrolysis methods require complicated procedures, exact temperatures, and long reaction times, leading to high costs and low yields of electrocatalysts in potential industrial applications. Herein, a rapid and economic laser-induced preparation strategy is proposed to synthesize three bimetallic sulfide/oxide composites (MMoOS, M=Fe, Co, and Ni) on a nickel foam (NF) substrate. A focused CO2 laser with high energy is applied to decompose Anderson-type polyoxometalate (POM)-based precursors, enabling the creation of abundant heteropore and defective structures in the MMoOS composites that have multi-components of MS/Mo4O11/MoS2. Remarkably, owing to the structural interactions between the active species, FeMoOS shows superior electrocatalytic performance for OER in an alkaline medium, exhibiting a low overpotential of 240 mV at 50 mA cm-2, a small Tafel slope of 79 mV dec-1, and good durability for 80 h. Physical characterizations after OER imply that partially dissolved Mo-based species and new-formed NiO/NiOOH can effectively uncover abundant active sites, fasten charge transfer, and modify defective structures. This work provides a rapid laser-induced irradiation method for the synthesis of POM-derived nanocomposites as promoted electrocatalysts.

Constructing Amorphous-Crystalline Interfacial Bifunctional Site Island-Sea Synergy by Morphology Engineering Boosts Alkaline Seawater Hydrogen Evolution

The development of efficient and durable non-precious hydrogen evolution reaction (HER) catalysts for scaling up alkaline water/seawater electrolysis is highly desirable but challenging. Amorphous-crystalline (A-C) heterostructures have garnered attention due to their unusual atomic arrangements at hetero-interfaces, highly exposed active sites, and excellent stability. Here, a heterogeneous synthesis strategy for constructing A-C non-homogeneous interfacial centers of electrocatalysts on nanocages is presented. Isolated PdCo clusters on nanoscale islands in conjunction with Co3S4 A-C, functioning as a bifunctional site "island-sea" synergy, enable the dynamic confinement design of metal active atoms, resulting in excellent HER catalytic activity and durability. The hierarchical structure of hollow porous nanocages and nanoclusters, along with their large surface area and multi-dimensional A-C boundaries and defects, provides the catalyst with abundant active centers. Theoretical calculations demonstrate that the combination of PdCo and Co3S4 regulates the redistribution of interface electrons effectively, promoting the sluggish water-dissociation kinetics at the cluster Co sites. Additionally, PdCo-Co3S4 heterostructure nanocages exhibit outstanding HER activity in alkaline seawater and long-term stability for 100 h, which can be powered by commercial silicon solar cells. This finding significantly advances the development of alkaline seawater electrolysis for large-scale hydrogen production.

In-situ fabrication of self-supported cobalt molybdenum sulphide on carbon paper for bifunctional water electrocatalysis

The fabrication of highly efficient yet stable noble-metal-free bifunctional electrocatalysts that can simultaneously catalyse both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) remains challenging. Herein, we employ the heterostructure coupling strategy, showcasing an aerosol-assisted chemical vapour deposition (AACVD) aided synthetic approach for the in-situ growth of cobalt molybdenum sulphide nanocomposites on carbon paper (CoMoS@CP) as a bifunctional electrocatalyst. The AACVD allows the rational incorporation of Co in the Mo-S binary structure, which modulates the morphology of CoMoS@CP, resulting in enhanced HER activity (ŋ10 = 171 mV in acidic and ŋ10 = 177 mV in alkaline conditions). Furthermore, the CoS2 species in the CoMoS@CP ternary structure extends the OER capability, yielding an ŋ100 of 455 mV in 1 M KOH. Lastly, we found that the synergistic effect of the Co-Mo-S interface elevates the bifunctional performance beyond binary counterparts, achieving a low cell voltage (1.70 V at 10 mA cm-2) in overall water splitting test and outstanding catalytic stability (∼90 % performance retention after 50-/30-h continuous operation at 10 and 100 mA cm-2, respectively). This work has opened up a new methodology for the controllable synthesis of self-supported transition metal-based electrocatalysts for applications in overall water splitting.

Efficient Catalytic Elimination of Toxic Volatile Organic Compounds via Advanced Oxidation Process Wet Scrubbing with Bifunctional Cobalt Sulfide/Activated Carbon Catalysts

Advanced oxidation process (AOP) wet scrubber is a powerful and clean technology for organic pollutant treatment but still presents great challenges in removing the highly toxic and hydrophobic volatile organic compounds (VOCs). Herein, we elaborately designed a bifunctional cobalt sulfide (CoS2)/activated carbon (AC) catalyst to activate peroxymonosulfate (PMS) for efficient toxic VOC removal in an AOP wet scrubber. By combining the excellent VOC adsorption capacity of AC with the highly efficient PMS activation activity of CoS2, CoS2/AC can rapidly capture VOCs from the gas phase to proceed with the SO4•- and HO• radical-induced oxidation reaction. More than 90% of aromatic VOCs were removed over a wide pH range (3-11) with low Co ion leaching (0.19 mg/L). The electron-rich sulfur vacancies and low-valence Co species were the main active sites for PMS activation. SO4•- was mainly responsible for the initial oxidation of VOCs, while HO• and O2 acted in the subsequent ring-opening and mineralization processes of intermediates. No gaseous intermediates from VOC oxidation were detected, and the highly toxic liquid intermediates like benzene were also greatly decreased, thus effectively reducing the health toxicity associated with byproduct emissions. This work provided a comprehensive understanding of the deep oxidation of VOCs via AOP wet scrubber, significantly accelerating its application in environmental remediation.

Precious Metal Free Hydrogen Evolution Catalyst Design and Application

The quest to identify precious metal free hydrogen evolution reaction catalysts has received unprecedented attention in the past decade. In this Review, we focus our attention to recent developments in precious metal free hydrogen evolution reactions in acidic and alkaline electrolyte owing to their relevance to commercial and near-commercial low-temperature electrolyzers. We provide a detailed review and critical analysis of catalyst activity and stability performance measurements and metrics commonly deployed in the literature, as well as review best practices for experimental measurements (both in half-cell three-electrode configurations and in two-electrode device testing). In particular, we discuss the transition from laboratory-scale hydrogen evolution reaction (HER) catalyst measurements to those in single cells, which is a critical aspect crucial for scaling up from laboratory to industrial settings but often overlooked. Furthermore, we review the numerous catalyst design strategies deployed across the precious metal free HER literature. Subsequently, we showcase some of the most commonly investigated families of precious metal free HER catalysts; molybdenum disulfide-based, transition metal phosphides, and transition metal carbides for acidic electrolyte; nickel molybdenum and transition metal phosphides for alkaline. This includes a comprehensive analysis comparing the HER activity between several families of materials highlighting the recent stagnation with regards to enhancing the intrinsic activity of precious metal free hydrogen evolution reaction catalysts. Finally, we summarize future directions and provide recommendations for the field in this area of electrocatalysis.

Bifunctional Electrocatalysts for Overall and Hybrid Water Splitting

Electrocatalytic water splitting driven by renewable electricity has been recognized as a promising approach for green hydrogen production. Different from conventional strategies in developing electrocatalysts for the two half-reactions of water splitting (e.g., the hydrogen and oxygen evolution reactions, HER and OER) separately, there has been a growing interest in designing and developing bifunctional electrocatalysts, which are able to catalyze both the HER and OER. In addition, considering the high overpotentials required for OER while limited value of the produced oxygen, there is another rapidly growing interest in exploring alternative oxidation reactions to replace OER for hybrid water splitting toward energy-efficient hydrogen generation. This Review begins with an introduction on the fundamental aspects of water splitting, followed by a thorough discussion on various physicochemical characterization techniques that are frequently employed in probing the active sites, with an emphasis on the reconstruction of bifunctional electrocatalysts during redox electrolysis. The design, synthesis, and performance of diverse bifunctional electrocatalysts based on noble metals, nonprecious metals, and metal-free nanocarbons, for overall water splitting in acidic and alkaline electrolytes, are thoroughly summarized and compared. Next, their application toward hybrid water splitting is also presented, wherein the alternative anodic reactions include sacrificing agents oxidation, pollutants oxidative degradation, and organics oxidative upgrading. Finally, a concise statement on the current challenges and future opportunities of bifunctional electrocatalysts for both overall and hybrid water splitting is presented in the hope of guiding future endeavors in the quest for energy-efficient and sustainable green hydrogen production.

Polyoxometalate-Structured Materials: Molecular Fundamentals and Electrocatalytic Roles in Energy Conversion

Polyoxometalates (POMs), a kind of molecular metal oxide cluster with unique physical-chemical properties, have made essential contributions to creating efficient and robust electrocatalysts in renewable energy systems. Due to the fundamental advantages of POMs, such as the diversity of molecular structures and large numbers of redox active sites, numerous efforts have been devoted to extending their application areas. Up to now, various strategies of assembling POM molecules into superstructures, supporting POMs on heterogeneous substrates, and POMs-derived metal compounds have been developed for synthesizing electrocatalysts. From a multidisciplinary perspective, the latest advances in creating POM-structured materials with a unique focus on their molecular fundamentals, electrocatalytic roles, and the recent breakthroughs of POMs and POM-derived electrocatalysts, are systematically summarized. Notably, this paper focuses on exposing the current states, essences, and mechanisms of how POM-structured materials influence their electrocatalytic activities and discloses the critical requirements for future developments. The future challenges, objectives, comparisons, and perspectives for creating POM-structured materials are also systematically discussed. It is anticipated that this review will offer a substantial impact on stimulating interdisciplinary efforts for the prosperities and widespread utilizations of POM-structured materials in electrocatalysis.

Composites of (NH2)-MIL-53(Al) and CBB as bifunctional electrocatalysts for overall electrochemical water splitting in all pH solutions

Electrochemical water splitting is one of the most active areas of energy research, yet the benchmark electrocatalysts used for this area are based on expensive noble metals and transition metals, thus mainly reactions in alkaline solution. MOFs and halide perovskite are novel electrochemical catalysts but unstable in water basically. Here we report a study on composites of (NH2)-MIL-53(Al) MOFs and CBB halide perovskite (Cs3Bi2Br9), which exhibit obvious activity for overall electrochemical water splitting for long-term stability with little deactivation after 10 h in all pH solutions.

Surface-Reconstructed Ru-Doped Nickel/Iron Oxyhydroxide Arrays for Efficient Oxygen Evolution

The generation of an active phase through dynamic surface reconstruction is a promising strategy for improving the activity of electrocatalysts. However, studies investigating the reconstruction process and its impact on the intrinsic properties of the catalysts are scarce. Herein, the surface reconstruction of NiFe2 O4 interfaced with NiMoO4 (Ru-NFO/NMO) facilitated by Ru doping is reported. The electrochemical and material characterizations demonstrate that Ru doping can regulate the electronic structure of NFO/NMO and induce the high-valence state of Ni3.6+ δ , facilitating the surface reconstruction to highly active Ru-doped NiFeOOH/NiOOH (SR-Ru-NFO/NMO). The optimized SR-Ru-NFO/NMO exhibits promising performance in the oxygen evolution reaction, displaying a low overpotential of 229 mV at 10 mA cm-2 and good stability at varying current densities for 80 h. Density functional theory calculations indicate that Ru doping can increase the electron density and optimize intermediate adsorption by shifting the d-band center downward. This work provides valuable insights into the tuning of electrocatalysts by surface reconstruction and offers a rational design strategy for the development of highly active oxygen evolution reaction electrocatalysts.

Heterostructure CoS2/MoS2 Nanosheets as a Dual-Active Electrocatalyst for the Oxygen Evolution Reaction

Cost-effective and earth-abundant oxygen evolution reaction (OER) electrocatalysts are an incredible research hotspot in numerous energy storage and conversion technology fields. Herein, CoS2/MoS2 nanosheets supported by carbon cloth as a dual-active CC@CoS2/MoS2 heterostructure electrocatalyst is prepared through a simple solvothermal method. The catalyst demonstrates admirable OER performance in 1 M KOH solution with a low overpotential of 243 mV at a current density of 10 mA cm-2 and a minor Tafel slope of 109 mV dec-1, displaying honorable stability after 1000 cyclic voltammetry (CV) cycles and long-term robustness over 60 h. Theoretical calculations further ascertain that the rate-determining step of the electrocatalytic course of the CC@CoS2/MoS2 heterostructure is the conversion *O + OH- → *OOH + e- with a lower energy barrier of 1.49 eV due to the heterojunction established by CoS2 and MoS2, which can promote the OER performance of electrocatalysts. The actual identification of the catalytic mechanism in the heterostructure is conducive to the improvement of electrocatalysis applications in the OER.

Co-Co Dinuclear Active Sites Dispersed on Zirconium-doped Heterostructured Co9 S8 /Co3 O4 for High-current-density and Durable Acidic Oxygen Evolution

Developing cost-effective and sustainable acidic water oxidation catalysts requires significant advances in material design and in-depth mechanism understanding for proton exchange membrane water electrolysis. Herein, we developed a single atom regulatory strategy to construct Co-Co dinuclear active sites (DASs) catalysts that atomically dispersed zirconium doped Co9 S8 /Co3 O4 heterostructure. The X-ray absorption fine structure elucidated the incorporation of Zr greatly facilitated the generation of Co-Co DASs layer with stretching of cobalt oxygen bond and S-Co-O heterogeneous grain boundaries interfaces, engineering attractive activity of significantly reduced overpotential of 75 mV at 10 mA cm-2 , a breakthrough of 500 mA cm-2 high current density, and water splitting stability of 500 hours in acid, making it one of the best-performing acid-stable OER non-noble metal materials. The optimized catalyst with interatomic Co-Co distance (ca. 2.80 Å) followed oxo-oxo coupling mechanism that involved obvious oxygen bridges on dinuclear Co sites (1,090 cm-1 ), confirmed by in situ SR-FTIR, XAFS and theoretical simulations. Furthermore, a major breakthrough of 120,000 mA g-1 high mass current density using the first reported noble metal-free cobalt anode catalyst of Co-Co DASs/ZCC in PEM-WE at 2.14 V was recorded.

Recent advances in interface engineering of Fe/Co/Ni-based heterostructure electrocatalysts for water splitting

Among various methods of developing hydrogen energy, electrocatalytic water splitting for hydrogen production is one of the approaches to achieve the goal of zero carbon emissions. It is of great significance to develop highly active and stable catalysts to improve the efficiency of hydrogen production. In recent years, the construction of nanoscale heterostructure electrocatalysts through interface engineering can not only overcome the shortcomings of single-component materials to effectively improve their electrocatalytic efficiency and stability but also adjust the intrinsic activity or design synergistic interfaces to improve catalytic performance. Among them, some researchers proposed to replace the slow oxygen evolution reaction at the anode with the oxidation reaction of renewable resources such as biomass to improve the catalytic efficiency of the overall water splitting. The existing reviews in the field of electrocatalysis mainly focus on the relationship between the interface structure, principle, and principle of catalytic reaction, and some articles summarize the performance and improvement schemes of transition metal electrocatalysts. Among them, few studies are focusing on Fe/Co/Ni-based heterogeneous compounds, and there are fewer summaries on the oxidation reactions of organic compounds at the anode. To this end, this paper comprehensively describes the interface design and synthesis, interface classification, and application in the field of electrocatalysis of Fe/Co/Ni-based electrocatalysts. Based on the development and application of current interface engineering strategies, the experimental results of biomass electrooxidation reaction (BEOR) replacing anode oxygen evolution reaction (OER) are discussed, and it is feasible to improve the overall electrocatalytic reaction efficiency by coupling with hydrogen evolution reaction (HER). In the end, the challenges and prospects for the application of Fe/Co/Ni-based heterogeneous compounds in water splitting are briefly discussed.

Engineering active heterojunction architecture with oxygenated-Co, Mo bimetallic sulfide heteronanosheet and graphene oxide for peroxymonosulfate activation

Bimetallic sulfides have distinctive catalytic property in activating peroxymonosulfate (PMS) for water remediation. Polyoxometalates as potential precursors have rarely been reported for the catalytic degradation of refractory organic pollutants. Herein, a composite catalyst of Co-Mo bimetallic sulfides supported onto graphene oxide (O-CoMoS/GO) with a heterojunction architecture was synthesized through a hydrothermal strategy with polyoxometalates ((NH₄)₄[Co^IIMo₆O₂₄H₆]·6H₂O) as the precursor and applied in the PMS activation. This material showed a superior performance for the catalytic degradation of the model organic pollutant, 4-chlorophenol (rapidly removed within 10 min with an apparent reaction rate constant of 0.5458 min^-1). O-CoMoS/GO outperformed most of the reported catalysts in terms of activity and had a strong tolerance towards common organic and inorganic compounds in water, and could perform well in different real water systems. Experimental and theoretical results indicated that the introduction of GO could achieve the enrichment of electrons on the metals and reduce the d band center (ε_d) of Co close to the Fermi level (ε_F), thereby facilitating the interfacial electron transfer process. The activation mechanism was due to the as-prepared bimetallic sulfides and the formation of heterojunction structure with GO, where Co(II) as the active center could be regenerated by the adjacent Mo element (as co-catalyst) and by gathering electrons from GO through the Co/Mo-O-C coupling. This work provides insights into the design of bimetallic sulfide catalysts in activating PMS for water remediation.

Synthetic Access to a Framework-Stabilized and Fully Sulfided Analogue of an Anderson Polyoxometalate that is Catalytically Competent for Reduction Reactions

Polyoxometalates (POMs) featuring 7, 12, 18, or more redox-accessible transition metal ions are ubiquitous as selective catalysts, especially for oxidation reactions. The corresponding synthetic and catalytic chemistry of stable, discrete, capping-ligand-free polythiometalates (PTMs), which could be especially attractive for reduction reactions, is much less well developed. Among the challenges are the propensity of PTMs to agglomerate and the tendency for agglomeration to block reactant access of catalyst active sites. Nevertheless, the pervasive presence of transition metal sulfur clusters metalloenzymes or cofactors that catalyze reduction reactions and the justifiable proliferation of studies of two-dimensional (2D) metal-chalcogenides as reduction catalysts point to the promise of well-defined and controllable PTMs as reduction catalysts. Here, we report the fabrication of agglomeration-immune, reactant-accessible, capping-ligand-free Co^IIMo₆^IVS₂₄^n- clusters as periodic arrays in a water-stable, hierarchically porous Zr-metal-organic framework (MOF; NU1K) by first installing a disk-like Anderson polyoxometalate, Co^IIIMo₆^VIO₂₄^m-, in size-matched micropores where the siting is established via difference electron density (DED) X-ray diffraction (XRD) experiments. Flowing H₂S, while heating, reduces molybdenum(VI) ions to Mo(IV) and quantitatively replaces oxygen anions with sulfur anions (S^2-, HS^-, S₂^2-). DED maps show that MOF-templated POM-to-PTM conversion leaves clusters individually isolated in open-channel-connected micropores. The structure of the immobilized cluster as determined, in part, by X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS) analysis, and pair distribution function (PDF) analysis of total X-ray scattering agrees well with the theoretically simulated structure. PTM@MOF displays both electrocatalytic and photocatalytic competency for hydrogen evolution. Nevertheless, the initially installed PTM appears to be a precatalyst, gaining competency only after the loss of ∼3 to 6 sulfurs and exposure to hydride-forming metal ions.

Magnetic Field-Enhanced Electrocatalytic Oxygen Evolution on a Mixed-Valent Cobalt-Modulated LaCoO3 Catalyst

Extensive efforts to enhance the oxygen evolution reaction (OER) catalytic performance of transition metal oxides mainly concentrate on the extrinsic morphology tailoring, lattice doping, and electrode interface optimizing. Nevertheless, little room is left for performance improvement using these methods and an obvious gap still exists compared to the precious metal catalysts. In this work, a novel "mixed-valent cobalt modulation" strategy is presented to enhance the electrocatalytic OER of perovskite LaCoO₃ (LCO) oxide. The valence transition of cobalt is realized by ethylenediamine post reduction procedure at room temperature, which further induces the variation of magnetic properties for LCO catalyst. The optimized LCO catalyst with Co²⁺ /Co³⁺ of 1.98 % exhibits the best OER activity, and the overpotential at 10 mA cm^-2 current density is decreased by 170 mV compared pristine LCO. Impressively, the ferromagnetic LCO catalyst can perform magnetic OER enhancement. By application of an external magnetic field, the overpotential of LCO at 10 mA cm^-2 can be further decreased by 20 mV compared to that of under zero magnetic field, which arises from the enhanced energy states of electrons and accelerated electron transfer process driven by magnetic field. Our findings may provide a promising strategy to break the bottleneck for further enhancement of OER performance.

A comprehensive review on the electrochemical parameters and recent material development of electrochemical water splitting electrocatalysts

Electrochemical splitting of water is an appealing solution for energy storage and conversion to overcome the reliance on depleting fossil fuel reserves and prevent severe deterioration of the global climate. Though there are several fuel cells, hydrogen (H2) and oxygen (O2) fuel cells have zero carbon emissions, and water is the only by-product. Countless researchers worldwide are working on the fundamentals, i.e. the parameters affecting the electrocatalysis of water splitting and electrocatalysts that could improve the performance of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) and overall simplify the water electrolysis process. Noble metals like platinum for HER and ruthenium and iridium for OER were used earlier; however, being expensive, there are more feasible options than employing these metals for all commercialization. The review discusses the recent developments in metal and metalloid HER and OER electrocatalysts from the s, p and d block elements. The evaluation perspectives for electrocatalysts of electrochemical water splitting are also highlighted.

Hydrothermal Synthesized CoS2 as Efficient Co-Catalyst to Improve the Interfacial Charge Transfer Efficiency in BiVO4

The bare surface of BiVO4 photoanode usually suffers from extremely low interfacial charge transfer efficiency which leads to a significantly suppressed photoelectrochemical water splitting performance. Various strategies, including surface modification and the loading of co-catalysts, facilitate the interface charge transfer process in BiVO4. In this study, we demonstrate that CoS2 synthesized from the hydrothermal method can be used as a high-efficient co-catalyst to sufficiently improve the interface charge transfer efficiency in BiVO4. The photoelectrochemical water splitting performance of BiVO4 was significantly improved after CoS2 surface modification. The BiVO4/CoS2 photoanode achieved an excellent photocurrent density of 5.2 mA/cm2 at 1.23 V versus RHE under AM 1.5 G illumination, corresponding to a 3.7 times enhancement in photocurrent compared with bare BiVO4. The onset potential of the BiVO4/CoS2 photoanode was also negatively shifted by 210 mV. The followed systematic combined optical and electrochemical characterization results reveal that the interfacial charge transfer efficiency of BiVO4 was largely improved from less than 20% to more than 70% due tor CoS2 surface modification. The further surface carrier dynamics study performed using an intensity modulated photocurrent spectroscopy displayed a 6–10 times suppression in surface recombination rate constants for CoS2 modified BiVO4, which suggests that the key reason for the improved interfacial charge transfer efficiency possibly originates from the passivated surface states due to the coating of CoS2.

Solar-Driven Catalytic Urea Oxidation for Environmental Remediation and Energy Recovery

The water-energy nexus is highly related to sustainable societal development. As one of the most abundant biowastes discharged into the environment, mild abatements and green conversions of urea wastewater have been widely investigated. Due to abundant sources, global distribution, and easy control, light-based catalytic strategies have become alternative on-site treatment approaches. After comprehensively surveying the recent progress, recent achievements of urea oxidation under light irradiation are reviewed herein. Several typical light-promoted systems employed in urea conversion, including photocatalysis, photo-electrocatalysis, photo-biocatalysis, and photocatalytic fuel cells, are meticulously introduced and discussed, from catalyst designs and medium conditions to established mechanisms. To realize the goal of sustainability, the chemical energy in urea-rich water could be utilized for the value-added production of hydrogen fuel and electricity. Finally, based on current developments, existing challenges are enumerated and developmental prospects in the future of light-driven urea conversion technologies are proposed.

Edge-oriented N-Doped WS2 Nanoparticles on Porous Co3 N Nanosheets for Efficient Alkaline Hydrogen Evolution and Nitrogenous Nucleophile Electrooxidation

Earth-abundant layered tungsten disulfide (WS₂ ) is a well-known electrocatalyst for acidic hydrogen evolution, but it becomes rather sluggish for alkaline hydrogen or oxygen evolution due to the low-density edge sites, poor conductivity, and unfavorable water dissociation behavior. Here, an interfacial engineering strategy to construct an efficient bifunctional electrocatalyst by in situ growing N-doped WS₂ nanoparticles on highly conductive cobalt nitride (N-WS₂ /Co₃ N) for concurrent hydrogen evolution reaction (HER) and urea oxidation reaction (UOR) is demonstrated. Benefiting from the good conductivity of Co₃ N, rich well-oriented edge sites and water-dissociation sites at the nanoscale interfaces between N-WS₂ and Co₃ N, the resultant N-WS₂ /Co₃ N exhibits remarkable HER activity in 1 m potasium hydroxide (KOH) requiring a small overpotential of 67 mV at 10 mA cm^-2 with outstanding long-term durability at 500 mA cm^-2 , representing the best alkaline hydrogen-evolving activity among reported WS₂ catalysts. In particular, this hybrid catalyst also shows exceptional catalytic activities toward theurea oxidation reaction featured by very low potentials of 1.378 and 1.41 V to deliver 100 and 500 mA cm^-2 along with superb large-current stability in 1 m KOH + 0.5 m urea. Moreover, the assembled two-electrode cell delivers the industrially practical current density of 500 mA cm^-2 at a low cell voltage of 1.72 V with excellent durability in alkaline urea-containing solutions, outperforming most MoS₂ -like bifunctional electrocatalysts for overall water splitting reported hitherto. This work provides a promising avenue for the development of high-performance WS₂ -based electrocatalysts for alkaline water splitting.

Interface Engineering-Induced 1T-MoS2/NiS Heterostructure for Efficient Hydrogen Evolution Reaction

Metal phase molybdenum disulfide (1T-MoS2) is considered a promising electrocatalyst for the hydrogen evolution reaction (HER). In this work, an interface engineering-induced strategy is reported to prepare a 1T-MoS2/NiS heterostructure. The 1T-MoS2/NiS heterostructure exhibits an enhanced HER activity compared with that of the 1T-MoS2 in 1.0 M KOH. It achieves an overpotential of 0.12 V at a current density of 10 mA cm−2 with a Tafel slope of 69 mV dec−1. The density functional theory (DFT) calculations reveal that the interface engineering-induced 1T-MoS2/NiS heterostructure exhibits regulated electronic states of the S sites in 1T-MoS2, thus promoting the HER activity. This work demonstrates that tuning the electronic structure through interface engineering to enhance the intrinsic activity of electrocatalysts is a feasible strategy.

Rapidly reconstructing the active surface of cobalt-based perovskites for alkaline seawater splitting

As a potential oxygen evolution reaction (OER) catalyst, Co-based perovskites have received intensive attention. However, Sr readily accumulates on their surface, and makes them inert toward the OER. Herein, we propose a simple but versatile electrochemical reduction method to reconstruct the active surface of Co-based perovskites within a few seconds. By this method, Sr rapidly precipitates from Co-based perovskites, accompanied by the introduction of Sr and oxygen vacancies. After reconstruction, the electrochemical active surface areas of Co-based perovskites greatly increase, and the OER overpotential of the optimized SrNb_0.1Co_0.7Fe_0.2O_3-δ (ER-SNCF-20s) reaches 278 mV at 10 mA cm^-2. This can be explained by the decrease of overpotentials at the rate-determining step. Using ER-SNCF-20s, the splitting voltage of alkaline natural seawater can reach 1.56 V at 10 mA cm^-2, and remains steady for 300 h. This effort offers a feasible method for reconstructing the active surface of Co-based perovskites.

Boosting Highly Active Exposed Mo Atoms by Fine-Tuning S-Vacancies of MoS2-Based Materials for Efficient Hydrogen Evolution

Guided by the theoretical calculation, achieving an efficient hydrogen evolution reaction (HER) by S-vacancy engineering toward MoS₂-based materials is quite challenging due to the contradictory relationship between the adsorption free energy of hydrogen atoms (ΔG_H) of the exposed Mo atoms (EMAs) and the number of EMAs per unit area (N_EMAs). Herein, we demonstrate a novel one-pot incorporating-assisted compositing strategy to realize fine-tuning the concentration of S-vacancies (C_S-vacancies) of MoS₂-based materials to boost highly active EMAs for efficient HER. In our strategy, S-vacancies are modulated into basal planes of MoS₂ via decreasing the formation energy of S-vacancies by oxygen incorporation; moreover, C_S-vacancies of the basal planes is precisely regulated by simply controlling the molar amount of the Co precursor based on the electron injection effect. At low or excessively high C_S-vacancies, the as-synthesized electrocatalysts lack "highly active EMAs" in quantity or nature. The balance between the intrinsic activity of EMAs and N_EMAs is realized for boosting EMAs with high catalytic performance. The optimal electrocatalysts exhibit excellent activity and stability at fine-tuning C_S-vacancies to 9.61%. Our results will pave a novel strategy for unlocking the potential of an inert basal plane in MoS₂ for high-performance HER.

Biaxially Strained MoS2 Nanoshells with Controllable Layers Boost Alkaline Hydrogen Evolution

Strain in layered transition-metal dichalcogenides (TMDs) is a type of effective approach to enhance the catalytic performance by activating their inert basal plane. However, compared with traditional uniaxial strain, the influence of biaxial strain and the TMD layer number on the local electronic configuration remains unexplored. Herein, via a new in situ self-vulcanization strategy, biaxially strained MoS₂ nanoshells in the form of a single-crystalline Ni₃ S₂ @MoS₂ core-shell heterostructure are realized, where the MoS₂ layer is precisely controlled between the 1 and 5 layers. In particular, an electrode with the bilayer MoS₂ nanoshells shows a remarkable hydrogen evolution reaction activity with a small overpotential of 78.1 mV at 10 mA cm^-2 , and negligible activity degradation after durability testing. Density functional theory calculations reveal the contribution of the optimized biaxial strain together with the induced sulfur vacancies and identify the origin of superior catalytic sites in these biaxially strained MoS₂ nanoshells. This work highlights the importance of the atomic-scale layer number and multiaxial strain in unlocking the potential of 2D TMD electrocatalysts.

Identification of Interface Structure for a Topological CoS2 Single Crystal in Oxygen Evolution Reaction with High Intrinsic Reactivity

Transition metal chalcogenides such as CoS₂ have been reported as competitive catalysts for oxygen evolution reaction. It has been well confirmed that surface modification is inevitable in such a process, with the formation of different re-constructed oxide layers. However, which oxide species should be responsible for the optimized catalytic efficiencies and the detailed interface structure between the modified layer and precatalyst remain controversial. Here, a topological CoS₂ single crystal with a well-defined exposed surface is used as a model catalyst, which makes the direct investigation of the interface structure possible. Cross-sectional transmission electron microscopy of the sample reveals the formation of a 2 nm thickness Co₃O₄ layer that grows epitaxially on the CoS₂ surface. Thick CoO pieces are also observed and are loosely attached to the bulk crystal. The compact Co₃O₄ interface structure can result in the fast electron transfer from adsorbed O species to the bulk crystal compared with CoO pieces as evidenced by the electrochemical impedance measurements. This leads to the competitive apparent and intrinsic reactivity of the crystal despite the low surface geometric area. These findings are helpful for the understanding of catalytic origins of transition metal chalcogenides and the designing of high-performance catalysts with interface-phase engineering.

Interfacial Engineering of a Phase-Controlled Heterojunction for High-Efficiency HER, OER, and ORR Trifunctional Electrocatalysis

The development of low-cost and high-performance electrocatalysts for simultaneously boosting the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) is highly crucial but still challenging. Herein, a facile one-step solid-phase polymerization and confined pyrolysis strategy is developed for scalable synthesis of a Fe _x P/Fe₃C-based (x = 1, 2) heterojunction with controllable iron phosphide crystal phases. By effective heterojunction interface regulation, the strong synergic effect between FeP/Fe₃C and N- and P-codoped carbon (NPC) modified the electronic structure, resulting in an excellent electrocatalytic performance for the HER, OER, and ORR synchronously. Typically, the FeP/Fe₃C@NPC catalyst exhibits efficient HER activity with a low overpotential of 10 mA cm^-2 for the HER (97 mV) and OER (440 mV) and a high half-wave potential of 0.87 V for the ORR, as well as excellent stability in alkaline media. Theoretical calculations demonstrated that Fe₃C can promote the activation of water molecules, while FeP is beneficial to the removal of H₂ and the FeP/Fe₃C heterojunction can facilitate both Volmer and Heyrovsky steps in the HER process simultaneously. Moreover, FeP has a stronger inhibitory effect on OH adsorption, revealing that the FeP/Fe₃C heterojunction also shows a better promoting effect for both the OER and ORR, respectively.

Surface engineering strategies for MoS2 towards electrochemical hydrogen evolution

Water splitting driven by renewable energy sources is an environmentally friendly and sustainable way to produce hydrogen as an ideal energy source in the future. Electrocatalysts can promote the water splitting performance at the both ends. Therefore, the development of cost-effective, high-performance electrocatalysis is a key factor in promoting water decomposition and renewable energy conversion. Among candidates, layered molybdenum disulfide (MoS 2 ) is considered as a most promising electrocatalyst to replace Pt for hydrogen evolution reaction (HER). Surface atomic engineering and interface engineering can induce new physicochemical properties for MoS 2 to greatly enhance HER activity. In this report, we summarize the latest improvement strategies and research progress to improve the catalytic activity of MoS 2 -based material catalysts through the surface and interface atomic and molecular engineering, thus effectively improving HER process. In addition, some unsolved problems in the large-scale application of modified MoS 2 catalyst are also discussed.

Zn-Doped CoS2 Nanoarrays for an Efficient Oxygen Evolution Reaction: Understanding the Doping Effect for a Precatalyst

Development of low-cost, efficient, and durable electrocatalysts for the oxygen evolution reaction (OER) is crucial for multiple energy conversions and storage devices. Herein, Zn-doped CoS₂ nanoarrays supported on carbon cloth, Co(Zn)S₂/CC, are fabricated through a facile sulfidization of CoZn metal-organic frameworks. This precatalyst, Co(Zn)S₂/CC, with a well-defined nanoarray structure affords excellent OER catalytic activity (η = 248 mV at 10 mA/cm²) and long-term durability in 1 M KOH. X-ray photoelectron and in situ Raman spectroscopic studies indicate that Co(Zn)S₂ undergoes surface reconstruction with the generation of Co(Zn)OOH adsorbed with SO₄^2- at the surface during the OER process. The Zn dopant is calculated to impact on the electronic structure of Co species and further the adsorption of intermediates. This work not only provides a novel method for the synthesis of bimetallic sulfides but also gives insights into the doping effect on the OER performance of transition metal sulfides.

Bifunctional P-Intercalated and Doped Metallic (1T)-Copper Molybdenum Sulfide Ultrathin 2D-Nanosheets with Enlarged Interlayers for Efficient Overall Water Splitting

Metallic (1T) molybdenum disulfide (MoS₂) is a much better electrocatalyst than the semiconducting (2H) MoS₂ because of its superior conductivity, presence of active basal planes, and bulky interlayers. However, the lack of thermodynamic stability has hindered its practical uses. The insertion of transition metals and nonmetals in the interlayers and the crystal is known to improve both the thermodynamic stability and the catalytic efficacy of 1T-MoS₂. In this study, for the first time we have developed an electrocatalyst for water splitting based on metallic copper molybdenum sulfide (1T-CMS). The present catalyst, P-doped and intercalated 1T-CMS ultrathin 2D nanosheets on carbon cloth (P-1T-CMS@CC), demonstrates excellent catalytic efficacy for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). It required an overpotential of 95 mV for HER and of 284 mV for OER at a current density of 10 mA cm^-2. The P-1T-CMS@CC(+ -) device also shows excellent performance, requiring a cell voltage of only 1.51 V at a current density of 10 mA cm^-2.

N-doped three-dimensional needle-like CoS2 bridge connection Co3O4 core-shell structure as high-efficiency room temperature NO2 gas sensor

The N-doped three-dimensional (3D) needle bridge connection core-shell structure N-CoS₂@Co₃O₄ synthesized in this work was prepared by simple hydrothermal and high-temperature vulcanization methods. The optimized N-CoS₂@Co₃O₄^-2 composite response to NO₂ is 62.3-100 ppm, a response time of 1.3 s, the recovery time of 17.98 s, the detection limit of 5 ppb and stability of as long as 10 weeks at room temperature (RT). Its excellent NO₂ sensing performance is attributed to the unique porous and bridge connection core-shell structure of the N-CoS₂@Co₃O₄^-2 with high specific surface area, interconnected internal channels, abundant exposed S edge active sites, and high catalytic performance promoted by N-doping. This simple manufacturing method of high-performance sensing materials paves the way for the design of N-doped bridge connection core-shell structures.

Flower-like Co3Ni1B nanosheets based on reduced graphene oxide (rGO) as an efficient electrocatalyst for the oxygen evolution reaction

Flower-like Co3Ni1B nanosheets based on a reduced graphene oxide electrocatalyst exhibit a better OER performance than commercial RuO2.

Achieving ultra-dispersed 1T-Co-MoS2@HMCS via space-confined engineering for highly efficient hydrogen evolution in the universal pH range

A multi-level spatial confinement strategy is proposed for the fabrication of ultra-dispersed 1T-Co-MoS2 nanoclusters, which exhibit remarkable electrocatalytic activity and durability for HER.

Interfacial Microenvironment Modulation Enhancing Catalytic Kinetics of Binary Metal Sulfides Heterostructures for Advanced Water Splitting Electrocatalysts

Interfacial microenvironment modulation has been proven to be a promising route to fabricate highly efficient catalysts. In this work, the lattice defect-rich NiS₂ /MoS₂ nanoflakes (NMS NFs) electrocatalysts are successfully synthesized by a simple strategy. Benefiting from the abundant lattice defects and modulated interfacial microenvironment between NiS₂ and MoS₂ , the prepared NMS NFs show superior catalytic activity for water splitting. Particularly, the optimized NMS NFs (the molar ratio of Ni:Mo = 5:5) exhibit remarkable catalytic activity toward overall water splitting with a voltage of 1.60 V at 10 mA cm^-2 in alkaline media, which is lower than that of the noble-metal-based electrocatalysts (1.68 V at 10 mA cm^-2 ). The NMS NFs electrocatalysts also show exceptional long-term stability (>50 h) for overall water splitting. The density functional theory results demonstrate that the injection of NiS₂ into MoS₂ can greatly optimize the catalytic kinetics and reduce the energy barrier for hydrogen/oxygen evolution reactions. The work does not only offer a promising candidate for a highly efficient water splitting electrocatalyst but also highlights that interfacial microenvironment modulation is a potential strategy to optimize the catalytic kinetics.

Self-supported Ni3S2@Ni2P/MoS2 heterostructures on nickel foam for an outstanding oxygen evolution reaction and efficient overall water splitting

Hydrogen production by electrocatalytic water splitting is a pollution-free, energy-saving, and efficient method. The low efficiency of hydrogen production, high overpotentials and expensive noble-metal catalysts have limited the development of hydrogen production from electrocatalytic water splitting. Therefore, the exploration of bifunctional electrocatalysts for water overall splitting to produce hydrogen is of profound significance. Herein, Ni₃S₂@Ni₂P/MoS₂ heterostructure electrocatalysts were synthesized on Ni foam through an environmentally friendly hydrothermal method and low-temperature phosphating method. The synergistic effects between different components and the mutual substitution principle between sulfur atoms and phosphorus atoms greatly improve the OER performance of the electrocatalyst. It is also an effective strategy to optimize the adsorption energies of intermediates by the design of heterostructured catalysts composed of multiple substances. Ni₃S₂@Ni₂P/MoS₂ only requires a low overpotential (η₁₀) of 175 mV at a current density of 10 mA cm^-2 in 1.0 M KOH solution and the stable duration exceeds 40 h. In addition, this heterogeneous structure is assembled into an electrolytic cell for overall water splitting, which exhibits a low cell voltage of 1.61 volts and retains the robust stability over 30 h at 10 mA cm^-2. The Ni₃S₂@Ni₂P/MoS₂ heterostructure prepared in this research provides a strategy for exploring other heterostructured electrocatalysts with different components.