Iron, rhodium-codoped Ni2P nanosheets arrays supported on nickel foam as an efficient bifunctional electrocatalyst for overall water splitting

Spin-state-regulated dual-metal orbital engineering in heterostructured nanosheets for d-band center-optimized electrocatalytic water splitting

A dual-metal orbital engineering strategy is developed to synergistically optimize active site reactivity and bulk-phase stability through precise d-band center modulation and enhanced charge transfer kinetics. Specifically, a flower-like NiMn selenide nanoarchitecture, modified with silver nanoparticles and sulfur-doped carbon quantum dots (Ag/NiSe2/MnSe/S-CQDs), is fabricated via controlled spin state regulation. The asymmetric configuration between NiSe2 and MnSe induces a significant elevation in the energy levels of Ni's eg and t2g orbitals, thereby optimizing intermediate conductivity, eg orbital electron occupancy, and adsorption free energy. Simultaneously, the reduced energy levels of Mn's eg and t2g orbitals strengthen the interaction between Ni 3d/Mn 3d and Se 2p orbitals, promoting synergistic coupling, optimizing the electronic structure, and ensuring electrocatalytic stability. Consequently, the optimized catalyst exhibits remarkable performance, requiring overpotentials of 54.0 ± 0.5 mV and 235.0 ± 0.5 mV for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, at 10 mA cm-2, while maintaining excellent stability. This work establishes a universal paradigm for d-band center manipulation in electrocatalyst design, providing critical insights for developing advanced energy conversion systems.

Engineering Defect-Mediated S-scheme heterojunctions in MOF-Derived N-doped NiO porous microrods and ZnIn2S4 nanosheets for superior photocatalytic hydrogen evolution

The development of efficient photocatalysts inspired by natural photosynthesis has drawn considerable interest for sustainable hydrogen (H2) production. Among the various strategies for enhancing H2 evolution, constructing step-scheme (S-scheme) heterojunctions has attracted extensive interest, thanks to their limited charge recombination and enhanced charge transport in comparison to the traditional photocatalytic systems. Herein, we report the engineering of a novel S-scheme heterojunction by integrating ultrathin ZnIn2S4 (ZIS) nanosheets with MOF-derived N-doped NiO porous microrods (ZIS/N-NiO) toward superior photocatalytic behaviors. It is witnessed that the atomic-level N-doping within NiO microrods could be accomplished by introducing nitrogen-containing ligands during Ni-MOF synthesis, resulting in the formation of the defect states to significantly improve charge carrier transport. Accordingly, the resultant ZIS/N-NiO heterojunctions deliver an outstanding H2 evolution rate of 2313 μmol·g-1·h-1, which is nearly 30 times to that of pure N-doped NiO, and 3 times to that of intrinsic ZIS, outperforming those of most NiO-based photocatalysts ever reported. Current work might provide some valuable insights into the rational design of advanced heterojunction photocatalysts for next-generation solar-driven H2 production and renewable energy technologies.

High-entropy layered double hydroxides tailor Pt electron state for promoting acidic hydrogen evolution reaction

Despite the advancement of the Pt-catalyzed hydrogen evolution reaction (HER) through oxophilic metal-hydroxide surface hybridization, its stability in acidic solutions remains unsatisfactory. This is primarily due to excessive aggregation of active hydrogen, which hinders subsequent hydrogen desorption, coupled with the poor operational stability of metal hydroxides. In this study, we have designed Pt nanoparticles-modified NiFeCoCuCr high-entropy layered double hydroxides (Pt/HE-LDH) that exhibit exceptional catalytic activity toward HER in acidic electrolytes. Our findings reveal that the built-in electric field (BIEF) between Pt and HE-LDH facilitates the charge redistribution at Pt/HE-LDH interface, driven by the difference in work function. Additionally, effective hydrogen spillover from Pt nanoparticles to HE-LDH bidirectionally optimizes the Gibbs free energy for hydrogen adsorption. Furthermore, the interactions among the multi-metal sites, along with high entropy-induced phase stability, contribute to superior stability in acidic electrolytes. This work not only presents a straightforward strategy for enhancing hydrogen spillover from Pt but also improves the durability of metal hydroxides under acidic HER conditions.

Electron transfer enhanced flower-like NiP2-Mo8P5 heterostructure synergistically accelerates fast HER kinetics for large-current overall water splitting

Developing an innovative metal-phosphorus heterostructure as an excellent electrocatalyst for hydrogen evolution reaction (HER) is crucial for achieving large-scale water electrolysis, although it remains challenging. Herein, we introduce a pioneering strategy entailing the coordination of two metal phosphides in a catalytic structure by employing a wide variety of catalytically active species and regulating the electronic structure. Our method involves an extraordinary heterostructure construction with nickel phosphide and molybdenum phosphide formed on nickel foam (NiP2-Mo8P5@NF) through a controlled-solvent thermal and low-temperature phosphorization strategy. Experiments disclose that heterostructure of nickel and molybdenum can effectively modulate the electronic structure of the metal center, foster a robust electronic interaction between Ni and Mo, and induce the formation of rich active sites. The resulting benefits include improved electrical conductivity, which is conducive to synergistically enhancing the electrocatalytic efficiency. Moreover, the NiP2-Mo8P5@NF achieves superhydrophilicity, ensuring effective electrolyte contact and accelerating reaction kinetics. Consequently, NiP2-Mo8P5@NF exhibits favorable HER performance and long-term stability, outperforming commercial Pt/C and most other contemporary electrocatalysts. In practical application, the overall water splitting device with NiP2-Mo8P5@NF as cathode delivers a low cell voltage and demonstrates noteworthy durability. This will pave the way for its prospective adoption in industrial water electrolysis applications.

In situ fabrication of Ni3S2/Cu2S heterojunction on nickel foam as a highly efficient and durable electrocatalyst for overall water splitting

The development of cost-efficient bifunctional electrocatalysts is significant for overall water splitting. Herein, we report the in situ fabrication of heterogeneous NF/Ni3S2/Cu2S-X (where X refers to Cu2+ concentrations of 50, 75, and 100 mM) on nickel foam (NF) using an electrodeposition-hydrothermal method. The in situ electrodeposited metallic Cu0 layers on the NF conferred higher stability to the resulting bimetallic sulfide of Ni3S2/Cu2S. In alkaline media (1 M KOH), the optimized NF/Ni3S2/Cu2S-75 exhibited ultra-low overpotentials of 108 and 166 mV during the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at 10 mA·cm-2. For overall water splitting, the catalyst showed a significantly low cell voltage of 1.50 V and long stabilization time (≥150h)at15mA·cm-2. Density functional theory calculations revealed that the formation of Ni3S2/Cu2S heterojunction reduced the Gibbs free energy of hydrogen adsorption (ΔGH*) on the S site, thus facilitating H2 generation. This study serves as a guide for tailoring transition metal-based catalysts with enhanced activity and long-term durability, thereby contributing to highly efficient water electrolysis for large-scale hydrogen production.

Low Rh doping accelerated HER/OER bifunctional catalytic activities of nanoflower-like Ni-Co sulfide for greatly boosting overall water splitting

Facile synthesis of high-efficiency and stable bifunctional electrocatalyst is essential for producing clean hydrogen in energy storage systems. Herein, low Rh-doped flower-like Ni3S2/Co3S4 heterostructures were facilely prepared on porous nickel foam (labeled Rh-Ni3S2/Co3S4/NF) by a hydrothermal method. The correlation of the precursors types with the morphological structures and catalytic properties were rigorously investigated for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in the control groups. The low Rh doping within the catalyst played important role in boosting the catalytic characteristics. The resulting catalyst showed the smaller overpotentials of 197 and 78 mV to drive a current density of 10 mA cm-2 for the OER and HER in alkaline electrolyte, respectively. And the potential only required 1.71 V to drive a current density of 100 mA cm-2 in a water splitting device. It reflects excellent overall water splitting of the home-made Rh-Ni3S2/Co3S4/NF. This strategy shed some constructive light for preparing transition metal sulfide-based electrocatalysts in water splitting devices.

Rapid construction of nickel phyllosilicate with ultrathin layers and high performance for CO2 methanation

The traditional techniques for the synthesis of nickel phyllosilicates usually time-consuming and energy-intensive, which often lead to the formation of layers with excessive thickness due to uncontrolled crystal growth. In order to overcome these challenges, this work introduces a microwave-assisted synthesis strategy to facilitate the synthesis of Ni-phyllosilicate-based catalysts within an exceptionally short duration of only five minutes, attaining a peak temperature of merely 102 °C. To enhance the specific surface area and to increase the exposure of active sites, an investigation was conducted involving three surfactants. The employment of hexadecyl trimethyl ammonium bromide (CTAB) has yielded remarkable results, with an ultrahigh specific surface area reaching 535 m2 g-1 and an ultrathin lamellar thickness of 1.43 nm. The catalyst exhibited an impressive CO2 conversion of 81.7 % at 400 °C, 60 L g-1 h-1, 0.1 MPa. It also demonstrated a substantial turnover frequency for CO2 (TOFCO2) of 5.4 ± 0.1 × 10-2 s-1, alongside a relatively low activation energy (Ea) of 80.74 kJ·mol-1. Moreover, the catalyst maintained its high stability over a period of 100 h and displayed high resistance to sintering. To further elucidate growth temperature gradient of the catalyst and concentration gradient of the materials involved, COMSOL Multiphysics (COMSOL) simulations were effectively utilized. In conclusion, this work breaks the limitation associated with traditional, laborious synthesis methods for Ni-phyllosilicates, which can produce materials with high surface area and thin-layer characteristics.

Designing core-shell heterostructure arrays based on snowflake NiCoFe-LTH shelled over W2N-WC nanowires as an advanced bi-functional electrocatalyst for boosting alkaline water/seawater electrolysis

The pursuit of efficient and sustainable hydrogen production through water splitting has led to intensive research in the field of electrocatalysis. However, the impediment posed by sluggish reaction kinetics has served as a significant barrier. This challenge has inspired the development of electrocatalysts characterized by high activity, abundance in earth's resources, and long-term stability. In addressing this obstacle, it is imperative to meticulously fine-tune the structure, morphology, and electronic state of electrocatalysts. By systematically manipulating these key parameters, the full potential of electrocatalysts can unleash, enhancing their catalytic activity and overall performance. Hence in this study, a novel heterostructure is designed, showcasing core-shell architectures achieved by covering W2N-WC nanowire arrays with tri-metallic Nickel-Cobalt-Iron layered triple hydroxide nanosheets on carbon felt support (NiCoFe-LTH/W2N-WC/CF). By integrating the different virtue such as binder free electrode design, synergistic effect between different components, core-shell structural advantages, high exposed active sites, high electrical conductivity and heterostructure design, NiCoFe-LTH/W2N-WC/CF demonstrates striking catalytic performances under alkaline conditions. The substantiation of all the mentioned advantages has been validated through electrochemical data in this study. According to these results NiCoFe-LTH/W2N-WC/CF achieves a current density of 10 mA cm-2 needs overpotential values of 101 mV for HER and 206 mV for OER, respectively. Moreover, as a bi-functional electrocatalyst for overall water splitting, a two-electrode device needs a voltage of 1.543 V and 1.569 V to reach a current density of 10 mA cm-2 for alkaline water and alkaline seawater electrolysis, respectively. Briefly, this research with attempting to combination of different factors try to present a promising stride towards advancing bi-functional catalytic activity with tailored architectures for practical green hydrogen production via electrochemical water splitting process.

Phase Electronic Structure Tuning via Pt, P-Doped Ni4Mo-Implanted Ti4O7 for Highly Efficient Water Splitting and Mg/Seawater Batteries

Fine-tuning nanoscale structures, morphologies, and electronic states are crucial for creating efficient water-splitting electrocatalysts. In this study, a method for electronic structure engineering to enhance overall water splitting in a corrosion-resistant electrocatalyst matrix by integrating Pt, P dual-doped Ni4Mo electrocatalysts onto a Ti4O7 nanorod grown on carbon cloth (Pt, P-Ni4Mo-Ti4O7/CC) is introduced. By optimizing platinum and phosphorus concentrations to 1.18% and 2.42%, respectively, low overpotentials are achieved remarkably: 24 mV at 10 mA cm-2 for the hydrogen evolution reaction and 290 mV at 20 mA cm-2 for the oxygen evolution reaction in 1.0 m KOH. These values approach or surpass those of benchmark Pt-C and IrO2 catalysts. Additionally, the Pt, P-Ni4Mo-Ti4O7/CC bifunctional electrocatalyst displays low cell potentials across various mediums, maintaining excellent current retention (96% stability after 40 h in mimic seawater at 20 mA cm-2) and demonstrating strong corrosion resistance and suitability for seawater  electrolysis. As a cathode in magnesium/seawater batteries, it achieves a power density of 7.2 mW cm-2 and maintains stability for 100 h. Density functional theory simulations confirm that P, Pt doping-assisted electronic structure modifications augment electrical conductivity and active sites in the hybrid electrocatalysts.

Oxygen-Deficient FeNbO4-x In-Situ Growth in Honey-Derived N-Doping Porous Carbon for Overall Water Splitting

It is still a great challenge to reasonably design green, low cost, high activity and good stability catalysts for overall water splitting (OWS). Here, we introduce a novel catalyst with ferric niobate (FeNbO4) in-situ growing in honey-derived porous carbon of high specific surface area, and its catalytic activity is further enhanced by micro-regulation (oxygen vacancy and N-doping). From the experimental results and density functional theory (DFT) calculations, the oxygen vacancy in catalyst FeNbO4-x@NC regulates the local charge density of active site, thus increasing conductivity and optimizing hydrogen/oxygen species adsorption energy. FeNbO4 in-situ grows within N-doping honey-derived porous carbon, which can enhance active specific surface area exposure, strengthen gaseous substances escape rate, and accelerate electrons/ions transfer and electrolytes diffusion. Moreover, in-situ Raman also confirms O-species generation in oxygen evolution reaction (OER). As a result, the catalyst FeNbO4-x@NC shows good electrochemical performance in OER, HER and OWS.

CoFeBP Micro Flowers (MFs) for Highly Efficient Hydrogen Evolution Reaction and Oxygen Evolution Reaction Electrocatalysts

Hydrogen is one of the most promising green energy alternatives due to its high gravimetric energy density, zero-carbon emissions, and other advantages. In this work, a CoFeBP micro-flower (MF) electrocatalyst is fabricated as an advanced water-splitting electrocatalyst by a hydrothermal approach for hydrogen production with the highly efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The fabrication process of the CoFeBP MF electrocatalyst is systematically optimized by thorough investigations on various hydrothermal synthesis and post-annealing parameters. The best optimized CoFeBP MF electrode demonstrates HER/OER overpotentials of 20 mV and 219 mV at 20 mA/cm2. The CoFeBP MFs also exhibit a low 2-electrode (2-E) cell voltage of 1.60 V at 50 mA/cm2, which is comparable to the benchmark electrodes of Pt/C and RuO2. The CoFeBP MFs demonstrate excellent 2-E stability of over 100 h operation under harsh industrial operational conditions at 60 °C in 6 M KOH at a high current density of 1000 mA/cm2. The flower-like morphology can offer a largely increased electrochemical active surface area (ECSA), and systematic post-annealing can lead to improved crystallinity in CoFeBP MFs.

Recent progress of Ni-based nanomaterials for the electrocatalytic oxygen evolution reaction at large current density

The precise design and development of high-performing oxygen evolution reaction (OER) for the production of industrial hydrogen gas through water electrolysis has been a widely studied topic. A profound understanding of the nature of electrocatalytic processes reveals that Ni-based catalysts are highly active toward OER that can stably operate at a high current density for a long period of time. Given the current gap between research and applications in industrial water electrolysis, we have completed a systematic review by constructively discussing the recent progress of Ni-based catalysts for electrocatalytic OER at a large current density, with special focus on the morphology and composition regulation of Ni-based electrocatalysts for achieving extraordinary OER performance. This review will facilitate future research toward rationally designing next-generation OER electrocatalysts that can meet industrial demands, thereby promoting new sustainable solutions for energy shortage and environment issues.

A broad horizon for sustainable catalytic oxidation of microplastics

Microplastics (MPs) have attracted tremendous attention due to their widespread appearance in the environment and biota, and their adverse effects on organisms. Since plastics are substantially produced to meet human needs, primary and secondary MPs are extensively trapped in wastewater treatment plants, freshwater, drinking water, ocean, air, and soil. The serious MPs pollution calls for efficient treatment strategies Herein, we discuss three catalytic processes (photocatalysis, electrocatalysis, and biocatalysis) for the sustainable management of MPs, and the relevant catalytic mechanisms are clarified. For photocatalysis, three categories (organic, inorganic, hybrid) of photocatalysts are listed, with degradation efficiency of 23%-100%. Next, relative impact factors on photocatalysis, such as characteristics of MPs and photocatalysts, are discussed. Then, some promising electrocatalysts for the degradation/conversion of (micro)plastics and standard electrolyzer designs are briefly introduced. This electrocatalytic method has achieved over 77% of Faradaic efficiency. Next, potential organisms with abundant biocatalysts for degrading different types of MPs are reviewed. Advances in three bioremediation techniques including biositimulation, bioaugmentation, and biosurfactant are outlined. Lastly, perspectives are put forward to promote scientific development in solving environmental issues on MPs pollution in broad fields. This paper provides insights into the development of next-generation techniques for MPs pollution management in a sustainable manner.

An efficient cerium dioxide incorporated nickel cobalt phosphide complex as electrocatalyst for All-pH hydrogen evolution reaction and overall water splitting

Transition metal phosphides (TMPs) have been considered as potential electrocatalysts with adjustable valence states, metal characteristics, and phase diversity. However, it is necessary but remains a major challenge to obtain efficient and durable TMPs catalysts, which can realize efficiently for not only all-pH hydrogen evolution reaction (HER), but also oxygen evolution reaction (OER). Hence, cerium dioxide incorporated nickel cobalt phosphide growth on nickel foam (CeO2/NiCoP) is fabricated by hydrothermal and phosphating reaction. CeO2/NiCoP shows excellent activity for all-pH HER (overpotentials of 48, 58 and 72 mV in alkaline, neutral and acidic solution at the current density of 10 mA cm-2), and has a small OER overpotential (231 mV @ 10 mA cm-2). Moreover, the voltage of overall water splitting in alkaline solution and simulated seawater electrolyte is only 1.46 and 1.41 V (10 mA cm-2), respectively, coupled with outstanding operational stability and corrosion resistance. Further mechanism research shows that CeO2/NiCoP possesses rich heterointerfaces, which serves more exposed active sites and possesses a promising superhydrophilic and superaerophobic surface. Density functional theory calculations manifest that CeO2/NiCoP has appropriate energy for intermediates of reactions. This work provides a deep insight into the CeO2/NiCoP catalyst for high-performance water/seawater electrolysis.

Enhanced electrocatalytic efficiencies for water electrolysis and para-nitrophenol hydrogenation by self-supported nickel cobalt phosphide-nickel iron layered double hydroxide p-n junction

Charge redistribution across heterointerfaces is an important tactic to enhance the catalytic activities and bifunctionality of hybrid catalysts, especially for green hydrogen production from water electrolysis and harmless electrocatalytic valorization of organics. Herein, a self-supported p-n junction catalytic electrode was constructed by tandem electrodeposition of nickel cobalt phosphide (NiCoP) and nickel iron layered double hydroxide (NiFe LDH) onto Ni foam (NF) substrate, denoted as NiCoP@NiFe LDH/NF, to enhance the electrocatalytic capabilities for water electrolysis and hydrogenation of an organic, para-nitrophenol (4-NP). Benefitting from the charge redistribution across the p-n junction, high electrocatalytic efficiencies for oxygen evolution reaction (OER, overpotential of 388 mV at 100 mA cm-2) and hydrogen evolution reaction (HER, overpotential of 132 mV at 10 mA cm-2) could be achieved concurrently by the NiCoP@NiFe LDH/NF electrode, and both overpotentials were located within the mainstream levels in this domain. The bifunctional catalytic features enabled a full water electrolysis response of 10 mA cm-2 at 1.61 V. In addition, the p-n junction electrode catalyzed the hydrogenation of 4-NP at a conversion of 100%, para-aminophenol (4-AP) selectivity of 90% and faradaic efficiency (FE) of 88% at -0.18 V. The current work offers a feasible strategy for fulfilling electrochemical H2 production and hydrogenation valorization of 4-NP pollutant by constructing a self-supported p-n junction catalytic electrode.

Dual Electronic Modulations on NiFeV Hydroxide@FeOx Boost Electrochemical Overall Water Splitting

Nickel-iron based hydroxides have been proven to be excellent oxygen evolution reaction (OER) electrocatalysts, whereas they are inactive toward hydrogen evolution reaction (HER), which severely limits their large-scale applications in electrochemical water splitting. Herein, a heterostructure consisted of NiFeV hydroxide and iron oxide supported on iron foam (NiFeV@FeOx /IF) has been designed as a highly efficient bifunctional (OER and HER) electrocatalyst. The V doping and intimate contact between NiFeV hydroxide and FeOx not only improve the entire electrical conductivity of the catalyst but also afford more high-valence Ni which serves as active sites for OER. Meanwhile, the introduction of V and FeOx reduces the electron density on lattice oxygen, which greatly facilitates desorption of Hads . All of these endow the NiFeV@FeOx /IF with exceptionally low overpotentials of 218 and 105 mV to achieve a current density of 100 mA cm-2 for OER and HER, respectively. More impressively, the electrolyzer requires an ultra-low cell voltage of 1.57 V to achieve 100 mA cm-2 and displays superior electrochemical stability for 180 h, which outperforms commercial RuO2 ||Pt/C and most of the representative catalysts reported to date. This work provides a unique route for developing high-efficiency electrocatalyst for overall water splitting.

3D nanostructured Ce-doped CoFe-LDH/NF self-supported catalyst for high-performance OER

Powder electrocatalysts for oxygen evolution reactions usually need adhesives for electrocatalytic performance tests, leading to the increase of resistance, reduction of catalyst loading, and easy stripping of the catalyst under long-time or high current operation. In this study, Ce-doped CoFe layered double hydroxides were uniformly grown on nickel foam by a one-step hydrothermal route. A nanostructured self-supported electrode Ce-CoFe-LDH/NF without adhesive was obtained directly, which has a regular nanoneedle morphology with a length of ∼1.2 μm and tip width of ∼20 nm. Adopting Ce3+ ions with a large radius to partially displace Fe3+ ions with a small radius produced lattice distortion and more defects in the host layer of CoFe-LDH, whereby possessing the great potential to enhance catalytic behaviors. Once used as an electrocatalyst for the oxygen evolution reaction, Ce-CoFe-LDH/NF shows an outstanding electrocatalytic performance, including an optimized overpotential of 225 mV at 10 mA cm-2, a decreased Tafel slope of 34.34 mV dec-1, and a low charge transfer impedance of 2.4 Ω in 1 M KOH electrolyte. Moreover, the overpotential of the working electrode increased by only 0.04 V after 24 hours and was maintained at a current density of 50 mA cm-2. These results demonstrate a low-cost strategy compared to using noble metal OER electrocatalysts. Thus, this study highlights a ready universal approach to fabricate high-performance supported catalysts for energy-related applications.

Tunable d-band center of a NiFeMo alloy with enlarged lattice strain enhancing the intrinsic catalytic activity for overall water-splitting

Developing efficient bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) under alkaline conditions is prospective for reducing energy consumption during water electrolysis. In this work, we successfully synthesized nanocluster structure composites composed of NiFeMo alloys with controllable lattice strain by the electrodeposition method at room temperature. The unique structure of NiFeMo/SSM (stainless steel mesh) facilitates the exposure of abundant active sites and promotes mass transfer and gas exportation. The NiFeMo/SSM electrode exhibits a low overpotential of 86 mV at 10 mA cm^-2 for the HER and 318 mV at 50 mA cm^-2 for the OER, and the assembled device reveals a low voltage of 1.764 V at 50 mA cm^-2. Moreover, both the experimental results and theoretical calculations reveal that the dual doping of Mo and Fe can induce the tunable lattice strain of nickel, which in turn changes the d-band center and electronic interaction of the catalytically active site, and finally enhances the HER and OER catalytic activity. This work may provide more options for the design and preparation of bifunctional catalysts based on non-noble metals.

Intensifying Hydrogen Spillover for Boosting Electrocatalytic Hydrogen Evolution Reaction

Hydrogen spillover has attracted increasing interests in the field of electrocatalytic hydrogen evolution reaction (HER) in recent years because of their distinct reaction mechanism and beneficial terms for simultaneously weakening the strong hydrogen adsorption on metal and strengthening the weak hydrogen adsorption on support. By taking advantageous merits of efficient hydrogen transfer, hydrogen spillover-based binary catalysts have been widely investigated, which paves a new way for boosting the development of hydrogen production by water electrolysis. In this paper, we summarize the recent progress of this interesting field by focusing on the advanced strategies for intensifying the hydrogen spillover towards HER. In addition, the challenging issues and some perspective insights in the future development of hydrogen spillover-based electrocatalysts are also systematically discussed.

In Situ Fabrication of Mn-Doped NiMoO4 Rod-like Arrays as High Performance OER Electrocatalyst

The slow kinetics of the oxygen evolution reaction (OER) is one of the significant reasons limiting the development of electrochemical hydrolysis. Doping metallic elements and building layered structures have been considered effective strategies for improving the electrocatalytic performance of the materials. Herein, we report flower-like nanosheet arrays of Mn-doped-NiMoO₄/NF (where NF is nickel foam) on nickel foam by a two-step hydrothermal method and a one-step calcination method. The doping manganese metal ion not only modulated the morphologies of the nickel nanosheet but also altered the electronic structure of the nickel center, which could be the result of superior electrocatalytic performance. The Mn-doped-NiMoO₄/NF electrocatalysts obtained at the optimum reaction time and the optimum Mn doping showed excellent OER activity, requiring overpotentials of 236 mV and 309 mV to drive 10 mA cm^-2 (62 mV lower than the pure NiMoO₄/NF) and 50 mA cm^-2 current densities, respectively. Furthermore, the high catalytic activity was maintained after continuous operation at a current density of 10 mA cm^-2 of 76 h in 1 M KOH. This work provides a new method to construct a high-efficiency, low-cost, stable transition metal electrocatalyst for OER electrocatalysts by using a heteroatom doping strategy.

Strategies for Promoting Catalytic Performance of Ru-based Electrocatalysts towards Oxygen/Hydrogen Evolution Reaction

Ru-based materials hold great promise for substituting Pt as potential electrocatalysts toward water electrolysis. Significant progress is made in the fabrication of advanced Ru-based electrocatalysts, but an in-depth understanding of the engineering methods and induced effects is still in their early stage. Herein, we organize a review that focusing on the engineering strategies toward the substantial improvement in electrocatalytic OER and HER performance of Ru-based catalysts, including geometric structure, interface, phase, electronic structure, size, and multicomponent engineering. Subsequently, the induced enhancement in catalytic performance by these engineering strategies are also elucidated. Furthermore, some representative Ru-based electrocatalysts for the electrocatalytic HER and OER applications are also well presented. Finally, the challenges and prospects are also elaborated for the future synthesis of more effective Ru-based catalysts and boost their future application.

Morphology Modulation and Phase Transformation of Manganese-Cobalt Carbonate Hydroxide Caused by Fluoride Doping and Its Effect on Boosting the Overall Water Electrolysis

Increasing demands for pollution-free energy resources have stimulated intense research on the design and fabrication of highly efficient, inexpensive, and stable non-noble earth-abundant metal catalysts with remarkable catalytic activity for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Morphology control of the catalysts is widely implemented as an effective strategy to change the surface atomic coordination and increase the catalytic behavior of the catalysts. In this study, we have designed a series of Mn-Co catalyts with different morphologies on the graphite paper substrate to enhance OER and HER activities in alkaline media. The prepared catalysts with different morphologies were successfully obtained by adjusting the amount of ammonium fluoride (NH₄F) in the hydrothermal process. The electrochemical tests display that the cubic-like Mn-Co catalyst with pyramids on the faces at a concentration of 0.21 M NH₄F exhibits the best activity toward both OER and HER. The cubic-like Mn-Co catalyst with pyramids on the faces showed overpotentials of 240 and 82 mV at a current density of 10 mA cm^-2 for OER and HER, respectively. Also, the cubic-like Mn-Co catalyst with pyramids on the faces required overpotentials of 319 and 216 mV to reach the current density of 100 mA cm^-2 for OER and HER, respectively. The current density of this catalyst at η = 0.32 V was 701.05 mA cm^-2 for OER, and for HER, the current density of the catalyst was 422.89 mA cm^-2 at η = 0.23 V. The Tafel slopes of the Mn-Co catalyst with cubic-like structures with pyramids on the faces were 78 and 121 mV dec^-1 for OER and HER, respectively. A two-electrode overall water electrolysis system using this bifunctional Mn-Co catalyst exhibited low cell voltages of 1.60 in the alkaline electrolyte at the standard current density of 10 mA cm^-2 with appropriate stability. These electrochemical merits exhibit the considerable potential of the cubic-like Mn-Co catalyst with pyramids on the faces for bifunctional OER and HER applications.

Phosphorus vacancies improve the hydrogen evolution of MoP electrocatalysts

Although molybdenum phosphide (MoP) has attracted increasing attention as an electrocatalyst in the hydrogen evolution reaction (HER), it is still worth exploring an effective approach to further improve the HER activities of MoP. To date, the generation and effect of P vacancies (Pv) on MoP have been rarely investigated for the HER in both alkaline and acidic media and remain unclear. Here, MoP rich in P vacancies (MoP-Pv) was prepared by hydrogen reduction to improve the HER catalytic performances. As a result, the overpotentials of MoP-Pv were 70 mV and 62 mV lower than those of pristine MoP in 1 M KOH and 0.5 M H₂SO₄ electrolytes, respectively. What's more, the TOFs of MoP-Pv were 3.14 s^-1 and 1.19 s^-1 at an overpotential of 200 mV in 1 M KOH and 0.5 M H₂SO₄, respectively, which are 4.1-fold and 2.5-fold higher than those of pristine MoP. Even when compared with other corresponding catalysts, the TOFs of MoP-Pv still ranked at the top. Due to the surface P vacancies, MoP-Pv possesses more electrochemically active sites and faster charge transfer capability, which all favor higher HER catalytic activities. Overall, our work validates a straightforward and vigorous strategy for improving the intrinsic HER catalytic activities of P vacancies, and also provides guidance for the development of vacancy engineering in electrocatalysts.

Ni2P Nanoparticle-Inserted Porous Layered NiO Hetero-Structured Nanosheets as a Durable Catalyst for the Electro-Oxidation of Urea

The electro-oxidation of urea (EOU) is a remarkable but challenging sustainable technology, which largely needs a reduced electro-chemical potential, that demonstrates the ability to remove a notable harmful material from wastewater and/or transform the excretory product of humans into treasure. In this work, an Ni₂P-nanoparticle-integrated porous nickel oxide (NiO) hetero-structured nanosheet (Ni₂P@NiO/NiF) catalyst was synthesized through in situ acid etching and a gas-phase phosphating process. The as-synthesized Ni₂P@NiO/NiF catalyst sample was then used to enhance the electro-oxidation reaction of urea with a higher urea oxidation response (50 mA cm^-2 at 1.31 V vs. RHE) and low onset oxidation potential (1.31 V). The enhanced activity of the Ni₂P@NiO/NiF catalyst was mainly attributed to effective electron transport after Ni₂P nanoparticle insertion through a substantial improvement in active sites due to a larger electrochemical surface area, and a faster diffusion of ions occurred via the interactive sites at the interface of Ni₂P and NiO; thus, the structural reliability was retained, which was further evidenced by the low charge transfer resistance. Further, the Ni₂P nanoparticle insertion process into the NiO hetero-structured nanosheets effectively enabled a synergetic effect when compared to the counter of the Ni₂P/NiF and NiO/NiF catalysts. Finally, we demonstrate that the as-synthesized Ni₂P@NiO/NiF catalyst could be a promising electrode for the EOU in urea-rich wastewater and human urine samples for environmental safety management. Overall, the Ni₂P@NiO/NiF catalyst electrode combines the advantages of the Ni₂P catalyst, NiO nanosheet network, and NiF current collector for enhanced EOU performance, which is highly valuable in catalyst development for environmental safety applications.

Hydrogen evolution reaction catalysis on RuM (M = Ni, Co) porous nanorods by cation etching

The development of efficient and stable nanomaterial electrocatalysts for the hydrogen evolution reaction (HER) is of great significance for renewable energy conversion via water electrolysis. Herein, we have developed a novel class of bimetallic RuM (M = Ni, Co) hollow nanorods (HNRs) through a facile Fe³⁺ etching strategy, as electrocatalysts for enhancing the HER. Morphological physical characterization and electrochemical tests demonstrated that RuM (M = Ni, Co) HNRs with hollow structures can effectively enhance electrocatalytic activity due to their high specific surface areas. Impressively, the RuNi HNRs exhibited superior HER performance with an overpotential of merely 25.6 mV in 1 M KOH solution at 10 mA cm^-2, which is significantly lower than that of commercial Pt/C (44.7 mV). Moreover, the as prepared RuNi HNRs showed excellent stability and could continuously work at a current density of 10 mA cm^-2 for 40 h with a negligible increase in potential. The Ru-based HNRs also showed high HER activity in an acidic solution. This study paves a new way for the universal fabrication of bimetallic hollow structured nanomaterials as efficient electrocatalysts for boosting the HER.

Hierarchical CoMoS3.13/MoS2 hollow nanosheet arrays as bifunctional electrocatalysts for overall water splitting

Hollow hetero-nanosheet arrays have attracted great attention due to their efficient catalytic abilities for water splitting. We successfully fabricated ZIF-67-derived hollow CoMoS_3.13/MoS₂ nanosheet arrays on carbon cloth in situ through a two-step heating-up hydrothermal method, in which the MoS₂ nanosheets were suitably distributed on the surface of the hollow CoMoS_3.13 nanosheet arrays. There was a distinct synergistic effect between CoMoS_3.13 and MoS₂, and a large number of defective and disordered interfaces were formed, which improved the charge transfer rate and provided abundant electrochemical active sites. CMM 0.5, with the optimal Mo doping concentration of 0.5 mmol, exhibited the best catalytic properties. The overpotential values of CMM 0.5 at 10 mA cm^-2 were only 107 and 169 mV for the HER and OER, respectively, and it had nearly 100% faradaic efficiency. A dual-electrode electrolytic cell assembled with CMM 0.5 required a voltage of only 1.507 V at 10 mA cm^-2 for overall water splitting, and it displayed remarkable long-term durable bifunctional stability.

Hierarchical Hollow CoWO4-Co(OH)2 Heterostructured Nanoboxes Enabling Efficient Water Oxidation Electrocatalysis

Rational design and construction of well-defined hollow heterostructured nanomaterials assembled by ultrathin nanosheets overtakes crucial role in developing high-efficiency oxygen evolution reaction (OER) electrocatalysts. Herein, a reliable metal-organic framework-mediated and cation-exchange strategy to tune the geometric structure and multicomponent heterostructures has been proposed for the fabrication of hollow CoWO₄-Co(OH)₂ hierarchical nanoboxes assembled by rich ultrathin nanosheets. Benefiting from the hierarchical hollow nanostructure, the CoWO₄-Co(OH)₂ nanoboxes offer plenty of metal active centers available for reaction intermediates. Moreover, the well-defined nanointerfaces between CoWO₄ and Co(OH)₂ can function as the bridge for boosting the efficient electron transfer from CoWO₄ to Co(OH)₂. As a consequence, the optimized CoWO₄-Co(OH)₂ nanoboxes can exhibit outstanding electrocatalytic performance toward OER by delivering 10 mA cm^-2 with a low overpotential of 280 mV and a small Tafel slope of 70.6 mV dec^-1 as well as outstanding electrochemical stability. More importantly, this CoWO₄-Co(OH)₂ heterostructured nanocatalyst can couple with Pt/C to drive overall water splitting to achieve 10 mA cm^-2 with a voltage of 1.57 V.

MoS2/Ni3S2 Schottky heterojunction regulating local charge distribution for efficient urea oxidation and hydrogen evolution

Electrocatalytic urea oxidation reaction (UOR) is a prospective method to substitute the slow oxygen evolution reaction (OER) and solve the problem of urea-rich water pollution due to the low thermodynamic voltage, but its complex six-electron oxidation process greatly impedes the overall efficiency of electrolysis. Here, density functional theory (DFT) calculations imply that the metallic Ni₃S₂ and semiconductive MoS₂ could form Mott-Schottky catalyst because of the suitable band structure. Therefore, we synthesized MoS₂/Ni₃S₂ electrocatalyst by a simple hydrothermal method, and studied its UOR and hydrogen evolution reaction (HER) performance. The formed MoS₂/Ni₃S₂ Schottky heterojunction is only required 109  and 166 mV to obtain ±10 mA cm^-2 for UOR and HER, respectively, showing great bifunctional catalytic activity. Moreover, the full urea electrolysis driven by MoS₂/Ni₃S₂ delivers 10 and 100 mA cm^-2 at a relatively low potential of 1.44 and 1.59 V. Comprehensive experiments and DFT calculations demonstrate that the MoS₂/Ni₃S₂ Schottky heterojunction causes self-driven charge transfer at the interface and forms built-in electric field, which is not only benefit to reduce H* adsorption energy, but also helps to adjust the absorption and directional distribution of urea molecules, thereby promoting the activity of decomposition of water and urea. This research furnishes a tactic to devise more efficient catalysts for H₂ generation and the treatment of urea-rich water pollution.

Template free-synthesis of cobalt-iron chalcogenides [Co0.8Fe0.2L2, L = S, Se] and their robust bifunctional electrocatalysis for the water splitting reaction and Cr(vi) reduction

The ease of production of materials and showing multiple applications are appealing in this modern era of advanced technology. This paper reports the synthesis of a pair of novel cobalt-iron chalcogenides [Co0.8Fe0.2S2 and Co0.8Fe0.2Se2] with enhanced electro catalytic activities. These ternary metal chalcogenides were synthesized by a one-step template-free approach via a hexamethyldisilazane (HMDS)-assisted synthetic method. Transient photocurrent (TPC) studies and electrochemical impedance spectra (EIS) of these materials showed free electron mobility. Their bifunctional activities were verified in both the electrochemical oxygen evolution reaction (OER) and in the electrochemical reduction of toxic inorganic heavy metal ions [Cr(vi)] in polluted water. The materials showed robust catalytic ability in the oxygen evolution reaction with minimum possible over potential (345 and 350 mV @ η10) as determined by linear sweep voltammetry and the lower Tafel values (52.4 and 84.5 mV dec-1) for Co0.8Fe0.2Se2 and Co0.8Fe0.2S2 respectively. Surprisingly, both the materials also showed an excellent activity towards electrochemical Cr(vi) reduction to Cr(iii). Besides the maximum current achieved for Co0.8Fe0.2S2, a minimum value for the Limit of detection (LOD) was obtained for Co0.8Fe0.2S2 (0.159 μg L-1) compared to Co0.8Fe0.2Se2 (0.196 μg L-1). We tested the durability of catalysts, the critical factor for the prolonged use of catalysts, through the recyclability measurements of these materials as catalysts. Both the catalysts presented outstanding durability and balanced electro catalytic activities for up to 1500 CV cycles, and chronoamperometry studies also confirmed exceptional stability. The enhanced catalytic activities of these materials are ascribed to the free electron movement, evidenced by the increased TPC measured and EIS. Therefore, the template-free synthesis of these electro catalysts containing non-noble metal illustrates the practical approach to develop such types of catalysts for multiple functions.

Chrysanthemum-like FeS/Ni3S2 heterostructure nanoarray as a robust bifunctional electrocatalyst for overall water splitting

The development of a scalable strategy to prepare highly efficient and stable bifunctional electrocatalysts is the key to industrial electrocatalytic water splitting cycles to produce clean hydrogen. Here, a simple and quick one-step hydrothermal method was used to successfully fabricate a three-dimensional core chrysanthemum-like FeS/Ni₃S₂ heterogeneous nanoarray (FeS/Ni₃S₂@NF) on a porous nickel foam skeleton. Compared with the monomer Ni₃S₂@NF, the chrysanthemum-like FeS/ Ni₃S₂@NF heterostructure nanomaterials have improved catalytic performance in alkaline media, showing low overpotentials of 192 mV (η₁₀) and 130 mV (η_-10) for OER and HER, respectively. This study attests that integrated interface engineering and precise morphology control are effective strategies for activating the Ni³⁺/Ni²⁺ coupling, promoting charge transfer and improving the intrinsic activity of the material to accelerate the OER reaction kinetics and promote the overall water splitting performance. The scheme can be reasonably applied to the design and development of transition metal sulfide-based electrocatalysts to put into industrial practice of electrochemical water oxidation.

A facile one-pot room-temperature growth of self-supported ultrathin rhodium-iridium nanosheets as high-efficiency electrocatalysts for hydrogen evolution reaction

The development of low-cost and high-efficiency electrocatalysts is very important for electrocatalytic hydrogen evolution reaction (HER) in water splitting system. Herein, ultrathin rhodium-iridium nanosheets were facilely in-situ grown on nickel foam (RhIr NSs/NF) by a one-pot aqueous strategy at room temperature. The sheet-like structures with the film thickness of 78 nm were identified by scanning electron microscopy and transmission electron microscopy. The catalyst showed greatly high HER features in both 1.0 M KOH and 0.5 M H₂SO₄ with the overpotentials of 15 and 14 mV to achieve 10 mA cm^-2, respectively, surpassing most Pt-free catalysts. Also, the RhIr NSs/NF exhibited amazing catalytic stability during the long-term operation. This study offers a facile and rational pathway for design and synthesis of advanced HER electrocatalysts for energy conversion devices.

Electrospun one-dimensional electrocatalysts for boosting electrocatalysis

Electrocatalytic reaction plays a crucial role in determining the energy conversion efficiency in advanced technology. However, it is limited by the sluggish reaction kinetics and high energy barrier. These shortcomings...

Enhanced hydrogen evolution reaction in alkaline solution by constructing strong metal-support interaction on Pd-CeO2-x-NC hybrids

Diminishing the size of metal nanostructures can significantly improve the performance of catalysts. However, the self-aggregation of small particles is still an insurmountable obstacle, resulting in the unfavorable stability and recyclability. Herein, we designed and fabricated the Pd-CeO_2-x-NC catalyst though an accurate deposition strategy to downsize the Pd particle to sub-nanometer level and enhance its running stability. The CeO_2-x nanoclusters were firstly dispersed on the nitrogen-doped carbon nanosheets. Further, the active Pd sub-nanoclusters were accurately scattered on the surface of CeO_2-x ascribing to the strong metal-support interaction (SMSI) between Pd and CeO_2-x, which was beneficial to promote the catalytic activity. Subsequently, the high oxidation state Pdⁿ⁺ species were formed due to the electron transfer from Pd to CeO_2-x caused by the SMSI effect. Strikingly, the HER performance of Pd-CeO_2-x-NC was surprisingly correlated with the ratio of Pdⁿ⁺, suggesting Pdⁿ⁺ acted as the dominant active species. Besides, the SMSI effect stabilized the valence state of active Pdⁿ⁺ species and prevented the sub-nanometer Pd clusters from aggregation, which played a vital role for the enhanced stability of the hybrid catalyst. This synthetic process described here is contributed to prepare various nanostructured catalysts with satisfactory stability through the direct targeting strategy.

Coordination regulated pyrolysis synthesis of ultrafine FeNi/(FeNi)9S8 nanoclusters/nitrogen, sulfur-codoped graphitic carbon nanosheets as efficient bifunctional oxygen electrocatalysts

Design of advanced carbon nanomaterials with high-efficiency oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities is still imperative yet challenging for searching green and renewable energies. Herein, we synthesized ultrafine FeNi/(FeNi)₉S₈ nanoclusters encapsulated in nitrogen, sulfur-codoped graphitic carbon nanosheets (FeNi/(FeNi)₉S₈/N,S-CNS) by coordination regulated pyrolyzing the mixture of the metal precursors, dithizone and g-C₃N₄ at 800 °C. The as-prepared FeNi/(FeNi)₉S₈/N,S-CNS exhibited distinct electrocatalytic activity and stability for the ORR with positive onset (E_onset) and half-wave (E_1/2) potentials (E_onset = 0.97 V; E_1/2 = 0.86 V) and OER with the small overpotential (η = 283 mV) at 10 mA cm^-2 in the alkaline media, outperforming commercial Pt/C and RuO₂ catalysts. This research provides some constructive guidelines for preparing efficient, low-cost and stable nanocatalysts for electrochemical energy devices.