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Efficient, durable and economic electrocatalysts are crucial for commercializing water electrolysis technology. Herein, we report an advanced bifunctional electrocatalyst for alkaline water splitting by growing NiFe-layered double hydroxide (NiFe-LDH) nanosheet arrays on the conductive NiMo-based nanorods deposited on Ni foam to form a three-dimensional (3D) architecture, which exhibits exceptional performances for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In overall water splitting, only the low operation voltages of 1.45/1.61 V are required to reach the current density of 10/500 mA·cm −2 , and the continuous water splitting at an industrial-level current density of 500 mA·cm −2 shows a negligible degradation (1.8%) of the cell voltage over 1000 h. The outstanding performance is ascribed to the synergism of the HER-active NiMo-based nanorods and the OER-active NiFe-LDH nanosheet arrays of the hybridized 3D architecture. Specifically, the dense NiFe-LDH nanosheet arrays enhance the local pH on cathode by retarding OH − diffusion and enlarge the electrochemically active surface area on anode, while the conductive NiMo-based nanorods on Ni foam much decrease the charge-transfer resistances of both electrodes. This study provides an efficient strategy to explore advanced bifunctional electrocatalysts for overall water splitting by rationally hybridizing HER- and OER-active components.

Electrochemical water splitting has attracted considerable attention for the production of hydrogen fuel by using renewable energy resources. However, the sluggish reaction kinetics make it essential to explore precious‐metal‐free electrocatalysts with superior activity and long‐term stability. Tremendous efforts have been made in exploring electrocatalysts to reduce the energy barriers and improve catalytic efficiency. This review summarizes different categories of precious‐metal‐free electrocatalysts developed in the past 5 years for alkaline water splitting. The design strategies for optimizing the electronic and geometric structures of electrocatalysts with enhanced catalytic performance are discussed, including composition modulation, defect engineering, and structural engineering. Particularly, the advancement of operando/in situ characterization techniques toward the understanding of structural evolution, reaction intermediates, and active sites during the water splitting process are summarized. Finally, current challenges and future perspectives toward achieving efficient catalyst systems for industrial applications are proposed. This review will provide insights and strategies to the design of precious‐metal‐free electrocatalysts and inspire future research in alkaline water splitting. This review summarizes recent advances in precious‐metal‐free electrocatalysts for efficient alkaline water splitting, and the design strategies for enhanced performance including component modulation, defect engineering, and structural engineering, along with insights into operando/in situ characterization for a comprehensive understanding of the structural evolution and functionalities of electrocatalysts during the water splitting reactions.

Devising an electrocatalyst with brilliant efficiency and satisfactory durability for hydrogen production is of considerable demand, especially for large-scale application. Herein, we adopt a multi-step consequential induced strategy to construct a bifunctional electrocatalyst for the overall water splitting. Graphene oxide (GO) was used as a carbon matrix and in situ oxygen source, which was supported by the octahedral PtNi alloy to form the Pt x Ni y -GO precursor. When calcinating in Ar atmosphere, the oxygen in GO induced the surface segregation of Ni from the PtNi octahedron to form a core-shell structure of Pt x @Ni y . Then, the surface-enriched Ni continuously induced the reformation of C in reduced graphene oxide (rGO) to enhance the degree of graphitization. This multi-step induction formed a nanocatalyst Pt x @Ni y -rGO which has very high catalytic efficiency and stability. By optimizing the feeding ratio of PtNi (Pt:Ni = 1:2), the electrolytic overall water splitting at 10 mA·cm −2 can be driven by an electrolytic voltage of as low as 1.485 V, and hydrogen evolution reaction (HER) only needs an overpotential of 37 mV in 1.0 M KOH aqueous solution. Additionally, the catalyst exhibited consistent existence form in both HER and oxygen evolution reaction (OER), which was verified by switching the anode and cathode of the cell in the electrolysis of water. This work provides a new idea for the synthesis and evaluation of the bifunctional catalysts for water splitting.

Developing cost-effective, highly catalytic active, and stable electrocatalysts in alkaline electrolytes is important for the development of highly efficient anion-exchange membrane water electrolysis (AEMWE). To this end, metal oxides/hydroxides have attracted wide research interest for efficient electrocatalysts in water splitting owing to their abundance and tunable electronic properties. It is very challenging to achieve an efficient overall catalytic performance based on single metal oxide/hydroxide-based electrocatalysts due to low charge mobilities and limited stability. This review is mainly focused on the advanced strategies to synthesize the multicomponent metal oxide/hydroxide-based materials that include nanostructure engineering, heterointerface engineering, single-atom catalysts, and chemical modification. The state of the art of metal oxide/hydroxide-based heterostructures with various architectures is extensively discussed. Finally, this review provides the fundamental challenges and perspectives regarding the potential future direction of multicomponent metal oxide/hydroxide-based electrocatalysts.

Globally, there are significant concerns about the steadily rising energy demand and depletion of conservative fuels. Water electrolysis provides hydrogen and oxygen, which can be used as a fuel with a highest energy conversion efficiency and gravimetric energy density. In future, hydrogen fuel will take the place of conventional fossil fuels, which are polluting the environment. For a greater range of energy generation devices, the highly appropriate, affordable electrocatalyst for OER is significant. In present work, a NbSe 2 /rGO nanocomposite was fabricated via hydrothermal process for OER electrochemical studies under 1.0 M KOH. The fabricated materials were verified by Raman spectroscopy, scanning electron microscopy (SEM), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray. Because of its distinct shape, nanocomposite has more surface area, which results in more active pores with lots of potential for transfer of charge and prolonged material stability. The surface area of NbSe2/rGO nanocomposite determined through BET was 51 m 2 /g, i.e., higher than that of NbSe 2 , thus providing greater number of active sites for OER performance. The electrocatalytic performance results represented that pure NbSe 2 nanosheets revealed a higher Tafel slope (51 mV/dec), conversely, NbSe 2 /rGO nanocomposite represented lower Tafel slope (36 mV/dec) respectively and efficient durability for 60 h with minor alternation in current density for long time period. As a consequence, the created nanocomposite proves to be an effective electrocatalyst for OER and energy conversion applications. Graphical Abstract Highlights The NbSe 2 /rGO nanocomposite was prepared with the help of Hydrothermal technique. The Bruner–Emmett–Teller (BET) results showed large number of active pores and big surface area. The electrochemical testing of nanocomposite was performed via using 1.0 M KOH alkaline medium using 3 electrode system. The electrochemical results of NbSe 2 /rGO nanocomposite were acquired for efficient OER process. The electrocatalytic results showed that NbSe 2 /rGO nanocomposite possessed Overpotential 199 mV and Tafel slope 36 mV/dec.

First d-block metal-based perovskite oxides (FDMPOs) have garnered significant attention in research for their utilization in the water oxidation reaction due to their low cost, earth abundance, and promising activities. Recently, FDMPOs are being applied in electrocatalysis for the hydrogen evolution reaction (HER) and overall water splitting reaction. Numerous promising FDMPO-based water splitting electrocatalysts have been reported, along with new catalytic mechanisms. Therefore, an in-time summary of the current progress of FDMPO-based water splitting electrocatalysts is now considered imperative. However, few reviews have focused on this particular subject thus far. In this contribution, we review the most recent advances (mainly within the years 2014–2020) of FDMPO electrocatalysts for alkaline water splitting, which is widely considered to be the most promising next-generation technology for future large-scale hydrogen production. This review begins with an introduction describing the fundamentals of alkaline water electrolysis and perovskite oxides. We then carefully elaborate on the various design strategies used for the preparation of FDMPO electrocatalysts applied in the alkaline water splitting reaction, including defecting engineering, strain tuning, nanostructuring, and hybridization. Finally, we discuss the current advances of various FDMPO-based water splitting electrocatalysts, including those based on Co, Ni, Fe, Mn, and other first d-block metal-based catalysts. By conveying various methods, developments, perspectives, and challenges, this review will contribute toward the understanding and development of FDMPO electrocatalysts for alkaline water splitting.

To address issues of global energy sustainability, it is essential to develop highly efficient bifunctional transition metal-based electrocatalysts to accelerate the kinetics of both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Herein, the heterogeneous molybdenum and vanadium codoped cobalt carbonate nanosheets loaded on nickel foam (VMoCoCOx@NF) are fabricated by facile hydrothermal deposition. Firstly, the mole ratio of V/Mo/Co in the composite is optimized by response surface methodology (RSM). When the optimized composite serves as a bifunctional catalyst, the water-splitting current density achieves 10 mA cm−2 and 100 mA cm−2 at cell voltages of 1.54 V and 1.61 V in a 1.0 M KOH electrolyte with robust stability. Furthermore, characterization is carried out using field emission scanning electron microscopy-energy dispersive spectroscopy (FESEM-EDS), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) calculations reveal that the fabricated VMoCoCOx@NF catalyst synergistically decreases the Gibbs free energy of hydrogen and oxygen-containing intermediates, thus accelerating OER/HER catalytic kinetics. Benefiting from the concerted advantages of porous NF substrates and clustered VMoCoCOx nanosheets, the fabricated catalyst exhibits superior electrocatalytic performance. This work presents a novel approach to developing transition metal catalysts for overall water splitting.

For efficient electrode development in an electrolysis system, Fe2O3, MnO, and heterojunction Fe2O3-MnO materials were synthesized via a simple sol–gel method. These particles were coated on a Ni-foam (NF) electrode, and the resulting material was used as an electrode to be used during an oxygen evolution reaction (OER). A 1000-cycle OER test in a KOH alkaline electrolyte indicated that the heterojunction Fe2O3-MnO/NF electrode exhibited the most stable and highest OER activity: it exhibited a low overvoltage (n) of 370 mV and a small Tafel slope of 66 mV/dec. X-ray photoelectron spectroscopy indicated that the excellent redox performance contributed to the synergy of Mn and Fe, which enhanced the OER performance of the Fe2O3-MnO/NF electrode. Furthermore, the effective redox reaction of Mn and Fe indicated that the structure maintained stability even under 1000 repeated OER cycles.

Alkaline water electrolysis (AWS) is a promising technology for hydrogen production, but the low performance of oxygen evolution reaction (OER) electrodes leads to high energy consumption. Enhancing OER efficiency is essential for reducing energy barriers and improving system performance. In this study, it develops a composite catalyst of PrBa0.5Sr0.5Co1.5Fe0.5O5+δ and IrO2 (PBSCF‐Ir), with a surface area of 18.68 m2g−1. The PBSCF‐Ir composite exhibits a low overpotential of 312 mV at 10 mA cm−2 and stability over 300 h. In water splitting tests, it achieves a lower cell voltage (1.95 V at 500 mA cm−2) compared to pure IrO2. X‐ray photoelectron spectroscopy reveals a 1 eV blueshift in Co 2p energy levels, indicating modified electronic structures. Density functional theory calculations show that IrO2 shifts the d‐band centers of Co and Fe, enhancing electrophilicity, OH− affinity, and OER activity. This study highlights the PBSCF‐Ir composite as an efficient and durable catalyst for AWS, thereby addressing the need for sustainable hydrogen production. This study highlights the innovative PrBa0.5Sr0.5Co1.5Fe0.5O5+δ‐IrO2 composite catalyst synthesized via high‐energy ball milling, showcasing exceptional oxygen evolution reaction performance with low overpotential and remarkable stability. Synergistic effects, enhanced surface area, and optimized electronic structures provide valuable insights for advancing electrocatalytic water‐splitting technologies.

High‐entropy materials (HEMs), which are newly manufactured compounds that contain five or more metal cations, can be a platform with desired properties, including improved electrocatalytic performance owing to the inherent complexity. Here, a strain engineering methodology is proposed to design transition‐metal‐based HEM by Li manipulation (LiTM) with tunable lattice strain, thus tailoring the electronic structure and boosting electrocatalytic performance. As confirmed by the experiments and calculation results, tensile strain in the LiTM after Li manipulation can optimize the d‐band center and increase the electrical conductivity. Accordingly, the as‐prepared LiTM‐25 demonstrates optimized oxygen evolution reaction and hydrogen evolution reaction activity in alkaline saline water, requiring ultralow overpotentials of 265 and 42 mV at 10 mA cm−2, respectively. More strikingly, LiTM‐25 retains 94.6% activity after 80 h of a durability test when assembled as an anion‐exchange membrane water electrolyzer. Finally, in order to show the general efficacy of strain engineering, we incorporate Li into electrocatalysts with higher entropies as well. Strain engineering of high‐entropy materials has been carried out with the involvement of Li. The presence of lattice strain leads to an upward shift of the transition‐metal d‐band centers, optimizing the free energy of the absorbate while increasing the electronic conductivity, which in turn greatly improves the electrocatalytic performance. As‐prepared high‐entropy electrocatalysts show excellent water‐splitting stability in alkaline saline water. Highlights An innovative design and fabrication method for high‐entropy electrocatalysts with strain strategies is reported. Optimized electrocatalysts show ultralow oxygen evolution reaction (265 mV) and hydrogen evolution reaction (42 mV) overpotentials at 10 mV cm−2 in alkaline saline water. The universal enhanced catalytic activity of high‐entropy electrocatalysts is verified by the addition of metal species. It is proved that the presence of lattice strain optimizes the d‐band center of the active site.