Recent progress in nickel-based electrocatalysts for hydrogen evolution reaction by hydrothermal synthesis method in alkaline media: A comprehensive review

Green hydrogen via the electrolysis method relies on hydrogen evolution reaction (HER) taking place at the cathode and the oxygen evolution reaction (OER) occurring at the anode. Although precious-metal catalysts are known for their exceptional electrochemical performance, their large-scale implementation is hampered by high costs and restricted availability. Consequently, the development of efficient and cost-effective transition-metal-based electrocatalysts has become a hot research topic. Among transition metals, nickel-based electrocatalysts have drawn much attention due to their abundance, low cost, good conductivity and appropriate hydrogen absorption property. A variety of nickel-based compounds and heterostructures have been produced to increase HER activities, including hydroxides, phosphides, nitrides, carbides, chalcogenides, borides and multicomponent alloys. The synthesis approach is next to the material design of paramount importance to achieve scalable catalyst manufacturing. Hydrothermal synthesis has been one of the most popular strategies in creating Ni-based electrocatalysts because of its outstanding control over shape, crystallinity and composition under very mild conditions. The technique offers operational simplicity, customizable synthesis parameters, relatively low cost and the possibility of producing high purity nanostructured materials. In this review, we summarize the development strategies for electrocatalysts utilizing various Ni-based materials produced through hydrothermal synthesis. Particular attention is paid to the effect of crucial hydrothermal synthesis factors (temperature, reaction duration, and precursor composition) on the catalyst structure and HER activity. We offer a critical discussion on the structure-activity correlations influencing catalytic performance, to provide insight into the rational design of next-generation Ni-based HER electrocatalysts for alkaline water electrolysis.