NiFe-based electrocatalysts for hydrogen evolution reaction in alkaline conditions Recent trends in the design and structure–activity correlations

One of the best alternatives to fossil fuels and a plausible solution to the issues related to its perpetual consumption such as carbon emission and energy crisis is the use of “green hydrogen” as the fuel of future with zero carbon emission. The electrocatalytic water-splitting reaction to produce ‘green hydrogen’ has a high kinetic energy barrier and hence developing a high performance electrocatalyst is very crucial and challenging. The electrocatalysts that based on NiFe catalyst system has received considerable attention because of their low cost, easy availability, increased electrochemically active surface sites compared to pure nickel and iron materials, and excellent electronic properties due to the synergistic interaction between Nickel and Iron. This review highlights the recent trends and a comprehensive analysis of the critical factors described in the literature for the design and optimization of an effective NiFe-based hydrogen evolution reaction (HER) electrocatalyst in alkaline medium. The important factors that influence the catalytic efficiency of NiFe-based electrocatalysts such as the modifications in the surface morphology, electronic structure of the catalyst, supporting material characteristics, doping with heteroatoms of metals or non-metals, heterostructuring, synthesis strategies, compositional variations, and pore structure of the catalyst are addressed from experimental and theoretical point of view. The variation of these parameters provides much exposed active sites, improved surface area, electronic conductivity, fast mass diffusion and easy desorption of hydrogen gas from the catalyst surface and stability. The NiFe-based overall water splitting, and various in situ/operando studies employed for elucidating the reaction mechanism as well as the structural evolution of the catalyst during the electrocatalytic water splitting reaction under alkaline conditions are also discussed in this review. The challenges and prospects for developing NiFe-based electrocatalyst for HER under alkaline medium are highlighted in the end. Even though advancement has made in the area of electrocatalytic HER, continuous efforts are needed to fabricate a highly efficient NiFe-based electrocatalyst that show long term electrochemical stability along with scalability for sustainable H₂ production and implementation of it for commercial applications.