Recent progress and advances in nickel (Ni) based amorphous metal alloys towards alkaline water splitting: A review

In the present scenario of new and renewable energy demands, reducing the cost and increasing the efficiency of the electrolysers is the major concern for adopting hydrogen energy as a sustainable source. The capital cost of electrolysers largely depends on the electrocatalyst. Among the developed low-cost electrocatalyst species, amorphous Ni-base alloys has been the focus of research interest for many researchers globally due to their unique advantages compared with their crystalline counterparts. Amorphous Ni-base alloys can exploit unique chemistries and short-range ordering instead of long-range periodicity. The structural tailoring, the high number of unsaturated sites, and the defects associated with the amorphous Ni-alloy electrocatalysts enhance their electrocatalytic water-splitting performance for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Despite all these advantages, further improvements in the intrinsic activity and geometry of amorphous nickel-base alloys (binary/ternary Ni-alloys) electrocatalysts are still required to enhance HER/ OER activity and stability. The choice of the secondary metal to form binary alloys and the synthesis route affect the fundamental characteristics of these alloys. The focus of the current review is to critically discuss the advantages and state-of -the -art performance of ternary amorphous Ni-alloys as effective electrocatalysts for the HER and OER. Mechanical alloying (MA), especially cryogenic ball milling, is regarded to be an economical and efficient synthesis route for electrocatalyst fabrication on an industrial scale. Subsequent surfactant-assisted high energy ball milling (SA-HEBM) for nanoparticle production enhances the surface features to further improve the HER and OER activity. The role of different surface species responsible for improving the HER/OER activity and stability has been discussed, incorporating both ex-situ and in-situ characterization techniques. The challenges and future perspectives for these amorphous alloy electrocatalysts are summarized herein.