Engineering non-noble bifunctional catalysts for alkaline hydrogen and oxygen evolution

The development of efficient, stable, and economically viable electrocatalysts for alkaline water electrolysis remains central to large-scale green hydrogen production. The replacement of noble-metal catalysts requires the rational design of non-precious materials capable of catalyzing both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline electrolytes, processes constrained by fundamentally distinct reaction kinetics. This Review analyzes the intrinsic kinetic limitations governing alkaline HER and OER, with emphasis on water-dissociation steps and the multielectron oxygen-evolution pathway controlled by adsorption-energy scaling relationships. Materials-engineering strategies aimed at addressing these constraints, including heterostructure construction, multi-anionic coordination, surface reconstruction under operating conditions, and confinement architectures, are examined in detail. Representative catalyst systems, such as NiFe layered double hydroxide/Ni₃S₂ heterostructures, Ni₂P/Fe₃N composites, high-entropy alloys, and graphene-modified materials, are discussed to illustrate how interfacial electronic interactions and site-specific structural tuning contribute to improved bifunctional activity. Research directions encompassing single-atom catalysts, ternary chalcogenides, and boron-based frameworks are also summarized. Outstanding challenges associated with scalability, durability at industrially relevant current densities, and degradation mechanisms are addressed, and priorities for translating laboratory-scale advances into practical alkaline electrolyzer technologies are outlined.