Transition-metal selenides in oxygen evolution electrocatalysis: from pre-catalysts to active regulators

Green hydrogen generated by renewable energy-driven water electrolysis is central to carbon-neutral energy systems. Yet the oxygen evolution reaction (OER) at the anode remains the primary kinetic bottleneck, limiting efficiency and long-term stability in alkaline and anion-exchange membrane electrolyzers. The development of cost-effective and durable OER catalysts based on earth-abundant elements is therefore critical for scalable hydrogen production. Transition-metal selenides have emerged as attractive pre-catalysts due to their high electrical conductivity, tunable composition, and dynamic reconstruction under anodic conditions. During OER, selenides usually transform into oxyhydroxide-like active phases, increasing the electrochemically active surface area and improving electrolyte access. In this established sacrificial-precursor model, selenium (Se) is typically viewed as a temporary component that enhances conductivity and morphology before dissolving. Recent evidence shows that Se does not always disappear during reconstruction. Instead, it can remain in chemically distinct forms, such as surface-associated, subsurface, and interlayer species, which influence catalytic behavior beyond increasing surface area. These retained Se species, along with the conductive selenide framework and structural changes from reconstruction, enhance activity and durability beyond the traditional precursor model. This review re-examines transition-metal selenides for alkaline OER by integrating insights on structural evolution, charge transport, and Se-state regulation. We highlight how controlled Se transformation and retention impact catalytic performance and present design principles for developing more efficient and stable OER electrocatalysts for green hydrogen production.