Advances in self-reconstructing stainless-steel electrocatalysts for water splitting: surface activation, alloy engineering, stability, and DFT insights

Stainless steel (SS) is emerging as a promising, earth-abundant platform for replacing precious-metal and pure-Ni electrodes in water electrolysis. Yet, it is still often treated as inert hardware rather than an active catalyst. Under HER/OER conditions, however, the classical Cr-rich passive film on Fe-Cr-Ni alloy SS is driven beyond its stability window. It can reconstruct into porous, Ni/Fe-rich (oxy)hydroxide layers that provide genuine catalytic activity while remaining anchored to a robust metallic backbone. This review consolidates evidence on how such self-reconstruction can be intentionally controlled and engineered to convert commercial SS into efficient, durable electrodes for overall water splitting. We first summarize the evolution of SS from a structural material to a self-reconstructing electrocatalyst, and critically discuss surface-activation strategies, including electrochemical activation (potential cycling, anodization, and cathodization), thermal oxidation, and hydrothermal/corrosion-engineering routes that drive Cr depletion and Ni/Fe enrichment. We then introduce the Ni-Fe-Cr-X reservoir concept to bridge the gap between traditional corrosion science and modern electrocatalysis, rationalizing how bulk alloy composition and microstructure govern reconstruction behavior, secondary passivation, and stability across alkaline and chloride-containing environments. Emphasis is placed on long-term durability, including self-replenishing Ni-rich electrodes that operate at ampere-level current densities, and on the limited but growing density functional theory (DFT) literature that links passive-film chemistry and electronic structure to HER/OER mechanisms. Finally, we outline key research directions, including multi-scale operando characterization, composition-designed SS, and specific DFT/ML frameworks needed to move from empirical activation toward rational, mechanism-guided design of SS-based electrocatalysts.