Crystallinity-dependent structural evolution of CoS2 catalysts for enhanced oxygen evolution reaction

Transition metal sulfides (TMSs) are promising catalysts for water oxidation due to their unique electronic properties, but their application is limited by structural instability during the oxygen evolution reaction (OER). The specific mechanisms by which crystallinity variations in TMSs influence their structural evolution and catalytic performance remain poorly understood. Here, we investigate the structural evolution of CoS₂ catalysts with varying crystallinities and their effect on the OER. In-situ characterization and density functional theory (DFT) calculations reveal that lower crystallinity enables rapid equilibrium among surface sulfur-oxygen exchange, metal site activation, and oxygen intermediate evolution, enhancing the transformation of bulk phase into small amounts of sulfur-stabilized oxyhydroxide and improving OER performance. Conversely, moderate crystallinity leads to self-corrosion and progressive structure collapse from the exterior inward, resulting in deactivation. This work highlights the potential of crystallinity control in optimizing the electronic states and catalytic behavior of water oxidation catalysts.