Anion-Exchange Strategy for the Optimization of Cu2MnS2-xSe x Nanostructures toward Bifunctional Electrocatalysis in Alkaline Water Splitting

The catalytic performance of multicomponent chalcogenides is highly dependent on their anionic composition, yet the role of controlled sulfur–selenium exchange in regulating electrocatalytic activity remains largely unexplored. Herein, a series of Cu2MnS2-xSex (0 ≤ x ≤ 2) catalysts were synthesized through a hydrothermal anion-exchange strategy, enabling systematic tuning of the chalcogen environment. Selenium (Se) incorporation induced lattice distortion and electronic redistribution within the Cu–Mn chalcogenide framework, leading to enhanced charge transport and increased accessibility of catalytic sites. Among all compositions, a two-electrode electrolyzer assembled using the Cu–Mn–Se (CMSe-5) multiphase system exhibited the best bifunctionality, requiring a low overall cell potential of 1.67 V to acquire 10 mA/cm2 current density, with excellent long-term stability in alkaline media. Fascinatingly, the equal chalcogen ratio Cu–Mn–S–Se (CMSSe-4) reveals very close performance with CMSe-5. The superior activity is attributed to the synergistic interaction between sulfur and selenium, which effectively modulates the electronic structure and facilitates adsorption and desorption of reaction intermediates. These findings demonstrate that precise anion engineering offers an effective pathway for optimizing multimetal chalcogenides and provides valuable insights for the development of high-performance, earth-abundant electrocatalysts for sustainable alkaline water electrolysis.