Electronegativity difference modulates cuprous chalcogenide catalysts for alkaline water splitting

Regulating the electronic structure of active sites through electronegativity difference offers a promising route to high-efficiency bifunctional electrocatalysis, yet systematic comparisons based on isostructural model catalysts remain limited. Herein, Cu 2 O nanocubes are used as a common precursor template to construct structurally comparable Cu 2 X (X = S, Se, and Te) nanocubes via a vapor-phase isomorphous substitution strategy for alkaline water splitting. Among the obtained catalysts, Cu 2 Se exhibits the best bifunctional activity, requiring overpotentials of only 56 mV for the hydrogen evolution reaction (HER) and 131 mV for the oxygen evolution reaction (OER) at 10 mA cm −2 . When employed as both the cathode and anode, the Cu 2 Se||Cu 2 Se electrolyzer delivered 10 mA cm −2 at 1.52 V, with a Faradaic efficiency close to 100%, and retained 95.2% of its initial activity after 150 h of continuous operation. In a single-cell anion exchange membrane water electrolyzer, the Cu 2 Se-based device further achieved 500 mA cm −2 at 2.89 V and operated stably for 1000 h at 70 °C. Structural and electrochemical analyses indicate that chalcogen substitution preserves the nanocube framework while modulating the local electronic structure of Cu sites. The moderate electronegativity difference between Cu and Se is found to be particularly favorable for optimizing the electron density of Cu, increasing electrochemically accessible active sites, and accelerating interfacial charge transfer. This study establishes a structurally comparable Cu 2 X platform for elucidating electronegativity difference driven electronic regulation and offers a feasible strategy for designing efficient Cu-based bifunctional catalysts for alkaline water splitting.