Multi‐Anion Electrocatalysts Stabilized by Anionic Configurational Entropy for Advanced Water Splitting

Anion regulation in transition metal compounds provides an effective strategy to modulate their electrocatalytic activity. However, the coexistence of multiple anions often results in thermodynamically favored phase separation, restricting the density and tunability of active sites. To address this limitation, we draw inspiration from the high-entropy strategy, where configurational entropy promotes uniform elemental mixing and is predominantly applied in multi-metal systems. Here, we extend this design to anion regulation, employing diverse anionic components to enhance configurational entropy, suppress the enthalpy-driven phase separation, and achieve thermodynamically stable single-phase structures. The atomic-level anion homogeneity thereby enables precise modulation of the electronic structure of metal sites. As a proof of concept, a multi-anion electrocatalyst containing hydroxide, sulfide, selenide, and phosphate anions is successfully synthesized and achieves low overpotentials of 25 mV for hydrogen evolution and 146 mV for oxygen evolution at 10 mA cm^-2. When integrated into an anion-exchange membrane water electrolyzer, the catalyst delivers a current density of 1,000 mA cm^-2 at 1.98 V and maintains stable operation for 200 h at 25 °C. Focusing on anionic configurational entropy, this study thermodynamically stabilizes conventionally metastable multi-anion compounds, broadens the scope of medium/high-entropy materials, and provides guidance for the design of next-generation electrocatalysts.