Cu ₂ O−Cu ₂ Se Mixed‐Phase Nanoflake Arrays: pH‐Universal Hydrogen Evolution Reactions with Ultralow Overpotential

Most developed hydrogen evolution reaction (HER) electrocatalysts have pH‐dependent functionalities, which limit their universal applications. Pt, the ideal HER electrocatalyst, is also highly effective in specific pH conditions. In the present article, we report a copper‐based transition‐metal chalcogenide from anion engineering. Hierarchical three‐dimensional (3D) Cu 2 O−Cu 2 Se nanoflake arrays (COCS NFs) are grown directly on nickel foam (NF) by combining the rapid electrodeposition technique with the room temperature wet‐chemical selenization method. Via the synergetic effects of the proper ratio of Se and O, as‐synthesized COCS NFs manage to accomplish key‐requirements for pH‐universal HER performances with overpotential values of 52.9, 62.8, and 77.8 mV, in alkaline, neutral, and acidic media, respectively, at 10 mA cm −2 . The electrocatalyst also possesses superb stability at constant 10 mA cm −2 current density for 50 h in all electrolytes. This work offers a synthesis protocol of a mixed‐anion composite with the revelation about the importance of anion modulation towards electrode surface properties and HER performances.