Cu₂O−Cu₂Se 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) Cu₂O−Cu₂Se 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.