Tetrafunctional Cu₂S thin layers on Cu₂O nanowires for efficient photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting by photocathodes based on p-type semiconductors is a promising process for direct and efficient hydrogen generation. The identification of ideal photocathode materials with a high photoconversion efficiency and long-term stability is still a significant challenge. Herein, we propose a new photocathode consisting of Cu₂S-coated Cu₂O nanowires (NWs) supported on a three-dimensional porous copper foam. The Cu₂S thin layer is generated in situ on the surface of the Cu₂O NWs and has four functions: (1) Sensitizer, with a band gap of 1.2 eV, for extending the range of optical absorption into the near-infrared region; (2) electron trapper, with appropriate energy level alignment to Cu₂O, for achieving effective electron transfer and trapping; (3) electrocatalyst, with excellent electrocatalytic activity for the hydrogen evolution reaction; and (4) protector, preventing direct contact between Cu₂O and the electrolyte in order to significantly increase the stability. A photocathode based on the tetrafunctional Cu₂S-coated Cu₂O NWs exhibits significantly enhanced PEC performance and remarkably improved long-term stability under illumination. The present strategy, based on the in situ generation of multifunctional layers, opens a new avenue for the rational design of photocathodes for PEC water reduction. [Figure not available: see fulltext.].