Rapid Charge Extraction via Hole and Electron Transfer Layers on Cu2O Photocathode for Stable and Efficient Photoelectrochemical Water Reduction.

Photoelectrochemical (PEC) water reduction offers a promising method for generating "green" hydrogen. The hydrogen evolution reaction (HER) at the photocathode is significantly constrained, primarily because of the rapid recombination of photogenerated electron-hole pairs and the high energy barrier encountered during the water splitting step. Here, a unique "sandwich" structure FeOOH/Cu₂O/ZnO composite photocathode is fabricated by hydrothermal and electrodeposition methods. Photogenerated holes are extracted and transferred from the Cu₂O to FTO substrates more easily via the introduction of FeOOH as a hole storage/transport layer. Charge recombination is hindered by the ZnO layer, which functions an electron transfer agent. Hence, the FeOOH/Cu₂O/ZnO photocathode presents remarkable PEC water reduction capability. The maximum photocurrent density of the FeOOH/Cu₂O/ZnO photocathode (-2.54 mA·cm^-2) is 12.7 times greater than that of pristine Cu₂O (-0.2 mA·cm^-2) at 0 V_RHE. The IPCE of FeOOH/Cu₂O/ZnO reaches 33.7% (455 nm), which is 8.1 times higher than the value of bare Cu₂O (4.18%). The theoretical calculations reveal that energy barrier of HER on FeOOH/Cu₂O/ZnO photocathode is dramatically reduced, greatly improving the catalytic activity for HER. This study highlights the crucial functions of solar PEC conversion and offers comprehensive insights into interfacial charge transfer in designing efficient photocathode materials.