Stable p‐type Cu:CdS1−xSex/Pt Thin‐Film Photocathodes with Fully Tunable Bandgap for Scavenger‐Free Photoelectrochemical Water Splitting

Abstract

Natural Cd‐based group II–VI semiconductors in photoelectrochemical (PEC) cells are normally used as photoanodes, whose applications are hence hindered by the heavy anodic photocorrosion. Herein, a series of p‐type Cu‐doped CdS1−xSex alloy thin films as photocathodes for water splitting is reported. These alloyed films, synthesized via a simple but well‐controlled physical vapor deposition (PVD) method, are fully tunable in chemical composition, which leads to a tunable bandgap from 1.69 to 2.40 eV. Benefiting from the broadened visible light response, the Cu:CdS0.7Se0.3 photocathode with Pt nanoparticles (NPs) as cocatalysts shows a 37% higher photocurrent density and a higher Faradaic efficiency compared with previously reported Cu:CdS/Pt. More importantly, good stability of the Cu:CdS0.7Se0.3/Pt photocathode in scavenger‐free electrolyte for PEC water splitting is first achieved, with 80% remaining photocurrent and no significant change in 5 h. The released Cd2+ in the electrolyte for the p‐type Cu:CdS1−xSex/Pt photocathode is suppressed by more than three orders of magnitude as compared with a traditional n‐type CdS1−xSex/Pt photoanode. The results reveal the feasibility of Cd‐based group II–VI materials as the thin‐film photocathode for PEC water splitting. The tunable bandgap and durability of p‐type Cu:CdS1−xSex can contribute to future heterojunction structure design in PEC cells.