Cadmium doping induced type-II to Z-scheme switching in CdSe/BiVO4 heterojunction for enhancing photocatalytic hydrogen production

Heterojunction type in composite photocatalysts determines their charge carrier transfer path, which is critical to the redox capacity of their charge carriers and needs careful modulation for their designed photocatalytic reactions. In this work, a transit from the type-II (BVO/CdSe) to Z-scheme (CdSe/BVO) in CdSe/BiVO4 heterojunction happened by changing the deposition sequence of CdSe and BiVO4 layers to introduce Cd-doping into the BiVO4 layer, which fundamentally changed their charge carrier separation and transfer behaviors as demonstrated by both experimental and calculation results. So, the charge carrier separation efficiency in CdSe got largely enhanced, more photogenerated electrons with high reduction potential were allowed to participate in the photocatalytic H2 production, and photogenerated hole accumulation in CdSe reduced. As a result, the CdSe/BVO photoelectrode demonstrated the best photocatalytic hydrogen production rate (2.59 μmol cm−2 h−1), which is about 136.3 and 5.9 times higher than that of BVO/CdSe and pure CdSe, and the stability under visible light irradiation is also greatly improved.