Al-ZnO/CdS Photoanode Modified with a Triple Functions Conformal TiO2 Film for Enhanced Photoelectrochemical Efficiency and Stability

ZnO/CdS based nanorod arrays is an excellent class of photoanode materials with high photoelectric response. However, the poor photostability of CdS in aqueous solution seriously prevents its practical application. Although efforts have been made, it still challengeable to improve stability while maintaining initial photo-current. Herein, a highly efficient photoanode system consisting of Al-doped ZnO nanorod arrays (NRs) served as effective electron-transfer layer and CdS as a light harvesting layer was designed. At last, TiO2 protective layer was deposited onto Al-ZnO/CdS photoanodes through atomic layer deposition (ALD) to enhance the photo-stability. The integrated Al-ZnO/CdS/TiO2 photoanode exhibits a photocurrent of 11.7 mA/cm(2) at 1.23 V versus reversible hydrogen potential (RHE) and conversion efficiency of 5.9 % at 0.48 V versus RHE for 60 ALD TiO2 cycles. More importantly, the photostability of Al-ZnO/CdS/TiO2 photoanode was significantly prolonged comparing with the untreated Al-ZnO/CdS photoanode. The strengthen stability is benefited from the triple functions of ALD TiO2 layer, that is, isolating the direct contact between the photoanode with the surrounding liquid environment, passivating the surface state of the CdS, and capturing as well as storing the photogenerated hole.