Enhanced photoelectrochemical efficiency and stability using nitrogen-doped TiO2 on a GaAs photoanode

GaAs has been attracting significant attention as a material for solar energy conversion because of its visible light absorption capability, high electron mobility, and direct band gap. However, its chemical stability is extremely low for utilization in applications associated with photoelectrochemical water splitting. TiO2 is known to exhibit an excellent chemical stability; however, it has a poor electrical conductivity and a wide band gap. In this study, we fabricated a heterogeneous Z-scheme photoanode by combining TiO2 and GaAs; this photoanode demonstrated a high chemical stability and a high visible light absorption capability. Herein, we propose an effective strategy for achieving nitrogen doping in TiO2 (N-TiO2) to form oxygen vacancies and TiN, which increase the electrical conductivity and reduce the overpotential of the photoanode. The TiN/N-TiO2/ITO/GaAs photoanode thus obtained significantly improved the electrochemical performances of the oxygen evolution reaction, as compared to those obtained with the undoped TiO2/ITO/GaAs photoanode. Further, the Tafel slope was observed to decrease from 315.4 mV/dec to 64.1 mV/dec and the open circuit potential shifted from 0.2 V to -0.2 V vs RHE. In addition, photoelectrochemical stability was significantly improved as compared to that obtained by bare GaAs. (C) 2020 Elsevier B.V. All rights reserved.