Cobalt-phosphate modified Fe-Zn0.2Cd0.8S/CuSbS2 heterojunction photoanode with multiple synergistic effect for enhancing photoelectrochemical water splitting

Abstract Carrier separation efficiency and visible light response range were key factors limiting the development of photoelectrochemical (PEC) water splitting. In this paper, multiple synergistic mechanisms of metal ion doping-heterojunctions and heterojunction-cocatalysts were proposed to broaden the visible light response range and improve carrier separation efficiency. The Fe-Zn0.2Cd0.8S/CuSbS2/Co-Pi was firstly synthesized by hydrothermal and electrochemical deposition, to study the multiple synergistic effects of the composite. Compared with the initial Zn0.2Cd0.8S (2.83 eV), the optical band gap of Fe-Zn0.2Cd0.8S/CuSbS2 was 2.44 eV, which was due to the synergistic effect of ion doping and heterojunction to improve its optical properties. The photocurrents of the ion doping and the heterojunction used alone were 0.24 mA/cm2 and 0.27 mA/cm2 at 0.9 V vs. RHE, respectively, and the photocurrent using the synergistic effect of the ion doping and the heterojunction was 0.31 mA/cm2 at 0.9 V vs. RHE. On the basis of this, the synergistic effect of the heterojunction-cocatalysts made the photocurrent 0.35 mA/cm2 at 0.9 V vs. RHE, which was 1.75 times of the initial Zn0.2Cd0.8S. Fe-Zn0.2Cd0.8S/CuSbS2/Co-Pi had the best photo-corrosion resistance, which was corroded to 94% at 6000 s, compared to Fe-Zn0.2Cd0.8S/CuSbS2 (85%) and Zn0.2Cd0.8S (78%). This multiple synergistic design not only enhances the PEC properties of Zn0.2Cd0.8S, but also expands the approach of constructing the ternary sulfide photoanode.