S-scheme assisted Cu2O/ZnO flower-shaped heterojunction catalyst for breakthrough hydrogen evolution by water splitting

Abstract

Zinc and copper are considered as excellent metals for oxidation and reducibility, respectively. This study aims to obtain a redox-coupled composite semiconductor, wherein oxides of Zn and Cu were obtained and junctioned, for application as a photocatalyst in hydrogen production. To create a large number of activated sites on the catalyst's surface, the morphologies of the catalysts were controlled and several angular parts were formed. During the junction process, Cu2O and ZnO particles were controlled in cubic and starfish shapes, respectively, and the structure of the junctioned Cu2O/ZnO composite was similar to that of a chrysanthemum flower. Kubelka–Munk and Mott–Schottky plots demonstrated that ZnO and Cu2O have band gaps of 3.2 and 1.9 eV, respectively, and they are n- and p-type semiconductors, respectively. The TRPL and IMVS, as well as the photocurrent density and IMPS, confirmed that the recombination between electrons and holes in the junctioned Cu2O/ZnO particles was very slow, and effective charge separation was achieved. As a result, the amount of hydrogen generated from the junction catalyst was significantly higher than that generated from the single catalysts. In particular, the accumulated amount of evolved hydrogen after 10 h in the 2Cu2O/1ZnO junction catalyst was 2089.5 μmol. Results obtained from spin-trapping ESR experiments suggest that the charge-transfer mechanism in the redox-coupled 2Cu2O/1ZnO junction catalyst follows the S-scheme with a stronger reducing power.