A oxygen vacancy-modulated homojunction structural CuBi2O4 photocathodes for efficient solar water reduction

Abstract

The photoelectrochemical (PEC) water reduction performance of CuBi₂O₄ (CBO)-based photocathodes is still far from their theoretical values due to low bulk and surface charge separation efficiencies. Herein, we propose a regrowth strategy to prepare a photocathode with CBO coating on Zn-doped CBO (CBO/Zn-CBO). Furthermore, NaBH₄ treatment of CBO/Zn-CBO introduced oxygen vacancies (O_v) on CBO/Zn-CBO. It was found that Zn-doping not only increases the charge carrier concentration of CBO, but also leads to appropriate band alignment to form homojunctions. This homojunction can effectively promote the separation of electron–hole pairs, thus obtaining excellent photocurrent density (0.5 mA cm⁻² at 0.3 V vs. RHE) and charge separation efficiency (1.5 times than CBO). The following surface treatment induced O_v on CBO/Zn-CBO, which significantly increased the active area of the surface catalytic reaction and further enhanced the photocurrent density (0.6 mA cm⁻²). In the absence of cocatalysts, the electron injection efficiency of O_v/CBO/Zn-CBO was 1.47 times improved than that of CBO. This work demonstrates a homojunction photocathode with O_v modulation, which provides a new view for future photoelectrochemical water splitting.