Defective Fe3+ self-doped spinel ZnFe2O4 with oxygen vacancies for highly efficient photoelectrochemical water splitting

Abstract

Defective Fe³⁺ self-doped spinel ZnFe₂O₄ with abundant oxygen vacancies, (Zn_1−xFe_x)Fe₂O_4−y, was successfully synthesized via a simple spin-coating method and subsequent hydrogen reduction treatment. It displays a photocurrent density of 0.22 mA cm⁻² at 1.23 (V vs. RHE), which is 11 times higher than that of pure ZnFe₂O₄. The largely enhanced photoelectrochemical (PEC) performance can be mainly ascribed to the synergism of the numerous oxygen vacancies and self-doped Fe³⁺, which has never been discussed carefully. Self-doped Fe³⁺ can be beneficial for increasing the charge carrier densities, while oxygen vacancies can improve the charge mobility and prompt the charge transfer process at the electrolyte interface, leading to improved electric conductivities and faster water oxidation kinetics. Furthermore, the effects of the concentrations of Fe³⁺ self-doping as well as oxygen vacancies on the PEC activities of ZnFe₂O₄ were also investigated. This work develops a novel and effective strategy to solve the critical problems existing in ZnFe₂O₄ for PEC applications and sheds light on the rational design of photoanode materials for efficient PEC water splitting.