Edge‐Sharing Octahedrally Coordinated NiFe Dual Active Sites on ZnFe2O4 for Photoelectrochemical Water Oxidation

Abstract

AbstractThe structural properties of octahedral sites (BOh) in spinel oxides (AB2O4) play vital roles in the electrochemical performance of oxygen‐related reactions. However, the precise manipulation of AB2O4 remains challenging due to the complexity of their crystal structure. Here, a simple and versatile molten‐salt‐mediated strategy is reported to introduce Ni2+ in Boh sites intentionally on the surface of zinc ferrite (ZnFe2O4, ZFO) to promote the active sites for photoelectrochemical (PEC) water splitting. The as‐created photoanode (ZFO‐MSNi) shows a remarkable cathodic shift of ≈ 450 mV (turn‐on voltage of ≈ 0.6 VRHE) as well as three times the 1‐sun photocurrent density at 1.23 VRHE for PEC water oxidation in comparison with bare ZFO. A comprehensive structural characterization clearly reveals the local structure of the introduced Ni2+ in ZFO‐MSNi. Fewer surface trapping states are observed while the precisely introduced Ni2+ and associated neighboring Fe(3‐σ)+ (0<σ<1) sites unite in an edge‐sharing octahedral configuration to function as NiFe dual active sites for PEC water oxidation. Moreover, open circuit potential measurements and rapid‐scan voltammetry investigation give further insight into the enhanced PEC performance. Overall, this work displays a versatile strategy to regulate the surface active sites of photoelectrodes for increasing performance in PEC solar energy conversion systems.