Edge-Sharing Octahedrally Coordinated Ni?Fe Dual Active Sites on ZnFe2O4 for Photoelectrochemical Water Oxidation

The structural properties of octahedral sites (B Oh ) in spinel oxides (AB 2 O 4 ) play vital roles in the electrochemical performance of oxygen-related reactions. However, the precise manipulation of AB 2 O 4 remains challenging due to the complexity of their crystal structure. Here, a simple and versatile molten-salt-mediated strategy is reported to introduce Ni 2+ in B oh sites intentionally on the surface of zinc ferrite (ZnFe 2 O 4 , 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 V RHE ) as well as three times the 1-sun photocurrent density at 1.23 V RHE for PEC water oxidation in comparison with bare ZFO. A comprehensive structural characterization clearly reveals the local structure of the introduced Ni 2+ in ZFO-MSNi. Fewer surface trapping states are observed while the precisely introduced Ni 2+ 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.