Edge-Sharing Octahedrally Coordinated NiFe Dual Active Sites on ZnFe2 O4 for Photoelectrochemical Water Oxidation.

The structural properties of octahedral sites (BOh ) in spinel oxides (AB2 O4 ) play vital roles in the electrochemical performance of oxygen-related reactions. However, the precise manipulation of AB2 O4 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 (ZnFe2 O4 , 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.

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