Activating Solar Water Oxidation Ability of ZnFe2O4 Photoanodes through Quasi-reversible Oxygen-Sulfur Anion Exchange

Abstract

The octahedral structure motif in spinel oxides photoelectrodes is usually recognized as a crucial factor for charge carriers transportation, which can directly influence the performance of oxygen-related photoelectrochemical (PEC) reactions at the electrode/electrolyte interface (EEI). Here in this work, a quasi-reversible oxygen-sulfur (O-S) exchange strategy is provided through facile anion exchange reaction followed by photo-assisted cyclic voltammetry (photo-CV) treatment to manipulate the FeO₆ octahedral structure motif in spinel zinc ferrite (ZnFe₂O₄) photoanodes. The obtained ZnFe₂O_4–xS_x photoanodes with FeO_6−xS_x units in bulk phase and activated FeO₆ units in surface region exhibit excellent PEC performance for water oxidation, delivering ≈2 orders of magnitude higher photocurrent density at 1.23 V vs. the reversible hydrogen electrode (V_RHE) compared to ZnFe₂O₄ photoanodes under AM 1.5G illumination. Additionally, the kinetics of water oxidation reaction on ZnFe₂O_4–xS_x photoanodes is further improved upon loading NiFeO_x cocatalyst, reaching a photocurrent density of 1.1 mA cm⁻² at 1.23 V_RHE, which ranks at the highest level among reported literature. This work opens up a new approach to facilitate the charge carriers’ transportation in spinel oxides and advances the solar water splitting performance of ZnFe₂O₄ photoanodes for application in relevant PEC devices.