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 FeO 6 octahedral structure motif in spinel zinc ferrite (ZnFe 2 O 4 ) photoanodes. The obtained ZnFe 2 O 4–x S x photoanodes with FeO 6−x S x units in bulk phase and activated FeO 6 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 ZnFe 2 O 4 photoanodes under AM 1.5G illumination. Additionally, the kinetics of water oxidation reaction on ZnFe 2 O 4–x S 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 ZnFe 2 O 4 photoanodes for application in relevant PEC devices.