Converting Undesirable Defects into Activity Sites Enhances the Photoelectrochemical Performance of The ZnIn₂S₄ Photoanode

Abstract Heteroatom doping can tune the band structure of semiconductors and enhance their carrier transfer capacity for improving the performance of photoelectrochemical water oxidation. Nevertheless, the introduction of dopants is not always beneficial. In this study, magnesium (Mg) is adopted to dope ZnIn₂S₄ nanosheet array photoanodes to form a type‐II band structure and reduce bulk recombination, but concurrently introduced deleterious oxygen (O) defects slow down the surface catalytic reaction kinetics. Furthermore, a facile heat treatment strategy is proposed to transform these O defects into Mg─O bonds. First‐principles calculations and electrochemical characterization indicate that the presence of Mg─O bonds provides abundant active sites and efficiently accelerates the surface oxygen evolution reaction by precisely realigning the rate‐determining step from OH* to O* (step 2) to OOH* to O₂ (step 4), thereby retarding charge trapping and recombination. As a result, such a photoanode achieves a remarkable performance with a photocurrent as high as 4.91 mA cm⁻² at 1.23 V versus reversible hydrogen electrode, and the onset potential shifts negatively about 340 mV. This work provides a new defect modulation idea for converting detrimental defects to favorable ones, and it can be expected to have wide applications in the fields of energy, catalysis, and optoelectronics, etc.