Abstract
Regulating the distribution of surface states at the photoanode/electrolyte interface is essential for advancing photoelectrochemical (PEC) water splitting. In this study, we systematically investigate the impact of surface hydroxyl coverage on the PEC performance of CdIn₂S₄ (CIS) photoanodes, with a particular focus on its influence on the water oxidation reaction. Our results demonstrate that an optimal level of hydroxyl coverage significantly enhances both photocurrent density and stability, with a CIS photoanode exhibiting 62.5% hydroxyl coverage and showing the highest photoresponse. Both experimental and theoretical analyses underscore the crucial role of surface hydroxyl groups in modulating the electronic structure of CIS photoanodes, leading to a regulated distribution of surface states that facilitates efficient charge transfer kinetics. Additionally, operando spectroscopic characterizations reveal that increasing hydroxyl coverage alters the water oxidation pathway, transitioning from the adsorbate evolution mechanism (AEM) to the oxide path mechanism (OPM). Thermodynamic analysis based on Gibbs free energy calculations further supports our findings, indicating that excessive hydroxyl coverage raises the kinetic overpotential for oxygen evolution. This work provides valuable insights into the role of surface hydroxyl groups in optimizing PEC performance for metal sulfide-based photoanodes and emphasizes the importance of balancing hydroxyl coverage to achieve optimal water oxidation kinetics.
Published Version
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