Potential-driven reaction order transitions of water oxidation on hematite photoanodes

Understanding the potential-dependent kinetics of photoelectrochemical (PEC) reactions is crucial for advancing the catalytic applications, particularly for water oxidation. This dependency arises because the accumulation of photogenerated charges, directly influenced by the applied potential, fundamentally dictates the intrinsic limitation of slow charge transfer rates. In this study, we investigated the water oxidation on hematite photoanodes with {012} facets exposed, analyzing the reaction kinetics under light and dark conditions. We found a direct correlation between the applied potential and the reaction mechanism, evidenced by a notable transition in the apparent reaction order which shifted from the 2nd- to the 4th- and then to the quasi-4th-order. This observed kinetic transition is specifically linked to the potential-driven changes in the termination and coverage of the surface oxyl intermediates.