Using Elementary Surface Reaction Kinetics to Probe Surface Concentrations of Photoexcited Charges on TiO ₂

Solar-driven photocatalysis offers a promising route to renewable energy; its overall efficiency hinges on the creation, separation, and eventual consumption of photoexcited charges within nanostructured photocatalysts. While substantial efforts have clarified charge dynamics in the bulk, the quantitative assessment of charges that actually reach the surface, those directly driving redox reactions, remains a major scientific challenge. In this Perspective, we highlight the use of an elementary reaction kinetic analysis method employing methanol as a molecular probe to quantify surface-reaching charges in diverse photocatalytic particle systems. By integrating insights into surface-reaching charge concentrations obtained through this kinetic approach and their correlation with charge separation dynamics and the influence of surface/interface structures, this Perspective aims to guide the rational design of next-generation photocatalysts for more precise regulation and efficient utilization of photogenerated charges.