Probing Charge Carrier Behavior in Engineered Photocatalysts with Time-Resolved Visible to Mid-IR Absorption Spectroscopy

Light-induced catalytic reactions on the photocatalyst surface are initiated by excited charge carriers. Therefore, the observed photocatalytic behavior is sensitive to the charge carrier behavior. In this regard, understanding charge carrier behavior is important to help us more efficiently improve the photocatalytic activity, which is often limited by unfavorable charge carrier dynamics and poor charge carrier management. In this review, we discuss how charge carrier behavior is elucidated in a diverse array of photocatalytic systems with time-resolved visible to mid-IR absorption spectroscopy (TRVIR) to reveal the reason behind their high activity. TRVIR is a promising technique that combines a visible-NIR probe and a near-mid-IR probe to characterize the behavior of both electron and hole. Interpretation of TRVIR spectra is described in sufficient detail here to shed light on how charge carriers behave upon structural modifications, thereby allowing one to foresee proper modifications for future photocatalysts. Perspectives are then presented to stimulate further discussions.