Photoexcited Hole and Electron-Polaron Entangled Photocatalytic Reaction on Metal Oxide Surface

Analyzing dynamics at both temporal and spatial scales of surface photocarrier interactions is pivotal for optimizing the photocatalytic chemical activity. Taking the photocatalytic conversion of CH3OH to HCOOCH3 on TiO2 surface as a prototypical system, we elucidate the correlated time- and spatial- evolution of photoexcited electron-hole (e-h) pairs, defining the polaron-catalyzed molecule-surface chemistry at the ab initio theory level. The photocatalytic process is driven by two photoexcited holes, each inducing C-H bond cleavage via a proton coupled electron transfer (PCET). It leads to the formation of HCOOCH3, with a pair of protons adsorbed on bridge oxygen atoms and the release of two electrons, forming two small polarons. The entire reaction occurs on picosecond timescale. Photoexcited electrons do not directly participate in the reaction but form small polarons in TiO2 within tens of femtoseconds, which lowers reactant energy and suppress the photocatalytic efficiency. This study illuminates novel insights on the design and optimization of surface photocatalytic reactions.