Polaron-Adsorbate Coupling at the TiO2(110)-Carboxylate Interface

Understanding how adsorbates influence polaron behavior is of fundamental importance in describing the catalytic properties of TiO2. Carboxylic acids adsorb readily at TiO2 surfaces, yet their influence on polaronic states is unknown. Using UV photoemission spectroscopy (UPS), two-photon photoemission spectroscopy (2PPE), and density functional theory (DFT) we show that dissociative adsorption of formic and acetic acids has profound, yet different, effects on the surface density, crystal field, and photoexcitation of polarons in rutile TiO2(110). We also show that these variations are governed by the contrasting electrostatic properties of the acids, which impacts the extent of polaron-adsorbate coupling. The density of polarons in the surface region increases more in formate-terminated TiO2(110) relative to acetate. Consequently, increased coupling gives rise to new photoexcitation channels via states 3.83 eV above the Fermi level. The onset of this process is 3.45 eV, likely adding to the catalytic photoyield.

Automated summary

This study demonstrates the profound and differing effects of the dissociative adsorption of formic and acetic acids on the surface density, crystal field, and photoexcitation of polarons in rutile TiO2(110). The contrasting electrostatic properties of the acids govern the extent of polaron-adsorbate coupling, leading to new photoexcitation channels and potentially increasing the catalytic photoyield. The density of polarons in the surface region increases more in formate-terminated TiO2(110) compared to acetate, with potential implications for catalytic activity.