Pt Single Atoms on TiO₂ Can Catalyze Water Oxidation in Photoelectrochemical Experiments

Photoelectrochemical water splitting on n-type semiconductors is highly dependent on catalysis of the rate-determining reaction of O₂ evolution. Conventionally, in electrochemistry and photoelectrochemistry O₂ evolution is catalyzed by metal oxide catalysts like IrO₂ and RuO₂, whereas noble metals such as Pt are considered unsuitable for this purpose. However, our study finds that Pt, in its single-atom form, exhibits exceptional cocatalytic properties for photoelectrochemical water oxidation on a TiO₂ photoanode, in contrast to Pt in a nanoparticle form. The decoration of Pt single atoms onto TiO₂ yields a remarkable current density of 5.89 mA cm^-2 at 1.23 V_RHE, surpassing bare TiO₂ (or Pt nanoparticle decorated TiO₂) by 2.52 times. Notably, this enhancement remains consistent over a wide pH range. By accompanying theoretical work, we assign this significant enhancement to an improved charge transfer and separation efficiency along with accelerated kinetics in the oxygen evolution reaction facilitated by the presence of Pt single atoms on the TiO₂ surface.