Primary Intermediates of Oxygen Photoevolution Reaction on TiO₂ (Rutile) Particles, Revealed by in Situ FTIR Absorption and Photoluminescence Measurements

Abstract

Primary intermediates of oxygen photoevolution (water photooxidation) reaction at the TiO2 (rutile)/aqueous solution interface were investigated by in situ multiple internal reflection infrared (MIRIR) absorption and photoluminescence (PL) measurements. UV irradiation of TiO2 in the presence of 10 mM Fe3+ in the solution caused the appearance of a new peak at 838 cm(-1) and a shoulder at 812 cm(-1). Detailed investigations of the effects of solution pH, the presence of methanol as a hole scavenger, and isotope exchange in water (H2(16)O-->H2(18)O) on the spectra have shown that the 838- and 812-cm(-1) bands can be assigned to the O-O stretching mode of surface TiOOH and TiOOTi, respectively, produced as primary intermediates of the oxygen photoevolution reaction. The results give strong support to our previously proposed mechanism that the oxygen photoevolution is initiated by a nucleophilic attack of a H2O molecule on a photogenerated hole at a surface lattice O site, not by oxidation of surface OH group by the hole. The conclusion is supported by PL measurements. A plausible reaction scheme is proposed for the oxygen photoevolution on TiO2 (rutile) in aqueous solutions of pH less than about 12.

Towards a Molecular Level Understanding of the Multi-Electron Catalysis of Water Oxidation on Metal Oxide Surfaces

“…Because of the built-in light absorption property, these systems offer the most straightforward approach for elucidating the elementary steps of charge transport across the oxide bulk to the catalyst surface and the subsequent processes that induce chemical reaction. In the case of films of TiO 2 (rutile) particles (30-50 nm) exposed to aqueous solution under UV excitation, in situ steady state FT-IR spectroscopy in the ATR mode has revealed two surface intermediates, namely TiOOH and TiOOTi [74]. Figure 14a shows the growth of the O-O stretch mode of the hydroperoxide intermediate (TiOOH) with a maximum at 838 cm -1 in acidic solution (pH 2.4) under continuous photolysis.…”

Water adsorption on rutile TiO2(110) for applications in solar hydrogen production: A systematic hybrid-exchange density functional study

“…This analysis of the electronic structure provides some insight into the reaction that controls the water oxidation process, known as the oxygen evolution reaction (OER), [81][82][83] in TiO 2 water splitting devices. The overall equation for the oxidation of H 2 O to O 2 on the TiO 2 surface is…”

Improving O2 production of WO3 photoanodes with IrO2 in acidic aqueous electrolyte

“…30,31 Even in acidic conditions, some photocorrosion of WO 3 has been observed due to the formation of peroxo-species as intermediates during water oxidation. [22][23][24]32 Although peroxide formation and the oxidation of most acid counterion species are reactions that are thermodynamically less feasible than water oxidation, the kinetics of these reactions are often more favorable than oxygen evolution. 14 The photogenerated minority-carrier holes in the valence band of WO 3 have a potential of B2.97 V vs. NHE at pH 0.…”