Hydrogen reactivity on highly-hydroxylated TiO2(110) surfaces prepared via carboxylic acid adsorption and photolysisElectronic supplementary information (ESI) available: (S1) H bulk diffusion energies for double-? and single-? basis sets for Ti atoms, (S2) STM movie, (S3) illustration of H bulk diffusion processes, (S4) effect of different tri-layer numbers and DFT + U on the results of H bulk diffusion, (S5) branching ratio analysis. See DOI: 10.1039/c1cp22515d

Combined scanning tunneling microscopy, temperature programmed desorption, photo stimulated desorption, and density functional theory studies have probed the formation and reactivity of highly-hydroxylated rutile TiO 2 (110) surfaces, which were prepared via a novel, photochemical route using trimethyl acetic acid (TMAA) dissociative adsorption and subsequent photolysis at 300 K. Deprotonation of TMAA molecules upon adsorption produces both surface bridging hydroxyls (OH b ) and bidentate trimethyl acetate (TMA) species with a saturation coverage of nearly 0.5 monolayers (ML). Ultra-violet light irradiation selectively removes TMA species, producing a highly-hydroxylated surface with up to ~0.5 ML OH b coverage. At high coverages, the OH b species typically occupy second-nearest neighbor sites along the bridging oxygen row locally forming linear (2 1) structures of different lengths, although the surface is less ordered on a long scale. The annealing of the highly-hydroxylated surface leads to hydroxyl recombination and H 2 O desorption with ~100% yield, thus ruling out the diffusion of H into the bulk that has been suggested in the literature. In agreement with experimental data, theoretical results show that the recombinative H 2 O desorption is preferred over both H bulk diffusion and H 2 desorption processes. Annealing of highly-hydroxylated TiO 2 (110) surfaces leads to hydroxyl recombination and H 2 O desorption rather than H diffusion into the bulk or H 2 desorption.