Computational and experimental studies on the effect of hydrogenation of Ni-doped TiO₂ anatase nanoparticles for the application of water splitting

We have studied theoretically and experimentally the effect of Ni-doping in TiO₂ nanoparticles (NPs) on hydrogenation. The doped NPs can be hydrogenated readily in a much shorter time at T < 623 K under near atmospheric H₂ pressure. The hydrogenated black NP films exhibit a broad UV-Vis absorption extending well beyond 800 nm. The experimental data can be corroborated by quantum calculations. The barriers for dissociative adsorption of H₂ at the Ni and O_2c sites on the 2Ni-doped TiO₂ surface are significantly reduced from 48 kcal mol^-1 on the undoped surface to 17 and 12 kcal mol^-1, respectively. The computed densities of states of the doped TiO₂ also show new absorption peaks in the band-gaps of the hydrogenated systems which exhibit a high efficiency of solar water-splitting over those of non-hydrogenated samples based on our preliminary study. The theoretical result also indicates that Ni-doping significantly affects the enthalpies of hydrogenation for formation of 2HO(b) and H₂O(b) in the bulk from 7 and 19 kcal mol^-1 in the undoped TiO₂ to -76 and -69 kcal mol^-1 in the 2Ni-TiO₂ system, respectively, with a > 80 kcal mol^-1 increase in exothermicities.