Theoretical Study On Modification Of TiO₂Nanotube Arrays And Its Photocatalytic Activity For Water Splitting

Photocatalytic water splitting into hydrogen and oxygen by utilizingsolar energy is regarded as an effective strategy to solve fuel crisis andenvironmental pollutions. Therefore, exploring hydrogen production undersolar irradiation has attracted enormous interests. TiO₂nanotube array notonly inherits the unique electronic properties of nano TiO₂, but alsopossesses confinement effects of nanochannel, which was considered as apromising photocatalyst. In this dissertation, based on density functionaltheory （DFT） calculations, taking TiO₂nanotube array as fundamentalmodel system, we investigated the effects of metal deposition andnonmental doping on photocatalytic water splitting, in theory, found aneffective catalytic material for water splitting.For N–doped TiO₂nanotube array, our studies show that the impurity2p state of doping nitrogen at the band gap region effectively changes theelectronic structure of TiO₂nanotube array, acting as an electron acceptorand transferring photon or electron from TiO₂nanotube array to substratemolecules. Furthermore, the activation processes of four elementary steps for water splitting were investigated. The thermodynamic results of fourelementary steps exhibit that the overpotential of water splitting onN–doped TiO₂nanotube array is nearly the same as that on the pristine one.Based on the transition states studies and thermodynamic propertiesanalyses, we found that the rate–determining step is the HOO*formationfrom the reaction of oxygen and the second H₂O.We further investigated water splitting properties on the Pt depostionand Pt deposition/N–doped TiO₂nanotube array. The electronic structuresof Pt deposition/N–doping reveal that the bond between Pt and N appears–1.0eV below the Fermi level, antibond between Ti and N locates abovethe Fermi level. Based on thermodynamic properties analyses, our studiesshow that for Pt deposition, the overpotential of water oxidation reaction is1.09V, which is almost the same as that of perfect TiO₂nanotube array.For Pt deposition/N–doping, the overpotential of water splitting is the least,compared with the previously studied systems including perfect, N–doped,and Pt depostion TiO₂nanotube array. Water oxidation reaction becomesmuch easier, which attributes to the synergistic effects between Pt and N.These studies are consistent with experimental reports and can provide away for designing effect catalysts for water splitting.