Enhancement of the O 2 or H 2 photoproduction rate in a Ce 3+/Ce 4+–TiO 2 system by the TiO 2 surface and structure modification

Abstract

The effect of structural and surface changes in the suspended TiO 2 on the dioxygen and dihydrogen evolution rates was studied with the purpose to improve photogenerated charges utilization efficiency for future solar light water splitting systems which use reversible inorganic electron relays. Prepared rutile and anatase catalysts are characterized by N 2 adsorption–desorption measurements, X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was discovered that the dioxygen photoproduction rate from the Ce 4+-containing TiO 2 suspension increased linearly with the rutile specific surface area. A further increase in the O 2 generation rate provides a modification of TiO 2 surface with Pt. Photodeposition (PD) of Pt resulted in a higher O 2 evolution rate than Pt deposition by soft chemical reduction (SCR). The highest photocatalytic activity at pH equal to 0.4 was obtained for 1 wt.% Pt/TiO 2 Degussa P25 platinized by PD. In contrast to O 2, the H 2 photocatalytic production from the Ce 3+-containing TiO 2 suspension solution was faster over Pt/TiO 2 prepared by SCR. Uniform coverage of the TiO 2 surface with Pt particles turned out to be more important for the H 2 generation than rather for the O 2 one. A lower quantum efficiency of the H 2 generation associated with the low Ce 3+ surface coverage on Pt/TiO 2 was attempted to be improved by treating TiO 2 surface with inorganic acids. Sulfuric acid increased the rate by 20% while phosphoric and hydrofluoric acids did not. The best photocatalytic dihydrogen production catalyst at pH equal to 1.0 was found to be 1 wt.% Pt/Degussa P25 prepared by SCR and treated with H 2SO 4. The results demonstrate that the bulk structure (phase composition), morphology (surface area), as well as the surface morphology (Pt distribution) and composition (acid additives) are all important for the O 2 and H 2 photogeneration in the separate TiO 2—suspended based.