Study of the Mechanism of Water Splitting on UV-Irradiated Rh/TiO2

Water cleavage induced by uv-irradiation of Rh/TiO 2 samples has been studied in gas/solid and liquid/solid interfaces. E.p.r. and electrical conductivity show an easy transfer of electrons at the metal-TiO 2 interface in the presence of H 2 while O 2 oxidizes the metal and suppress H 2 photo-generation but not oxygen photo-adsorption. Only H2 evolution occurs, in an autocatalytic process, from irradiated suspensions of the sample in 1M NaOH solutions. The presence of O 2 readily suppress this H 2 generation while O 2 photo-uptake is observed. A mechanism is proposed for the process that involves photo-chemical generation of H 2 and H 2 O 2 and thermal (dark) decomposition of the latter catalysed by the metal which is progresively oxidized to Rh 2 O 3 xH 2 O.