Temperature Dependence of Photocatalytic Water Splitting under Visible Light Irradiation over Ir- and Sb-Codoped SrTiO3:Al

Abstract

Temperature dependence of photocatalytic water splitting over CrO_x/Rh and CoOOH cocatalyst-coloaded SrTiO₃:Al codoped with Ir and Sb single-particulate photocatalysts (CrO_x/Rh/SrTiO₃:Ir,Sb,Al/CoOOH) under visible light irradiation was investigated. When the reaction temperature was increased from 280 to 340 K, the activity became low, and degradation became significant. Moreover, the activity was partially revived with lowering reaction temperature from 340 to 290 K. These results suggest that reversible and irreversible negative factors worked with rising reaction temperature. The temperature dependence was caused by the working of the negative factors such as the irreversible degradation of photocatalyst · cocatalyst and the reversible increase of recombination probability of photogenerated carriers more than the positive factor such as increasing the rate of surface reaction. X-ray photoelectron spectra revealed that detachment and/or aggregation of CoOOH loaded on SrTiO₃:Ir,Sb,Al brought the irreversible degradation of the photocatalyst material at 340 K. In contrast to it, the change of a CrO_x shell in the CrO_x/Rh cocatalyst was not observed, suggesting that the reverse reactions to form water from evolved H₂ and O₂ and to reduce O₂ were not enhanced even though reaction temperature was risen. On the other hand, the photoluminescence intensity of Eu³⁺ as a guest doped to SrTiO₃:Ir,Sb,Al as a host due to band gap excitation of SrTiO₃ became low with rising reaction temperature, suggesting that the recombination probability as a nonradiative deactivation of photogenerated carriers in the host of SrTiO₃ increased. Therefore, it was suggested that the negative factors such as degradation of a CoOOH cocatalyst and increasing recombination probability of photogenerated carriers caused the decrease of the photocatalytic water-splitting activity of CrO_x/Rh/SrTiO₃:Ir,Sb,Al/CoOOH.