Water Oxidation over Au-Pd/TiO$_2$ as a Substitute for Iridium-Based Catalysts

Water oxidation is one of the most important reactions needed for a transition to a green economy. The reaction relies on extracting electrons from oxygen anions and is commonly studied using homogenous catalysts based on Ru or Ir metals. Because of Ir scarcity and its relative instability in acidic environments, metals to replace it are sought after. In this study, we have synthesized Au-Pd-based catalysts deposited on TiO$_2$ with different ratios in order to mimic IrO$_2$ valence orbitals (Ir5d) by the hybrid valence orbitals of Au5d and Pd4d and compared their heterogeneous catalytic activity for the evolution of O$_2$ from water in the presence of cerium ammonium nitrate (CAN). Au-Pd-based catalysts were found to be active at a particular nominal atomic ratio. At an atomic ratio of 1 Au to 2 Pd and 1 Au to 3 Pd, the catalysts were active and stable for oxygen production from water. Long-term runs up to 20,000 min still showed the expected stoichiometry between O$_2$ production and CAN consumption (1 to 4). However, catalysts with a reverse ratio were not active. Also, the monometallic catalysts were found to be not active for the reaction. ... mehrWe link the reason for the activity of Au-Pd with this specific ratio to the shape and energy position of their valence band that might be similar to those of IrO$_2$ particles. While the turnover numbers of the Au-Pd-based catalysts were found to be lower than those of IrO$_2$-based catalysts, on the same support in a heterogenous system, there is considerable potential upon further optimization for these two metals to replace IrO$_2$ for a water oxidation reaction.