Synergetic effect of dual cocatalysts in photocatalytic H2 production on Pd-IrOx/TiO2: a new insight into dual cocatalyst location

Introducing appropriate dual cocatalysts is one of the most efficient strategies to improve the photocatalytic activity. Herein, we investigated the promotion effect of dual cocatalysts on TiO2 for hydrogen production. Compared with the Pd/TiO2 and Ir/TiO2 with the individual cocatalyst, TiO2 coloaded with Pd and Ir species exhibited an obviously enhanced H-2 production activity and reduced CO/H-2 ratio. XPS and IR spectra of CO adsorption analysis indicated that the dual cocatalysts on TiO2 were actually composed of Pd-0 and partially oxidized IrOx, which acted as the reduction and oxidation cocatalysts, respectively. Interestingly, EDX elemental mappings of Pd and Ir indicated that the two elements on TiO2 were inclined to depositing together. The synergetic effect of reduction and oxidation cocatalysts with their intimate contact is proposed to contribute to the high H-2 production activity, which is different from the common view that the reduction and oxidation sites should be spatially separated to avoid the charge recombination.