Platinum Group Metal Catalyst (RuOx, PtOx, and IrOx)-Decorated Ceria-Zirconia Solid Solution as High Active Oxygen Carriers for Solar Thermochemical CO2 Splitting

Ceria substituted with zirconium (Ce1-xZrxO2) is a promising material in two-step thermochemical CO2/H2O splitting cycles due to its great oxygen storage capacity and potential fuel production. However, the Ce1-xZrxO2 solid solution exhibits a relatively slower fuel release rate than cerium oxide alone. Herein, in order to improve the solar-to-fuel energy conversion efficiency, noble metal catalysts (RuOx, PtOx, and IrOx) are used to boost the CO release rate of Ce-0.85Zr0.15O2 (CZ15)-based two-step thermochemical CO2 splitting. Compared with intrinsic Ce0.85Zr0.15O2, the maximal CO release rate can be increased by 35% after loading 0.4 atom % IrOx as a catalyst on the surface of Ce0.85Zr0.15O2. Interestingly, the initial CO release rate can be increased by three times when a small amount of IrOx (1.0 atom %) is doped into the crystal structure of Ce0.85Zr0.15O2 through a solution combustion method. This catalytic effect is ascribed to the increased mixed ionic and electric conductivity within the ceramic bulk and the enhanced chemical reaction rate at the gassolid interface for iridium-decorated ceria-zirconia solid solution. Our work demonstrates that interface engineering and bulk modification through adding the selected catalyst can effectively enhance the CO2 splitting rate of Ce1-xZrxO2 oxygen carriers, which provides a promising strategy to promote the fuel release rates of other kinetics-restricted thermochemical CO2/H2O splitting cycles.