Reactivity and Efficiency of Ceria-Based Oxides for Solar CO₂ Splitting via Isothermal and Near-Isothermal Cycles

In this work, different doping strategies for ceria were investigated in isothermal and near-isothermal cycles for solar fuel production. The system efficiency was evaluated by a more realistic model with the whole oxidation process concerned. In terms of fuel productivity, doping ions with lower valences seems to be a disadvantageous strategy due to formation of inert oxygen vacancies. Zr doped ceria exhibited the highest productivity under all of the reaction conditions investigated. The efficiency comparison of pure and Zr doped ceria is different from theoretical prediction, and the influence of oxidation rate is highlighted. The advantage of higher productivity caused by adding Zr is traded off by its drawbacks in kinetics for isothermal cycles at 1300 and 1400 °C. Benefit in efficiency only could be observed in an isothermal cycle at 1500 °C. Compared to the isothermal cycle, the near-isothermal cycle with a small temperature swing showed improvement in both fuel productivity and efficiency. Pure ceria showed better performance than 10% Zr doped ceria in 1500 °C/1300 °C near-isothermal cycles.