Improving the efficiency of a ceria reduction-oxidation cycle through the choice of operating conditions and ceria morphology

Abstract

Pathways for improving the efficiency of ceria-based thermochemical cycling for solar-driven fuel production are investigated. First, the operating conditions of an isothermal CO₂ splitting cycle are optimized to improve process efficiency. The optimum conditions are a sweep gas flow rate of 150 mL min<super>-1</super> g<super>-1</super>, a CO₂ flow rate of 50 mL min<super>-1</super> g<super>-1</super>, a reduction time of 100 s, and an oxidation time of 155 s. A quasi-equilibrium model is developed to predict the rates of ceria reduction and oxidation. Finally, a new ceria morphology, wood templated ceria, is used to improve the heterogeneous oxidation reaction rates by maintaining a high surface area when exposed to the extreme temperatures required for ceria reduction. Wood templated ceria performs well at reduction temperatures up to 1400 &deg;C, reaching peak CO production rates of 9 mL min<super>-1</super> g<super>-1</super>, but rates decrease due to sintering when it is reduced at 1500 &deg;C.