Thermodynamic Analysis of Syngas Production via the Solar Thermochemical Cerium Oxide Redox Cycle with Methane-Driven Reduction

The present work considers the convergence of two approaches for syngas production: solar fuels via the cerium oxide (ceria) redox cycle and the partial oxidation of methane. The chemical thermodynamics of the ceria–methane system reveal that coupling the reduction of ceria to the partial oxidation of methane enables isothermal cycling at temperatures as low as 1223 K with the additional production of high-quality syngas during the reduction step. The equilibrium non-stoichiometry of the oxidation step has a substantial impact on the conversion of the oxidizer to fuel, with important implications for cycle efficiency. A model of the process thermodynamics is used to evaluate the efficiency of the cycle and its sensitivity to oxidation non-stoichiometry, temperature, and concentration ratio. Reduction with methane enables significant gains in efficiency over other proposed approaches, with plausible solar-to-fuel efficiencies reaching 40% without any heat recovery.