Nonstoichiometric metal oxides with variable valence are attractive redox materials for thermochemical and electrochemical fuel processing.

Porous structures made of redox active ceria are attractive for high‐temperature concentrating solar applications and particularly for the thermochemical splitting of H2O and CO2 as their enhanced heat and mass transport properties lead to fast reaction rates, especially with regard to the absorption of concentrated solar radiation during the endothermic reduction step. Hierarchically ordered porous structures, fabricated by the Schwartzwald replica method on 3D‐printed polymer scaffolds, are experimentally assessed for their ability to volumetrically absorb high‐flux irradiation of up to 670 suns. Temperature distributions across the porosity‐gradient path are measured (peak 1724 K) and compared with that obtained for a reticulated porous ceramic (RPC) structure with a uniform porosity. To assist the analysis, a Monte Carlo ray‐tracing model is developed for pore‐level numerical simulations of the ordered geometries and applied to analyze the absorbing–emitting–scattering exchange and determine the radiation attenuation and the temperature distribution at a radiative equilibrium. In contrast to the Bouguer's law exponential‐decay attenuation of incident radiation observed for the RPC, the ordered structures with a porosity gradient exhibit a step‐wise radiative attenuation that leads to a more uniform temperature distribution across the structure. This in turn predicts a superior redox performance.

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