The effects of morphology on the thermal reduction of nonstoichiometric ceria

A numerical heat and mass transfer model is used to study the effects of the morphological features of a porous medium composed of ceria when it is placed in a cavity and exposed to high-flux solar irradiation to drive a nonstoichiometric reduction. The morphological features are described by the porosity and pore-level Sauter mean diameter. For porosities of 0.60, 0.75, and 0.90, the rate of oxygen production and the efficiency of solar-to-chemical energy conversion increase monotonically as the Sauter mean diameter is decreased from 1000 to 30 µm. For a porosity of 0.90, these performance metrics continue to increase down to 10 µm. The primary effect of the changes in porosity and Sauter mean diameter are through their influence on the permeability and the extinction coefficient of the medium. For appropriately selected time duration, an energy conversion efficiency of 10.9% is achieved with a Sauter mean diameter of 10 µm and a porosity of 0.90.