Abstract
Porous ceria-based architected materials offer high potential for solar fuels production via thermochemical H 2 O and CO 2-splitting cycles. Novel porous morphologies and micro-scale architectures of redox materials are desired to provide suitable thermochemical activities and long-term stability. Considering particle-based solar reactors, porous ceria microspheres are promising because of their excellent flowability and large surface area. In this work, such porous microspheres with perfect spherical shape, high density and interconnected pore network were fabricated by a chemical route involving ion-exchange resins. The method involved the cationic loading of the resin in aqueous medium followed by thermal treatment for oxide formation and porous microstructure stabilization. The utilization of these microspheres (~150-350 µm in size) as redox materials for solar fuel production was investigated in packed-bed solar reactors (directly and indirectly-irradiated). Superior redox performance was obtained for the pure ceria microspheres in comparison with other morphologies (powders and reticulated foams). Low p O2 values thermodynamically favored the reduction extent and associated fuel yield, whereas high p CO2 kinetically promoted the oxidation rate. The highest fuel production rate reached 1.8 mL/min/g with reduction step at 1400°C and low total pressure (~0.1 bar), and oxidation step below 1050°C under pure CO 2. Low pressure during reduction both improved reduction extent (oxygen under-stoichiometry up to 0.052) and associated fuel production yield (331 µmol/g CO). After 19 redox cycles (~32h under high-flux solar irradiation), the porous microspheres maintained their individual integrity (no agglomeration), spherical shape, and internal porosity, with great potential for stable fuel production capacity in particle-based solar reactors.