Solar-Driven Redox Splitting of CO2 Using 3D-Printed Hierarchically Channeled Ceria Structures

Fuel produced from CO2 and H2O using solar energy can contribute to making aviation more sustainable. Particularly attractive is the thermochemical production pathway via a ceria-based redox cycle, which uses the entire solar spectrum as the source of high-temperature process heat to directly produce a syngas mixture suitable for synthetizing kerosene. However, its solar-to-fuel energy efficiency is hindered by the inadequate isotropic topology of the ceria porous structure, which fails to absorb the incident concentrated solar radiation within its entire volume. This study presents the design and 3D-print of hierarchically channeled structures of pure ceria by direct ink writing (DIW) to enable volumetric radiative absorption while maintaining high effective densities required for maximizing the fuel yield. The complex interplay between radiative heat transfer and thermochemical reaction is investigated in a solar thermogravimetric analyzer with samples exposed to high-flux irradiation, mimicking realistic operation of solar reactors. Channeled structures with a stepwise optical thickness achieve a higher and more uniform temperature profile compared to that of state-of-art isotropic structures, doubling the volume-specific fuel yield for the same solar flux input. Thermomechanical stability of the ceria graded structures, DIW-printed using a novel ink formulation with optimal rheological behavior, is validated by performing 100 consecutive redox cycles.