Improving solar fuel production performance from H2O and CO2 thermochemical dissociation using custom-made reticulated porous ceria

Thermochemical CO2- and H2O-splitting cycles for sustainable fuel generation were investigated by using custom-made reticulated ceria foams integrated in a solar-heated cavity reactor. A parametric study revealed the suitable conditions to produce H2/CO with maximum fuel rates and yields per unit mass of redox material. Various operating parameters such as the total pressure during the reduction step, the gas inlet flowrates, the temperature, or the reactive gas content during the oxidation step were studied in detail. A series of on-sun experiments including more than 20 cycles under different cycling conditions were carried out with relevant performance repeatability and stability. With a ceria foam reduction temperature in the range 1400-1470 degrees C and a reduction pressure of 103 mbar, the ceria foams produced 281 mu mol of H2 and 332 mu mol of CO per gram of material during oxidation below 1000 degrees C under cooling with a maximum production rate of 3.0 mL/min.g and 10.2 mL/min.g, respectively. Direct syngas pro-duction was also evidenced during on-sun experiments with simultaneous H2O-and CO2-splitting, which yielded a H2:CO ratio ranging from 0.7 to 1.14. The dual-scale porous ceria structures were characterized using X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis to confirm material thermal stability during cycling. Finally, optimization of fuel production capacity was achieved by maximizing the total amount of ceria foam loaded into the reactor, yielding 667 mL of CO (409 mu mol/g) and 513 mL of H2 (314 mu mol/g) per cycle. A maximum solar-to-fuel efficiency of 10.1% was calculated for CO2-splitting vs. 4.9% for H2O-splitting cycle. This study thus demonstrated noteworthy fuel production performance in an efficient monolithic reactor under real concentrated solar radiation, from highly reactive customized ceria foams.(c) 2023 Elsevier Ltd. All rights reserved.