Two-step CO2 and H2O splitting using perovskite-coated ceria foam for enhanced green fuel production in a porous volumetric solar reactor

Abstract

Solar thermochemical cycles offer a viable option for the production of green synthetic fuels from CO 2 and H 2 O. Two-step cycles using redox materials consist of a high-temperature reduction creating oxygen vacancies, followed by a re-oxidation step with an oxidant gas (CO 2 and/or H 2 O), resulting in CO and/or H 2 production. This study focuses on the thermochemical performance in a solar reactor of a new kind of composite reactive material: reticulated ceria foam with uniform perovskite coating, forming a dual-phase layered heterostructure. La 0.5 Sr 0.5 Mn 0.9 Mg 0.1 O 3 (LSMMg) was selected as perovskite coating due to its high fuel productivity and thermochemical stability upon cycling. The perovskite coating improves the reduction step by increasing the reduction extent reached by the reactive material. The results revealed significant enhancement of oxygen exchange in the dual-phase composite material during reduction compared to individual components. The enhanced reduction extent had a beneficial effect on the oxygen release rate and the total amount of fuel produced by CO 2 and H 2 O splitting, whereas an adverse impact on the peak rate during H 2 /CO evolution was noticed. Decreasing the reduction pressure allowed enhancing the non-stoichiometric oxygen extent, while the re-oxidation extent increased with the inlet oxidant molar fraction. With suitable operating conditions (reduction at 0.100 bar and oxidation in 100% CO 2 ), the LSMMg-coated ceria foam produced a higher amount of fuel but with lower fuel production rate in comparison with pure ceria foam. This study points out the beneficial effects of composite redox materials consisting of LSMMg-coated ceria foam in enhancing the oxygen exchange capacity of ceria for solar fuel production.

Two-step thermochemical cycles using fibrous ceria pellets for H2 production and CO2 reduction in packed-bed solar reactors

“…A lower pressure during reduction promoted the reduction extent ( up to 0.056 in cycle #4 and 0.051 in cycle #11) and a lower temperature during oxidation was thermodynamically more favorable. This is consistent with previous studies performed with ceria foams, in which the effect of the operating conditions was assessed [27,38].…”

“…The directly-irradiated solar reactor (SUNFUEL) was previously developed for two-step redox cycles using various forms of reacting materials including reticulated ceria foams, perovskite-coated foams, or porous biomimetic cork-templated ceria granules [27,29,37,38]. It was placed at the focus of a medium-size vertical axis solar furnace (same characteristics as those mentioned in the previous section).…”

Solar Carbo-Thermal and Methano-Thermal Reduction of MgO and ZnO for Metallic Powder and Syngas Production by Green Extractive Metallurgy

“…Thus, only oxygen is released from their structures, bypassing the recombination issue experienced during gas cooling at the reactor outlet. Generally, non-volatile MOs are used as oxygen carriers in H 2 O/CO 2 splitting redox cycle systems [18] and chemical-looping reforming [19]. However, their drawbacks are related to their physicochemical characteristics, such as sintering (iron oxides) [12] and non-stoichiometric reactions (in the case of ceria and perovskites) [20].…”

Thermochemical solar-driven reduction of CO2 into separate streams of CO and O2 via an isothermal oxygen-conducting ceria membrane reactor

“…In a previous work, a monolithic solar reactor was developed for integrating the reactive materials as porous media (such as foams acting as porous volumetric solar absorbers) with interconnected network of macropores and high surface area available for solid-gas reactions [30][31]. Heterostructures composed of perovskite coating on a ceria foam substrate were also considered, as well as microstructured biomimetic ceria [32][33]. During reactor operation, the material was first thermally activated by increasing the solar receiver temperature, delivering oxygen from its lattice and creating oxygen vacancies.…”