Intensified solar thermochemical CO₂ splitting over iron-based redox materials via perovskite-mediated dealloying-exsolution cycles

Solar thermochemical CO₂-splitting (STCS) is a promising solution for solar energy harvesting and storage. However, practical solar fuel production by utilizing earth-abundant iron/iron oxides remains a great challenge because of the formation of passivation layers, resulting in slow reaction kinetics and limited CO₂ conversion. Here, we report a novel material consisting of an iron-nickel alloy embedded in a perovskite substrate for intensified CO production via a two-step STCS process. The novel material achieved an unprecedented CO production rate of 381 mL g⁻¹ min⁻¹ with 99% CO₂ conversion at 850 °C, outperforming state-of-the-art materials. In situ structural analyses and density functional theory calculations show that the alloy/substrate interface is the main active site for CO₂ splitting. Preferential oxidation of the FeNi alloy at the interface (as opposed to forming an FeO_x passivation shell encapsulating bare metallic iron) and rapid stabilization of the iron oxide species by the robust perovskite matrix significantly promoted the conversion of CO₂ to CO. Facile regeneration of the alloy/perovskite interfaces was realized by isothermal methane reduction with simultaneous production of syngas (H₂/CO = 2, syngas yield > 96%). Overall, the novel perovskite-mediated dealloying-exsolution redox system facilitates highly efficient solar fuel production, with a theoretical solar-to-fuel efficiency of up to 58%, in the absence of any heat integration.