Ceria -Mediated Dynamic Sn⁰/Sn^δ+ Redox Cycle for CO₂ Electroreduction

Electrocatalytic CO₂ reduction has been considered an effective carbon neutrality as well as energy storage strategy integrated with renewable electricity. CO₂ conversion to formate is a feasible route using earth-abundant and nontoxic tin-based catalysts. However, they suffer from degradation and thus decrease in formate selectivity during operation. Guided by density functional theory (DFT) calculations, herein, we synthesized CeO₂-SnO₂ heterostructures by a facile electrospinning method, which exhibited a maximum formate partial current density of ∼500 mA·cm^-2 with 87.1% faradaic efficiency and a long-term stability in a flow cell. Proved by in situ attenuated total reflectance infrared absorption spectroscopy (ATR-IRAS) and Raman spectra as well as post-X-ray photoelectron spectroscopy (XPS) analysis, a dynamic CeO₂-mediated Sn⁰/Sn^δ+ redox cycle mechanism was proposed: oxygen vacancies generated on cerium oxides prompted water dissociation to produce *OH and *H species, where the former oxidize Sn⁰ into active Sn^δ+, facilitating the conversion of CO₂ to the key intermediate *OCHO with the help of the latter. This work may provide a general strategy to design stable and efficient catalysts for practical CO₂ electrolyzers.