In situ imaging electrocatalytic CO₂ reduction and evolution reactions in all-solid-state Li-CO₂ nanobatteries

Li-CO₂ batteries are promising energy storage devices owing to their high energy density and possible applications for CO₂ capture. However, still some critical issues, such as high charging overpotential and poor cycling stability caused by the sluggish decomposition of Li₂CO₃ discharge products, need to be addressed before the practical applications of Li-CO₂ batteries. Exploring highly efficient catalysts and understanding their catalytic mechanisms for the CO₂ reduction reaction (CORR) and evolution reaction (COER) are critical for the application of Li-CO₂ batteries. However, the direct imaging of electrocatalysis during CORR and COER is still elusive. Herein, we report the in situ imaging of electrocatalysis during CORR and COER in a Li-CO₂ nanobattery using a Ni-Ru-coated α-MnO₂ nanowire (Ni-Ru/MnO₂) cathode in an advanced aberration corrected environmental transmission electron microscope. During the CORR, a thick Li₂CO₃ and carbon mixture layer was formed on the surface of the Ni-Ru/MnO₂ nanowires via 4Li⁺ + 3CO₂ + 4e^-→ 2Li₂CO₃ + C. During the COER, the as-formed Li₂CO₃ decomposed via 2Li₂CO₃→ 2CO₂ + O₂ + 4Li⁺ + 4e^-, while the as-formed amorphous carbon remained. In contrast, the decomposition of Li₂CO₃ on bare MnO₂ nanowires was difficult, underscoring the important Ni-Ru bimetal electrocatalytic role in facilitating the COER. Our results provide an important understanding of the CO₂ chemistry in Li-CO₂ batteries, possibly helping in the designing of Li-CO₂ batteries for energy storage applications.