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.