A Nonaqueous Mg‐CO₂ Battery with Low Overpotential

Abstract Mg‐CO₂ batteries, which exploit the greenhouse gas CO₂ as cathode active species, are an appealing next‐generation battery candidate due to their high efficiency energy storage and value‐added CO₂ utilization. However, compared with other metal‐CO₂ systems, few aprotic Mg‐CO₂ batteries have been reported so far as a result of several crucial problems including the comparatively slow redox reaction kinetics, a large decomposition energy barrier of the reduction products, and poor reversibility in their multi‐electron three‐phase cathodic reactions in nonaqueous environments. Herein, a rechargeable Mg‐CO₂ battery is developed by using a Mo₂C‐CNTs catalytic cathode, a nonaqueous electrolyte, and a magnesium metal anode. The Mo₂C‐CNTs catalytic cathode can greatly reduce the charge overpotential of the Mg‐CO₂ battery through tuning the CO₂ reduction pathways. The results of a variety of ex situ and in situ experiments as well as theoretical calculations show the Mo₂C catalyst not only induces surface molecular adsorption for faster reaction kinetics but also improves the selectivity toward MgC₂O₄ in the CO₂ reduction process for a higher Faraday efficiency. An exceptional low voltage hysteresis is achieved for the Mg‐CO₂ battery. This work demonstrates a promising strategic option for rechargeable nonaqueous Mg‐CO₂ batteries for simultaneously addressing energy and environmental issues.