A Nonaqueous Mg-CO2 Battery with Low Overpotential

Mg-CO 2 batteries, which exploit the greenhouse gas CO 2 as cathode active species, are an appealing next-generation battery candidate due to their high efficiency energy storage and value-added CO 2 utilization. However, compared with other metal-CO 2 systems, few aprotic Mg-CO 2 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-CO 2 battery is developed by using a Mo 2 C-CNTs catalytic cathode, a nonaqueous electrolyte, and a magnesium metal anode. The Mo 2 C-CNTs catalytic cathode can greatly reduce the charge overpotential of the Mg-CO 2 battery through tuning the CO 2 reduction pathways. The results of a variety of ex situ and in situ experiments as well as theoretical calculations show the Mo 2 C catalyst not only induces surface molecular adsorption for faster reaction kinetics but also improves the selectivity toward MgC 2 O 4 in the CO 2 reduction process for a higher Faraday efficiency. An exceptional low voltage hysteresis is achieved for the Mg-CO 2 battery. This work demonstrates a promising strategic option for rechargeable nonaqueous Mg-CO 2 batteries for simultaneously addressing energy and environmental issues.