Quantum tunneling of homogeneous catalyst altering CO2 reduction reaction pathway for stable Mg-CO2 batteries.

Mg-CO2 battery has emerged as a promising battery technology by harnessing greenhouse gas as an active material. However, its development is greatly hindered by sluggish CO2 conversion kinetics, resulting in high overpotentials and poor reversibility. Herein, we report a class of 2,2,6,6-tetramethylpiperidoxyl (TEMPO) homogeneous catalyst to regulate CO2 adsorption and optimize reaction pathways through a quantum tunneling effect induced by electron transfer from the TEMPO free radical to CO2 that classical electron transfer mechanisms cannot overcome. This quantum tunneling effect not only enables CO2 reduction at lower voltage but also regulates the CO2 adsorption environment, leading to the alternated reaction pathway for the formation of flower-like MgC2O4 as the discharge product, rather than the dense MgCO3 typically formed in traditional models. The TEMPO-based Mg-CO2 batteries achieve an exceptional discharge voltage of 1.1 volts and a charge voltage of 1.3 volts, with stable cycling performance for over 450 hours, representing the best-reported performance among Mg-CO2 battery systems to date.