Quantum tunneling of homogeneous catalyst altering CO ₂ reduction reaction pathway for stable Mg-CO ₂ batteries

Mg-CO 2 battery has emerged as a promising battery technology by harnessing greenhouse gas as an active material. However, its development is greatly hindered by sluggish CO 2 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 CO 2 adsorption and optimize reaction pathways through a quantum tunneling effect induced by electron transfer from the TEMPO free radical to CO 2 that classical electron transfer mechanisms cannot overcome. This quantum tunneling effect not only enables CO 2 reduction at lower voltage but also regulates the CO 2 adsorption environment, leading to the alternated reaction pathway for the formation of flower-like MgC 2 O 4 as the discharge product, rather than the dense MgCO 3 typically formed in traditional models. The TEMPO-based Mg-CO 2 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-CO 2 battery systems to date.