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.