Electron-Localized RuNi Nanosheet Assemblies Enable Low-Overpotential Mg-CO₂ Battery

Mg-CO₂ battery is emerging as a promising energy storage system that simultaneously converts CO₂ into value-added products. However, its practical application is hindered by formation thermodynamically stable and electrically insulating discharge product MgCO₃, which severely limits energy efficiency of Mg-CO₂ battery. Herein, we report an electron-localized Ru₆₁Ni₃₉ nanosheet assembly catalyst that overcomes these limitations by precisely engineering the surface electronic structure for achieving precise tuning of product from MgCO₃ to MgC₂O₄ of Mg-CO₂ battery. We demonstrate that electron transfer from Ni to Ru creates the localized electron at the Ru sites, weakening MgC₂O₄ binding and suppressing its conversion to MgCO₃, thereby enabling reversible formation and decomposition of MgC₂O₄ and mitigating cathode passivation. The Mg-CO₂ battery incorporating the electron-localized Ru₆₁Ni₃₉ nanosheet assembly catalyst achieves an ultralow charge overpotential of 0.07 V and a record-high energy conversion efficiency of 94.1%, with the stable cycling for over 580 h. In situ electrochemical spectroscopy and theoretical studies reveal that the electron-localized between Ru and Ni stabilizes the product intermediates (C₂O₄ ^2-) and prevents the MgC₂O₄ conversion to MgCO₃.