Synergistic Dual d-Band Engineering at the Ru-N₄/MXene Interface for High-Efficiency and Long-Lived Li-CO₂ Batteries

The cyclability of Li-CO₂ batteries is fundamentally limited by the sluggish kinetics of Li₂CO₃ formation and decomposition. In this work, we develop a Ru‑N₄ single‑atom catalyst anchored on MXene (MX‑Ru_SA), in which the atomic interface establishes a synergistic dual d‑band center to overcome this kinetic constraint. The N coordination modifies the electronic state of Ru, upshifting its d-band center to strengthen intermediate adsorption and steer the growth of vertically aligned Li₂CO₃ nanosheets that facilitate efficient electron and ion transport. Meanwhile, the presence of Ru-N₄ sites modulates the electronic structure of the MXene support, optimizing the d-band center of Ti, which weakens the Li─O bonds in Li₂CO₃ and significantly reduces its decomposition barrier. As a result, the Li-CO₂ battery with MX‑Ru_SA delivers a high discharge capacity of 14757 mA h g^-1, along with an ultralow charging overpotential of 0.56 V and a long cycle life over 3000 h at 100 mA g^-1. This work demonstrates interfacial dual d‑band synergy as a promising design principle toward high‑performance catalysts for metal-gas battery systems.