Revealing Redox‐Mediated CO2 Reduction Reaction Mechanisms in Aprotic Li–CO2 Batteries

Abstract Redox‐mediated electrocatalysis represents an innovative strategy to unlock the energy capabilities of aprotic Li–CO 2 batteries by enabling solution‐mediated CO 2 reduction reaction (CO 2 RR). However, the underlying reaction pathways remain incompletely understood due to the lack of direct molecular evidence. Herein, multimodal in situ spectroscopic techniques are integrated with theoretical calculations to interrogate a model 9,10‐phenanthrenequinone (PQ)‐mediated CO 2 RR. Direct spectroscopic evidence reveals a current‐density‐dependent CO 2 RR pathway: the reduced PQ reacts with CO 2 to form metastable Li 2 (PQ‐CO 2 ) adduct via ECE and EEC pathways at low and high current densities, respectively. Subsequently, the metastable Li 2 (PQ‐CO 2 ) adduct dissociates to form the LiCO 2 intermediate and regenerate Li n PQ ( n = 0 and 1 at low and high current densities, respectively). Two LiCO 2 intermediates dimerize to produce the final discharge products of Li 2 CO 3 and CO in bulk solution. Therefore, the operation of Li–CO 2 batteries at low‐current densities reduces the activation barrier of CO 2 RR and regenerates PQ for sustained redox cycling, enabling significantly minimized overpotential and enhanced discharge capacity. Additionally, the suppression effects of weakly acidic cations (e.g., K + , TBA + ) are elucidated for the redox‐mediated CO 2 RR. This work highlights the pivotal chemical dissociation step in PQ‐mediated CO₂RR and provides a mechanistic framework for designing better metal–CO 2 batteries.