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

Abstract

AbstractRedox‐mediated electrocatalysis represents an innovative strategy to unlock the energy capabilities of aprotic Li–CO2 batteries by enabling solution‐mediated CO2 reduction reaction (CO2RR). 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 CO2RR. Direct spectroscopic evidence reveals a current‐density‐dependent CO2RR pathway: the reduced PQ reacts with CO2 to form metastable Li2(PQ‐CO2) adduct via ECE and EEC pathways at low and high current densities, respectively. Subsequently, the metastable Li2(PQ‐CO2) adduct dissociates to form the LiCO2 intermediate and regenerate LinPQ (n = 0 and 1 at low and high current densities, respectively). Two LiCO2 intermediates dimerize to produce the final discharge products of Li2CO3 and CO in bulk solution. Therefore, the operation of Li–CO2 batteries at low‐current densities reduces the activation barrier of CO2RR 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 CO2RR. This work highlights the pivotal chemical dissociation step in PQ‐mediated CO₂RR and provides a mechanistic framework for designing better metal–CO2 batteries.