Revealing Redox‐Mediated CO<sub>2</sub> Reduction Reaction Mechanisms in Aprotic Li–CO<sub>2</sub> Batteries
Zhiwei Zhao, Yuyue Wu, Tianfeng Yao, Long Pang, J. M. Liu, Xinliang Feng, Zhangquan Peng
Abstract
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.