Deciphering CO₂ Reduction Reaction Mechanism in Aprotic Li–CO₂ Batteries using In Situ Vibrational Spectroscopy Coupled with Theoretical Calculations

Abstract

The aprotic Li–CO2 battery represents a sustainable technology by virtue of energy storage capability and CO2 recyclability. However, the CO2 reduction reaction (CO2RR) mechanism underpinning the operation of Li–CO2 batteries is not yet completely understood. Herein, using in situ surface-enhanced Raman spectroscopy coupled with density functional theory calculations, we obtain direct spectroscopic evidence of the CO2RR (i.e., CO2 –, CO, and Li2CO3) and propose a surface-mediated discharge pathway (i.e., 2Li+ + 2CO2 + 2e– → CO + Li2CO3) in Li–CO2 batteries. We also highlight the significant effect of the electrocatalysts’ near-Fermi-level d-orbital states on the CO2RR activity through a systematic comparative study of model electrocatalysts. Moreover, deep CO2RR via “4Li+ + 3CO2 + 4e– → 2Li2CO3 + C” may be difficult to proceed because of the sluggish chemical steps involved (e.g., dimerization of two CO2 – intermediates). This work provides molecular insights into the CO2RR mechanism in a Li+-aprotic medium and will be beneficial for next-generation Li–CO2 batteries.

Designing Electrophilic and Nucleophilic Dual Centers in the ReS2 Plane toward Efficient Bifunctional Catalysts for Li-CO2 Batteries

“…Moreover, there is no CO production during CO 2 RR. The theoretical CO 2 mass-to-charge ratio is 0.75 for the typical CO 2 RR: 3CO 2 + 4e − + 4Li + → 2Li 2 CO 3 + C. Therefore, NS V -ReS 2 (5)/CP shows a 100% faradic efficiency of 4e − /3CO 2 process, 51 giving superior CO 2 RR activity, while ReS 2 /CP has the poorest CO 2 RR activity. In the charge process (Figure 4b, d, and f), the amount of CO 2 evolved for NS V -ReS 2 (5)/CP is significantly higher than those for ReS 2 /CP and NS V -ReS 2 ( The DEMS measurements show the highly reversible CO 2 RR and CO 2 ER of the NS V -ReS 2 (5)/CP cathode.…”

“…Recently, some authors have proposed a simplified reaction step: the *CO reacts with CO 2 to directly form *CO 3 and *C, and the *CO 3 then reacts with 2 Li to form the second Li 2 CO 3 . 21,35 The Gibbs free energies of intermediates for the five reaction paths on the five planes at U = 0 V and at the theoretical equilibrium potential (U = U 0 = 2.85 V, supplementary method) are shown in Figures S41−S45, 51,52 and the corresponding Gibbs free energy changes (ΔG f ) for every reaction step are summarized in Tables S6−S11. The energy profiles at U 0 were used to obtain the best possible reaction path for the five planes in Li-CO 2 batteries.…”

Carbon Tube-Based Cathode for Li-CO2 Batteries: A Review

“…The charge-discharge e − /reaction gas ratio can be calculated by Faraday's law so as to speculate on the reaction path (Figure 4b). Another advantage of mass spectrometry is that it can be combined with isotope calibration methods, such as an isotope reaction gas or electrolyte, to track the intermediate products in the reaction process, and to effectively analyze the ion migration process and catalytic mechanism of the interface by in situ chemical testing methods [26].…”

High Efficient Catalyst of N‐doped Carbon Modified Copper Containing Rich Cu−N−C Active Sites for Electrocatalytic CO2 Reduction

“…Therefore, low-cost, clean, and efficient methods should be sought to eliminate excess carbon dioxide to achieve sustainable development. [4,5] Electrochemical CO 2 reduction technology (CO 2 RR) has attracted great attention. It is the reduction of CO 2 into high value-added chemicals using renewable power, while the reaction is environmentally friendly and can be achieved at room temperature and atmospheric pressure.…”

“…To effectively alleviate the environmental problems caused by CO 2 such as the greenhouse effect, in addition to reducing CO 2 emission, the recovery and transformation of CO 2 are also one of the important ways. Therefore, low‐cost, clean, and efficient methods should be sought to eliminate excess carbon dioxide to achieve sustainable development [4,5] . Electrochemical CO 2 reduction technology (CO 2 RR) has attracted great attention.…”