Unraveling Mechanistic Reaction Pathways of the Electrochemical CO₂ Reduction on Fe–N–C Single-Site Catalysts

Abstract

We report a joint experimental−computational mechanistic study of electrochemical reduction of CO 2 to CH 4 , catalyzed by solid-state Fe−N−C catalysts, which feature atomically dispersed, catalytically active Fe−N x sites and represent one of the very rare examples of solid, non-Cu-based electrocatalysts that yield hydrocarbon products. Work reported here focuses on the identification of plausible mechanistic pathways from CO 2 to various C 1 products including methane. It is found that Fe−N x sites convert only CO 2 , CO, and CH 2 O into methane, whereas CH 3 OH appears to be an end product. Distinctly different pH dependence of the catalytic CH 4 evolution from CH 2 O in comparison with that of CO 2 and CO reduction indicates differences in the proton participation of ratedetermining steps. By comparing the experimental observations with density functional theory derived free energy diagrams of reactive intermediates along the CO 2 reduction reaction coordinates, we unravel the dominant mechanistic pathways and roles of CO and CH 2 O during the catalytic CO 2 -to-CH 4 cascades and their rate-determining steps. We close with a comprehensive reaction network of CO 2 RR on single-site Fe−N−C catalysts, which may prove useful in developing efficient, non-Cubased catalysts for hydrocarbon production.

Transition metal-based catalysts for the electrochemical CO2reduction: from atoms and molecules to nanostructured materials

“…In a recent integrated experimental-computational study, Ju et al also elucidated the possible pathways for CO 2 RR to CH 4 at the Fe-N x sites as well as the role of the possible intermediate products formed during the CO 2 -to-CH 4 cascades. 357 As a result, CO was found to be the key intermediate toward CH 4 , CH 3 OH and CH 2 O production, yet CH 2 O (but not CH 3 OH) could be further reduced to CH 4 . Moreover, the isolated nature of atomically dispersed Fe-N x units was identified as the main origin for low hydrocarbon selectivity, suggesting ''dual-site'' or ''hybrid-tandem'' catalysts, featuring cooperative sites for *CO and *H adsorption, as viable promising strategies.…”

Engineering Local Coordination Environments of Atomically Dispersed and Heteroatom‐Coordinated Single Metal Site Electrocatalysts for Clean Energy‐Conversion

“…The electroreduction of CO 2 to C 1 or C 2 products other than CO has also been studied on these carbon‐based SACs. For instance, Ju et al revealed the mechanistic reaction pathways of the CO 2 RR on FeN 4 sites to form methane, formaldehyde, and methanol. Huang et al prepared atomically dispersed Mo sites on N‐doped graphene, which achieved a formate yield of 747 mmol h −1 mg−1 cat.…”

Synergistic Catalysis over Iron‐Nitrogen Sites Anchored with Cobalt Phthalocyanine for Efficient CO2 Electroreduction

“…Considering the fact that the reaction conditions were controlled to be the same for each catalyst, the possible impurities such as heavy metal ions and organic substances should have the same impacts on different electrodes. We speculate that the differences in stability might arise from the distinction of binding of adsorbed intermediates and the desorption of products over the catalysts . Aforementioned strong interaction between CoPc and Fe‐N‐C (Figure b) would decrease the *CO poisoning and accelerate the desorption of CO over reaction sites.…”