Unveiling the In Situ Generation of a Monovalent Fe(I) Site in the Single-Fe-Atom Catalyst for Electrochemical CO₂ Reduction

Abstract

Atomically dispersed single-atom catalysts are among the most attractive electrocatalysts for the CO2 reduction reaction (CRR). To elucidate the origin of the exceptional activity of atomically dispersed Fe–N–C catalyst in CRR, we have performed operando 57Fe Mössbauer spectroscopic studies on a model single-Fe-atom catalyst with a well-defined N coordination environment. Combining with operando X-ray absorption spectroscopy, the in situ-generated four pyrrolic nitrogen atom-coordinated low-spin Fe­(I) (LS FeIN4) featuring monovalent iron is identified as the reactive center for the conversion of CO2 to CO. Furthermore, density functional theory calculations reveal that the optimal binding strength of CO2 to the LS FeIN4 site, with strong orbital interactions between the singly occupied d z 2 orbital of the Fe­(I) site and the singly occupied π* orbital of [COOH] fragment, is the key factor for the excellent CRR performance.

Nurturing the marriages of single atoms with atomic clusters and nanoparticles for better heterogeneous electrocatalysis

“…Hence, the dynamic nature of single atoms has focused on the changes/transformations at the atomic level. [ 128,129 ] Based on the published literature, we summarized the dynamic evolution of single atoms into the following four types: (ⅰ) variation in geometry configuration and valence state, (ⅱ) Transition to near‐free state, (ⅲ) emergence of reversible cluster species, and (ⅳ) generation of irreversible cluster species. …”

Mechanistic understanding and design of non-noble metal-based single-atom catalysts supported on two-dimensional materials for CO2 electroreduction

“…The monovalent Fe species emerged when potential was applied to catalysts with a relative content of ∼17.1% (−0.9 V vs. RHE) and disappeared after electrolysis. 78 These inconsistent results may originate from the complexity of the geometric and electronic structure of the single-Fe-atom sites, which require advanced operando characterization, and this will be discussed in detail in the section on spectroscopy.…”

“…6f and g. 78 The three doublets in orange, green, and blue represent LS Fe 2+ in Fe II N 4 , This journal is © The Royal Society of Chemistry 2022 MS Fe 2+ in Fe II N 4 , and high-spin (HS) Fe 2+ in N-Fe II N 4 , respectively. When applying a voltage of À0.9 V vs.…”

Synchrotron-radiation spectroscopic identification towards diverse local environments of single-atom catalysts

“…Combining in situ or operando XANES and EXAFS, a detailed reaction mechanism can be postulated. 116 2.1.3 So XAS. The feature of relatively lower energy makes so XAS sensitive to investigating the bond types and orbital hybridization of light elements.…”