Promoting Electrochemical CO2 Reduction via Boosting Activation of Adsorbed Intermediates on Iron Single-Atom Catalyst

Single-atom catalysts show great promise as non-precious electrocatalysts for CO2 electroreduction reaction (CO2ER). However, it is still challenging to gain a fundamental understanding of the complicated dynamic behavior of CO2 activation to achieve high product selectivity. Herein, the authors report an unusual iron single-atom catalyst, containing atomically dispersed Fe-N-4 species and Fe3C nanoparticles (NPs) (Fe3C|Fe1N4). Having a fragmental-rock-shaped nanocarbon architecture, isolated Fe-N-4 sites uniformly disperse with adjacent Fe3C NPs (<30 nm) in a carbon matrix. Benefiting from the strong coupling effect between Fe3C and Fe1N4 and unique spatial nanostructure, Fe3C|Fe1N4 displays exceptional CO2ER activity with a low onset potential of -0.3 V and high Faradaic efficiency of 94.6% at -0.5 V for CO production, acting as one of the most active Fe-N-C catalysts and even exceeding most other carbon supported non-precious metal NPs. Experimental observations discover that the excellent CO2ER activity of Fe3C|Fe1N4 catalyst is attributable to the presence of Fe3C NPs that optimizes J(CO) of the coexisted Fe-N-4 active sites. In situ attenuated total reflectance-Fourier transform infrared analysis and theoretical calculations reveal that the Fe3C NPs strengthen the adsorption of CO2 on the isolated Fe-N-4 sites to accelerate the formation of *COOH intermediate, and hence enhance the whole CO2ER performance.