Fabricating penta-coordinated Fe single atoms for electrochemical CO2 reduction to syngas

Abstract

The electrochemical reduction of CO₂ (CO₂RR) has recently attracted increasing attention for converting intermittent electric energy to chemical energy and reducing CO₂ emission. Generally, various products including C₁ and C₂₊ chemicals can be produced through CO₂RR, and the selectivities of products are strongly determined by the structures of the active sites. In this work, we demonstrate that a penta-coordinated Fe single atom with N (Fe–N₅/C) can serve as an efficient catalyst for CO₂RR to syngas with tunable compositions. Detailed characterizations reveal that Fe atoms present as single atoms on a N-doped carbon support derived from the thermal treatment of zeolitic tetrazolate framework (ZTF). Specifically, each Fe single atom coordinates with five N atoms to form a pentahedral structure (Fe–N₅). Theoretical calculations indicate that CO* desorption is energetically preferred, while CO₂ activation to COOH* is the potential-limiting step for CO₂RR on the Fe–N₅/C surface, leading to an enhancement in CO₂RR and suppression of hydrogen evolution reaction (HER). Consequently, the ratio of H₂/CO ranges from 0.15 to 2.8 in the potential range of −0.5–−1.0 V when Fe–N₅/C is used as the catalyst for CO₂RR in 0.1 M KHCO₃. This work reports a penta-coordinated Fe single atom for CO₂RR to produce syngas with a tunable H₂/CO ratio, which may promote the fundamental research on catalyst design for CO₂RR.