Boosting faradaic efficiency of CO₂ electroreduction to CO for Fe-N-C single-site catalysts by stabilizing Fe³⁺ sites via F-doping

The atomically dispersed Fe³⁺ sites of Fe-N-C single-site catalysts (SSCs) are demonstrated as the active sites for CO₂ electroreduction (CO₂RR) to CO but suffer from the reduction to Fe²⁺ at ~ −0.5 V, accompanied by the drop of CO faradaic efficiency (FE_CO) and deterioration of partial current (J_CO). Herein, we report the construction of F-doped Fe-N-C SSCs and the electron-withdrawing character of fluorine could stabilize Fe³⁺ sites, which promotes the FE_CO from the volcano-like highest value (88.2%@−0.40 V) to the high plateau (> 88.5%@−0.40–−0.60 V), with a much-increasedJ_CO (from 3.24 to 11.23 mA·cm⁻²). The enhancement is ascribed to the thermodynamically facilitated CO₂RR and suppressed competing hydrogen evolution reaction, as well as the kinetically increased electroactive surface area and improved charge transfer, due to the stabilized Fe³⁺ sites and enriched defects by fluorine doping. This finding provides an efficient strategy to enhance the CO₂RR performance of Fe-N-C SSCs by stabilizing Fe³⁺.