Regulating the Water Dissociation on Atomic Iron Sites to Speed Up CO2 Protonation and Achieve pH-Universal CO2 Electroreduction

Atomic Fe sites enabled electrochemical carbon dioxide (CO2) reduction (ECO2R) to carbon monoxide (CO) at low overpotentials. However, the narrow potential ranges for selective CO2 conversion on atomic Fe sites hindered the CO production at high current densities. Therefore, unveiling the CO2 electroreduction processes and clarifying the catalytic mechanisms on different atomic Fe sites are important for better design of atomic Fe catalysts toward efficient ECO2R. Herein, the ECO2R processes on single-atom, dual-atom, and cluster Fe sites are systematically investigated, and clarify that the balanced water dissociation and CO2 protonation on dual-atom Fe sites promote the efficient CO production. The dual-atom Fe catalyst achieves Faradaic efficiencies of CO (FECO) above 92% over a wide potential range of -0.4--0.9 V versus reversible hydrogen electrode and maintains FECO of 91% after 153-h electrolysis in H-type cell. Benefitting from the favorable CO2 protonation for ECO2R on dual-atom Fe sites, pH-universal CO2 electroreduction is achieved in alkali-/acid-/bicarbonate-fed membrane electrode assembly electrolyzer, with FECO exceeds 98% in strongly acidic/alkaline and neutral mediums. The work reveals a water dissociation-promoted CO2 electroreduction on dual-atom Fe sites and presents a feasible regulation of atomic Fe sites for highly active/selective ECO2R.