Gas Diffusion Strategy for Inserting Atomic Iron Sites into Graphitized Carbon Supports for Unusually High-Efficient...

Emerging single-atom catalysts (SACs) hold great promise for CO₂ electroreduction (CO₂ ER)_, but the design of highly active and cost-efficient SACs is still challenging. Herein, a gas diffusion strategy, along with one-step thermal activation, for fabricating N-doped porous carbon polyhedrons with trace isolated Fe atoms (Fe₁ NC) is developed. The optimized Fe₁ NC/S₁ -1000 with atomic Fe-N₃ sites supported by N-doped graphitic carbons exhibits superior CO₂ ER performance with the CO Faradaic efficiency up to 96% at -0.5 V, turnover frequency of 2225 h^-1 , and outstanding stability, outperforming almost all previously reported SACs based on N-doped carbon supported nonprecious metals. The observed excellent CO₂ ER performance is attributed to the greatly enhanced accessibility and intrinsic activity of active centers due to the increased electrochemical surface area through size modulation and the redistribution of doped N species by thermal activation. Experimental observations and theoretical calculations reveal that the Fe-N₃ sites possess balanced adsorption energies of *COOH and *CO intermediates, facilitating CO formation. A universal gas diffusion strategy is used to exclusively yield a series of dimension-controlled carbon-supported SACs with single Fe atoms while a rechargeable Zn-CO₂ battery with Fe₁ NC/S₁ -1000 as cathode is developed to deliver a maximal power density of 0.6 mW cm^-2 .