Electrochemical CO2 reduction reaction (CO2RR) is a promising process for reducing CO2 emissions and producing high-value chemicals. However, this process remains hindered by diffusion-limited mass transfer, low activity, and high overpotentials. Here, we controllably prepared hierarchically porous nitrogen-doped carbon, carbon nanosheets, and carbon nanotubes confined single-atom Fe catalysts for electrochemical CO2 reduction. The hierarchically porous Fe-N-C (Fe-HP) exhibited prominent performance with a Faradaic efficiency of CO (FECO) up to 80% and a CO partial current density (jCO) of −5.2 mA·cm−2 at −0.5 V vs. reversible hydrogen electrode (RHE), far outperforming the single-atom Fe on N-C nanosheets (Fe-NS) and N-C nanotubes (Fe-NT). The detailed characterizations and kinetic analysis revealed that the hierarchically porous structure accelerated the mass transfer and electron transfer processes toward single-atom Fe sites, promoting the desorption of CO and thereby enhancing CO2 reduction efficiency. This study provides a promising approach to designing efficient single-atom catalysts with porous structures for energy conversion applications.
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