Fabrication of Fully Exposed Iron Single-Atom Catalyst for Efficient CO2 Electroreduction Reaction

Nitrogen-doped carbon nanoparticle-supported single-iron-atom catalysts (denoted as Fe-N-C) have been widely investigated in the electrocatalytic CO2 reduction reaction (CO2RR). However, for most Fe-N-C catalysts fabricated via high-temperature pyrolysis, abundant active Fe sites are buried in the bulk of microporous carbon substrate, with poor accessibility. The morphology limitation immensely alleviates the exposure of active sites at the critical three-phase interfaces and hinders the mass transfer of reactant molecules within electrodes. Herein, we present a facile soft-template coating approach to fabricate a core–shell Fe-N-C catalyst with highly accessible Fe sites at the surface by pyrolysis of an iron-coordinated polydopamine-coated ZIF-8 composite precursor. The unique core–shell structure of Fe-N-C shortens the diffusion path of ions and CO2, and it facilitates CO product elimination. Such an electrode assembly significantly boosts the electrocatalytic CO2RR in a gas-diffusion-electrode with a CO Faradaic efficiency (FECO) of ∼97% at an industrial current density of 100 mA/cm2. This work sheds light on the synthesis of single-atom catalysts with highly accessible active sites in surface layers for the CO2RR and other electrocatalytic reactions with high activity and efficient mass transport.