Microporous Hard Carbon Support Provokes Exceptional Performance of Single Atom Electrocatalysts for Advanced Air Cathodes

Single atom catalysts embracing metal-nitrogen (MN_x) moieties show promising performance for oxygen reduction reaction (ORR). The modification on spatially confined microenvironments, which won copious attention with respect to achieving efficient catalysts, are auspicious but yet to be inspected for MN_x moieties from modulating the energetics and kinetics of ORR. Here, Fe single atoms (SAs) are immobilized in microporous hard carbon (Fe-SAs/MPC), in which the microporous structure with crumpled graphene sheets serves confined microenvironment for catalysis. Fe-SAs/MPC holds a remarkable half-wave potential of 0.927 V and excellent stability for ORR. Theoretical studies unveil that hydrogen bonding between the intermediate of O* and micropore interior surfaces substantially promote its protonation and accelerate the overall ORR kinetics. Both the aqueous and quasi-solid-state zinc-air batteries driven by Fe-SAs/MPC air cathode show excellent stability with small charging/discharging voltage gaps. Importantly, when used as the air cathode for industrial chlor-alkali process, the applied voltage of Fe-SAs/MPC-based flow cell to reach 300 mA cm^-2 is 1.57 V, which is 210 mV smaller than Pt/C-based one. These findings provide in-depth insights into the confined microenvironment of MN_x moieties for boosted electrochemical performance, and pave the pathways for future catalyst development satisfying the requirement of industrial applications.