Hierarchical-Pore-Stabilization Strategy for Fabricating 18.3 wt% High-Loading Single-Atom Catalyst for Oxygen Reduction Reaction.

Metal single-atom catalysts (M-SACs) attract extraordinary attention for promoting oxygen reduction reaction (ORR) with 100% atomic utilization. However, low metal loading (usually less than 2 wt%) limits their overall catalytic performance. Herein, a hierarchical-structure-stabilization strategy for fabricating high-loading (18.3%) M-SACs with efficient ORR activity is reported. Hierarchical pores structure generated with high N content by SiO2 can provide more coordination sites and facilitate the adsorption of Fe3+ through mesoporous and confinement effect of it stabilizes Fe atoms in micropores on it during pyrolysis. High N content on hierarchical pores structure could provide more anchor sites of Fe atoms during the subsequent secondary pyrolysis and synthesize the dense and accessible Fe-N4 sites after subsequent pyrolysis. In addition, Se power is introduced to modulate the electronic structure of Fe-N4 sites and further decrease the energy barrier of the ORR rate-determining step. As a result, the Fe single atom catalyst delivers unprecedentedly high ORR activity with a half-wave potential of 0.895 V in 0.1 M KOH aqueous solution and 0.791 V in 0.1 M HClO4 aqueous solution. Therefore, a hierarchical-pore-stabilization strategy for boosting the density and accessibility of Fe-N4 species paves a new avenue toward high-loading M-SACs for various applications such as thermocatalysis and photocatalysis.