Honeycomb-like Fe/Fe3C-doped porous carbon with more Fe-Nx active sites for promoting the electrocatalytic activity of oxygen reduction

Fe-N-C electrocatalysts with abundant Fe-N-x active sites are considered to be one of the most promising nonprecious metal catalysts (NPMCs) toward the oxygen reduction reaction (ORR) in metal-air batteries and hydrogen-oxygen fuel cells. However, the catalytic activity of Fe-N-C electrocatalysts is restricted by the low Fe loading and the limited availability of active sites. In this work, Fe-doped nitrogen-enriched porous carbon (Fe-DPC) electrocatalysts with enhanced catalytic activity are successfully synthesized by a simple and general strategy. The long-term interaction between Fe-doped 2,6-diaminopyridine (DAP) and ZIF-8 can contribute to constructing a honeycomb-like structure in Fe-DPC through the Kirkendall effect, promoting the accessibility of electrolyte and effective mass transfer. Moreover, the effect of Fe doping amounts on the structure and ORR activity is systematically expounded. Due to the presence of Fe nanoparticles and Fe3C species as well as the construction of the unique structure and the full exposure of active sites, 5Fe-DPC exhibits a high onset potential of 1.01 V and a decent half-wave potential of 0.92 V under alkaline conditions, much better than that of the commercial 40 wt% Pt/C catalyst. Notably, a zinc-air battery (ZAB) assembled with 5Fe-DPC as the cathode catalyst exhibits impressive performance with high energy density and outstanding durability. These findings can provide an effective reference for the rational design of NPMCs to improve the ORR performance in the future.