Mononuclear iron-dependent electrocatalytic activity of metal-nitrogen-carbon catalysts for efficient oxygen reduction reaction

Abstract

As a low-cost nonprecious metal-based catalyst, the mononuclear iron embedded in nitrogen-doped carbons has been regarded as one type of the best electrocatalytic materials for the oxygen reduction reaction (ORR). Herein, we proposed a silica-protective-layer assisted strategy for fabricating the catalysts with mononuclear iron site coordinated with adjacent nitrogen and carbon atoms, through high temperature pyrolysis of melamine, carbon black and FeCl3. At 800 °C, the fabricated catalyst features completely atomic level iron-nitrogen-carbon catalysts without Fe-based phases. In concentrated 1 M NaOH solution, this catalyst displays a remarkably improved catalytic activity with half-wave potential of 0.90 V. The mass activity of catalyst can reach 1.06 times that of commercial Pt/C (20 wt%, Pt). The correlation of the mononuclear iron composition and coordination structure with the promoted ORR kinetics was discussed in detail. The superior activity can be attributed to lots of the mononuclear iron moieties with a non-planar Fe(II)-N4 structure and increased surface area of the as-synthesized heterogeneous catalyst.