Fe-based non-noble metal catalysts with dual active sites of nanosized metal carbide and single-atomic species for oxygen reduction reaction

Abstract

Single-atom catalysts have been considered as representative non-noble metal catalysts for replacing the platinum catalyst. Fundamentally, the dispersion of metal atoms on a carbon support with limited surface area results in extremely low loading of the active metal, leading to a thick electrode and low volumetric energy density. In this study, we present a facile strategy for increasing the active metal densities on the M？N？C catalyst through the use of dual active sites such as Fe？Nx and nanosized Fe3C that have different reaction pathways involving 4 and 2 + 2 (or 2 × 2) electrons, respectively. The dual active sites were realized by the addition of Zn that affects the physical shielding of Fe and energy bypass, leading to the formation of single-atomic Fe？Nx species and nanosized Fe3C with ∼2 nm. Our catalyst exhibits superior oxygen reduction reaction activity to that of the commercial 20 wt% Pt/C catalysts both in half cell (onset potential, 0.95 V

half-wave potential, 0.9 V) and single cell (maximum power density, 367 mW cm？2). Therefore, we expect that our facile strategy would open an avenue for the rational design and synthesis of highly loaded active Fe-based catalysts.