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–N_x 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–N_x 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.