Nitrogen-Doped Porous Carbon Cages for Electrocatalytic Reduction of Oxygen: Enhanced Performance with Iron and Cobalt Dual Metal Centers

Heteroatom-doped carbon materials are promising electrocatalysts towards the oxygen reduction reaction (ORR). In this study, dual metals (Fe an Co) and nitrogen-codoped porous carbon cages (CHS−FeCo) were synthesized by controlled pyrolysis of silica nanoparticle-supported melamine-formaldehyde resin embedded with iron and cobalt precursors, followed by acid etching. Transmission electron microscopy measurements confirmed the formation of hollow carbon cages, and the absence of metal (oxide) nanoparticles suggested atomic dispersion of the metal species within the mesoporous carbon skeletons. X-ray photoelectron spectroscopic analysis revealed a composition of mostly carbon, oxygen, and nitrogen, with ca. 1 % metals. Electrochemically, the dual-metal ones showed a significant enhancement of the catalytic performance towards ORR in alkaline media, as compared to samples with single or no metal dopants. This was accounted for by the synergistic interaction between the Fe and Co centers in the carbon samples, as evidenced in X-ray absorption spectroscopic studies. Remarkably, the CHS−FeCo sample exhibited apparent resistance against KSCN poisoning, where XPS analysis revealed oxidation of KSCN and no metal-sulfur interaction, in sharp contrast to the Fe counterpart which was easily poisoned. Results from this study suggest that the synergistic interactions between dual metal centers may be exploited for enhanced ORR performance of carbon-based nanocomposite catalysts.