A highly efficient electrocatalyst for the oxygen reduction reaction: N-doped ketjenblack incorporated into Fe/Fe3C-functionalized melamine foam.

Polarization caused by the oxygen reduction reaction (ORR) on cathodes still contributes significantly to the energy efficiency loss of metal–air batteries and fuel cells. Thus, ways of increasing the ORR kinetics while maintaining fast mass transfer is a grand challenge in the development of a new generation of metal–air batteries and fuel cells. Catalysts based on platinum and other precious metals are very effective in facilitating the rate of ORR in batteries and fuel cells. However, their high cost and low stability have hindered their practical applications in air-breathing electrodes. Accordingly, much attention has been devoted to rational design of non-precious-metal or metal-free catalysts with unique architectures to dramatically enhance ORR activity (Supporting Information, Figure S1). For example, Jasinski and co-workers reported that metal/nitrogen/carbon (M/N/C) catalysts have high catalytic activity for the ORR. These composite materials were synthesized by pyrolizing proper precursors with nitrogen, carbon, and abundant transition metals. While the superior catalytic activity for ORR are demonstrated, there is still debate on active sites for ORR of N-M-C catalysts and their performance seems to be limited by mass transfer. To dramatically enhance mass transfer through porous oxygen-breathing electrodes, we have created some unique electrode architectures that are similar to breakwaters composed of highly porous tetrapod structures (Figure 1a). To imitate this structure, we started with a commercially available melamine foam. After pyrolysis, the open-cell