Nitrogen-doped hierarchically porous carbon as efficient oxygen reduction electrocatalysts in acid electrolyte†
Nitrogen-doped carbon was found to exhibit excellent activity as an electrocatalyst in renewable energy devices. A controllable method to synthesize N-doped hierarchically porous carbons (PNCEs) partly with graphene-like structure using polyaniline (PANI)–polyvinylpyrrolidone (PVP) composite as a carbon source via a soft-template process was reported. The catalytic mechanism was thoroughly studied to better understand the relationship between the structure, Fe species and catalytic activity. The PNCE prepared at 1000 °C displays the best performance achieving a maximum power density of 456 mW cm−2 and oxygen reduction reaction (ORR) onset potential of 0.90 V. More prominently, the catalyst presents superior stability, as well as poison tolerance including methanol and SO2 to the commercial JM-Pt/C catalyst in 0.5 M H2SO4. The PVP is proven to tailor the structure, improve the surface area, and alter the transition metal species. The PNCEs synthesized under NH3 exhibit considerably better catalytic activity toward ORR compared with the undoped carbon and PNCEs synthesized under an N2 atmosphere. Furthermore, we find that the nitrogen bonding configurations, textural structure, Fe species and surface areas of PNCEs play key roles in the electrocatalytic activity towards the ORR. The formed FeN4 species hosted in the micropores acts as the active component for ORR activity in PNCEs, although it is not the only contributor to the high performance of PNCEs. The catalyst is expected to be a promising non-noble electrocatalyst for use in polymer electrolyte membrane fuel cells.