Polypyrrole-derived mesoporous nitrogen-doped carbons with intrinsic catalytic activity in the oxygen reduction reaction

Abstract

N-doped mesoporous carbons containing small amounts of graphitic carbon have been successfully prepared using the nanocasting technique. Polypyrrole was used as N-dopant carbon precursor and SBA-15 or silica xerogel as templates. Graphitic carbon domains provide a good electronic conductivity of up to 0.33 S cm⁻¹, a necessary property for electrochemical applications, while a mesoporous structure reduces mass transport limitations. These characteristics are further combined with a high N content (3.55–5.45 wt%). As a result, the as-prepared materials exhibit an enhanced intrinsic electrocatalytic activity towards the oxygen reduction reaction (ORR). They exhibit an onset potential of ∼−90 to −70 mV vs. Ag/AgCl and a current density in the lower potential regime that exceeds that of a commercial platinum catalyst in a basic medium. Their behavior is superior to that of Vulcan XC72R carbon. Furthermore, unlike commercial Pt catalysts, they are unaffected by the methanol cross-over effect. It was found that the graphitic content must be well-balanced as, on the one hand, it enhances conductivity but, on the other hand, it selectively catalyses an unfavorable 2e⁻ process.