N,P Co-Coordinated Manganese Atoms in Mesoporous Carbon for Electrochemical Oxygen Reduction

Abstract

The increasing interest in fuel cell technology encourages the development of efficient and low-cost electrocatalysts to replace the Pt based materials for catalyzing the cathodic oxygen reduction reaction (ORR). In the present work, a nitrogen and phosphorus co-coordinated manganese atom embedded mesoporous carbon composite (MnNPC-900) is successfully prepared via a polymerization of o-phenylenediamine followed by calcination at 900 °C. The MnNPC-900 composite shows a high ORR activity in alkaline media, offering an onset potential of 0.97 V, and a half-wave potential of 0.84 V (both vs reversible hydrogen electrode) with a loading of 0.4 mg cm^-2 . This performance not only exceeds its phosphorus-free counterpart (MnNC-900), but also is comparable to the Pt/C catalyst under identical measuring conditions. The significantly enhanced ORR performance of MnNPC-900 can be ascribed to: i) the introduction of phosphorus assists the generation of mesopores during the pyrolysis and endows the MnNPC-900 composite with large surface area and pore volume, thus facilitating the mass transfer process and increases the number of exposed active sites. ii) The formation of N,P co-coordinated atomic-scale Mn sites (MnN_x P_y ), which modifies the electronic configuration of the Mn atoms and thereby boosts the ORR catalytic activity.

Keywords: N; P co-coordination; isolated Mn species; mesoporous carbon; oxygen reduction reaction.