Cobalt- and iron-coordinated graphitic carbon nitride on reduced graphene oxide: A nonprecious bimetallic M-N_x-C analogue electrocatalyst for efficient oxygen reduction reaction in acidic media

摘要

The electrocatalytic oxygen reduction reaction (ORR) in acidic media is quite strenuous. Although platinum (Pt)-based materials are considered state-of-the-art ORR catalysts, their high cost and poor durability greatly impede their extensive application in polymer electrolyte membrane fuel cells and direct methanol fuel cells. Here, we report a bimetallic M-N-x-C-class electrocatalyst comprising Co- and Fe-coordinated graphitic carbon nitride ((Co,Fe)-CN) and reduced graphene oxide (RGO) as an effective substitute for expensive Pt-based catalysts for the ORR in acidic media. The fabricated (Co,Fe)-CN/RGO catalyst exhibits a high surface area, high porosity, fast charge-transfer kinetics at the (Co,Fe)-CN/RGO 2D/2D interface, and abundant Co-Nx-C and Fe-N-x-C active sites. Because of these favorable properties, the optimized (Co,Fe)-CN/RGO catalyst displayed extra-ordinary electrocatalytic ORR activity, with an onset potential of 875 mV, which is only 41 mV more negative than that of a commercial Pt/C, and follows an efficient four-electron reaction pathway in acidic media. Notably, the fabricated catalyst demonstrated excellent methanol tolerance and long-term stability compared with the reference Pt/C. Therefore, this work provides a rational design approach to fabricating graphitic-C3N4-based nonprecious bimetallic electrocatalysts with M-N-x-C active sites for enhanced ORR activity in fuel-cell applications.