Simultaneous co-doping of N and S by a facile in-situ polymerization of 6-N,N-dibutylamine-1,3,5-triazine-2,4-dithiol on graphene framework: An efficient and durable oxygen reduction catalyst in alkaline medium

Abstract

Development of an efficient, nonprecious, and durable oxygen reduction catalyst to replace high-cost Pt-based catalysts is one of the critical challenges in polymer electrolyte membrane fuel cells. In the present study, we report a novel chemical method for the simultaneous doping of nitrogen and sulfur by in-situ polymerization of 6-N,N-dibutylamine-1,3,5-triazine-2,4-dithiol on a graphene framework. The composites are subjected to annealing at temperature between 900 °C and 1100 °C to form N-S/Gr catalysts. N-S/Gr-1000 catalyst exhibits an enhanced oxygen reduction reaction (ORR) activity dominated through 4e− pathway compared to other catalysts. The excellent durability of N-S/Gr-1000 catalyst with only a 20-mV negative shift in its half-wave potential after 10,000 repeated cycling contributes to the enhanced ORR. Although a larger shift in onset and half-wave potentials is observed for commercial Pt/C from the initial cycle, the linear sweep voltammogram recorded after 5000 cycles shows poor ORR kinetics with several redox steps. The potential of N-S/Gr-1000 catalyst as a cathode catalyst was validated in a membrane electrode assembly and in a real anion-exchange membrane fuel cell (AEMFC). A peak power density of ∼20 mW cm−2 was achieved under ambient temperature and pressure, which makes N-S/Gr-1000 a promising alternative nonprecious metal catalyst in AEMFCs.