Nitrogen and Fluorine co-doped carbon catalyst with high oxygen reduction performance, prepared by pyrolyzing a mixture of melamine and PTFE

Abstract

A novel nitrogen and fluorine co-doped carbon catalyst (C-Mela-PTFE) is prepared by pyrolyzing a mixture of melamine and polytetrafluoroethylene (PTFE), the catalyst has a three-dimensional vesicular structure with ultrathin wall, and exhibits excellent ORR performance in both alkaline and acidic mediums. In an alkaline medium, the catalyst exhibits superior ORR activity to that of commercial Pt/C catalyst. Notably, the ORR activity of the catalyst is just slightly lower than that of Pt/C catalyst in acidic medium. It is interesting that the ORR limiting current density of our C-Mela-PTFE catalyst is much higher than that of Pt/C catalyst. The effects of the melamine/PTFE ratio and the pyrolysis temperature on the catalyst's ORR performance are investigated. The optimal melamine/PTFE ratio by weight is 1:1.5, and the optimal pyrolysis temperature is 950°C. The catalyst samples are characterized by XRD, SEM/TEM, Raman analysis, and XPS, the results reveal the ultra-thin-walled vesicular structure, high surface area and porosity, and high doping amounts of N and F of the catalyst. For the optimal sample, the N and F contents are up to 13 and 6at.%, respectively, the proportion of pyridinic N is up to 45at.% according to the deconvolution results from its XPS spectrum. The ORR on our catalyst seems follow a four-electron transfer pathway, according to RDE-RRDE analysis results, the four-electron selectivity is up to 97%. We suggest that the high ORR performance of our catalyst is attributable to its high N content and high proportion of pyridinic N, co-doping of fluorine, as well as the high surface area and high porosity caused by its ultra-thin-walled vesicular structure.