Preparation of Nitrogen-Doped Porous Carbon Nanofibers and the Effect of Porosity, Electrical Conductivity, and Nitrogen Content on Their Oxygen Reduction Performance

Abstract

Nitrogen-doped carbon nanostructures are considered as a possible alternative to platinum-based catalysts for fuel cells. The surface density of catalytic sites, electrical conductivity, and nitrogen content play important roles in designing electrode materials for fuel cells. Herein, N-doped carbon fibers are prepared by electrospinning the poly(acrylonitrile) (PAN) solution followed by carbonization. Some of the key issues of the oxygen reduction reaction (ORR) are addressed in terms of nitrogen content, porosity, and electrical conductivity in the N-containing carbon nanofibrous system. Nitrogen content and the amount of the graphitic phase are varied by changing the carbonization temperature. In addition, N-doped carbon fibers with high porosity are prepared by electrospinning the solution mixture of poly(ethylene oxide) (PEO)/PAN followed by carbonization, and the porosity is tuned by varying the ratio of PEO to PAN. The effect of porosity or the surface density of catalytic sites on the ORR is studied. A medium porous sample prepared from the PEO/PAN mixture in a 1:1 ratio by carbonization at 1000 degrees C is found to be favorable for improved ORR performance for such a system. The observations made herein are explained in terms of trade-offs between electrical conductivity, nitrogen content, and surface density of active sites.