Development of non-precious metal oxygen-reduction catalysts for PEM fuel cells based on N-doped ordered porous carbon

摘要

N-doped ordered porous carbon (CN_x) was synthesized via a nano-casting process using polyacryloni-trile (PAN) as the carbon and nitrogen precursor and mesoporous silica as a hard template. Nitrogen adsorption/desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the synthesized CN_x and the derived non-precious metal oxygen-reduction catalysts. The CN_x exhibited a highly ordered porosity and high graphitization with a surface area of 1132 m~2 g~(-1) and a nitrogen content of 6.88 at.%. The non-precious metal oxygen-reduction catalysts were prepared by pyrolyzing iron acetate-impregnated CN_x in argon, followed by post-treatments. Optimizations of the iron loading and the pyrolyzing temperature were also explored. The catalytic activities of the CN_x products for the oxygen reduction reaction (ORR) were examined by rotating disc electrode (RDE) measurements and single-cell tests. The onset potential for oxygen reduction in 0.5 M H2SO4 of the best catalyst was as high as 0.88 V vs. normal hydrogen electrode (NHE). The current density obtained in an H2/O2 proton exchange membrane fuel cell (PEMFC) was as high as 0.6 A cm~(-2) at 0.5 V with a cathode catalyst loading of 2 mg cm~(-2).