Development of non-precious metal oxygen-reduction catalysts for PEM fuel cells based on N-doped ordered porous carbon
N-doped ordered porous carbon (CNx) was synthesized via a nano-casting process using polyacrylonitrile (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 CNx and the derived non-precious metal oxygen-reduction catalysts. The CNx exhibited a highly ordered porosity and high graphitization with a surface area of 1132 m2 g−1 and a nitrogen content of 6.88 at.%. The non-precious metal oxygen-reduction catalysts were prepared by pyrolyzing iron acetate-impregnated CNx in argon, followed by post-treatments. Optimizations of the iron loading and the pyrolyzing temperature were also explored. The catalytic activities of the CNx 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.
Journal: Applied Catalysis B: Environmental - Volume 93, Issues 1–2, 25 November 2009, Pages 156–165