Novel highly active oxygen reduction reaction (ORR) catalysts for PEM fuel cells

S.H. Lim, L. Lai, Z. Luo, C.K. Poh, Z. Shen, J. Lin
Institute of Chemical and Engineering Sciences, SG

Keywords: ORR, non-noble-metal catalysts, N-FeCo catalysts, graphene, MWCNT

Summary:

Various catalysts for ORR have been studied in our lab, including functionalized-carbon-supported Pt, graphene-supported Pt and N-doped carbon-nanotube supported non-noble metals. The modifications of carbon support were proved to reduce Pt loading significantly. N-doping was found to be important in improving the ORR catalysts performance. Nitrogen-doped graphene was a better metal-free catalyst than pristine graphene for ORR due to the enhanced electron density in the catalyst valence band. Non-noble metal catalysts supported on N-doped graphene showed performance compatible to commercial Pt catalysts, much better than the same transition metals supported on conventional carbon carriers. By a very simple procedure MWCNTs were coated with wrapping polymer PVP. The presence of N-containing functional groups 2-pyrridone facilitated the subsequent N-coordination of metal ions via annealing. The best ORR catalyst MWCNT-N-FeCo was synthesized at >700 oC, which exhibited high performance and nearly four-electron oxygen reduction pathway (n ~3.8) in ORR. SEM, XRD, XPS and BET showed that low loading (<1wt%) of N, Fe and Co were uniformly distributed on the high specific area MWCNT surface. The presence of Co favored the formation of pyridinic nitrogen which may play important role in the oxygen activation.