Development of N-doped carbon nanomaterials with controlled shape and composition for fundamental studies of electrocatalytic systems based on PGM and PGM-free catalysts

Abstract

Renewable energy technologies such as polymer electrolyte membrane fuel cells (PEMFCs) can potentially offset growing energy demands, however challenges such as cost and stability of oxygen reduction catalysts (ORR) remain to be addressed. Some of these challenges can be addressed by development of efficient catalysts and supports. Research has shown that stability of the platinum group metal (PGM) and PGM-free nanoparticle catalysts can be improved by modifying properties of the carbon support with nitrogen dopants. Development of more active and stable PGM-free catalysts such as those based on N-doped carbon and atomically dispersed iron species (Fe-N-Cs) would have drastic effect on the cost of the catalysts. Fundamental understanding of N-doped systems and their impact on performance of PGM and PGM-free catalysts can be advanced by utilizing novel characterization approaches and employing model high-surface area materials. This work focuses on development of N-doped carbon nanospheres (N-CS) with controlled composition and shape to serve as model high-surface area substrates. In fabricated N-CS, it was found that both N at% and at% of pyridinic N species decrease as pyrolization temperature increases. N-CS in the range of 50-100 and 100-200 nm were selected as best candidates for use in further catalyst studies and were used to develop a series of model Fe-N-C nanospheres. Among Fe precursors used, FeCl3 · 6 H2O resulted in the best dispersion of Fe, presumably as atomically dispersed species. Further, N-CS were used as substrates for Pt nanoparticle catalysts which were shown to contain 2-4 nm Pt nanoparticles dispersed over the surface of the N-CS substrate. The range of compositions of the series of developed materials demonstrates their applicability for future studies using novel ex-situ and in-situ methods.