  Electrocatalysts for the oxygen reduction reaction (ORR) based on complexes
of iron and nitrogen in a carbon matrix (Fe-N-C) are a promising alternative to
platinum group metal (PGM) based catalysts in polymer electrolyte membrane
(PEM) fuel cells. Further improvements of Fe-N-C catalysts would benefit from
model thin film studies of activity and stability of catalytic sites, but
synthesis of Fe-N-C model thin films is challenging. Here we report on
synthesis and characterization of Fe-N-C thin films produced by co-sputtering
iron and carbon in a reactive nitrogen atmosphere onto removable glassy carbon
rotating disk electrode (RDE) tips. Scanning electron microscopy (SEM)
measurements indicate that the Fe-N-C films deposited at high temperature are
smoother than the films annealed at high temperature. ORR activity measured on
the thin Fe-N-C films is greater for both high-temperature samples than for the
room-temperature sample. From the analysis of X-ray photoelectron spectroscopy
(XPS) data, exposure of the films to high temperatures results in increased
graphitization of the carbon with the Fe-N-C films, and increased relative
amount of graphitic and hydrogenated nitrogen species. Overall the results of
this study demonstrate the feasibility of a thin film model system approach for
studying active sites in PGM-free catalysts.

Materials Science