Oxygen Reduction Reaction and X-ray Photoelectron Spectroscopy of Sputtered Fe-N-C Films

TL;DR

This study develops a method to synthesize and analyze Fe-N-C thin films for oxygen reduction catalysis, providing insights into their structure and activity to aid in designing better fuel cell catalysts.

Contribution

It introduces a co-sputtering synthesis technique for Fe-N-C thin films and characterizes their structure and activity, advancing model systems for catalyst study.

Findings

High-temperature films are smoother and more active.

High-temperature exposure increases graphitization and nitrogen species.

Fe-N-C thin films are feasible as model catalysts for ORR.

Abstract

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.