Non-PGM Fe-N-C Catalysts for Oxygen Reduction Reaction in Pemfcs: MEA Design and Post-Mortem Analysis

Abstract

Clean energy sources are currently in high demand. Fuel cells, such as proton exchange membrane fuel cells (PEMFCs,) are a potential solution. Current technologies use platinum-based catalysts, which are expensive and contribute to over 40% of the total cost of a PEMFC.(1) However, considerable research has been undertaken in the past decade examining non-platinum group metal (non-PGM) catalysts. One rapidly developing class of non-PGM catalysts for oxygen reduction reaction (ORR) are nano-materials based on transition metal-carbon-nitrogen networks (M-N-C).(2) These materials include Fe, Co or Mn salt and N-containing organic precursors (either polymeric or low molecular weight ones). It is widely recognized that nitrogen moieties of M-N-Cs play a crucial role in the ORR mechanism. It has been suggested that the nitrogen stabilizes the attachment of the transition metals to the underlying carbon support creating the ORR active sites.(2-4) We have examined a number of different organic precursors in our previous research. They include Co-tetramethoxy phenylporphyrin(6), poly(ethyleneimine)(7), 4-aminoantipyrine(1), and carbendazim(8). The catalysts presented in this work were synthesized using novel organic precursors. These catalysts showed promising results when tested in membrane electrode assembly configurations in both H2/Air and H2/O2. (Fig. 1a and 1b) The two best preforming catalysts (made with imidazole-family of precursors - IFoP Fig. 1c) and the worst performing catalyst (made with phenylenediamine and piperazine organic precursors Fig. 1d) were selected for further chemical post-mortem analysis that will be obtained by high-resolution X-ray Photoelectron Spectroscopy (XPS). XPS allows for the quantification of surface oxides, an increase in surface oxides after testing indicates degradation of the catalyst layer. Focused Ion Beam/Scanning Electron Microscopy (FIB-SEM) will also be used to obtain a visual 2d cross-section and 3d representation of the catalyst layer. Understanding the chemical and morphological changes that occur in catalyst layers during fuel cell operation and its relationship to original properties of the catalysts is of critical importance for designing not only active but also durable M-N-C ORR electrocatalysts. Acknowledgments: This work is supported by DOE-EERE Fuel Cell Technology Program: “Development of Novel Non Pt Group Metal Electrocatalysts for PEMFC” (S.Mukerjee, PI)