ABSTRACT: Typical catalyst layers (CL) employed in PEM fuel cells are composed of a carbon supported Pt catalyst bound together with an ionomer, most often Nafion. Both the carbon support and ionomer play a crucial role in optimizing the catalyst utilization by proving electronic and ionic conductive pathways, respectively, without hindering gas transport. Upon fuel cell operation, the catalyst layer can degrade by one of 3 primary pathways:
- Loss of Pt surfaces area through Pt dissolution/Ostwald ripening
- Corrosion of the carbon support
- Degradation of the ionomer network
The contribution of each of these pathways depends upon CL compositions as well as the cell operating conditions. The extent of degradation is normally monitored in situ by cyclic voltammetry (CV) by measuring changes in the electrochemically active surface area (ECSA) of Pt. However, CV is limited in that it can only conclusively confirm the presence of the first pathway. Contributions from the other 2 pathways are typically confirmed by post mortem analysis of the CL.
We have recently reported that the addition of periodic electrochemical impedance spectroscopy (EIS) measurements to an accelerated degradation testing protocol (ADTP) allows one to clearly diagnose the presence of the other 2 degradation pathways. By performing EIS under conditions where the transmission line model is valid, the presence of carbon corrosion can be clearly detected by a characteristic shift in the EIS response over time. Likewise, the loss of ionic conductivity can also be observed through a unique change in the EIS response. Our methodology has since been extended and further validated by studying the stability of numerous commercial and in-house prepared catalysts using with different carbon supports. In this seminar, I will describe how EIS can be incorporated into almost any ADTP and how changes in the EIS response can be used for in situ diagnosis of degradation pathways that can be attributed to CL components.
Biosketch of E. Bradley Easton
Brad Easton was born and raised in St. John’s, NL
Current Position
Associate Professor of Chemistry (2011 – Present)
Assistant Professor of Chemistry (2006 – 2011)
Faculty of Science, University of Ontario Institute of Technology
Research Interests
Electrochemical materials, electrocatalysis, fuel cell, breath alcohol sensors, inorganic-organic hybrid materials, carbon surface chemistry
Education
- B.Sc. (Hon), Memorial University of Newfoundland
- PhD, Memorial University of Newfoundland (Jan. 2003, Chemistry, with Peter Pickup)
Experience
- NSERC Postdoctoral Fellow, Chemistry Department, Simon Fraser University (2003, with Steven Holdcroft)
- NSERC Postdoctoral Fellow, Physics Department Dalhousie University (2004 – 2006, with Jeff Dahn)
Awards
- 2013 Recipient of UOIT’s Research Excellence Award (Early Stage Researcher)
Brad Easton was born and raised in St. John’s, Newfoundland. He obtained both his B.Sc. (1998) and Ph.D. (2003) in Chemistry from Memorial University of Newfoundland. Easton then worked as an NSERC postdoctoral fellow at Simon Fraser University (2003 – 2004) and Dalhousie University (2004 – 2006). In 2006, he joined Faculty of Science at UOIT where he is currently an Associate Professor of Chemistry and leads a research group in materials chemistry that prepares and characterizes new materials with primary applications in electrochemical systems. His research explored fundamental problems in electrochemistry as well as materials in highly applied electrochemical systems.