Susan G. Yan

Catalyst Development Needs and Pathways for Automotive PEM Fuel Cells

Mass production of fuel cell light-duty vehicles at competitive cost requires cathode (oxygen reduction reaction [ORR]) kinetic mass activities 4-fold higher than those of current state-of-the-art platinum / carbon black catalysts. 1 A catalyst-related cell voltage loss less than 50 mV over the entire current density range is sought over a >10 year automotive lifetime including ~300,000 large load cycles and ~30,000 start-stop cycles. While the materials set used in current demonstration vehicles falls short of these goals, pathways to these challenging targets are visible via increased attention to the structural details of Pt-containing multicomponent catalysts and through development of catalyst and support as a single system.

Catalyst Degradation Mechanisms in PEM and Direct Methanol Fuel Cells

While much attention has been given to optimizing initial fuel cell performance, only recent research has focused on the various materials degradation mechanisms observed over the life-time of fuel cells under real-life operating conditions. This presentation will focus on fuel cell durability constraints produced by platinum sintering/dissolution, carbon-support oxidation, and membrane chemical and mechanical degradations. Over the past 10 years, extensive R&D efforts were directed towards optimizing catalysts, membranes, and gas diffusion layers (GDL) as well as combining them into improved membrane electrode assemblies (MEAs), leading to significant improvements in initial performance of H2/air-fed proton exchange membrane fuel cells (PEMFCs) and methanol/air-fed direct methanol fuel cells (DMFCs). 3 While the required performance targets have not yet been met, current PEMFC and DMFC performance are close to meeting entry-level applications and many prototypes have been developed for field testing. This partially shifted the R&D focus from performance optimization to more closely examining materials degradation phenomena which limit fuel cell durability under real-life testing conditions. The predominant degradation mechanisms are sintering/dissolution of platinum-based cathode catalysts under highly dynamic operating conditions, dissolution of ruthenium from DMFC anode catalysts, the oxidation of carbon-supports of the cathode catalyst during fuel cell startup and shutdown, and the formation of pinholes in proton exchange membranes if