Impact of Platinum Loading and Catalyst Layer Structure on PEMFC Performance

Reducing Pt in proton exchange membrane fuel cells is the subject of intense research and development. Recently, researchers have observed significant performance loss due to a transport limitation at the Pt surface. This is investigated here with loading studies that fix electrode thickness and bulk properties. Within these layers, the impact of Pt dispersion is probed by varying the wt% of Pt/C while holding Pt loading and electrode thickness constant by diluting with carbon, effectively varying the average distance between Pt particles while maintaining gas phase loss in the catalyst layer. Results elucidate how the electrode structure impacts local transport loss. It is demonstrated that local transport loss is not fully captured with a normalized Pt area. Additional geometric considerations that account for ionomer surface area relative to the Pt particles are required to resolve performance loss at low Pt loading as electrode structure varies. Furthermore, within this ionomer layer an interfacial resistance at both the gas and Pt interfaces are necessary to account for performance trends observed. These results demonstrate that residual performance loss associated with low cathode Pt loading can be mitigated by electrode design, where oxygen flux through the gas/ionomer interface to the Pt surface is minimized.