Catalyst layer network formation and its effect on fuel cell performance

A new deposition technique, in situ sonication (ISS), which produced a more uniform and less porous datalyst layer (CL) was developed. Simultaneous sonication and solvent evaporation during CL preparation deterred catalyst particle agglomeration. This suggested that prolonged sonication during deposition hinders the van der Waals attractive forces between catalyst particles that promote agglomeration. The MEA prepared by multilayer hand painting of the catalyst ink directly onto Nafion 117 (Method B) displayed the lowest performance. CL made by ISS, regardless of whether the decal/hot press transfer or direct deposition technique was used (Method C and D), had a similar fuel cell performance, while the standard multilayer hand painting and decal/hot press transfer method (Method A) demonstrated the highest performance. A network of Nafion fibers connecting catalyst particles disposed throughout provided a more favorable triple phase boundary, where high porosity allows for reactant gas diffusion, smaller catalyst agglomerates possess a higher available surface area for reaction, and the Nafion fibers provide a pathway for proton diffusion to the polymer electrolyte membrane. This network was found within the CL microstructure in areas of high porosity. CL with higher initial porosity (Method A) allowed for more network formation during fuel cell testing. This is an abstract of a paper presented at the ACS Fuel Chemistry Meeting (Washington, DC Fall 2005).

Catalyst layer network formation and its effect on fuel cell performance Conference Paper