| Summary: | The performance of polymer electrolyte fuel cells depends on the nanostructure of the polymer composites in their components. The microporous layer within the cells, which generally comprises a composite of carbon black and polytetrafluoroethylene (PTFE), is a key component that prevents mass-transport losses in electrochemical reactions of the cells; therefore, we studied the distribution of PTFE within microporous layers using contrast-variation small-angle neutron scattering. By performing annealing above the PTFE melting point, its self-aggregations were reduced, and this effect was explained via the surface energies of PTFE and carbon black. Moreover, fuel cell performance testing demonstrated that better mass-transport properties were achieved when there were fewer PTFE self-aggregations within the microporous layers. Our findings suggest that an optimal PTFE distribution within fuel cell microporous layers can be achieved by engineering the surface energies of carbon black.
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