Study of Co-electrospun Nafion and Polyaniline Nanofibers as Potential Catalyst Support for Fuel Cell Electrodes

Nanostructured composites of electron and proton conducting materials were fabricated via simultaneous electrospinning of Nafion and PANI solutions on a rotating collector for application as fuel cell catalyst supports. Poly (ethylene oxide) (PEO) was used as a carrier polymer to enhance chain entanglements and therefore the electrospinnability of both solutions. Dual nanofiber mat with a Nafion/PANI composition of 50/50 wt% was prepared. Post electrospinning annealing at 150 °C for 5 mins and densification at 500 psi was performed to enhance Nafion domain crystallinity and fiber fraction (i.e. reduce void volume), respectively. PEO was selectively removed by treatment of the electrospun mats in boiling acid solution for one hour. Conductivity of the nanofiber mats was investigated using electrochemical impedance spectroscopy and equivalent circuit was used to decouple impedance from electron and proton transfer in the composite fiber mat. The resultant dual nanofiber mat exhibited an in-plane conductivity (σ=) of 0.014 and 0.023 S/cm for electrons and protons, respectively. Through plane conductivity (σ⊥) was also studied and the dual nanofiber mat showed anisotropy for both proton and electron conductivities with (σ=)/(σ⊥) = 1.27 and 1.4, respectively. Such dual nanofiber mats with percolating phases of both electron- and proton-conductors and three dimensional through-connected inter-fiber pore structure (for gas transport) can potentially serve as excellent catalyst supports for fuel cells.