Dual Nafion/Polyaniline Nanofibers Architecture for Applications in Fuel Cells Electrodes

We demonstrate a facile route for fabrication of nanostructured fuel cell cathode catalyst support via simultaneous co-electrospinning of electron and proton conducting materials. Solutions of Nafion and polyaniline (PANI) were electrospun simultaneously from two separate nozzles on a common substrate with the aim to develop co-percolating electron and proton conducting pathways. Owing to the lack of entanglements in Nafion and PANI solutions, PEO was used to aid in electrospinning of both solutions. The composition of the dual nanofiber mat was tailored by varying the relative solution concentrations and flow rates. SEM micrographs (fig.1 (a)) of the mats show three-dimensional porous non-woven morphology, which is ideal for facile gas transport and also for enhancement of the triple phase surfaces. Electrochemical impedance spectroscopy show presence of independent charge transfer channels in the composite fiber mats (fig.1 (b)). Equivalent circuits were used to decouple electrical conductivity from protonic conductivity. Electrical conductivity was also verified via current/voltage (I-V) curves. Dual fiber mat with a Nafion/PANI/PEO composition of 50/32/18 showed proton conductivity of 0.032 S/cm and electron conductivity of 0.042 S/cm. Such proton conductivity was shown to be higher than the pure Nafion (with 2wt% PEO as the carrier polymer) nanofiber mat. The dual fiber mat also showed the highest water intake capacity (presumably due to its high composition of the hydrophilic PEO), which we believe is responsible for its higher proton conductivity. Such dual fiber mats with percolating phases of both electron and proton conductors and a three dimensional through–connected inter-fiber pore structure (for gas transport) can serve as an excellent catalyst support for PEMFCs.

Figure 1 Nanofiber mat with a Nafion/PANi/PEO weight composition of 50/32/18 (a): SEM micrograph, Scale bar; 1µm, b) Nyquist plot  showing experimentally-obtained data and fitted impedance data obtained via an equivalent circuit.