Nafion/poly(vinyl alcohol) nano-fiber composite and Nafion/poly(vinyl alcohol) blend membranes for direct methanol fuel cells

The poly(vinyl alcohol) (PVA) electrospun nano-fiber film supported Nafion resin composite (N/VA-f) membranes as well as the PVA blended in Nafion (N/VA-b) cast membranes are prepared and used for direct methanol fuel cell (DMFC) applications. The morphologies, conductivities, methanol permeability, and DMFC performances of these membranes are studied and compared with the commercial Nafion-117 (thickness ~175 μm) and Nafion-212 (thickness ~50 μm) membranes. We show that the membranes with a thickness of ~50 μm have an optimum PVA contents of ~10 wt% and ~5 wt% for both N/VA-f and N/VA-b membranes, respectively, for DMFC applications. The unit cell tests demonstrate the DMFC performance decreases with following sequence N/VA-f>N/VA-b>Nafion-117>Nafion-212. Using scanning electron microscopy and energy dispersion X-ray analyses, we show that PVA fiber film distributes in the middle plane of the N/VA-f membrane. However, agglomeration and non-homogeneous distribution of PVA are observed in the N/VA-b membrane. The more straight and less tortuous proton traveling pathway around the PVA fiber in the N/VA-f membrane than around the large PVA agglomeration domain in the N/VA-b membrane leads N/VA-f to have a higher proton conductivity optimum PVA content and better DMFC performance than the N/VA-b membrane.