Power Output and Durability of Electrospun Fuel Cell Fiber Cathodes with PVDF and Nafion/PVDF Binders

Abstract

Membrane-electrode-assemblies (MEAs) with electrospun nanofiber mat electrodes (0.10 mg/cm2 Pt loading) and a Nafion 211 membrane were prepared and tested in a H2/air fuel cell at 100% and 40% relative humidity. The cathode binder was either neat poly(vinylidene fluoride) (PVDF) or a Nafion/PVDF blend (20 to 80 wt% Nafion) and the anode binder was Nafion with poly(acrylic acid). Polarization curves were recorded at 80°C and ambient pressure before, intermittently, and after a carbon corrosion voltage cycling experiment. The Nafion/PVDF cathode MEA with the smallest amount of PVDF (80/20 Nafion/PVDF weight ratio) produced the highest maximum power at beginning-of-life (BoL), 545 mW/cm2 at 100% RH, which was 35% greater than that for a conventional MEA with a neat Nafion binder. Carbon corrosion scaled inversely with cathode PVDF content, with a 33/67 Nafion/PVDF cathode binder MEA producing the highest end-of-life (EoL) power (330 mW/cm2). MEAs with < 50 wt% PVDF in the cathode binder exhibited a power density decline during carbon corrosion, whereas the power increased during/after carbon corrosion for nanofiber cathodes with binders containing > 50 wt% PVDF due to favorable increases in the hydrophilicity of the carbon support and Pt mass activity, coupled with a lower carbon loss.