Nafion/PVDF nanofiber composite membranes for regenerative hydrogen/bromine fuel cells

•Nafion/PVDF composite membranes were made for H2/Br2 fuel cells by electrospinning.•A dual fiber electrospinning method was employed.•Two complementary nanofiber/matrix morphologies were investigated.•Membranes with Nafion fibers embedded in PVDF matrix were superior to Nafion 115.

Nanofiber composite proton exchange membranes were fabricated and their properties measured, for possible use in a regenerative hydrogen/bromine fuel cell. The membranes were prepared from dual nanofiber mats, composed of Nafion® perfluorosulfonic acid (PFSA) ionomer for proton transport and polyvinylidene fluoride (PVDF) for mechanical reinforcement. Two composite membranes structures containing Nafion volume fractions ranging from 0.30 to 0.65 were investigated: (1) Nafion nanofibers embedded in a PVDF matrix (N(fibers)/PVDF) and (2) PVDF nanofibers embedded in a Nafion matrix (N/PVDF(fibers)). The in-plane conductivity for films equilibrated in water and 2.0 M HBr scaled linearly with Nafion volume fraction for both morphologies. The through-plane proton conductivity of N(fibers)/PVDF membranes in water was lower than that of N/PVDF(fibers) films with the same Nafion content for films with less than 55 vol% Nafion, e.g., 0.03 S/cm for N(fibers)/PVDF membrane vs. 0.04 S/cm for N/PVDF(fibers) membrane at 40 vol% Nafion. N(fibers)/PVDF membranes exhibited excellent Br2/Br3−Br3− barrier properties with a reasonable membrane resistance, e.g., a N(fibers)/PVDF membrane with 40 vol% Nafion and a thickness of 48 µm had the same area-specific-resistance as Nafion® 115 (0.13 Ω cm2) but its steady-state Br2/Br3−Br3− crossover flux was 3.0 times lower than that of Nafion 115 (1.43×10−9 mol/s/cm2vs. 4.28×10−9 mol/s/cm2).