Optimizing the Molecular Weight of Poly(vinylidene Fluoride) for Competitive Perfluorosulfonic Acid Membranes

Homogeneous proton exchange membrane with high mechanical strength and low gas permeation is of paramount importance for the application of proton exchange membrane fuel cells (PEMFCs). Herein, the impact of different molecular weight of poly(vinylidene fluoride) (PVDF, M-w = 350 000-1 100 000 g mol(-1)) on the performance of the perfluorosulfonic acid (PFSA)/PVDF blend membrane is studied systematically for the first time. The mechanical strength of the PFSA/PVDF blend membrane increases and the H-2 crossover of PFSA/PVDF blend membrane is decreased with increasing molecular weight of PVDF. Due to the fact that ultra-high molecular weight PVDF has more long-chain molecules which can enhance the adhesive strength between PVDF and PFSA, the tensile strength of 25 wt% PVDF5130-PFSA (M-w = 1 100 000) membrane reaches 33.5 MPa with the thickness of 15 mu m, 200% higher than that of pure PFSA membrane and 60% higher than that of commercial Nafion 211. The H-2 crossover of the blend membrane is 0.69 mA cm(-2), much lower than that of commercial Nafion 211 (2.05 mA cm(-2)). When applied in PEMFCs, the blend membrane shows comparable power density to Nafion 211 with an output of 1.17 W cm(-2).