Notably enhanced proton conductivity by thermally-induced phase-separation transition of Nafion/ Poly(vinylidene fluoride) blend membranes

Blending perfluorosulfonic acid (e.g. Nafion) with other polymers is an effective approach to reduce the cost and adjust the properties of durable proton conducting membranes. In particular, poly(vinylidene fluoride) (PVDF) composites have attracted much attention because of its outstanding chemical/thermal stability and it can enhance the barrier property, mechanical strength and processibility of the membranes. One of the major issues with this approach, however, is that the proton conductivity of the Nafion/PVDF composite drops rapidly with increasing PVDF content. In this work, we demonstrate for the first time that through a simple and facile annealing process at 180 degrees C, the proton conductivity of the Nafion/PVDF blend membrane can be boosted by more than 200%, and the annealed membrane with 60 wt% Nafion shows proton conductivity as high as 45.2 mS cm(-1). The barrier properties of the blend membranes are significantly superior to the neat Nafion as indicated by the vanadium ion permeability of approximately one third of the Nafion. In the single cell test of vanadium redox flow battery, the energy efficiency of the annealed membrane with 60 wt% Nafion reaches 83.6% at 100 mA cm(-2), which is comparable to Nafion membranes. The annealed blend membranes possess a high chemical and dimensional stability, which makes them promising for practical applications in redox flow batteries or fuel cells.