Perparation And Characteraiton Of Pfsa/Fluororesin Blend Membranes For Vanadium Redox Flow Battery

Vanadium redox flow battery（VRFB）is a promising large-scale electrochemical energy storage technology with fast response,high capacity and high safety.A traditional VRFB consists of anode and cathode separated by a piece of membrane,which has great influence on the properties of VRFB system.The proton exchange membrane（PEM）is a key component of VRFB that has been researched extensively for increasing proton conductivity and preventing ions crossover between catholyte and anolyte.Dupont’s Nafion?series are the most commonly used PEMs at present for their superior proton conductivity and chemical stability.Dispiritedly,the high cost and relatively low ions selectivity of Nafion?bring great obstacles to the commercialization of VRFB.Thus,developing other alternative membranes is of urgent priority.In order to ameliorate the properties of PEMs in VRFBs,three novel PEMs have been prepared.（1）by mixing Nafion resin with Poly（vinylidene fluoride）（PVDF）and annealing at 180℃for 3 h,a membrane with high ion selectivity and tensile strength is prepared.Both ion selectivity and tensile strength are more than 60%higher than those of Nafion.After annealing,the proton conductivity of Nafion/PVDF blend membrane can reach 45.2mS·cm^-1.（2）blend membrane with better ductility and battery efficiency is prepared by using Poly(vinylidene-fluoride-co-hexafluoropropylene（PVDF-HFP）to instead PVDF because of its lower crystallinity.The conductivity and permeability of Nafion/PVDF-HFP blend membranes are similar to those of Nafion/PVDF blend membranes,however,the ductility is increased by 3 times while the energy efficiency of cell testing is as high as 85.9%.（3）by reinforcing Nafion/PVDF ion exchange resin with expanded-Poly（tetrafluoroethylene）（ePTFE）fiber membrane,a method to prepare ultra-thin PEM with extremely high mechanical properties and small area resistance is proposed.The tensile strength of the fiber reinforced membrane is 50%higher than that of the original Nafion/PVDF blend membrane,and the elongation rate is also increased by 2 times.In single cell test,the capacity retention rate of fiber-reinforced membrane is also increased by more than 20%compared to that of Nafion.The above three PEMs hold the similar cell performance as Nafion,and the content of Nafion resin in all these membranes are lower than 60%,which significantly reduces the costs of PEMs and provides new ideas for the subsequent development.