Modification And Property Study Of Proton Exchange Membranes For Batteries

With the increasing demand for energy and the depletion of traditional fossil energy,all sectors of society are devoting themselves to the development of green and pollution-free clean energy technologies.All-vanadium flow batteries?VRFBs?and proton exchange membrane fuel cells?PEMFCs?are considered as the most promising electrochemical technologies for electricity storage and automotive power source,respectively,due to their advantages of good safety,long lifetime and high energy efficiency.Proton exchange membrane is the key component for both of the batteries to achieve high performance.However,the widely used perfluorosulfonic acid membranes,such as Nafion^?membranes,have several drawbacks,including high cost,insufficient conductivity under low humidity for PEMFCs,serious vanadium ion penetration in VRFBs and poor dimensional stability,which seriously hinder the further development of battery technology.In order to solve these problems and improve the membrane properties for PEMFCs and VRFBs,three novel proton exchange membranes have been designed and prepared:a)by introducing mesoporous and hollow silica spheres as micro-water-tanks in polymer matrix,the water uptake of proton exchange membranes significantly increases,while the swelling is obviously restricted.The modified membrane also shows a better adaptability to the sudden change of environmental humidity;b)highly proton-conducting ionic liquid is selected as proton donor to help the membrane conductivity get rid of the dependence of environmental humidity.The membranes exhibit high stability and proton conductivity under intermediate temperatures and ultra-low humidities,which is of great significance for the development of intermediate temperature PEMFCs;c)being different from traditional organic-inorganic composite membranes,sulfonated zirconium is successfully prepared and applied as a novel functional additive in PEMs.Abundant sulfonic groups on the surface of the S-ZrO₂ make great contributions to promote proton conduction of sulfonated polyethersulfone?SPES?.At the same time,the migration of vanadium ions is effectively inhibited due to the blocking effect,and therefore,the ion selectivity of the membrane is considerably improved for the application in VRFBs.The energy efficiency of the composite membrane in VRFB single cell reaches as high as 86.78%at a current density of 100mA cm^-2,which is superior to that of Nafion 212 membrane.Moreover,the chemical stability of various chemically stable polymer materials is tested and compared.The results show that,the sulfonation of polymers significantly decreases the chemical stability of the membrane,which provides experimental data as the reference for materials evaluation of VRFB proton exchange membranes,from the viewpoint of chemical stability.