Investigation On The Preparation And Performances Of Polysulfone Anion Composite Membranes For All Vanadium Flow Battery

In order to solve unstable and discontinuous power transmission of wind,solar and other reweably energy,it is particularly necessary to use of large energy storage equipment.All vanadium flow battery(VRB)posseses advantages of adjustable capacity,green to environment and so on,which makes it an important candidtate for large scale energy storage.Membrane is one of the key materials in VRB.Reducing the cost of ion exchange membrane and improving its cost-effective have significance to promote the development of the VRB.To improve the mechanical properties and reduce the vanadium permeability of the ion exchange membrane,a quaternized polysulfone/polyvinylidene fluoride blend membranes(Q/P blend membranes)for vanadium redox flow battery are prepared by solution casting method,and the properties are tested in detail.Compared with Nafion117 membrane,Q/P blend membrane shows smaller swelling ratio,ultra-low vanadium permeability,better stability and excellent cycle performance.VRB with Q/P-20% membrane has a high coulombic efficiency due to its low vanadium permeability,which reaches up to 99.29% at 80 mA cm-2.At the current density of 40 mA cm-2,the Q/P-15% membrane has the highest voltage efficiency of 91.12%.And all the results show that the introduction of PVDF plays an important role in improving the performance of Q/P blend membranes.The lower conductivity of the anion exchange membrane and the higher vanadium permeability of the cation exchange membrane are the main obstacle for their further application in VRB.To solve this problem,QAPSF(quaternized polysulfone)and SPEEK(sulfonated poly ether ether ketone)are used as anion and cation exchange resin,respectively,to prepare the amphoteric membrane with different anion and cation exchange resin ratio,and the properties are studied.The Q/P/S-2 membrane with anionic and cation exchange resin ratio of 3:2 has a better property due to its combination of lower vanadium permeability of the anion exchange resin and the higher conductivity of the cation exchange resin.As a result,its vanadium permeability coefficient is only 0.60 × 10-7 cm2 min-1,self-discharge time is 58.05 h,and energy efficiency is above 80%.To further improve the conductivity of amphoteric membrane,different contents of carbon nanotubes are used as additives to prepare modified amphoteric membranes.Results show that the conductivity of the modified membrane has increased to a certain degree compared with the membrane without carbon nanotubes.The horizontal conductivity of the C-3% membrane is 13.90 mS cm-1,which is 3.8 mS cm-1 higher than that of Q/P/S-2 membrane.In the single cell test,the energy efficiency of the C-2% membrane is 89.36% at the current density of 40 mA cm-2,which is 2.56% higher than that of the Q/P/S-2 membrane.At the end of this paper,the cost of Q/P blend anion exchange membrane,Q/P/S amphoteric membrane and carbon nanotube modified amphoteric membrane are estimated.It was found that all the ion exchange membranes prepared in this paper have relatively low price and the cost of ion exchange membrane can be reduced effectively,which is significant to promote the development of VRB.