Preparation And Research Of New Proton Exchange Membrane For All-Vanadium Flow Battery Based On Polybenzimidazole

Increasing energy demand and increasingly depleted fossil fuel resources require sustainable energy alternatives,such as renewable clean energy.However,the instability of renewable energy sources leads to low quality output power.In energy storage systems,VRFB has been widely used due to its long life,stable output power,and good safety for large-scale applications.As a key component in VRFBs,the proton exchange membrane has become an important factor restricting the development of VRFBs.In past years,commercial Nafion membrane was the best available and commonly used membrane in VRFBs.However,the price of these membranes has reached 500 to 1000 USD/m2,which limits its further commercialization in VRFBs.Therefore,it is meaningful to develop a membrane with low cost and excellent electrochemical performance.Recently the use of PBI membranes in VRFBs has also been discussed and shows a good application prospect.And H3PO4 doping was used to optimize the conductivity of PBI membrane.After doping by H3PO4,the positive charge on the imidazole of PBI polymer backbone can repel vanadium ions,and the excessive free H3PO4 molecule results in higher conductivity.Therefore,we use PBI as raw material to prepare different proton exchange membranes and conduct further research.In this paper,a pore-filling proton exchange membrane is fabricated by combining a porous polyethylene(PE)substrate and polybenzimidazole(PBI)resin for vanadium redox flow batteries(VRFB).The PE substrate not only optimized the structure of the composite membrane,but also significantly reduces its cost.Compared with Nafion212 and pure PBI membrane,PE/PBI composite membrane exhibits higher VRFB energy efficiency(88.62%-80.11%)in a current density range of 100-200 mA cm-2.And within 150 cycles at 180 mA cm-2,the composite membrane maintains stable charge-discharge performance with slower capacity decay rate,indicating a promising membrane candidate for VRFBs.In addition,in order to solve the short life of PBI materials due to phosphoric acid leakage and the low conductivity of PBI membrane after phosphoric acid doping,we used dopamine solution to process PBI membrane.The results show that the presence of amino groups in the dopamine molecules on the surface of the composite membrane enhance the acid-base interaction and improved the proton conductivity of the composite membranes.Compared with pure PBI membrane,PBI-NH2-16 membrane not only has better single cell efficiency,but also shows longer cycle life within 100 cycles.