Preparation And VRFB Performance Of The Modified Sulfonated Polybenzimidazole Amphoteric Membrane

Responding to rapid growth of the renewable energy applications,it is crucial to develop low cost and high efficient large-scale energy storage systems in order to smooth out the intermittency of the renewable energy resources.As one of the most promising large-scale energy storage systems,vanadium redox flow battery?VRFB?has attracted great attention in recent times.Membrane is one of the key components of VRFB which not only affects the whole cyclability performance but also determines the economic viability of the system.The Amphoteric ion exchange membrane is a membrane containing both anion and cation exchange groups,It can effectively solve the problems of VRFB ion exchange membranes that are difficult to balance because of its high conductivity and selectivity,and become a research hotspot.However,general amphoteric membranes face defects such as insufficient mass transfer efficiency and stability,in this paper,three amphoteric ion exchange membranes with novel structures were prepared by modifying the design of amphoteric membranes,and their properties were tested comprehensivelyIn order to solve the problems of amphiphilic membrane mass transfer efficiency,firstly,A novel hydrophilic/hydrophobic bi-comb-shaped amphoteric membrane was f designed by the one-pot reactions of PBI with bromohexane and 1,3-propanesultone.The sulfonic acid chain promotes the formation of amphoteric ion clusters,while the alkyl side chain enhances the packing of hydrophobic segments.This unique structure design optimizes the segregated microphase morphology of the membrane.Compared to the membrane without alkyl side chain,the bi-comb-shaped membrane shows a lowered area resistance?0.58 vs.0.96?cm²?as well as a reduced swelling ratio?11.7%vs.14.3%?.As a result,the cell with the bi-comb-shaped membrane exhibits improved voltage efficiency,thus achieving increased energy efficiency.In addition,the membrane of this structure occupies excellent cycle stability.The cell efficiencies maintain almost stable for 250 cycles,and the chemical structure has no change after immersing in the electrolyte solution for 28 days.Then,the cell efficiency of the pure material amphoteric membrane needs to be further improved,a kind of highly hydrogenated polyethylene bond?PEI?was introduced into the sulfonated polybenzimidazole to construct an ion crosslink to form an efficient hydrogen bonding network ionic cross-linked amphoteric membrane?PBI-PS/PEI?.This structure contains a large number of ion conducting groups,the sulfonated long side chains and hydrophilic PEI in the membrane promote the formation of hydrophilic channels,which greatly reduces the area resistance of the membrane The area resistance of PBI-PS/PEI 5%membrane only 0.39?cm²,which is better than Nafion 212 membrane,and exhibits a high VRBB performance.At a current density of 120 mA cm^-2,the EE of PBI-PS/PEI 5%membrane can reach 86.7%,and it can still reach more than 80%at 200 mA cm^-2.On the basis of ensuring high ion conductivity,the vanadium penetration of the prepared PBI-PS was reduced and the stability was improved.A novel blend membrane?PBI-PS/MoS₂?was prepared by blending two-dimensional nanostructured molybdenum disulfide?MoS₂?.The MoS₂ in the membrane adjusts the internal ion channel to increase the selective permeability of ions and effectively prevent the membrane from being attacked by vanadium ions,improving the selectivity and stability of the membrane,making it show excellent battery performance at all current density.The PBI-PS/MoS₂ 1%membrane has a vanadium penetration of only 0.78×10-9 cm² s^-1.The CE of all PBI-PS/MoS₂ membranes exceeds 97%at all current density range and 99%at 120²00 mA cm^-2,resulting in a excellent cell performance.In addition,due to its good chemical stability and vanadium resistance,the PBI-PS/MoS₂ 1%membrane can maintain stably for nearly 800 cycles,and its capacity retention?100 cycles of 82%?is much lower than that of Nafion 212 membrane?29.1%?.