PTFE/SPEEK/PDDA/PSS composite membrane for vanadium redox flow battery application
How to solve the crossover of vanadium ions through ion exchange membrane is a key issue in vanadium redox flow battery (VRB), especially for ultra-thin membranes used for VRB to obtain a lower cell resistance. Herein, an ultra-thin (~ 30 μm) PTFE/SPEEK [polytetrafluoroethylene/sulfonated poly(ether ether ketone), P/S] membrane is successfully prepared and modified by using layer-by-layer (LBL) self-assembly technique with polycation poly(diallyldimethylammonium chloride) (PDDA) and polyanion poly(sodium styrene sulfonate) (PSS). P/S membranes are alternatively immersed in positively and negatively charged polyelectrolyte to form 2 to 8 bilayers onto its surface. Consequently, a series of P/S-[PDDA/PSS] n (n is the number of multilayers) membranes are fabricated. Both the physicochemical properties and VRB performances of the P/S-[PDDA/PSS] n membranes are then investigated in detail. Results show that the ion selectivity of the P/S-[PDDA/PSS] n membranes is much higher than that of pristine P/S membrane, especially for P/S-[PDDA/PSS]6 membrane. As a result, the VRB with the P/S-[PDDA/PSS]6 membrane exhibits the highest coulombic efficiency (CE) of 96.5% at 80 mA cm−2, the highest voltage efficiency of 94.7% at 40 mA cm−2 and the highest energy efficiency of 87.7% at both 40 and 50 mA cm−2, respectively. In addition, 80 times charge–discharge test proves that the P/S-[PDDA/PSS]6 membrane possesses high stability and no obvious CE decay after running. All the results show that the LBL technique is an effective way to prepare ultra-thin membrane with high ion selectivity for VRB application.
The authors gratefully thank the financial supports of this work by the Shandong Provincial Natural Science Foundation of China (Grant No. ZR2017MB032), the National Natural Science Foundation of China (Grant No. 21703048) and the Fundamental Research Funds for the Central Universities (Grant No. HIT. NSRIF. 201707).
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Conflict of interest
There are no conflicts of interest for all authors.
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