全钒液流电池用磺化聚芴醚酮质子交换膜的制备及性能

Preparation and properties of sulfonated poly(fluorenyl ether ketone) proton exchange membranes for vanadium redox flow batteries

摘要:

质子交换膜(PEM)作为全钒液流电池(VRFB)的核心组件之一,应当解决成本高昂、合成过程复杂等问题,并具备高质子传导率、低钒离子渗透率、高机械强度和优异化学稳定性等关键性能。本文基于四甲基双酚芴单体通过缩聚反应合成了一系列聚芴醚酮化合物PFEKs,再利用溴代反应将苯甲基功能化为溴甲基,接着通过4-羟基苯磺酸钠的SN₂亲核取代制得了一系列不同离子交换容量的磺化聚芴醚酮聚合物(SPFEKs)。通过溶液浇铸法成膜并酸化,得到一系列新型低成本PEMs。该合成路线的原料来源广泛,价格低廉,不涉及危险的磺化反应,易于工业放大。所得膜都具有良好的机械性能和氧化稳定性,其中SPFEK-40膜具有较高的质子传导率及离子选择性、较低的钒离子渗透率及面电阻,综合性能优异。以SPFEK-40膜组装的VRFB在电流密度为80 mA/cm₂^{时的能量效率}(EE)为88.2%,高于以Nafion 212膜组装的VRFB的84.8%。此外,以SPFEK-40膜组装的VRFB在30次循环后放电容量仅衰减至84.3%,远高于以Nafion 212膜组装的VRFB的66.1%。

Abstract:

Proton exchange membrane (PEM) is one of the core components of vanadium redox flow battery (VRFB). Excellent PEMs should solve the current problems of high cost and complicated synthesis process and have key properties such as high proton conductivity, low vanadium ion permeability, high mechanical strength and excellent chemical stability. Herein, a series of poly(fluorenyl ether ketone)s (PFEKs) were synthesized based on tetramethylbisphenolfluorene monomer by condensation polymerization, and the phenylmethyl groups were functionalized to bromomethyl groups followed by SN₂ nucleophilic substitution with sodium 4-hydroxybenzenesulfonate to yield a series of sulfonated poly(fluorenyl ether ketone)s (SPFEKs) with different ion exchange capacities. A series of novel low-cost PEMs were obtained by solution casting SPFEKs into membranes and acidification. The synthetic route is based on a wide and inexpensive source of raw materials, which avoids dangerous sulfonation reactions, making it easy for industrial scale-up. All of the prepared PEMs have good mechanical properties and oxidative stability, among which the SPFEK-40 membrane has the most balanced properties such as high proton conductivity, high ion selectivity, low vanadium ion permeability, and low areal resistance. The energy efficiency of the VRFB assembled with SPFEK-40 membrane was 88.2% at a current density of 80 mA/cm^₂, which is higher than that of the VRFB assembled with Nafion 212 membrane (84.8%). In addition, the discharge capacity of the VRFB assembled with SPFEK-40 membrane only decreased to 84.3% after 30 cycles, which is much higher than that of the VRFB assembled Nafion 212 membrane (66.1%).