Structure and Properties of Sulfonated Poly (ether ether ketone) / Laponite Proton Exchange Membrane for All Vanadium Redox Flow Battery

A series of sulfonated poly (ether ether ketone) /laponite (SPEEK/Lap) composite membranes was prepared by solution-casting method using SPEEK with a sulfonation degree of 58% as membrane matrix. The membrane properties such as water uptake (WU), swelling ratio (SR), proton conductivity (u), vanadium ion permeability and ion selectivity were detailly characterized and discussed. The results show that the introduced Lap nanofillers effectively improve sigma-, SR and mechanical properties of SPEEK composite membranes. The tensile strength of the SPEEK/Lap-0. 2 composite membrane is 1. 64 times that of pure SPEEK membrane. When the mass fraction of Lap increases from 0. 2% to 1. 5%, u(19. 9-23. 6 mS/cm) increases accordingly. The ion selectivity of SPEEK/Lap-0. 2 composite membrane is the best(5. 55x 103 S.min.cm(-3)), which is about 1. 39 times that of Nafion 117 membrane(3. 99 S.min.cm(-3)). In the single cell test, the self-discharge time of SPEEK/Lap-0. 2 composite membrane is 57. 2 h, which is 2. 4 times that of Nafion 117 and 1. 5 times that of pure SPEEK membrane. At a current density of 80 mA/cm(2), the voltage efficiency(VE, 86. 5%) and energy efficiency(EE, 84. 0%) of SPEEK/Lap-0. 2 composite membrane are much higher than those of Nafion 117(VE; 83. 8%, EE; 80. 7%) and SPEEK membrane(VE; 81. 4%, EE; 78. 9%). During the 100 times charge-discharge test, SPEEK/Lap-0. 2 composite membrane exhibits a stable energy efficiency, proving its good structure stability. In addition, SPEEK/Lap composite membranes exhibit a higher chemical stability in harsh oxidizing environment as compared with SPEEK membrane. Laponite nanofillers demonstrate a promising application as the low-cost high proton conductor, which can be used to prepare the proton exchange membrane (PEM) with high ion selectivity and low vanadium ion permeability for vanadium redox flow battery (VRFB) application.