An improved proton conductivity and structure stability of SPEEK/SPPS blend membranes for vanadium redox flow battery

The sulfonated polyphenylene sulfide (SPPS) containing a rigid main chain is introduced into the SPEEK-based proton exchange membrane to approach the high proton conductivity and dimensional stability. Under the varied contents of SPPS, the SPEEK/SPPS blend membranes present an increased proton conductivity, and at 15wt% SPPS, the SPEEK/SPPS-15% shows higher proton conductivity (30.9 mS cm-1) and ion selectivity (10.5×103 S min cm-3) than that of Nafion 117 (26.8 mS cm-1, 4×103 S min cm-3). And, the cell assembled with SPEEK/SPPS-15% membrane demonstrates better voltage efficiency (VE: 92.5-75.0%) and energy efficiency (EE: 90.0-74.2%) at the current density of 60-150 mA cm-2. During a 100-time charge-discharge cycle at 100 mA cm-2, excellent cycling stability and high charge capacity retention are proved, and the SPEEK/SPPS-15% blend membrane proves its outstanding structural stability and durability after 300 cycles at 150 mA cm-2. This shows that the structural similarity of the membrane matrix is beneficial to develop a high-performance SPEEK/SPPS blend membrane with desirable structural stability.