Tuning the Ion Selectivity and Chemical Stability of a Biocellulose Membrane by PFSA lonomer Reinforcement for Vanadium Redox Flow Battery Applications

A low-cost biocellulose (BC) membrane is incorporated and coated with the perfluorosulfonic acid (PFSA) ionomer through a new facile preparation route to develop an efficient membrane for vanadium redox flow batteries (VRFBs). Scanning electron microscopy and Brunauer-Emmett-Teller analysis revealed that the BC-PFSA membrane had a dense and smooth surface morphology, thus confirming the efficacious incorporation of PFSA into the pores, between the layers, and on the surface of the microfibrils of the BC membrane. The BC-PFSA membrane exhibited superior physicochemical properties, chemical stability, and electrochemical performance compared to those of the BC membrane. The proton conductivity of the BC-PFSA membrane (0.0605 S/cm) was 12.1 times higher than that of the BC membrane (0.005 S/cm). The presence of proton carriers in the BC-PFSA membrane caused rapid proton mobility through the formation of ionic clusters in the membrane. The pore-filling behavior significantly controlled the vanadium ion crossover in the BC-PFSA membrane. Because of higher selectivity, the charge and discharge behavior of the VRFB system containing the BC-PFSA membrane was superior to that of the BC membrane system. The BC membrane had a low energy efficiency of 63.02% at 80 mA/cm(2) in the fifth cycle, while the BC-PFSA membrane showed a much higher energy efficiency of 78.92% under identical conditions. The interaction between the BC microfibrils and the PFSA led to the formation of BC-PFSA, thus increasing the chemical stability of the BC membrane. Furthermore, the BC-PFSA membrane showed a comparable membrane characteristic performance with Nafion and the cost of the BC-PFSA membrane is lower than that of the Nafion membrane. In addition to reducing the cost of the membrane, the BC membrane decreases the environmental impact of PFSA polymer membranes. Because of its remarkable performance, low cost, and great environmental benefits, the BC-PFSA membrane is a promising membrane candidate for VRFB applications.