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.

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The research work examines effects of organic-inorganic hybrid membrane made of low-cost sulfonated poly(2,6-dimethyl-1,4phenylene oxide) (SPPO) and graphene oxide (GO) to improve the membrane properties for application in vanadium redox flow battery (VRFB). SPPO membrane alone is economical but undesirable for VRFB operation because it is significantly vulnerable to degradation in vanadium electrolyte. For this reason, the inorganic GO is introduced into the SPPO polymer matrix, thus beneficial effects are acquired specifically that the hybrid SPPO-GO membrane shows enhanced chemical-physical properties, especially higher ion selectivity is obtained for 2 wt% GO incorporated into SPPO, the greater than pure SPPO and Nafion 212 membrane. Furthermore, vanadium permeability is lowered for composite membrane incorporated with GO. Importantly, the hybrid membrane shows increased oxidizing stability in comparison to the SPPO membrane alone. Accordingly, the hybrid SPPO-GO membrane obtains higher efficiencies than pure SPPO membrane in VRFB cell test. Therefore, the results of this work can reveal promising consideration on the use of economical polymer membrane for further development in VRFB application.

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