Composite Membranes of PVDF/PES/SPEES for Flow Battery Applications

This work reports the preparation and characterization of composite membranes with potential applications in flow battery devices. A polymer solution of polyvinylidene fluoride (PVDF), sulfonated polyether ether sulfone (SPEES), and polyether sulfone (PES) was used to prepare proton exchange membranes with low permeation of cationic species, which is a desirable feature in energy conversion devices, such as vanadium flow batteries (VRFB). Vanadyl ion (VO²⁺) acidic solution was selected as a model to reveal the permeation capacity through the membranes as an affordable alternative to the Nafion^® 117 commercial membrane. The effects of the chemical composition and the thickness of the membranes on the morphology and proton exchange properties were evaluated. Characterization of the membranes was performed using physicochemical techniques including water uptake, swelling ratio, thermogravimetric analysis, scanning electron microscopy, Fourier transform infrared, surface charge density, atomic force microscopy, dynamic mechanical analysis, electrochemical impedance spectroscopy for proton conductivity, proton exchange rate, and the permeability of VO²⁺ ions. With VO²⁺ ion permeability of the order of 0.62 mM and H⁺ exchange rates of up to 498.5 × 10¹⁸ H⁺ cm⁻²*µm⁻¹*min⁻¹, the PVDF/PES/SPEES composite membranes emerge as an option with potential application for VRFB compared to the Nafion^® 117 membrane, which presented a VO²⁺ ion permeation value of 2.72 mM and H⁺ exchange rates of 445.2 × 10¹⁸ H⁺ cm⁻²*µm⁻¹*min⁻¹.