Development of hydrocarbon-based composite membranes with enhanced ion selectivity for vanadium redox flow batteries

초록

To overcome the limitations of conventional PFSA membranes in vanadium redox flow batteries (VRFBs), a reinforced composite membrane based on sulfonated poly (p-phenylene) (sPP-PSK) and PTFE support was developed. The membrane, denoted as F/PSK-1.6, was designed to improve ion selectivity, mechanical strength, and long-term electrochemical stability. The optimized membrane exhibited a proton conductivity of 0.0902 S cm-1 at 25 degrees C and a vanadium ion permeability reduction of 57.6 % compared to Nafion 212. This improvement was achieved by significantly reducing vanadium crossover through structural reinforcement with a porous PTFE support. Consequently, the ion selectivity was enhanced 2.36-fold. Mechanical testing revealed a tensile strength of 63.37 MPa, confirming superior durability over the pristine hydrocarbon membrane. In single-cell performance evaluations, the composite membrane achieved a Coulombic efficiency of 98.0 %, voltage efficiency of 84.6 %, and energy efficiency of 82.9 % at 100 mA cm-2. Notably, the membrane retained 73.5 % of its capacity after 1000 cycles at 200 mA cm-2, indicating excellent long-term stability. These findings suggest that the PTFE/ sPP-PSK composite membrane is a promising alternative to the PFSA membranes, enabling high performance and durability in VRFB applications. Future research will focus on further tuning the polymer structure and reinforcement interface to improve scalability and application potential.

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