Alternative Low Cost Membranes for All-Vanadium Redox Flow Batteries

A large-scale electrical energy storage is in high demand to efficiently utilize solar and wind renewables because of their intermittent and fluctuating power production. Among several technologies, the all-vanadium redox flow battery (VRFB) has received much attention because of its good electrochemical reversibility, high efficiency, long cycle life and absence of cross-contamination between the anolyte and catholyte. A MW-class system has been demonstrated for grid applications and renewable integration [1]. The high capital cost (($500~600/kWh) of the VRFB system, which is attributed to relatively high cost of vanadium and membrane materials, makes widespread deployment challenging. Nafion membrane, an expensive component, is typically employed because of its good conductivity and robust chemical and mechanical durability under the highly corrosive and oxidative environment of V ions. Recent efforts to reduce the cost of the VRFB system are focused on developing a high current design to decrease the stack size and low-cost alternative membranes to decrease the per-cell cost. However, most alternative hydrocarbon membranes used in polymer electrolyte fuel cells or electrolysis have suffered from degradation in VRFBs [2]. We have been investigating degradation mechanisms of low cost membranes with a number of aromatic architectures to address the cost and cycle efficiency issues of VRFBs with Nafion membranes. In this research, we have investigated effects of polymer backbone composition, ion exchange capacity, and extent of fluorination on the durability and cycling efficiency of VRFBs. Accelerated degradation tests have also been conducted using high temperature ex-situ soaking in V solutions as well as flow cell cycling. As a part of our efforts, partial fluorination significantly improved its durability as shown in Figure 1. Degradation mechanisms and cell performance test results will be discussed in this presentation.