Nafion-WO3 and SPEEK-WO3 hybrid membranes for Vanadium Redox Flow Batteries

To fulfill the rapidly increasing global use of renewable energy, such as wind and solar energy, it is imperative to develop a safe and effective electrical energy storage system [1]. One such technology is the vanadium redox flow battery (VRFB). As an energy storage/conversion device, VRFBs have been considered to be promising candidates owing to their long cycle life, low cost, flexible design and high energy efficiency [2]. However, the lack of high performance low-cost membranes limits wide-scale commercialization of VRFBs. Commonly used membranes at the heart of VRFBs are typically based on perfluorosulfonic polymers such as Nafion®. These possess a high vanadium ion permeability as well as a high stability, however they suffer from low efficiency and fast capacity decay [3]. As an alternative, sulfonated poly aromatic membranes, such as sulfonated poly(ether ether ketone) (SPEEK) membranes have been receiving attention owing to their ease of preparation and high VRFB performance [4]. However, degrees of sulfonation that are too high, cause high vanadium ion permeability and low membrane stability thus limiting potential applications. It is known that incorporation of inorganic fillers in polymer matrices can suppress the vanadium ion crossover [5]. The distribution of fillers in the polymeric matrix and the compatibility between two phases play an essential role in the chemical–physical property of the composite membrane [6]. Two hybrid membranes, SPEEK with WO3 nanofiller and Nafion with WO3 nanofiller are presented in this work. Hybrid membranes with different mass ratios of nanofiller have been prepared by the solution casting method. Ionic conductivity is measured by Broadband Electrical Spectroscopy (BES) before and after a variety of battery tests conducted at different current densities. In comparison to Nafion and SPEEK, these new hybrid membranes show higher efficiencies and lower capacity losses, as well as higher ionic selectivity. Therefore, the hybrid membranes with optimized mass ratio exhibit good potential usage in VRFB systems. References [1] Armaroli N, Balzani V. Towards an electricity-powered world. Energy & Environmental Science, 4.9 (2011) 3193-3222. [2] Cunha Á, Martins J, Rodrigues N, et al. Vanadium redox flow batteries: a technology review. International Journal of Energy Research, 39.7 (2015) 889-918. [3] Luo Q, Li L, Wang W, et al. Capacity Decay and Remediation of Nafion based All Vanadium Redox Flow Batteries. ChemSusChem, 6.2 (2013) 268-274. [4] Winardi S, Raghu S C, Oo M O, et al. Sulfonated poly (ether ether ketone)-based proton exchange membranes for vanadium redox battery applications. Journal of Membrane Science, 450 (2014) 313-322. [5] Davis E M, Kim J, Oleshko V P, et al. Uncovering the Structure of Nafion-SiO2 Hybrid Ionomer Membranes for Prospective Large Scale Energy Storage Devices. Advanced Functional Materials, 25.26 (2015) 4064-4075. [6] Di Noto V, Piga M, Giffin G A, et al. Interplay between Mechanical, Electrical, and Thermal Relaxations in Nanocomposite Proton Conducting Membranes Based on Nafion and a [(ZrO2)•(Ta2O5) 0.119] Core-Shell Nanofiller. Journal of the American Chemical Society, 134.46 (2012) 19099-19107.