An Advanced Composite Membrane for the All-Vanadium Redox Flow Battery

Redox flow batteries (RFBs) are a promising technology for grid scale stationary energy storage to complement renewable energy systems. These batteries have a relatively low energy density; however, they offer important advantages, including: long life-time; decoupled energy (arbitrarily large electrolyte volume) and power (electrode area); high round-trip efficiency; scalability and design flexibility; fast response; and low environmental impacts. These advantages make them superior to many energy storage technologies for stationary applications [1-4]. Among the various types of RFBs, vanadium RFBs (VRFBs) are an emerging technology for grid scale energy storage and the integration of renewable energy generation [5]. The membrane is a key component of a VRFB that separates the two half-cell electrolytes and prevents cross-mixing, while allowing the transport of ions during charge-discharge cycles [6]. The VRFB membrane should exhibit low vanadium ion permeability to minimize self-discharge, low cost, and long‐term chemical stability under normal operating conditions. A high proton conductivity and low vanadium ion crossover are known to improve the efficiency of VRFBs [6-7]. In this study, we present a novel composite Nafion based membrane that results in a significant increase in the VRFB performance. The composite membrane has been characterized for its chemical, structural, and thermal properties using appropriate analytical techniques. The battery performance was evaluated in a flow cell using a ‘zero-gap’ design with an electrode area of 5 cm 2 . The electrolytic solution, 1.6 M VOSO 4 in 3 M H 2 SO 4 , was circulated through the cell. Thermally treated carbon papers were used as the cathode and anode electrodes. For charge-discharge experiments, a constant current density (10 to 80 mA cm −2 ) was applied with upper and lower voltage cut-offs of 1.65 and 0.8 V, respectively. The stability of the battery using the composite membrane was evaluated over 100 cycles. Figures 1 and 2 show the energy efficiency and capacity retention during 100 charge-discharge cycles. The results reveal that the energy efficiency was improved from 51% to 63% by using the composite membrane. In addition, the charge-discharge capacity and capacity retention improved by around 200% and 25%, respectively. This improvement can be attributed to a higher proton conductivity and lower vanadium permeability of the composite membrane. References: [1] M. Skyllas-Kazacos, L. Cao, M. Kazacos, N. Kausar, A. Mousa, Vanadium Electrolyte Studies for the Vanadium Redox Battery-A Review, ChemSusChem. 9 (2016) 1521–1543. [2] A.K. Singh, M. Pahlevaninezhad, N. Yasri, E. Roberts, Degradation of Carbon Electrodes in the All-Vanadium Redox Flow Battery, ChemSusChem. (2021). [3] K.E. Rodby, T.J. Carney, Y. Ashraf Gandomi, J.L. Barton, R.M. Darling, F.R. Brushett, Assessing the levelized cost of vanadium redox flow batteries with capacity fade and rebalancing, J. Power Sources. 460 (2020) 227958. [4] M. Pahlevaninezhad, P. Leung, M. Pahlevani, F. C. Walsh, C. Ponce de Leon, and E. P. L. Roberts, Experimental and Computational Studies of Disperse Blue-1 in Organic Non-Aqueous Redox Flow Batteries, J. Power Sources, Volume 500, 15 July 2021, 229942. [5] X.Z. Yuan, C. Song, A. Platt, N. Zhao, H. Wang, H. Li, K. Fatih, D. Jang, A review of all-vanadium redox flow battery durability: Degradation mechanisms and mitigation strategies, Int. J. Energy Res. (2019). https://doi.org/10.1002/er.4607. [6] X. Li, H. Zhang, Zh. Mai, H. Zhang, I. Vankelecom, Ion exchange membranes for vanadium redox flow battery (VRB) applications, Energy Environ. Sci., 2011, 4, 1147. [7] L. Yu, F. Lin, L. Xua, J. Xi, A recast Nafion/graphene oxide composite membrane for advanced vanadium redox flow batteries, RSC Adv., 2016, 6, 3756. Figure 1