Novel Ion-Exchange (Blend)-Membranes Based on Free Amines for All-Vanadium Redox Flow Batteries

Abstract

For reaching the aim of a climate-neutral EU within the European Green Deal until 2050 several new innovations in different fields, especially in the field of renewable energies, are necessary [1]. One challenge which has to be overcome is the fluctuating nature of wind and solar energy and the associated storage and release of excess energy for stabilisation of the power-grid [2]. One promising technology in this regard is the All-Vanadium Redox Flow Battery (VRFB) in which Nafion-based membranes are usually utilised [3, 4]. However, due to high costs and a low H+/V selectivity there are many attempts to find alternative materials with better performance, lower crossover and reduced costs [5, 6].In this work we present a new aromatic, ether-free and side-chain containing polymer with free non-quaternised amine groups prepared by polyhydroxyalkylation. A new monomer was designed to improve the conductivity and morphology of the resulting membranes. The membranes show sufficient mechanical properties in the wet state and improved conductivity compared to commercially available free-amine based VRFB membranes. Blend membranes with a PBI derivative were produced to improve the mechanical properties in the dry state and the crossover of vanadium species.The above-mentioned membranes were characterised ex-situ by using EIS, NMR spectroscopy, TGA, DMA and permeability tests. In addition, first promising in-situ characterisations were performed in a VRFB single-cell test station.Literature[1] European Commission: The European Green Deal, Brussels, 2019; URL: https://ec.europa.eu/info/strategy/priorities-2019-2024/european-green-deal_de#documents, accessed: 21.11.2022.[2] Reihani, E; Motalleb, M; Ghorbani, R; Saad Saoud, L.: Load peak shaving and power smoothing of a distribution grid with high renewable energy penetration. Renewable Energy 2016, 1372 – 1379.[3] Düerkop, D; Widdecke, H; Schilde, C; Kunz, U; Schmiemann, A.: Polymer Membranes for All-Vanadium Redox Flow Batteries: A Review. Membranes 2021.[4] Guarnieri, M; Mattavelli, P; Petrone, G; Spagnuolo, G.: Vanadium Redox Flow Batteries: Potentials and Challenges of an Emerging Storage Technology. EEE Ind. Electron. Mag. 2016, 20 – 31.[5] Zeng, L; Zhao, T.S; Wei, L; Jiang, H.R; Wu, M.C.: Anion exchange membranes for aqueous acid-based redox flow batteries: Current status and challenges. Applied Energy 2019, 622 – 643.[6] Gubler, L.: Membranes and separators for redox flow batteries. Current Opinion in Electrochemistry 2019, 31 – 36.