Composite membranes based on sulfonated poly(ether ether ketone) and SiO2 for a vanadium redox flow battery

An overview on the progress and development of modified sulfonated polyether ether ketone membranes for vanadium redox flow battery applications

Vanadium redox flow batteries (VRFB) are among the most promising approaches to efficiently store renewable energies. In such battery type, Nafion is commonly used as membrane material but suffers from high vanadium crossover and cost. These drawbacks negatively influence the widespread commercial application of VRFBs. Alternative membrane materials with high performance and low cost are thus being developed to address these shortfalls. Among those, possible materials for the VRFB membrane is sulfonated polyether ether ketone (SPEEK), which recently attracted considerable attention due to its low cost, combined with mechanical and chemical stability, and ease of preparation. This review summarizes the research activities related to the development of SPEEK-based membranes for VRFB applications and gives an overview of the properties of PEEK and its sulfonated form. A critical analysis on the challenges of SPEEK-based membranes is also discussed.

Polymer Membranes for All-Vanadium Redox Flow Batteries: A Review

Redox flow batteries such as the all-vanadium redox flow battery (VRFB) are a technical solution for storing fluctuating renewable energies on a large scale. The optimization of cells regarding performance, cycle stability as well as cost reduction are the main areas of research which aim to enable more environmentally friendly energy conversion, especially for stationary applications. As a critical component of the electrochemical cell, the membrane influences battery performance, cycle stability, initial investment and maintenance costs. This review provides an overview about flow-battery targeted membranes in the past years (1995-2020). More than 200 membrane samples are sorted into fluoro-carbons, hydro-carbons or N-heterocycles according to the basic polymer used. Furthermore, the common description in membrane technology regarding the membrane structure is applied, whereby the samples are categorized as dense homogeneous, dense heterogeneous, symmetrical or asymmetrically porous. Moreover, these properties as well as the efficiencies achieved from VRFB cycling tests are discussed, e.g., membrane samples of fluoro-carbons, hydro-carbons and N-heterocycles as a function of current density. Membrane properties taken into consideration include membrane thickness, ion-exchange capacity, water uptake and vanadium-ion diffusion. The data on cycle stability and costs of commercial membranes, as well as membrane developments, are compared. Overall, this investigation shows that dense anion-exchange membranes (AEM) and N-heterocycle-based membranes, especially poly(benzimidazole) (PBI) membranes, are suitable for VRFB requiring low self-discharge. Symmetric and asymmetric porous membranes, as well as cation-exchange membranes (CEM) enable VRFB operation at high current densities. Amphoteric ion-exchange membranes (AIEM) and dense heterogeneous CEM are the choice for operation mode with the highest energy efficiency.

GO-modified membranes for vanadium redox flow battery

Graphene oxide (GO) has attracted tremendous attention in membrane-based separation field as it can filter ions and molecules. Recently, GO-based materials have emerged as excellent modifiers for vanadium redox flow battery (VRFB) application. Its high mechanical and chemical stability, nearly frictionless surface, high flexibility, and low cost make GO-based materials as proper materials for the membranes in VRFB. In VRFB, a membrane acts as the key component to determine the performance. Therefore, employing low vanadium ion permeability with excellent stability membrane in vanadium electrolytes is important to ensure high battery performance. Herein, recent progress of GO-modified membranes for VRFB is briefly reviewed. This review begins with current membranes used for VRFB, followed by the challenges faced by the membranes. In addition, the transport mechanism of vanadium ion and the stability properties of GO-modified membranes are also discussed to enlighten the role of GO in the modified membranes.

Approach to high proton/vanadium selectivity in an ionic exchange membrane via a hyperbranching design

High H⁺/V selectivity was achieved for the ion exchange membrane due to specially designed hyperbranching structure and intermolecular force.