Effects of different kinds of surfactants on Nafion membranes for all vanadium redox flow battery

Abstract

To investigate the effects of different surfactants on the properties of Nafion membrane, recast Nafion membranes were prepared with cationic (tetramethylammonium bromide (TMAB)), anionic (sodium dodecyl sulfate (SDS)), and nonionic surfactants (Triton X-100 (TX-100)). The prepared composite membranes were analyzed by Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), AFM, WXRD, and small-angle X-ray scattering (SAXS) to investigate the microstructure of the membrane. The properties of the composite membrane, including the water uptake, ion exchange capacity, proton conductivity, VO 2+ permeability, water transport, as well as the single cell performance are evaluated in detail. Results show that both the physical and electrochemical properties of the surfactant-modified Nafion membranes were quite different from the unmodified recast Nafion (r-Nafion) membrane. Vanadium redox flow battery (VRB) single cell tests indicate that the nonionic modified Nafion membrane possesses the best comprehensive performances among the three surfactants modified and r-Nafion membranes. At current density of 40-80 mA cm −2 , the average energy efficiency (EE) of the VRB with TX-100 Nafion membrane is 2.6 % higher than that of unmodified r-Nafion membrane, while the average EE of the VRB with TMAB/Nafion is 3.2 % lower than that of r-Nafion membrane. Another important effect of surfactants on the Nafion is the water transport behavior across the different membranes. TMAB can decrease the water transport across Nafion membrane, while the SDS and TX-100 can slightly increase the water transport across Nafion membrane.

Polymer Electrolyte Membranes for Vanadium Redox Flow Batteries: Fundamentals and Applications

“…67,73,74 , have been developed to determine the ionic conductivity of membranes used in VRFBs. It is worth mentioning that, while many studies conducted the ionic conductivity test of membranes in deionized water, [75][76][77] some have also performed the test in sulfuric acid 67,78 or vanadium electrolyte 79 which is the actual scenario during the operation of VRFBs. Considering the real operating condition in VRFBs, the evaluation of membrane conductivity using vanadium electrolyte would provide substantial information relevant to membranes used in the battery system.…”

“…[84][85][86] The Nafion series membranes have been tested and reported to have a water uptake ratio within 20-40 %. 69,76,77 While such water uptake ratio facilitates the transport of protons through the membrane, the Nafion series membranes are exposed to high permeability of active species and undesired effects. Therefore, the membranes prepared for RFBs are desired to possess an optimized water uptake ratio in order to attain an optimal balance among other properties mentioned above.…”

“…For instance, the widely used Nafion membranes have been reported to possess a tensile strength within the range of 14-24 MPa with an elongation of 170-250 % under both wet and dry conditions. 77,80,98,112 This could serve as a benchmark for assessing the mechanical properties of membranes to be used in flow batteries.…”

“…This idea was first inspired by the promising results obtained from direct methanol fuel cell, where inorganic materials have been proven to efficiently decrease methanol permeability through membrane, as the inorganic materials can block the hydrophilic regions of membranes. 54 Guided by this idea, silicalite, 158 amino-silica, 68 SiO2, 97,104,159,160 TiO2, 69 delaminated AMH-3, 161 ZrO2 nanotubes (ZrNT), 100 graphene oxide (GO), 98,162,163 fluorocarbon, 80 N,N-dimethylaminoethylmethacrylate, 75 and other materials 77,91,142,[164][165][166][167][168][169] are some of the organic/inorganic materials that have been integrated with Nafion to prepare composite membranes for use in VRFBs. A look at the performance and properties of some of these Nafion membranes recently modified through combining with organic/inorganic materials are summarized in Table S3 98,100,137,163,164,[167][168][169][170] .…”

Enhanced Proton Selectivity in Ionomer Nanocomposites Containing Hydrophobically Functionalized Silica Nanoparticles

“…To date, the vast majority of modification strategies involving the introduction of a second phase into the PFSA ionomer have focused on tuning (or modifying) the electrostatic interactions of the second phase and the ionic domains of the ionomer, as it is widely accepted that the transport of water and hydrated ions occurs within these hydrophilic channels. ,, Specifically, for PFSA–SiO 2 nanocomposite membranes, it is believed that the silica nanoparticles (SiNPs) reside at least partially within the ionic domains, , reducing vanadium ion crossover by impeding the transport of bulky, hydrated vanadium ions while still providing pathways for proton transport through the ionic network. ,− Utilizing this modification strategy, a wide range of surface functionalizations of the SiNPs has been explored including hydroxyl-coated (unfunctionalized SiNPs), amine-functionalized, and sulfonic acid-functionalized. ,− In contrast, few investigations have explored the addition of a second, hydrophobic phase to improve the transport properties (and ion selectivity) of the PFSA ionomer. For example, other investigations that have blended PTFE with Nafion or incorporated hydrophobic surfactants − into Nafion have demonstrated drastic reductions in vanadium ion permeability while maintaining (or even increasing) proton conductivity when compared to those of unmodified Nafion. This indicates that variations in the hydrophobic domain affect ion transport. − However, the introduction of fluorocarbon-functionalized SiNPs in proton-exchange membranes (PEMs) for VRFBs has, to the best of the authors’ knowledge, never been explored.…”