Morphology and Electrochemical Properties of Perfluorosulfonic Acid Ionomers for Vanadium Flow Battery Applications: Effect of Side‐Chain Length

Abstract

Perfluorosulfonic acid ionomers (PFSI) with different side-chain lengths have been investigated with respect to their morphology and electrochemical properties in vanadium flow batteries (VFB). The results indicated that the membrane with the shortest side chains (SSC-M2) displayed small ion clusters and a low degree of hydrophobic-hydrophilic separation, which is favourable to reduce the cross-over of vanadium ions in the VFB. SSC-M2 shows a similar proton conductivity to Nafion, which carries longer ionic side chains but with much lower ion permeability. As a result, the VFB assembled with SSC-M2 exhibited a superior coulombic efficiency and a voltage efficiency close to that of Nafion115. In situ mass transfer revealed that SSC-M2 had a remarkably low degree of vanadium and water transfer across the membrane, which resulted in lower capacity fading than in the case of Nafion115. These results indicate that a membrane with short side chains is an ideal option in the fabrication of high-performance VFBs with low capacity loss.

Temperature‐ and Humidity‐Controlled SAXS Analysis of Proton‐Conductive Ionomer Membranes for Fuel Cells

“…These morphological studies suggest that the hydrophilic clusters become larger with increasing water content in the membranes, resulting in the development of ion channels in the PFSA ionomer membranes 5. 11, 13–17 Cylindrical and spherical ionic domains have been reported, depending on the water content in the membranes 14. 15, 18 Similar morphological studies have been carried out for some aromatic ionomer membranes 19–22.…”

Neutral Red and Ferroin as Reversible and Rapid Redox Materials for Redox Flow Batteries

“…However,t he low solubility and conductivity of organic solvents for non-aqueous RFBs result in lower capacities, energy densities, and potentials than expected. [7,8] However,t hese commercial aqueous RFBs still suffer from limitations of solubility, [6,9,10] poor kinetics, [11][12][13][14][15] and crossover issues [16][17][18][19] that must be resolved. In contrast, aqueous materials are relatively safe and easy to handle.…”

Sulfonated polyimide membranes with different non-sulfonated diamines for vanadium redox battery applications

“…Besides, Nafion 117 membrane with the thickness of 175 mm was also chosen to the cyclic charge-discharge testing for comparison because of the following reasons: On one hand, serious vanadium ion crossover will happen once Nafion membranes thinner than 100 mm, e.g., Nafion 1125 or Nafion 113, are employed [19]; On the other hand, Nafion 117 exhibits the highest energy efficiency among Nafion 212, 1135, 115 and 117 membranes [20] …”