Leveraging sulfonated poly(ether ether ketone) for superior performance in zinc iodine redox flow batteries

• Published in: Journal of energy storage 2023-12, Vol.73, p.108937, Article 108937
• Main Authors: Williams, Abena A., Wang, Xueting, Davis, Eric M., Roberts, Mark E.
• Format: Article
• Language: English
• Subjects: Cation exchange membranes; Ionomer; Redox flow batteries; SPEEK; Zinc iodide electrolyte
• ISSN: 2352-152X; 2352-1538
• DOI: 10.1016/j.est.2023.108937

Sulfonated poly (ether ether ketone) SPEEK membranes with a degree of sulfonation of approximately 73 % were synthesized and investigated as the cation exchange membrane (CEM) for the zinc iodine (ZI) redox flow battery (RFB). Specifically, SPEEK was used in ZI RFB with 1 mol L−1 electrolyte and its performance was compared to the current benchmark CEM, Nafion™. Notably, columbic and energy efficiencies of 92.9 % and 75.9 %, respectively, were measured for the ZI battery with SPEEK at 17 mA cm−2, which was a 370 % increase in energy density compared to those with Nafion 212 membranes. RFBs with SPEEK exbibit a peak power density of 122 mW cm−2 at a current density of 166 mA cm−2 (98 mW/cm2 at 133 mA/cm2 with Nafion 212) because of their lower overpotential and higher discharge voltage. These results demonstrate the high cation selectivity of the SPEEK membranes in neutral, salt-based electrolytes, and provide the groundwork to develop a suitable replacement to Nafion for low-cost RFBs. [Display omitted] •Sulfonated poly (ether ether ketone) (SPEEK) membranes were used as cation exchange membranes (CEM) in zinc iodine redox flow batteries.•SPEEK membranes exhibit higher equilibrium water uptake and ion exchange capacity compared to Nafion 212.•RFBs with SPEEK exhibit a 24% increase in peak power density over RFBs with Nafion in a zinc iodine electrolyte.•The energy density of RFBs with SPEEK is 370% higher than those with Nafion 212.