Sandwich-structured thin film composite anion exchange membrane for redox flow battery applications

A redox flow battery system, comprising:

• at least one rechargeable cell, each rechargeable cell comprising a positive electrolyte, a negative electrolyte, and thin film composite anion exchange membrane positioned between the positive electrolyte and the negative electrolyte, the positive electrolyte in contact with a positive electrode, and the negative electrolyte in contact with a negative electrode, wherein the thin film composite anion exchange membrane comprises a microporous substrate membrane;
• a first nonporous water-insoluble hydrophilic ionomeric polymer coating layer on a surface of the microporous substrate membrane;
• a cross-linked protonated polymeric polyamine anion exchange layer on a second surface of the first nonporous water-insoluble hydrophilic ionomeric polymer coating layer;
• a second nonporous water-insoluble hydrophilic ionomeric polymer coating layer on a second surface of the cross-linked protonated polymeric polyamine anion exchange layer;
• the positive electrolyte consisting essentially of FeCl2 at a concentration of 1.0-4.5 M, NH4Cl at a concentration of 1.0-4.0 M or KCl at a concentration of 1.0-3.0 M, HCl at a concentration of 0.05-2.5 M, and glycine at a concentration of 0.01-3.0 M, optionally boric acid at a concentration of 0.01-1.0 M, and optionally FeCl3 at a concentration of 0.1-1.0 M;
• and
• the negative electrolyte consisting essentially of FeCl2 at a concentration of 1.0-4.5 M, NH4Cl at a concentration of 1.0-4.0 M or KCl at a concentration of 1.0-3.0 M, optionally boric acid at a concentration of 0.01-1.0 M, optionally glycine at a concentration of 0.01-3.0 M, and optionally FeCl3 at a concentration of 0.1-1.0 M,
• wherein the first and second hydrophilic ionomeric polymer coating layers comprise a alginic acid, hyaluronic acid, carrageenic acid, or a mixture thereof.