High performance positively charged membranes with selective swelling-induced ion transport channels for vanadium flow battery application

The selective swelling technique is adopted for the first time to construct positively charged membranes with selective swelling-induced ion transport channels for vanadium redox flow battery (VRFB). These membranes are prepared based on pyridine and adamantane groups containing poly(aryl ether ketone ketone) (PyAPEKK) polymer. Polymer chains with pyridine groups are selective swelled to form ion transport channels in the polymer membrane using the base-acid interaction between the pyridine groups and mineral acids (H3PO4 and H2SO4). The bulky, rigid, hydrophobic adamantane groups in the polymer increase the rigidity and hydrophobicity of the polymer backbone that reduce the swelling of the membrane and enhance the membrane selectivity. Consequently, a VRFB utilizing this PyAPEKK membrane exhibit impressive battery performance (CE = 98.9%, EE = 92.3% at 80 mA cm−2; CE = 99.3%, EE = 80.56% at 240 mAcm−2). The PyAPEKK membranes exhibited stable VRFB performance for more than 1500 cycles and exhibited excellent chemical stability in ex-situ stability tests. This work demonstrated a convenient, facile, and environmental-friendly way to fabricate advanced positively charged membranes for VRFB.