Robust selective swelling-induced pyridine-containing membranes with advanced conductivity for vanadium redox flow batteries

Abstract

Various electrochemical energy conversion and storage devices, such as membrane-based fuel cells and redox flow batteries, are in high demand for low-cost, easy-to-fabricate membranes with high conductivity, selectivity, and robust stability. In this work, unique pyridine-containing membranes (PyEPEK) are prepared for vanadium redox flow batteries (VRFBs), one of the most promising large-scale energy storage technologies. Selective swelling-induced PyEPEK membranes are facilely prepared, in which the basic pyridine-containing segments are selectively swelled with hot H3PO4 (50 wt%) to generate wider ion transport channels for enhanced conductivity, and the hydrophobic trifluoromethyl-containing segments provide a rigid backbone and endow the membrane with high selectivity. Compared to the benchmark Nafion212 membrane (area resistance 0.14 Ωcm2, mechanical strength 17.0 MPa), the resulting PyEPEK membrane exhibits better conductivity (area resistance, 0.13 Ωcm2) and about 2.8 times higher mechanical strength (>49.0 MPa). The PyEPEK-80 membrane exhibits impressive VRFB performance (coulombic efficiency = 99.56%, voltage efficiency = 93.40%, and energy efficiency = 92.98%) at 80 mA cm−2, which is the highest energy efficiency reported so far using dense ion exchange membranes. This work provides a strategy for designing and fabricating easy-to-prepare, low-cost, high-performance membranes for electrochemical energy conversion and storage devices.