Hydrogen-bond-rich composite membrane with improved conductivity and selectivity for flow battery

Flow batteries have gained remarkable attention for large scale energy storage due to high safety and high efficiency. Membrane is the key component of the flow battery, directly affecting the efficiency and power density of the battery. However, the membrane development faces the challenge of the trade off between ion conductivity and ion selectivity. Herein, we propose a strategy to break the trade off, that is to improve the ion conductivity by creating rich hydrogen bonding networks in the membrane and maintain the ion selectivity via the spatial effect of the nanoparticles. A hydrogen-bond-rich composite membrane is prepared by incorporating the titanium oxynitride (TiON) nanoparticles into the SPEEK matrix, where TiON will form –OH and –NH2 functional groups on the surface of nanoparticles in the aqueous solution. The interaction between water molecules and –OH or –NH2 functional groups forms continuous and rich hydrogen bonding networks in the composite membrane, which remarkably improves the ion conductivity of the membrane. As a result, the iron chromium flow battery with SPEEK/TiON composite membrane exhibits excellent performance, with an energy efficiency of 82.7% at the current density of 80 mA/cm2, which was 4.4% higher than that with the commercial Nafion 212 membrane.