Highly conductive and vanadium sieving Microporous Tröger's Base Membranes for vanadium redox flow battery

The grid-scale integration of solar or wind energy that fluctuates over time will compromise the stability of the power grid. All-vanadium redox flow battery (VRFB) is among the most feasible electrochemical energy storage solutions, while the grand challenge is to develop membranes that separate vanadium electrolytes effectively and transport protons rapidly. Here we present highly conductive and vanadium sieving microporous membranes from shape persistent Trӧger's Base polymer. The N-rich and microporous polymer skeleton facilitate H+ transport. In contrast, hydrated vanadium ions are blocked due to size exclusion and coulombic repulsion. This increases the H/V selectivity of the membrane to >6300, lowers the membrane resistance to 0.57 Ω cm2, and raises the battery power density to 710.9 mW cm−2. A round-trip energy efficiency of 80% and a coulombic efficiency of >99% are maintained during long periods of charge/discharge. We believe the results will stimulate new directions for advanced VRFB membranes.