CNT@polydopamine embedded mixed matrix membranes for high-rate and long-life vanadium flow batteries

Developing low-cost and high selectivity membranes is critical for vanadium flow batteries (VFB) energy storage system. Among several potential candidates, sulfonated poly(ether ether ketone) (SPEEK) membrane is most promising, yet its proton conductivity and durability are still insufficient to meet the needs of practical applications. Here we report the preparation of a mussel-inspired polydopamine coated carbon nanotube embedded SPEEK mixed matrix membrane (S/CNT@PDA MMM) and its successful application in VFB. The acid-base interface interaction between the SPEEK matrix and the CNT@PDA filler is beneficial to construct additional proton transfer pathway as well as improve the mechanical property of the S/CNT@PDA MMM. Compared to pristine SPEEK membrane, the S/CNT@PDA MMM demonstrates higher proton conductivity, superior proton to vanadium ion selectivity and significantly enhanced stability. As a result, the VFB assembled with the S/CNT@PDA MMM exhibits greatly improved rate performance compared with the benchmark Nafion 115 membrane, and reaches the peak power density of 580 mW cm(-2) at 650 mA cm(-2). Moreover, the S/CNT@PDA MMM shows super long-term stability over 1000 cycles at 200 mA cm(-2), and wide temperature adaptability from - 20 degrees C to 50 degrees C, indicating the great potential of this MMM for practical application in VFB.