Colloidal silicalite-nafion composite ion exchange membrane for vanadium redox-flow battery

• Nonionic silicalite used for the first time in composite ion exchange membranes.
• Obtained colloidal silicalite-Nafion two-layer structure stable in acid solutions.
• Ion diffusion behaviors reveal exclusion of metal ion by H+- permeable silicalite.
• Composite thin membranes show much lower resistance with improved H+-selectivity.
• Composite membrane achieves much higher energy efficiency in RFB than Nafion-117.

Colloidal silicalite-Nafion composite membranes have been synthesized with a two-layer structure consisting of a top layer of colloidal silicalite in Nafion matrix and a base layer of pure Nafion. The composite membrane with an overall thickness of 120–130 μm exhibited higher proton-to-vanadyl ion transport selectivity and lower electrical resistance than the 183 μm-thick commercial Nafion-117® membrane. The improved proton selectivity in the composite membrane is due primarily to the ability of the sub-nanometer-sized zeolitic pores to block the hydrated metal ions while permitting the small hydrated protons to enter and diffuse through. The low electrical resistance of the composite membrane is attributed to the reduced thickness of the Nafion base film and the thinness of the layer containing silicalite nanoparticles (<30 μm). When being used as ion exchange membrane in the vanadium redox flow battery, the composite membrane with a silicalite content of 5 wt% has achieved an energy efficiency of 77% at 60 mA/cm2 which is significantly higher than the 65% efficiency obtained by the Nafion-117 membrane. The composite membrane also has shown excellent stability after one month of cyclic operation of the battery.

The colloidal silicalite-Nafion composite membrane significantly improves energy efficiency of the vanadium redox flow battery because of enhanced proton selectivity and reduced electrical resistance. Figure optionsDownload high-quality image (240 K)Download as PowerPoint slide