Are Membranes the Key Component for Energy Storage?

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Pörner Ingenieurgesellschaft mbH

Anton Paar GmbH

ProMinent GmbH

DWI - Leibniz-Institut für Interaktive Materialien e.V.

“We were pleasantly surprised when we discovered tiny pores and channels in the hydrophobic material and they appear to be filled with water. These water channels allow protons to travel through the membrane with high speed. The vanadium ions, however, are too large to pass the membrane.”

The diameter of the channels is less than two nanometers and the barrier function seems to be stable over time: Even after one week or 100 charging and discharging cycles vanadium ions could not pass the membrane. “We reached an energy efficiency of up to 99 percent, depending on the current. This shows that our membrane is a true barrier for the vanadium ions,” says Wessling. At all current densities tested, between 1 and 40 milliampere per square centimeter, the scientists reached 85 percent energy efficiency or more whereas conventional systems do not exceed 76 percent.

A Puzzling Phenomenon...

These results suggest a new transport model. Instead of swelling, the polymer with intrinsic microporosity, named PIM, condensed significantly. Water molecules that accumulate in the pores, but not in the polymer itself, might be the reason for this phenomenon. The researchers hope to initiate further studies to analyze this effect in detail.

While the phenomenon is puzzling, the scientists from Aachen and Seoul will perform additional application tests: Can they still improve the hydrophobic membrane for an application in a redox flow battery? And is the membrane stable in the long run? If this is the case, the hydrophobic membrane might indeed advance the practical use of redox flow batteries and similar energy storage systems. The researchers are highly motivated by the idea of a stable energy supply when using sustainable energy sources, by making a contribution to power system and frequency stability.

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