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April 14, 2020 03:30 am

Redox-Flow Cell Stores Renewable Energy As Hydrogen

An anonymous reader quotes a report from IEEE Spectrum: Hydrogen is a very good carrier for this type of work," says Wei Wang, who is the chief scientist for stationary energy storage research at the Pacific Northwest National Laboratory in Washington. It's an efficient energy carrier, and can be easily stored in pressurized tanks. When needed, the gas can then be converted back into electrical energy via a fuel cell and fed into the grid. But water electrolyzers are expensive. They work under acidic conditions which require corrosion-resistant metal plates and catalysts made from precious metals such as titanium, platinum, and iridium. "Also, the oxygen electrode isn't very efficient," says Kathy Ayers, vice-president of R&D at Nel Hydrogen, an Oslo-based company that specializes in hydrogen production and storage. "You lose about 0.3 volts just from the fact that you're trying to convert water to oxygen or vice versa," she says. Splitting a water molecule requires 1.23 V of energy. In a bid to overcome this problem, Nel Hydrogen and Wang's team at Pacific Northwest joined forces in 2016, after receiving funding from the U.S. Department of Energy's Advanced Research Projects Agency-Energy. The solution they've come up with is a fuel cell that acts as both a battery and hydrogen generator. "We call it a redox-flow cell because it's a hybrid between a redox-flow battery and a water electrolyzer," explains Wang. A redox-flow battery, in essence a reversible fuel cell, is typically made up of a positive and negative electrolyte stored in two separate tanks. When the liquids are pumped into the battery cell stack situated between the tanks, a redox reaction occurs, and generates electricity at the battery's electrodes. Compared to normal flow batteries, the new redox-flow cell exhibited a charge capacity of up to one ampere per square centimeter, a ten-fold increase. "It was also able to withstand 'several hundred cycles' of charging, which has never been demonstrated before in hydrogen ion flow batteries," the report says.

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