A redox flow battery in a Japanese power plant. A new process could replace the rare metals in these batteries with an industrial by-product
Alessandro Gandolfi/Panos Pictures
An industrial waste has become a component of batteries that can store large amounts of charge. Batteries can play a vital role in power grids, smoothing out the peaks and troughs of renewable energy.
Redox flow batteries (RFBs) store energy in a pair of tanks as two liquids called anolyte and catholyte. When these fluids are present pumped into a central chamberseparated by a thin membrane, they react chemically and produce electrons to generate energy. The process can be reversed to charge the battery by putting a current through the membrane.
Such batteries are cheap, but they have downsides. They are bulky, often as big as a shipping container, and require constant maintenance due to the moving parts involved in pumping the liquid. They are also based on metals such as lithium and cobalt, those who are in short supply.
now, Emily Mahoney At Northwestern University in Evanston, Illinois, and his colleagues have discovered a simple process that can turn a previously useless industrial waste into a useful anolyte that can replace these rare metals.
Their process takes triphenylphosphine oxide produced during the manufacture of products including vitamin pills and converts it into cyclic triphenylphosphine oxide, which has a high potential for storing a negative charge. When used as an anolyte, it shows no reduction in efficiency even after 350 loads and discharges.
“Having an anolyte with a very negative potential increases the overall cell potential and therefore the efficiency of the battery,” says Mahoney. “However, the increase in potency is often accompanied by stability issues, so having a compound that can be stable and highly negative is exciting.”
Mahoney says RFBs are designed to be safe and have large capacities, so they could be used to store energy from wind and solar power, but they are unlikely to replace lithium-ion batteries in cars or smartphones because of their weight.
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