Researchers at Utah State University have developed a type of flow battery that uses iron, Science Magazine reported in November. The advance, once scaled up, promises to fill a gap in bulk electricity storage, cheaply and safely.
Current battery storage technologies, currently dominated by the element lithium, but including designs using sulphur and other substances, have a natural economic niche operating in the time frame of a few hours. A need remains for storage technologies that can economically support power storage cycles on the scale of a day or more. Flow batteries serve that field well, but currently rely on relatively rare and expensive vanadium, the price of which would impede wide deployment. A search has been on for a cheaper replacement, and iron looks ready to fill the bill, but recent test designs have used highly corrosive electrolytes to mediate electron exchange, with attendant wear and tear on pumps and piping, Science Mag explains.
“Now, [Tianbiao] Liu and his colleagues have come up with a flow battery that operates at neutral pH. They started with an iron-containing electrolyte, ferrocyanide, that has been studied in the past. But in previous ferrocyanide batteries, the electrolyte was dissolved in water containing sodium or potassium salts, which provide positively charged ions that move through the cell to balance the electron movement during charging and discharging. Ferrocyanide isn’t very soluble in those salt solutions, limiting the electrical storage capacity of the battery.
“So Liu and his colleagues replaced the salts with a nitrogen-based compound called ammonium that allows at least twice as much ferrocyanide to dissolve, doubling the battery’s capacity. The resulting battery is not as energy-dense as a vanadium flow battery. But in last week’s issue of Joule, Liu and his colleagues reported that their iron-based organic flow battery shows no signs of degradation after 1000 charge-discharge cycles, equivalent to about 3 years of operation. And because the electrolytes are neutral pH and water-based, a leak likely wouldn’t produce environmental damage.”
See the full story at sciencemag.org, October 31.