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Safer Flow Battery Chemistry for Renewable Energy Storage
The problem of renewable energy sources such as solar and wind is the inability to control production. You end up needing a grid inter-tie just to compensate for night and calm days. Either that, or you need to be able to store energy somehow. Energy harvesting, windmills and solar arrays, are mature technologies, easily "good enough" to deploy on industrial scale. But storage of energy on industrial scale is still in its infancy.
Last year, Harvard University developed scale-able Flow Batteries [wikipedia.org]. The batteries can scale from basement installations the size of a couple water heaters to industrial storage parks the size of tank farms.
At the heart of flow batteries is a sandwich of electrodes, known as a stack, separated by an ion-conducting membrane. The electrolytes are pumped through the stack during charging and discharging. In most designs, when the battery is discharged to provide power, a positively charged electrode strips electrons from molecules in one electrolyte and sends them through a circuit to charge-accepting molecules in the second electrolyte. This process produces positively charged ions in the first electrolyte that travel through the membrane into the second electrolyte, where they balance the charges coming in from the electrons. When the battery is charged, the flow of electrolytes, electrons, and ions is reversed and electrons are dumped into the first electrolyte.
(See conceptual image [rsc.org]).
Excess solar or wind power can simply be stored in the electrolyte and these charged electrolytes can be pumped to tank farms for long term storage.
The problem was the one of electrolytes contained bromine [wikipedia.org], a toxic, ozone depleating compound that also readily corrodes steel and other materials commonly used to contain the liquid electrolyte and pipe it around.
Chemistry World [rsc.org] and ScienceNews [sciencemag.org] and many others are reporting that the same Harvard team has developed new electrolytes that are even more stable, non toxic, and non corrosive.
The Harvard team realized that a possible bromine replacement was a charge-carrying molecule called ferrocyanide, which sounds dangerous but is actually used as a food additive. Ferrocyanide, however, dissolves in alkaline solutions, not acidic ones. So Aziz and his colleagues tweaked the chemical structure of their electrolytes—ripping off a couple of sulfur groups and replacing them with pairs of hydrogen and oxygen atoms—in the end converting the compound into one that readily dissolves in an alkaline solution.
The scheme worked, and as the researchers report today in Science, the battery readily stores power with only components that are cheap, abundant, and nontoxic.
The obligatory "10 years away" rule probably applies, but this technology is probably the closest thing to feasible storage for large scale installations.
