A study advancing the safety of flow-battery technology could further enable electricity generated by solar cells and wind farms to be used on a large scale when it is needed, as opposed to only when the sun shines and wind blows (Science 2015, DOI: 10.1126/science.aab3033). Flow batteries may be better suited than conventional batteries for storing and supplying electricity on a grid scale because the compounds undergoing electrochemical reactions are housed in storage tanks outside of the electrochemical cell. That separation enables flow-battery components to be optimized independently to suit the application. Last year, a Harvard University team including Michael J. Aziz and Roy G. Gordon reported on a low-cost, catalyst-free flow-battery design based on redox-active fused-ring quinones. That design avoided the corrosiveness and hydrogen evolution concerns associated with standard flow batteries, which use acidic solutions of metal ions. But the Harvard battery required a redox-active bromine-containing solution, a separate hazard. The same researchers now report they have designed and tested a flow battery that operates at 50% higher voltage in which bromine has been replaced with ferrocyanide, an inexpensive compound that, among other things, is used as a food additive.