Expanding the chemical space for redox flow batteries

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Science  25 Sep 2015:
Vol. 349, Issue 6255, pp. 1452
DOI: 10.1126/science.aad0698

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Redox flow batteries (RFBs) have many advantages for grid-level energy storage, a key requirement for implementing intermittent renewable sources. Like other rechargeable batteries, a flow battery uses reversible electrochemical couples on two electrodes to store chemical energy (1). However, instead of storing the active materials within the electrodes, the reactants are dissolved in two electrolyte solutions and stored in external tanks (see the figure). This configuration allows their cost to scale better as size increases compared to conventional batteries. To date, the redox-active species have often been transition-metal ions, which can have limited electrochemical potential range. On page 1529 of this issue, Lin et al. (2) report on the use of transition-metal complexes and organic molecules as redox species that are both low in cost and relatively nontoxic.