POM Anolyte for All-anion Redox Flow Batteries with High Capacity Retention and Coulombic Efficiency at Mild pH.

A highly soluble and stable Li5 BW12 O40 cluster delivers 2 e- redox reaction with fast electron transfer rates (2.5 * 10-2  cm s-1 ) and high diffusion coefficients (∼2.08 * 10-6 cm2 s-1 ) at mild pH ranging from 3 to 8. In-operando aqueous-flowing Raman spectroscopy and DFT calculations reveals that Raman shift changing of {BW12} clusters should be due to the bond length changing between W-Ob -W and W-Oc -W at different redox states of clusters. All above structure changing and redox chemistry of Li5 BW12 O40 are highly reversible, which makes the Li5 BW12 O40 cluster versatile to construct all-anion aqueous redox flow batteries at different pH. The cation-exchange Nafion membrane will also repel the cross permeability of the anion redox couples. As a result, by coupling with Li3 K[Fe(CN)6 ] catholyte, the aqueous RFB can be operated at pH 8 with a capacity retention up to 95% and an average Coulombic efficiency (CE) more than 99.79% over 300 cycles within the voltage window ranging from 0 to 1.2 V. Meanwhile, Li5 BW12 O40 cluster can also be paired with LiI catholyte to form aqueous RFBs at pH 7 and pH 3, the capacity retention of 94% and 90% can be realized over 300 cycles within 0 to 1.3 V. This article is protected by copyright. All rights reserved.