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

Authors: Le Yang, Yahui Hao, Jiande Lin, Ke Li, Siheng Luo, Jie Lei, Yanhong Han, Ruming Yuan, Guokun Liu, Bin Ren, Jiajia Chen*

Abstract: A highly soluble and stable Li₅BW₁₂O₄₀ 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-O_b-W and W-O_c-W at different redox states of clusters. All above structure changing and redox chemistry of Li₅BW₁₂O₄₀ are highly reversible, which makes the Li₅BW₁₂O₄₀ 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 Li₃K[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, Li₅BW₁₂O₄₀ 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.

Full-Link: https://onlinelibrary.wiley.com/doi/10.1002/adma.202107425