Realized potential as neutral pH flow batteries achieve high power densities

Abstract

High power density operation of redox flow batteries (RFBs) is essential for lowering system costs, but until now, only acid-based chemistries have achieved such performance, primarily due to rapid membrane proton (H + ) transport. Here, we report a neutral pH RFB using the highly reducing Cr-(1,3-propylenediaminetetraacetate) (CrPDTA) complex that achieves acid-like power performance while utilizing potassium ion (K + ) transport. We investigate RFB resistance components and demonstrate the high and consistent K + conductivity of the Fumasep E-620(K) membrane. When combined with a robust bismuth electrocatalyst, this membrane enables constant voltage efficiency operation of a CrPDTA|Fe(CN) 6 RFB for 200 cycles. An optimized CrPDTA|Fe(CN) 6 RFB, which combines a high cell potential with a low area-specific resistance (0.46 Ω cm 2 ), demonstrates a maximum discharge power density of 1.63 W cm −2 and an average discharge power density over 500 mW cm −2 while maintaining 80% round-trip energy efficiency cycling, which are records for non-acid-based RFBs. • High-power flow battery operates at neutral pH with potassium membrane transport • Record discharge-power performance for a flow battery not using proton transport • Inexpensive membrane provides high conductivity and constant efficiency cycling • Chelated metal electrolyte enables high voltage battery and high-power operation High-power flow battery operation lowers system costs but has previously required proton transport. By combining high voltage with low resistance from a highly selective and conductive membrane, Robb et al. demonstrate an aqueous flow battery that achieves record non-acidic power performance while utilizing potassium membrane transport at neutral pH.