Scalable Alkaline Zinc-Iron/Nickel Hybrid Flow Battery with Energy Density up to 200 Wh L -1 .

Achieving net-zero emissions requires low-cost and reliable energy storage devices that are essential to deploy renewables. Alkaline zinc-based flow batteries such as alkaline zinc-iron (or nickel) flow batteries are well-suited for energy storage because of their high safety, high efficiency, and low cost. Nevertheless, their energy density is limited by the low solubility of ferro/ferricyanide and the limited areal capacity of sintered nickel electrodes. Here, combining the electrochemical reaction with the chemical reaction of ferro/ferricyanide couple in a home-made nickel electrode, we report an alkaline zinc-iron/nickel hybrid flow battery with a high energy density of 208.9 Wh L -1 and an energy efficiency of 84.7% at a high current density of 80 mA cm -2 . The reversible chemical reactions between dual couples are proven to stabilize the nickel electrode by promoting the activation of the nickel electrode and further preventing the formation of γ-NiOOH. A kW-scale stack is demonstrated by the integration of ferro/ferricyanide couple with nickel electrode, delivering a coulombic efficiency of 98% and an energy efficiency of 89% at 40 mA cm -2 . This work demonstrates a promising pathway for constructing and upscaling flow batteries with high energy density and low cost. This article is protected by copyright. All rights reserved.