Metal-Organic Framework Cathodes Based on a Vanadium Hexacyanoferrate Prussian Blue Analogue for High-Performance Aqueous Rechargeable Batteries

Despite the unique advantages of the metal-organic framework of Prussian blue analogues (PBAs), including a favorable crystallographic structure and facile diffusion kinetics, the capacity of PBAs delivered in aqueous systems has been limited to ≈60 mA h g⁻¹ because only single species of transition metal ions incorporated into the PBAs are electrochemically activated. Herein, vanadium hexacyanoferrate (V/Fe PBA) is proposed as a breakthrough to this limitation, and its electrochemical performance as a cathode for aqueous rechargeable batteries (ARBs) is investigated for the first time. V/Fe PBAs are synthesized by a simple co-precipitation method with optimization of the acidity and molar ratios of precursor solutions. The V/Fe PBAs provide an improved capacity of 91 mA h⁻¹ under a current density of 110 mA g⁻¹ (C-rate of ≈1.2 C), taking advantage of the multiple-electron redox reactions of V and Fe ions. Under an extremely fast charge/discharge rate of 3520 mA g⁻¹, the V/Fe PBA exhibits a sufficiently high discharge capacity of 54 mA h g⁻¹ due to its opened structure and 3D hydrogen bonding networks. V/Fe PBA-based ARBs are the most promising candidates for large-scale stationary energy storage systems due to their high electrochemical performance, reasonable cost, and high efficiency.