Metal‐Organic Open‐Framework Molecular Magnet Based on Vanadium Hexacyanoferrate Prussian Blue Analogs as Cathode Material for Advanced Potassium Ion Aqueous Battery

The development of high‐performance electrode materials is vital for advancing next‐generation energy storage systems. In this study, we successfully synthesized an open‐framework vanadium hexacyanoferrate (VHCF) compound and explored its application as a cathode for aqueous potassium‐ion batteries (AKIBs). Infrared and Raman studies confirmed VHCF formation through characteristic –C≡N– stretching (≈1900–2200 cm − ¹), while structural analysis revealed a stable face‐centered cubic ( Fm3m ) framework with open tunnels enabling efficient K + diffusion. Magnetic measurements and neutron depolarization confirmed the compound's paramagnetic nature. X‐ray photoelectron, Mössbauer, and synchrotron X‐ray absorption studies revealed Fe² + (low spin) and V 4 + oxidation states, with evidence of ligand‐to‐metal and metal‐to‐ligand charge transfer. Electrochemical analysis showed high specific capacity (≈121 mAh g − ¹ at 0.5 A g − ¹) with ≈99% coulombic efficiency, and ≈96% efficiency at 2 A g − ¹ with 45% capacity retention after 620 cycles. The open‐tunnel‐like network of V(O)‐Fe(CN) 6 is responsible for the compound's higher cyclic stability and reversibility. However, ex‐situ X‐ray diffraction showed slight amorphization and lattice contraction from 10.22 Å to 10.13 Å after 350 cycles. The K + diffusion coefficient (D k + ) obtained from the galvanostatic intermittent titration technique displayed a V‐shaped charging trend (9.46 × 10 − ¹¹ cm²·s − ¹), increasing to 1.96 × 10 − 8 cm²·s − ¹ during discharge. Density functional theory calculations indicated a low K + migration barrier energy (≈0.45 eV). With cost‐effective synthesis, a robust metal‐organic framework, and excellent structural, magnetic, and electrochemical properties, VHCF is a promising cathode material for future AKIBs.