Compositional Tuning of Mixed Chromium Monopotassium Phosphates by Ni²⁺/Co²⁺ Substitution for Energy Storage...

This study synthesized a solid-solution series of KCo_1-xNi_xCr₂(PO₄)₃ phosphates with the α-CrPO₄-type three-dimensional framework, in which edge-sharing CrO₆ octahedra and PO₄ tetrahedra create tunnels hosting K⁺ cations. Systematic Ni²⁺/Co²⁺ substitution was used to tune dielectric and charge-transport properties. All compounds showed stable paraelectric behavior; increasing Co content enhanced polarizability and dielectric permittivity while maintaining low dielectric loss. When used as electrode materials in graphite-based supercapacitors, higher Co content led to improved electrochemical performance, with the Co1Ni0 composition delivering a specific capacitance of 447 F/g, an energy density of 48.18 Wh/kg, and a power density of 1752 W/kg. The results demonstrate that Ni²⁺/Co²⁺ substitution is an effective strategy for designing advanced supercapacitor electrodes that combine high charge-storage capacity (due to increased permittivity) with improved power capability (due to higher conductivity).