Novel mixed nickel/cobalt hexacyanoferrate microcubes with synergistic effects for aqueous hybrid supercapacitors†

Abstract

Combining different metals in coordination compounds is an efficient strategy to improve their various properties. Herein, mixed nickel–cobalt hexacyanoferrate (Ni_xCo_yHCF) microcubes of varying x : y molar ratios are synthesized via a co-precipitation route and comprehensively characterized to study their material and electrochemical properties. Ni_xCo_yHCF microcubes display the battery-type electrochemical energy storage mechanism in aqueous electrolytes. Among the samples, Ni₁Co₂HCF microcubes deliver the highest specific capacity of 134 mA h g⁻¹ (1068 F g⁻¹) at a specific current of 1 A g⁻¹. This significant enhancement in the capacity indicates the synergistic and cooperative effects between Ni and Co sites in Ni₁Co₂HCF microcubes. The asymmetric supercapacitor device assembled with Ni₁Co₂HCF microcubes delivers an excellent energy density of 74.4 μW h cm⁻² at a power density of 750 μW cm⁻² and retains 87.7% of its initial capacity after 2000 cycles at a current density of 5 mA cm⁻², indicating its robust structural integrity and electrochemical durability. This study highlights the promising potential of mixed-metal hexacyanoferrates as high-performance electrodes for aqueous supercapacitors.