Facile synthesis of Mn-doped NiCo₂O₄ nanoparticles with enhanced electrochemical performance for a battery-type supercapacitor electrode

We report the synthesis of manganese-doped nickel cobalt oxide (Mn-doped NiCo₂O₄) nanoparticles (NPs) by an efficient hydrothermal and subsequent calcination route. The material exhibits a homogeneous distribution of the Mn dopant and a battery-type behavior when tested as a supercapacitor electrode material. Mn-doped NiCo₂O₄ NPs show an excellent specific capacity of 417 C g^-1 at a scan rate of 10 mV s^-1 and 204.3 C g^-1 at a current density of 1 A g^-1 in a standard three-electrode configuration, ca. 152-466% higher than that of pristine NiCo₂O₄ or MnCo₂O₄. In addition, Mn-doped NiCo₂O₄ NPs showed an excellent capacitance retention of 99% after 1000 charge-discharge cycles at a current density of 2 A g^-1. The symmetric solid-state supercapacitor device assembled using this material delivered an energy density of 0.87 μW h cm^-2 at a power density of 25 μW h cm^-2 and 0.39 μW h cm^-2 at a high power density of 500 μW h cm^-2. The cost-effective synthesis and high electrochemical performance suggest that Mn-doped NiCo₂O₄ is a promising material for supercapacitors.