Electrochemical performance of NiO and Ni(OH)₂-based supercapacitors derived from recycled Ni–Ti rotary files: a hydrometallurgical approach

Metallic values from the Ni–Ti rotary files have been recovered using a reflux system for leaching experiments. H₂SO₄ was employed as the leaching agent, achieving leaching efficiencies of 94.75% for titanium and 88.66% for nickel. After leaching, titanium precipitated as TiO₂ and nickel as Ni(OH)₂. Nickel oxide (NiO) is a popular material for supercapacitor electrodes. To convert the precipitated Ni(OH)₂ to NiO, calcination was carried out at temperatures of 450, 650, and 850 °C. For the production of supercapacitor electrodes, nickel oxide and nickel hydroxide were used separately. The electrochemical behavior of supercapacitors with different electrodes was investigated in a two-electrode system at a scanning rate of 10 mV.s⁻¹. Specific capacitance values of 58.01, 87.91, 73, and 61.41 mF.cm⁻² were obtained for electrodes produced from Ni(OH)2, and obtained after Ni(OH)₂ was calcined at temperatures of 450, 650, and 850, respectively. Long cycle stability tests were performed on the supercapacitors at 1 mA.cm⁻² current density, yielding capacitance retention results of 126.24, 103.47, 94.45, and 122%, respectively.