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 degrees 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.