Facile synthesis of MCo2O4(M= Ni, Cu, and Zn) materials for high-performing electrochemical capacitors with robust cyclic stability using redox additive electrolyte

Developing efficient electrochemical capacitors relies heavily on the quality of electrode materials and electrolytes used. This report presents the successful solvothermal synthesis of three cobaltites, NiCo 2 O 4 , CuCo 2 O 4 , and ZnCo 2 O 4 , and their electrochemical performance in a 2M KOH solution. Among the three cobaltites, NiCo 2 O 4 showed the best electrochemical performance with a specific capacity of 178 C/g with FTO (fluorine-doped tin oxide) as the current collector. In addition, the performance of NiCo 2 O 4 was tested in different aqueous electrolytes, including KOH, NaOH, NaCl, and Na 2 SO 4 , and the specific capacity was found to vary in the order of 2 M KOH > 2 M NaOH > 2 M NaCl > 2 M Na 2 SO 4 . The performance of NiCo 2 O 4 was also assessed in various concentrations of KOH electrolyte (2 M KOH, 3 M KOH, and 4 M KOH), and the best performance was observed in 3 M KOH with a specific capacity of 928.3 C/g with Ni foam as the current collector. Finally, using redox additive electrolytes, the performance of synthesized NiCo 2 O 4 was evaluated in both 3-electrode and 2-electrode systems. No studies have been conducted on the electrochemical performance of NiCo 2 O 4 with KFCN redox additive in a 3 M KOH electrolyte. In the three-electrode system, NiCo 2 O 4 showed a high specific capacity of 1005.5 C/g at 1 A/g, with 167 % capacity retention after 1000 charge-discharge cycles at a high current density of 30 A/g. The NiCo 2 O 4 //Activated Carbon asymmetric hybrid supercapacitors in two-electrode systems exhibited a maximum specific capacity of 115.6 C/g and a specific energy density of 85 Wh/kg at a specific current density of 1 A/g. They also showed a capacitive retention of 120% after 5000 charge-discharge cycles. The maximum power density was 13225 W/kg at a current density of 5 A/g while maintaining an energy density of 22 Wh/kg.