Design and fabrication of gold nanoparticles decorated SSM@NiCo₂O₄ as a binder-free electrode for solid-state symmetric supercapacitor application

Supercapacitor phenomenon deals with the electrode surface and electrolyte, hence we have modified the surface of NiCo₂O₄ by depositing it on low-cost stainless steel mesh (SSM@NiCo₂O₄) to enhance the electrochemical properties. The thermal decomposition of gold (HAuCl₄) to the gold nanoparticles (AuNPs) at temperature above 300 °C was well matched with the annealing temperature of SSM@NiCo₂O₄ become the center of attraction. Hence, we have decorated AuNPs on a binder-free SSM@NiCo₂O₄ (SSM@NiCo₂O₄-AuNPs) with the aid of the dip coating method followed by heat treatment. The specific capacitance of SSM@NiCo₂O₄-AuNPs was 1008.9 F g⁻¹ at a current density of 1 mA cm⁻² and is 1.6 times greater compared to SSM@NiCo₂O₄ (615.3 F g⁻¹). Specific capacitance retention after the decoration of AuNPs for 5000 GCD cycles is improved to 82.35 % (30 mA cm⁻²) compared to SSM@NiCo₂O₄ of 72.22 % (18 mA cm⁻²). Such an outcome is obtained due to improved frequency of electrode-electrolyte interaction and decreased internal resistance accompanied by AuNPs. To evaluate the practical applicability, the solid-state symmetric device, SSM@NiCo₂O₄-AuNPs//SSM@NiCo₂O₄-AuNPs is fabricated which exhibits exceptional specific capacitance of 117.74 F g⁻¹ (2 mA cm⁻²), remarkable specific capacitance retention of 84.61 % (5000 cycles), high energy density of 59.03 Wh Kg⁻¹ and high power density of 5094.75 W kg⁻¹. Device glowed two red light emitting diodes (LED) for 227 s by charging 15 s only, demonstrating the enormous potential for the developing energy sector.