Unveiling the effect of precursor concentration on pseudocapacitive performance of hydrothermally grown binder-free zinc cobalt oxide films

Binder-less electrodes of transition metal cobaltites for supercapacitors have gained increasing attention in recent years. This approach directly addresses the need of integrated, structurally tunable electrodes while minimizing binder associated resistances. In this context, vertical hydrothermal offers the potential for growing binder-less films with controlled morphology. In this work, synthesis of binder less ZnCo 2 O 4 microrods are carried out by vertical hydrothermal method on the stainless steel. The relationship between precursor concentration, microrod growth, and ion transport kinetics of ZnCo 2 O 4 films is systematically investigated. The structural properties and phase confirmation of ZnCo 2 O 4 films is analyzed using XRD, FT-IR and RAMAN spectroscopy. XRD and RAMAN spectroscopy showed the nano-polycrystalline nature of spinel ZnCo 2 O 4 . The growth of ZnCo 2 O 4 microrod assembly on the stainless steel is observed by SEM microscopy and analyzed by growth mechanism. The electrochemical properties of ZnCo 2 O 4 films are investigated in 1 M KOH electrolyte and have showed pseudocapacitive nature. From CV analysis, ZnCo 2 O 4 film have exhibited diffusion coefficient of 3.4 × 10 −8 cm 2 /s, while EIS analysis revealed diffusion coefficient of 5.08 × 10 −10 cm 2 /s. The highest specific capacitance of 913.1 F/g at 3 mA/cm 2 is depicted by ZnCo 2 O 4 film with 90.1% capacitance retention after 5000 cycles. The symmetric supercapacitor device based on ZnCo 2 O 4 film exhibited specific energy of 6.87 Wh/kg at 1315 W/kg specific power. The results demonstrate the effect of precursor concentration for controlling nucleation, growth of microrods, and ion transport kinetics of ZnCo 2 O 4 , establishing relationship between structural and electrochemical performance and highlighting promising potential in supercapacitor application.