Binder-free synthesis of high-quality nanocrystalline $$\text {ZnCo}₂\text {O}₄$$ thin film electrodes for supercapacitor application

Supercapacitors as energy storage devices have attracted great attention due to their high-specific capacitance, fast rechargeability, high-power density, performance, long cycle life and low-maintenance cost. These unique advantages enable their applications in portable electronic devices, gadgets, hybrid electric vehicles, etc. However, developing flexible, high performance, stable and economic storage devices is the need of time. With this motivation, binder-free ( ext {ZnCo}₂ ext {O}₄) thin films are synthesized on flexible stainless steel mesh by a hydrothermal method. The structural, morphological and physicochemical properties of ( ext {ZnCo}₂ ext {O}₄) are investigated using X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy. FESEM images reveal thin films with flower-shaped microspheres composed of bunched nanowires providing a large surface area ((72, ext {m}², ext {g}^-1)) which is confirmed by Brunauer–Emmett–Teller analysis. The electrochemical performance of the ( ext {ZnCo}₂ ext {O}₄) thin film electrode exhibited a specific capacitance of 127.8 F ( ext {g}^-1) at a current density of 1 mA ( ext {cm}^-2). It also shows good rate capability and excellent electrochemical cycling stability (80.66% specific capacitance retention after 3000 cycles).