Sol-Gel-Derived NiO/ZnO Thin Films with Single and Heterostructure Layers for Electrochemical Energy Storage

TL;DR

This study synthesized NiO/ZnO thin films with different configurations to evaluate their electrochemical performance for supercapacitors, demonstrating enhanced capacitance through heterostructure design and doping.

Contribution

It introduces sol-gel-derived NiO/ZnO heterostructure thin films with doping to improve supercapacitor performance, highlighting their potential as scalable electrode materials.

Findings

Single-layer NiO achieved a capacitance of 1.391 Fg^{-1}.

Heterostructure NiO/ZnO showed increased capacitance of 1.627 Fg^{-1}.

Na doping significantly enhanced ZnO's capacitance.

Abstract

NiO/ZnO-based thin films, including single-layer and heterostructure configurations, were synthesized to investigate the influence of stacking order on their electrochemical performance for supercapacitor applications. To improve the relatively low capacitive performance of ZnO compared to NiO, NaCl was introduced as a dopant. All films were deposited using a non-vacuum spin-coating method on fluorine-doped tin oxide (FTO) substrates, chosen for their excellent electrical conductivity and stability as electrode materials. The surface morphology and structural parameters were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Optical properties were analyzed via UV-Vis spectroscopy, revealing direct band gaps in the range of 3.17-3.31 eV for ZnO and Na-ZnO, and wider gaps up to 3.81 eV for NiO. Electrochemical performance was evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) in a three-electrode configuration with 1 M KOH as the electrolyte. Among the electrodes, the single-layer NiO film exhibited the highest specific capacitance of 1.391 Fg^{-1}. In contrast, the NiO/ZnO heterostructure demonstrated a synergistic effect, resulting in enhanced charge storage and achieving a maximum specific capacitance of 1.627 Fg^{-1} at a current density of 2.0 mA cm^{-2}. Furthermore, sodium doping significantly improved the capacitance of ZnO. Overall, the results highlight the potential of sol-gel-derived oxide heterostructures and doped thin films as cost-effective and scalable electrode materials for supercapacitors in portable electronics and energy storage systems.