Nickel to nickel oxide: A scalable two-step electrochemical approach for transparent and porous thin film fabrication

Abstract

In this study, a two-step electrochemical approach was employed to fabricate transparent and porous nickel oxide (NiO) thin films on indium tin oxide glass substrates. Initially, nickel thin films were electrodeposited from Watt's solution utilizing a two-electrode configuration under varying current densities (0.25–2 mA/cm²) and deposition times (15–60 s). The deposited films were subsequently anodized in an ethylene glycol-based electrolyte under controlled voltages (4–6 V) and anodization times (1–7 h) to achieve porous NiO structures. The structural, morphological, optical, and electrical properties of the films were characterized using a range of analytical methods, including X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, UV–Vis spectroscopy, Hall effect measurements, and contact angle analysis. The results indicate that optimized anodization at 4V for extended durations yielded highly porous, well-adherent NiO films with enhanced transparency (>80 %) and p-type conductivity (hole mobility up to 36.03 cm²/Vs). The electrochemical approach is scalable, cost-effective and environmentally friendly, and offers promising applications in electrochromic devices, transparent electrodes and energy storage systems.