A highly sensitive and reliable pH sensor based on a polyaniline-nickel hydroxide modified nickel foam electrode: electrochemical and DFT investigations

Abstract

In this study, a highly porous three-dimensional (3D) pH sensor was developed using polyaniline (PANI)-modified nickel hydroxide-coated nickel foam (NF/Ni(OH)₂/PANI). The fabrication process involved the electrodeposition of nickel hydroxide onto nickel foam, followed by heat treatment and subsequent electropolymerisation of aniline at a constant current. The structural and morphological properties of the NF/Ni(OH)₂/PANI electrode were analysed using field emission scanning electron microscopy (FSEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, and Raman spectroscopy. FESEM images show oblate and spherical particles of NF/Ni(OH)₂/PANI, while XPS analysis confirms the elemental composition and the presence of different chemical bonds. The pH response was evaluated via open-circuit potential measurements, revealing a sensitivity of 46.00 mV per pH (R² = 0.99) over the pH range of 3 to 11. The sensor demonstrated excellent stability, reproducibility, and minimal drift, ensuring reliability for practical applications. Real sample analysis using vinegar, orange juice, and baking soda solutions confirmed the sensor's accuracy, showing strong correlation with commercial pH meters. Additionally, density functional theory calculations were performed to investigate the interaction energy between PANI and H₃O⁺ ions, revealing increasing binding affinity with longer PANI chain lengths (−68.01, −159.72, and −682.78 kJ mol⁻¹ for 1PANI, 2PANI, and 4PANI, respectively). HOMO–LUMO energy gap analysis further supported the electronic interactions governing the sensing mechanism. This combined experimental and theoretical approach confirms the potential of the NF/Ni(OH)₂/PANI sensor for real-time assessment in food safety, environmental monitoring, and biomedical analysis.