A comprehensive study on PANI-MnO2 solid-state reference electrodes for in-situ corrosion assessment in concrete infrastructure

Abstract

Traditionally, liquid-based reference electrodes mounted on surfaces have been the predominant method for monitoring the corrosion of steel rebars in concrete structures. However, solid-state reference electrodes offer a robust alternative, overcoming several limitations of their liquid-based counterparts. The present study aims to evaluate the electrochemical characteristics and effectiveness of solid-state reference electrodes fabricated from PANI-MnO₂ nanocomposites in a simulated concrete environment. The nanocomposite material was synthesized through the chemical oxidative polymerization of aniline in the presence of MnO₂, leading to oriented coupling and dissolution-recrystallization processes that initiated the nucleation growth of MnO₂ crystals. This was followed by the oxidative coupling of aniline monomers onto the MnO₂ crystals, forming the PANI-MnO₂ nanocomposite. A comprehensive suite of analytical techniques, including Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), was employed to corroborate the composition, morphology, and crystal structure of the nanocomposite. SEM/TEM imaging confirmed the envelopment of MnO₂ nanorods by PANI layers, while FTIR and XPS analyses substantiated the chemical interaction between PANI and MnO₂. The fabricated PANI-MnO₂-based solid-state reference electrodes (PM-SSRE) were subsequently characterized for their electrochemical stability, reversibility, and polarization resistance in simulated concrete pore (SCP) solutions and cement extracts containing varying concentrations of NaCl (0 %, 1 %, 2 % and 3 %). Various electrochemical techniques, including open-circuit potential (OCP), cyclic polarization, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization, were utilized for this purpose. The results indicated that PM-SSRE demonstrated superior electrochemical stability, reversibility, and polarization resistance across all test solutions. Hence, PM-SSREs are recommended for in-situ corrosion monitoring applications in concrete structures, given their ability to assess steel rebars’ passive and corrosive states accurately.