Fabrication of a cerium-doped nickel ferrite solid-state reference electrode and its performance evaluation in concrete environment

In this study, we fabricated a solid-state reference electrode (SSRE) using cerium (Ce) doping in nickel ferrite (NiFe2O4) nanoparticles (NPs) to monitor the corrosion of steel rebar in concrete. The process for synthesis of NPs was sol-gel combustion. The NPs were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) probed with energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). These techniques confirmed that the Ce doping was achieved successfully. The electrochemical stability of the fabricated SSRE was studied in buffer solution at different pH (7, 9, and 12) as well as in synthetic concrete pore solution (SCPS) and 3% NaCl-contaminated SCPS. Chloride ions do not affect the property of Ce-doped NiFe2O4. The stability of Ce-doped SSREs in different solutions as well as in concrete was constant throughout the exposure periods. The reversibility test results of Ce-doped NiFe2O4 in SCPS solution for NiCe0.1Fe1.9O4 (NFC1) and NiCe0.5Fe1.5O4 (NFC5) showed 20 and 15 mV, respective differences in potential between the forward and reverse scan. This result indicates that Ce-doped NiFe2O4 SSREs have better reversibility behavior than NiFe2O4 in SCPS. The reliability of NFC5 SSRE is excellent in SCPS and a concrete environment, and the maximum difference in both conditions was 5 mV, which is within the range of acceptable values. This indicates that Ce-doped NiFe2O4 SSRE can be used as a reliable embeddable sensor in concrete structures.