Multi-walled carbon nanotubes decorated polyaniline- α-Fe2O3 nanocomposite as an efficient photoanode for photoelectrochemical water splitting and photoelectrochemical cathodic protection of mild steel

In this research, polyaniline nanocomposites with iron (III) oxide and multi-walled carbon nanotubes (PANi-Fe and PANi-Fe-CNT) were synthesized and successfully characterized by various techniques such as X ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, Field emission scanning electron microscopy (FESEM), and X-ray energy dispersive spectroscopy (EDS). The photoelectrochemical (PEC) performance of PANi, α-Fe₂O₃ nanoparticles, PANi-Fe and PANi-Fe-CNT on indium tin oxide (ITO) substrate was evaluated by linear sweep voltammetry (LSV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) in the dark and under simulated sunlight (100 mW/cm²). The results showed that ITO/PANi-Fe-CNT photoanode had higher photocurrent density (1.05 mA/cm²), more significant applied bias photo-to-current efficiency percentage (0.16%), and smaller charge transfer resistance (1008 Ωcm²) than other photoanodes under light irradiation. To study the photoelectrochemical cathodic protection (PEC cathodic protection) properties, the pastes were prepared from synthesized compounds and doctor-bladed on the pre-treated titanium (Ti) substrates and used as the photoanodes for the protection of mild steel. The performance of the as-prepared photoanodes in photoelectrochemical cathodic protection of mild steel was investigated using electrochemical impedance spectroscopy (EIS) and Tafel polarization. The corrosion potential (E_corr) of mild steel decreased from −706 mV (without connection to the photoanode) to −864 mV in the state of connection to Ti/PANi-Fe-CNT photoanode under light irradiation, which indicated its cathodic protection.