Fabrication and Corrosion Behaviour of Platinum-Coated Titanium Electrodes from Low Temperature Molten Salt Electrolytes

Abstract

The development of corrosion-resistant platinum coated titanium (Pt/Ti) electrodes for seawater electrolysis in the production of sodium hypochlorite is an important requirement. In this study a new ternary low temperature molten salt (LTMS) LiCl—NaCl—KCl system was chosen as the electrolyte. The direct current method of four Pt electrodes combined with a computer program was employed to measure the relationship between conductivity and temperature of the chosen electrolyte at various PtCl2 concentrations. The pulse current technique was used for fabrication of Pt/Ti electrodes from the chosen LTMS electrolyte at the temperature and PtCl2 concentration where the conductivity of the LTMS system was highest by changing the duty-cycle and plating current density. The morphology and composition of the Pt-coated layer was examined by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Tafel plots, anodic polarization curves and electrochemical impedance spectroscopy (EIS) were employed to evaluate the corrosion behaviour of the Pt/Ti electrodes. The best quality Pt-coated electrodes were obtained from the pulse plating condition of Ton:Toff= 3:1 with a current density (iplat) of 127.5 mA cm−2. These had a higher Pt content, nobler corrosion potential (Ecorr), lower corrosion current density (icorr), lower passive current density (ipass) and higher impedance. Furthermore, AFM demonstrated that the best quality Pt/Ti electrode had the lowest surface roughness (Ra) with the finest grain size.