In situ gravimetry of nickel thin film during potentiodynamic polarization in acidic and alkaline sulfate solutions

The passivation process of nickel thin films during potentiodynamic polarization in acidic and alkaline sulfate solutions was analyzed by an electrochemical quartz crystal microbalance (EQCM) to separate the partial current density of nickel dissolution through the passive film, iNi2+iNi2+, and the partial current density of film growth, iO2-iO2-. The values of iNi2+iNi2+ and iO2-iO2- during potentiodynamic polarization (20 mV s−1) in the passive potential region could be separated by comparing the mass change rate and net polarization current as a function of electrode potential. It is found that iNi2+iNi2+ is larger than iO2-iO2- in pH 3.0, 0.5 M sulfate solution, while the situation reverses in pH 12, 0.5 M sulfate solution. The sulfate concentration dependences of iNi2+iNi2+ and iO2-iO2- in pH 3.0, sulfate solution were significant as compared to those in pH 12, sulfate solution.