2.2. Electrochemistry quartz crystal microbalance measurements
For ECQM Experiments, a 50.0ml Pyrex® cell was used. The cover was made of Teflon® and included holes for the introduction of saturated Ag/AgCl/NaCl reference and platinum auxiliary electrodes, with a geometric area of 0.50 cm2. The working electrode was introduced at the bottom of the cell. Working electrodes were composed of quartz crystal covered with platinum of fundamental frequency of 9.00MHz (SEIKO) and had a geometric area of 0.20 cm2. The platinum electrode was cleaned with sulphonitric solution and washed with dilutes. Afterward, it was submitted to an electrochemistry cleaner, which consisted of successive platinum oxidation and reduction cycles in a solution of H2SO4 0.10mol l−1 until characteristic cyclic voltammograms curves of the platinum in acid were obtained.
EQCM measurements were accomplished simultaneously with potentiodynamic and potentiostatic studies. For potentiodynamic measurements, the initial potential was 0.00V, where no reaction occurs at the electrode, and the final potential was −1.00V. A scan rate of 20.00mVs−1 was used. Potentiostatic measurements were made by applying a potential jump from−0.10V (no reaction at the electrode) to −0.90 or −1.00V. The systemwas polarized for 30 s at these potentials.EQCM measures were performed using a Quartz Crystal SEIKOEG&G model QCA917 microbalance. This was coupled to a PAR model 263A power supply. The system was managed using M270 software from EG&G EVEN. The frequency measures conversion in mass variation was made with base in Sauerbrey’s equation (Eq.(9)). A sensibility coefficient of 858.80gHz−1 was used.