Its value of the M/z when the cobalt is being deposited with 100% efficiency, i.e., without any other parallel process on the surface of the electrode. If electrochemical processes occur with parallel chemical processes as for example with deposit of mass by precipitation, the ratio M/z will be higher value than theoretical. If electrochemical process occur with lower or no mass change, the experimental M/z will be lower than the theoretical value for the reaction considered.
From Fig. 2b, it was observed that experimental M/z values obtained during cobalt electrodeposition in a solution of pH5.40
moved toward a value of 32.00 gmol−1 as the deposition advanced in the cathodic direction. This result suggests that deposition is occurring in agreement with Eq. (1). Already at pH 2.70,M/z values tended toward a value of 13.00 gmol−1.
This result suggests that cobalt electrodeposition might be occurring via the formation reaction of Co(OH)2 or by the mechanismof adsorbed hydrogen. As observed by Matsushima et al. [11],however, the formation of Co(OH)2 does not occur in solutions of pH< 2.70. Therefore, the decrease in observed M/z values might be associated with the formation of adsorbed hydrogen. This reaction occurred in solutions with pH< 2.70 when H3BO3 was added as a buffer to prevent local pH variations in the solution. Experimental M/z values were lower than theoretical values owing to the hydrogen reduction reaction, which decreases the efficiency for cobalt electrodeposition.
The voltammograms curves for cobalt electrodissolution at both analyzed pHvalues are shown in Fig. 2a.According to Soto et al. [23], peak I can be associated with cobalt oxidation containing hydrogenrich phase. The shoulder of current II can be related with cobalt electrodissolution without adsorbed hydrogen.
Turning to the anodic scan, cobalt deposition continues until reachedthepotential of−0.1V,whenis observeda currentpeakdue to the cobalt electrodissolution (Fig. 2a). In Fig. 2b is observed that the ratio M/z increase to 60.00 gmol−1. That resulted indicate that themetallic Co electrodissolution occurs through a formation of an intermediary Co1+ in the interface metal solution. In the following stage, the Co+ is oxidized to Co2+, as can be see in Eq. (11). Finally, at potential more positive than 0.100V, the metallic cobalt film is dissolved and the ratio M/z attains the starting value. This behavior
also was observed by Martin et al. [24].