Acceleration of the Cathodic Kinetics on Aluminum Alloys by Aluminum Ions

The effect of Al3+ on the cathodic kinetics of Al alloys as well as Pt and SS316L has been investigated by a number of electrochemical techniques. It has been observed that the addition of Al3+ into NaCl solution can significantly increase the diffusion limited cathodic kinetics of Al alloys, and this increase is proportional to the [Al3+]. The same phenomenon was also observed on Pt and SS316L, which indicates that this enhancement in cathodic kinetics is not related the surface structure of Al alloy, and it is the HER diffusion-limited kinetics that are increased rather than ORR kinetics as a result. Based on electrochemical studies on Pt, it is proposed that although the addition of Al3+ can lead to the precipitation of an oxide/hydroxide film on Pt there is a greatly enhanced proton diffusivity which overwhelms the barrier effect of the precipitate film, leading to substantially increased cathodic kinetics. The results are interpreted in terms of an extension of the Grotthuss Theory in which Al3+ can facilitate transport of the proton.