A Potentiostatic and Atomic Force Microscopy Study of the Nucleation and Growth Mechanisms of Certain Metallic Cyanometalates

Nucleation and growth mechanisms (NGMs) of nickel(II) hexacyanoferrate, nickel(II) octacyanomolibdate, and copper(II) octacyanomolibdate were performed by means of the potential step technique by oxidizing the respective metal electrode in 0.02 M sulfuric acid containing the potassium salt of either hexacyanoferrate or octacyanomolibdate compounds. The obtained current−time transients (I/t) were analyzed using the theory of electrocrystallization of the metallic phase. As evidenced through these experiments, we can state that for the nickel cyanometalate compounds, electroformation takes place through a three-dimensional progressive NGM, and for the copper(II) octacyanomolibdate compound, electroformation occurs by means of a three-dimensional instantaneous NGM. The electrochemical results were verified through the use of atomic force microscopy (AFM). From these results, we can conclude that AFM is a good complementary technique to determine the nature of the NGMs through which electroformation of a solid phase occurs on an electrode surface.