New aspects of zinc-nickel alloy co-deposition

The electrochemical behaviour of a zinc electrode in dilute solutions containing Zn(II) and Ni(II) ions has been studied. It is shown, that preferential deposition of the less noble Zn rather than Ni occurs due to kinetic features of simultaneous Ni(II) and Zn(II) discharges both under activation control. The simple modelling of the composition alloy has been based on the component current densities described by first order Butler-Volmer kinetics. A coplanar built-in antimony microelectrode assembly for potentiometric investigations is presented. The dependences of pH values near the cathode surface (pHs) on working electrode potentials, obtained by using the above mentioned electrode are discussed. It is shown, that in the so-called 'anomalous' region of Zn-Ni alloy deposition pHs remained close to the bulk pH value (pHb). In the 'normal' region of alloy deposition pHs value exceeds pHb throughout deposition runs and the effects of electrical connection between electrodes are noted. The possibility of bifunctional electrochemical film formation in the so-called 'normal' region of Zn-Ni alloy deposition is briefly discussed.