The growth of compact layers at the electrode interface Part I. Complexes of cobalt, nickel and iron with 2,2′-bipyridine and 2,2′,2″-terpyridine in aqueous sodium perchlorate

Abstract

Tris-2,2′-bipyridine complexes of Co(II), Ni(II), and Fe(II) and a bis-2,2′,2″-terpyridine complex of Co(II) in aqueous perchlorate media were studied by means of electrode double-layer capacitance measurements at the hanging mercury drop electrode. At potentials where no faradaic process takes place all compounds form two types of compact films with different orientations of species at the interface. The solid-like nature of these films was confirmed from the hysteresis of capacitance vs. potential curves and from the sigmoidal Avrami-type capacitance vs. time dependence. As a new feature of the nucleation/growth process, long-time deviations from the Avrami shapes were found. At potentials where the nucleation rate is very small, the C—t curves exhibit an S-shape, followed by a maximum usually at time s $ ̆ 1000 s. An interpretation in terms of a change from 2D- to 3D-type growth is suggested.