Electrochemical adsorption and phase formation of TlBr and TlI on Tl(Hg)

Abstract

The formation of TlBr and TlI on thallium amalgam electrodes in KBr and KI solutions has been investigated in detail by linear sweep voltammetry, potential step and galvanostatic methods. The results show that growth of the three dimensional bulk phase is preceded by the formation of two-dimensional layers. The behaviour of both systems in the two-dimensional regime clearly does not correspond to the nucleation and growth of a two dimensional layer by the incorporation of new material at the periphery of expanding circular centres; instead, the first monolayers of TlBr and TlI are formed by ohmic controlled adsorption after an initial activated step which appears to involve nucleative behaviour. The adsorption isotherm in both systems shows a step that is probably associated with a transformation which leads to an increase in packing density of the adsorbate. The second monolayers, which appear as metastable phases under dynamic conditions, are formed by a nucleation and growth mechanism.