ON THE TRANSITION FROM ELECTRODESORPTION OF A 2-PHASE ADSORBATE TO 2D HOLE NUCLEATION IN THE DISSOLUTION OF HGS LAYERS AT THE MERCURY ELECTROLYTE INTERFACE

The dissolution of anodic films of HgS was investigated by analysing current i-time t transients. The dissolution of the first monolayer and the bilayer can be theoretically well described by a new model which involves an exponential increase in the current followed by an exponential decrease in it. The model implies that the anodic layer consists of adclusters and adomlecules, that the adclusters dissolve at their rims into admolecules which diffuse across the surface and that only the admolecules can be reduced and desorbed (electrodesorption). Here the electrodesorption is assumed to be much slower than the dissolution of the adclusters and the surface diffusion of the admolecules. When all adculsters are dissolved, the electrodesorption of the admolecules follows a first-order process. The dissolution of an HgS multilayer proceeds via 2D progressive hole nucleation and growth.