DIFFUSE LAYER EFFECT AND EFFECT OF CURVATURE ON THE MECHANISM AND THEPROPERTIES OF PHASE-TRANSITIONS AT ELECTRIFIED INTERFACES

The criteria for an adsorbed layer to undergo a reversible phase trans ition on an electrode surface are examined by means of classical therm odynamics. It is shown that, although this process takes place always at a constant value of the potential drop across the adsorbed layer, i t may occur at either a constant value of the applied potential or ove r a certain range of applied potentials. The first possibility can be realised when the concentration of ions in the diffuse layer is high e nough to produce an approximately equipotential plane just beyond the adsorbed layer or when the diffuse layer is imposed to undergo a kind of phase transition characterised by its separation into two parts wit h different total electrical charge but the same potential drop or the transition extends throughout the interface. If neither of the above processes can be realised, then the second possibility is very likely due to a diffuse layer effect. For the examination of the diffuse laye r effect in more detail, the classical supersaturation theory is exten ded to two-dimensional phase transitions on electrode surfaces and an attempt is made to explain the existence and extent of metastable stat es as well as the mechanism and the properties of irreversible transit ions. The results obtained are compared with current views on two-dime nsional phase transitions. (C) 1998 Elsevier Science S.A. All rights r eserved.