An atomistic description of dealloying - Porosity evolution, the critical potential, and rate-limiting behavior

We describe the microscopic details of porosity formation during dealloying as illuminated by a kinetic Monte Carlo model incorporating site coordination-dependent surface diffusion of all alloy components, and site coordination-dependent dissolution of the less-noble atoms. Our simulation model reproduces the entire range of phenomena associated with selective dissolution. These phenomena include composition and geometric restrictions on dealloying (parting limits), a composition-dependent critical potential, a passivation regime, a regime of steady-state dissolution flux, and porosity formation. We find that an intrinsic critical potential exists as a well-defined threshold potential separating surface passivation and porosity formation behaviors, but this intrinsic critical potential typically sits at values well below the experimental measurements of the empirical critical potential. Finally, by detailed examination of the temperature dependence of the dissolution flux, and also of the types of surface sites contributing to the dissolution flux, we predict that the binding energy of a terrace atom may be straightforwardly extracted from analysis of experimental polarization curves. (C) 2004 The Electrochemical Society.