Photopotential probe of space charge and field profiles at electrolyte/silver halide interfaces: Part I. Combined electrochemical thermodynamic, adsorption and solid state vacuum interface models

Abstract

A unified model for charge, field and potential distributions at silver halide/solution interfaces is developed by combining electrochemical thermodynamics with general and specific ion adsorption models. Important aspects include equality of electrochemical potential across the interface, dopant dependent internal specific adsorption of Ag i + or Ag v − as ionic surface states and specific adsorption of ions from the electrolyte. These two sources of surface charge combine to cancel or reinforce each other such that there is potential continuity between phases to provide Nernstian response. This picture allows oppositely doped silver halide electrodes to have the same interfacial potential difference while having quite different fields at the inner crystal surface. These field differences explain the diversity of photopotential effects observed.