  In any consistent electrochemical systems model that addresses more than one
interface, the total current at the interfaces should be equal to one another
and to the current in the external circuit. The point defect model of Macdonald
and co-workers fails to recognize this basic requirement. Hence there is no
assurance that currents predicted by the PDM will be the same at the metal/film
and the film/solution interfaces. This deficiency is corrected in the present
work. Besides, The point defect model lacks a proper book-keeping of ion and
electron currents and in particular missed the role of a purely electron
channel (e-channel) at the metal/film interface [1]. In this work we describe
this book-keeping, include the e-channel and show how this affects the forms of
the metal-film and film-solution potential drops.
