Space charge storage in composites: thermodynamics

Contacts of two phases, which allow for synergistic dissociative storage of a component in two space charge zones ("job-sharing storage"), are considered from the viewpoint of point defect thermodynamics. The respective relations between charge and component activity (chemical potential of the component) are derived, or - for more complex cases - the recipes for their derivation are given. These relations describe - according to different experimental conditions - the connection between mass storage and outer partial pressure or between mass storage and the cell voltage in a coulometric titration cell. They also reflect theoretical charge/discharge curves in battery cells when job-sharing storage predominates, and thus are also significant for supercapacitors. In addition to explicitly worked-out cases, it is pointed out how more general situations, such as simultaneous storage in bulk and in boundaries, specific adsorption or size effects, are to be treated.