AN ANALYTICAL DESCRIPTION OF THE CONSEQUENCES OF ABANDONING THE PRINCIPLES OF DETAILED BALANCE AND MICROSCOPIC REVERSIBILITY IN SEMICONDUCTOR PHOTOELECTROCHEMISTRY

Key differences between the conventional and ''irreversible'' models o f semiconductor photoelectrochemistry are identified and discussed wit hin the framework of experimental observations. Conceptual differences between these two models appear to lie in the treatment of interfacia l charge-transfer processes for photogenerated charge carriers. The co nventional model utilizes detailed balance principles for obtaining ra te constant relationships for all interfacial charge-transfer events a t semiconductor/liquid contacts and uses the principle of microscopic reversibility to evaluate these rate constants for situations away fro m equilibrium. In contrast, the irreversible model postulates that loc al statistical detailed balance does not apply to charge-transfer even ts in photoelectrolysis, and that such charge-transfer events are high ly irreversible, like photoemission into a vacuum. It is shown analyti cally that the two models predict differences in the behavior of the a vailable free energy produced by a photoelectrochemical cell at a fixe d incident Light intensity. The conceptual implications of these diffe rences are evaluated analytically and are also compared to experimenta l results for semiconductor/liquid junctions.