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 of semiconductor photoelectrochemistry are identified and discussed within the framework of experimental observations. Conceptual differences between these two models appear to lie in the treatment of interfacial charge-transfer processes for photogenerated charge carriers. The conventional model utilizes detailed balance principles for obtaining rate constant relationships for all interfacial charge-transfer events at semiconductor/liquid contacts and uses the principle of microscopic reversibility to evaluate these rate constants for situations away from equilibrium. In contrast, the irreversible model postulates that local statistical detailed balance does not apply to charge-transfer events in photoelectrolysis, and that such charge-transfer events are highly irreversible, like photoemission into a vacuum. It is shown analytically that the two models predict differences in the behavior of the available free energy produced by a photoelectrochemical cell at a fixed incident light intensity. The conceptual implications of these differences are evaluated analytically and are also compared to experimental results for semiconductor/liquid junctions