An Analytical Description of the Consequences of Abandoning the Principles of Detailed Balance and Microscopic Reversibility in Semiconductor Photoelectrochemistry

Abstract

Key differences between the conventional nd "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 vents in photoeleetrolysis, and that such charge-transfer vents are highly irreversible, like photoemission i to a vacuum. It is shown analytically that the two models predict differences in the behavior of the available free energy produced by a photoelectrochemical cel 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. Renewed interest in the photoelectrochemistry of metal oxides, for applications in wastewater treatment and pho-tochemical energy conversion, 14has focused attention on