Progress in Understanding Electron-Transfer Reactions at Semiconductor/Liquid Interfaces

Abstract

This article describes theoretical treatments and experimental data focused on the rates of interfacial electron-transfer processes at semiconductor/liquid contacts. These systems are of practical interest because such electron transfers are a critical factor in understanding the behavior of photoelectrochemical cells as energy conversion devices. These processes are of theoretical interest because the description of how a delocalized charge carrier in a semiconducting solid reacts with a localized redox acceptor that is dissolved in the liquid electrolyte is a relatively undeveloped area of electron-transfer theory. The general principles of these processes, a discussion of past and present experimental data, and a comparison between theoretical expectations and experimental observations on a variety of semiconducting electrode systems are the main focus of this article.

Reactivity of Trapped and Accumulated Electrons in Titanium Dioxide Photocatalysis

“…The energy distribution of Ti ds in TiO 2 powders and colloids can be obtained by photochemical [60], electrochemical [61,62], and RDB-PAS [56] methods. The acceptor levels of AP derivatives can be estimated by the Marcus theory [72,[74][75][76]. Table 1.…”

Theoretical Aspects of Light-Activated Microelectrodes in Redox Electrolytes

“…1 More specifically, we seek steady-state solutions for the transport equations for electrons ͑n͒ and holes ͑p͒, including both generation and recombination of n-p pairs, 5,6 self-consistently coupled to Poisson's equation for the electrostatic potential within the semiconductor, , and to the transport equations for the donor ͓red ͑reduction͔͒ and the acceptor ͓ox ͑oxidation͔͒ species in a quiescent solution phase subject to the appropriate boundary conditions. The latter includes second-order kinetics 7,8 to account for the interfacial reactions between p ͑in the valence band͒ and red and between n ͑in the conduction band͒ and ox, which, for the parameters selected for this study, may be regarded as the dominant contributions to the measured current. A similar problem involving the partial illumination of a semiconductor without taking into account the mass transport from species in the solution phase was reported earlier by Mannheim and co-workers 9 within the context of photocorrosion.…”

“…For these simulations, the values of the relevant physical constants were obtained from either the literature 10,11 or prescribed by the characteristics of the semiconductor. Specifically, for n-InP, the direct recombination coefficient C dir = 6 ϫ 10 Other parameters, such as the magnitudes of the second-order, potential independent rate constants 7 for reactions between n and ox ͑k etn ͒ and between p and red ͑k etp ͒, were adjusted to obtain values for the currents in line with those in the literature 1,10 ͑see the caption of Fig. 3͒.…”

“…The latter includes second-order kinetics 7,8 to account for the interfacial reactions between p ͑in the valence band͒ and red and between n ͑in the conduction band͒ and ox, which, for the parameters selected for this study, may be regarded as the dominant contributions to the measured current. A similar problem involving the partial illumination of a semiconductor without taking into account the mass transport from species in the solution phase was reported earlier by Mannheim and co-workers 9 within the context of photocorrosion.…”

Photoreductive Sequestration of Co2 to Form C1 Products and Fuel

“…The redox potential for reaction (R4) is-0.42 V, very close to the potential for water reduction to H 2 (-0.41 V), or about 2 eV or 620 nm (Goren et al, 1990). R2, the recombination of charge carriers with heat formation, is very likely the chief source of inefficiency in the semiconductorcatalyzed process (Lewis, 1998;Upadhya et al, 1997).…”