Photoelectrochemistry at semiconductors

Nakato, Y., Photoelectrochemistry at semiconductor/liquid interfaces, in Photocatalysis, Science and Technology, Kaneko, M. and Okura, I. (Eds), Kodansha/Springer, Berlin, 2002, Chap. 4. 

Fujihira, M., Satoh, Y., and Osa, T, Photoelectrochemistry at semiconductor titanium dioxide/ insulating hydrocarbon liquid interface,/. Electroanal. Chem., 126, 277, 1981. 

After starting his own laboratory in 1982, the author built microwave measurement facilities with his collaborators and resumed research on microwave electrochemical phenomena. While the potential of combining photoelectrochemistry with microwave conductivity techniques became evident very soon,6,7 it was some time before microwave experiments could be performed at semiconductor electrodes under better-defined microwave technical conditions.8... 

Bard AJ (1979) Photoelectrochemistry and heterogeneous photocatalysis at semiconductors. J Photochem 10 59-75... 

Kohei Uosaki received his B.Eng. and M.Eng. degrees from Osaka University and his Ph.D. in Physical Chemistry from flinders University of South Australia. He vas a Research Chemist at Mitsubishi Petrochemical Co. Ltd. from 1971 to 1978 and a Research Officer at Inorganic Chemistry Laboratory, Oxford University, U.K. bet veen 1978 and 1980 before joining Hokkaido University in 1980 as Assistant Professor in the Department of Chemistry. He vas promoted to Associate Professor in 1981 and Professor in 1990. He is also a Principal Investigator of International Center for Materials Nanoarchitectonics (MANA) Satellite, National Institute for Materials Science (NIMS) since 2008. His scientific interests include photoelectrochemistry of semiconductor electrodes, surface electrochemistry of single crystalline metal electrodes, electrocatalysis, modification of solid surfaces by molecular layers, and non-linear optical spectroscopy at interfaces. 

The photoelectrochemistry of semiconductors studies processes of various nature that occur at a semiconductor-electrolyte solution interface under the action of electromagnetic radiation (mainly in the visible, UV and IR regions). These processes include ... 

The theoretical developments in the above areas were influenced, to a considerable extent, by concepts borrowed from semiconductor physics and the physics of surfaces. Other fields of photoelectrochemistry of semiconductors were affected to a greater degree by progress achieved in the study of metal electrodes. Here we mean photoemission of electrons from semiconductors into solutions and electroreflection at a semiconductor-electrolyte interface. 

Eventually, photoelectrochemistry of semiconductors emerged as an autonomous field of electrochemical physics after the works of Dewald (1960) who developed a detailed mechanism for the occurrence of photopotential at a semiconductor electrode. For greater details in the development of this early stage of photoelectrochemistry of semiconductors, the reader is referred, in particular, to the book by Myamlin and Pleskov (1967). 

Solar energy conversion in photoelectrochemical cells with semiconductor electrodes is considered in detail in the reviews by Gerischer (1975, 1979), Nozik (1978), Heller and Miller (1980), Wrighton (1979), Bard (1980), and Pleskov (1981) and will not be discussed. The present chapter deals with the main principles of the theory of photoelectrochemical processes at semiconductor electrodes and discusses the most important experimental results concerning various aspects of photoelectrochemistry of a semiconductor-electrolyte interface a more comprehensive consideration of these problems can be found in the book by the authors (Pleskov and Gurevich,... 

This concluding part deals with a number of trends in photoelectrochemistry of semiconductors that have not so far been widely developed, the reasons often being of momentary character. At the same time, these trends are not only of significant scientific interest, but some of them may, in prospect, form the basis for important practical applications. In this respect, it appears to be quite reasonable to discuss the existing problems and the most important results. 

At present there is a sufficiently complete picture of photoelectrochemical behavior of the most important semiconductor materials. This is not, however, the only merit of photoelectrochemistry of semiconductors. First, photoelectrochemistry of semiconductors has stimulated the study of photoprocesses on materials, which are not conventional for electrochemistry, namely on insulators (Mehl and Hale, 1967 Gerischer and Willig, 1976). The basic concepts and mathematical formalism of electrochemistry and photoelectrochemistry of semiconductors have successfully been used in this study. Second, photoelectrochemistry of semiconductors has provided possibilities, unique in certain cases, of studying thermodynamic and kinetic characteristics of photoexcited particles in the solution and electrode, and also processes of electron transfer with these particles involved. (Note that the processes of quenching of photoexcited reactants often prevent from the performing of such investigations on metal electrodes.) The study of photo-electrochemical processes under the excitation of the electron-hole ensemble of a semiconductor permits the direct experimental verification of the applicability of the Fermi quasilevel concept to the description of electron transitions at an interface. 

Photoelectrochemistry (PEC) is emerging from the research laboratories with the promise of significant practical applications. One application of PEC systems is the conversion and storage of solar energy. Chapter 4 reviews the main principles of the theory of PEC processes at semiconductor electrodes and discusses the most important experimental results of interactions at an illuminated semiconductor-electrolyte interface. In addition to the fundamentals of electrochemistry and photoexcitation of semiconductors, the phenomena of photocorrosion and photoetching are discussed. Other PEC phenomena treated are photoelectron emission, electrogenerated luminescence, and electroreflection. Relationships among the various PEC effects are established. 

Photoelectrochemistry in general and electrocatalysis at semiconductor electrodes in particular are not considered, since in this field too many unknowns and in general a lack of long-term performance and technical experience render the technical relevance of published data still questionable. Furthermore, the technical applicability and practical relevance of photoelectrochemistry are still disputed a great deal, and no case of this type of energy conversion has yet been technically demonstrated. 

Semiconductor systems have other advantages in that the visible and near uv light can be absorbed effeciently and the electrons and holes in the semiconductor in general have much higher mobilities than ions in solution. In the present chapter, the basic properties of the semiconductor/soiution interface are described followed by discussion of some recent topics of photoelectrochemistry at this interface. 

The photoelectrochemistry at atomically well-defined semiconductor surfaces is one of the current topics related to the nanostructuring of the semiconductor surfaces. Most studies have been made on silicon (Si) surfaces, and it is now well established that hydrogen fluoride (HF)-etched Si surfaces are terminated mainly with Si-hydrogen bonds (SiH , n = 1, 2, or 3)14-171 and that, for Si (111), successive etching with 40% ammonium fluoride (NH4F) produces atomically flat Si(l 11) surfaces, terminated mainly with monohydride (= Si-H).18-221 Alkali etching under negatively applied biases also produces similar atomically flat Si (111) surfaces.231... 

This volume, based on the symposium Photoeffects at Semiconductor-Electrolyte Interfaces, consists of 25 invited and contributed papers. Although the emphasis of the symposium was on the more basic aspects of research in photoelectrochemistry, the covered topics included applied research on photoelectrochemical cells. This is natural since it is clear that the driving force for the intense current interest and activity in photoelectrochemistry is the potential development of photoelectrochemical cells for solar energy conversion. These versatile cells can be designed either to produce electricity (electrochemical photovoltaic cells) or to produce fuels and chemicals (photoelectrosynthetic cells). 

Sviridov, Dmitry V. he obtained his Ph.D. (1987) and D.Sc. (1999) degrees in Physical Chemistry from Belarussian State University (BSU). He currently holds an appointment of Professor of Chemistry at BSU and Principle Investigator in the Institute for Physico-Chemical Problems, BSU, Minsk, Belarus Republic. His scientific interests include photoelectrochemistry of semiconductors and molecular aggregates, electrocatalysis and environmental photocatalysis. E-mail ... 

At present, photoelectrochemistry on semiconductor (Ti02) electrodes seems to be the most promising way forward towards light energy conversion by chemical means [36, 76-78]. Figure 6 shows schematically a photoelectrochemical cell. In principle, an electron can be excited directly from semiconductor s valence band into its conduction band, followed by the passage of current to a counter electrode. 

---