Semiconductor photo-electrodes

GaAs, CuInS2, CuInSe2- Semiconductor electrodes have received increasing attention as a consequence of their potential application in photoelectrochemical energy conversion devices. In order to achieve optimum efficiency, the knowledge of the surface composition plays a crucial role. Surface modifications may occur during operation of the photo electrode, or may be the result of a chemical or electrochemical treatment process prior to operation. 

This chapter considers photo-electrodes consisting of non-oxide semiconductors, alone and in combination with oxide semiconductors for water splitting. 

The study of heterogeneous systems in which a donor or acceptor is linked to the surface of a conductor or semiconductor has been of considerable interest, especially when electron injection into the semiconductor or electrode can be induced by light absorption of the linked dye molecule. Such systems have potential for the transduction of solar radiation into electrical energy. Gratzel and co-workers have used a ruthenium(II) complex linked to Ti02 by means of a Aw-carboxylato-bipyridine ligand to construct a reasonably efficient photo-ceii 16.381-383,390,402 details of the functioning of this photocell are not well understood,... 

The illumination of semiconductor electrodes can give rise to a photocurrent due to the interband excitation of electrons. Although semiconductor photo-electrochemistry lies outside the scope of this chapter (an excellent review has been published by Morrison [57]), photocurrent spectroscopy has found more general application as an in-situ technique for the characterisation of surface films formed on metal electrodes such as Fe [58] and Pb [59] during corrosion. Quantitative analysis of photocurrent spectra can be used to identify semiconductor surface phases and to characterise their thickness and electronic properties. 

Tin dioxide, an n-type semiconductor with a wide bandgap (3.6 eV at 300 K), has been widely studied as a sensor, a (photo)electrode material and in oxidation reactions for depollution. The performance of tin(iv) oxide is closely linked to structural features, such as nanosized crystallites, surface-to-volume ratio and surface electronic properties. The incentive for carbon-dioxide transformation into value-added products led to examination of the electroreduction of carbon dioxide at different cathodes. It has been recognised that the faradic yield and selectivity to carbon monoxide, methane, methanol, and formic acid rely upon the nature of the cathode and pH. ° Tin(iv) oxide, as cathode, was found to be selective in formate formation at pH = 10.2 with a faradic yield of 67%, whereas copper is selective for methane and ethene, and gold and silver for carbon monoxide. Nano-tin(iv) oxide has been shown to be active and selective in the carboigrlation of methanol to dimethyl carbonate at 150 °C and 20 MPa pressure. The catalyst was recyclable and its activity and selectivity compare with that of soluble organotins (see Section 21.5). 

Semiconductor-electrolyte interface, photo generation and loss mechanism, 458 Semiconductor-oxide junctions, 472 Semiconductor-solution interface, and the space charge region, 484 Sensitivity, of electrodes, under photo irradiation, 491 Silicon, n-type... 

The (photo)electrochemical behavior of p-InSe single-crystal vdW surface was studied in 0.5 M H2SO4 and 1.0 M NaOH solutions, in relation to the effect of surface steps on the crystal [183]. The pH-potential diagram was constructed, in order to examine the thermodynamic stability of the InSe crystals (Fig. 5.12). The mechanism of photoelectrochemical hydrogen evolution in 0.5 M H2SO4 and the effect of Pt modification were discussed. A several hundred mV anodic shift of the photocurrent onset potential was observed by depositing Pt on the semiconductor electrode. 

Pan ERE, Bard AJ (1985) Semiconductor Electrodes. 58. The effect of temperature on photo- and electroluminescence in Al-doped self-activated ZnS crystals. J Phys Chem 89 1232-1236... 

Photoreactions on ZnO powder in aqueous suspension and in contact with gases have often been studied during the last few decades, and only a few aspects of this work are reviewed here. For example, nitrous oxide and methyl iodide were found to decompose when brought into contact at 20 °C with the illuminated surface of ZnO and nitrate, indigo carmine and p-nitrosodimethylaniline were found to be reduced in aqueous suspensions ZnO is of special interest as it is one of the standard electrode materials in conventional semiconductor electrochemistry and photo-electrochemistry Colloidal ZnO has not been available until recently. It... 

Platinum-loaded Ti02 systems can be considered as a short-circuited photo-electrochemical cell where the Ti02 semiconductor electrode and metal Pt counterelectrode are brought into contact [159]. Light irradiation can induce electron-hole (e -h +) pair formation and surface oxidation and also reduction reactions on each Pt/Ti02 particle (Figure 4.11). These powder-based systems lack the advantage of... 

Photo)electrochemistry (electrodes, oxide electrodes and semiconductors)... 

Under light illumination, semiconductor electrodes absorb the energy of photons to produce excited electrons and holes in the conduction and valence bands. Compared with photoelectrons in metals, photoexcited electrons and holes in semiconductors are relatively stable so that the photo-effect on electrode reactions manifests itself more distinctly with semiconductor electrodes than with metal electrodes. 

Fig. 10-6. Generation of the greatest possible photopotential in n-type and p-type semiconductor electrodes (a) in the dark, (b) in a highly photoezcited state. = -he /e = greatest possible photo-potential.

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