Semiconduction oxides

Gerischer H (1989) Neglected problems in the pH dependence of the flatband potential of semiconducting oxides and semiconductors covered with oxide layers. Electrochim Acta 34 1005-1009... 

Various other semiconductor materials, such as CdSe, MoSe, WSe, and InP were also used in electrochemistry, mainly as n-type photoanodes. Stability against photoanodic corrosion is, naturally, much higher with semiconducting oxides (Ti02, ZnO, SrTi03, BaTi03, W03, etc.). For this reason, they are the most important n-type semiconductors for photoanodes. The semiconducting metal oxide electrodes are discussed in more detail below. 

Tseung A.C.C., Jasem S., Oxygen evolution on semiconducting oxides, Electrochim. Acta, 22(1), 31-34,1977. 

Semiconducting oxides Resistance Dupont 0-1,000 ppm Can have environmental, 02 effects ... 

At present, several stable photocatalytic systems for production of hydrogen from water and organic compounds are made of semiconducting oxides and suitable proton reducing catalyzer. An efficient electron transfer between inorganic semiconductor and bacterial hydrogenase was shown to result in hydrogen photoproduction. 

Figure 7.3 Theoretical variation of the conductivity as a function of composition for a hopping semiconducting oxide MOx, where x can take values of between 1.0 and 2.0.

Shin, K.-S., et al., High quality graphene-semiconducting oxide heterostructure for inverted organicphotovoltaics. Journal of Materials Chemistry, 2012. 22(26) p. 13032-13038. 

E. Comini, G. Faglia, G. Sberveglieri, Z.W. Pan, and Z.L. Wang. Stable and highly sensitive gas sensors based on semiconducting oxide nanobelts . Applied Physics Letters 81 (2002), 1869-1871. 

Titanium as a carrier metal Titanium (or a similar metal such as tantalum, etc.) cannot work directly as anode because a semiconducting oxide layer inhibits any electron transport in anodic direction ( valve metal ). But coated with an electrocatalytic layer, for example, of platinum or of metal oxides (see below), it is an interesting carrier metal due to the excellent corrosion stability in aqueous media, caused by the self-healing passivation layer (e.g. stability against chlorine in the large scale industrial application of Dimension Stable Anodes DSA , see below). 

Optically transparent electrodes. In situ spectroelectrochemistry was discussed in the previous chapter. The most common materials for constructing optically transparent electrodes for use in such analyses are thin films of semiconducting oxide deposited on to glass. Such materials are readily available commercially. 

With ionic crystals, there are some rather interesting possibilities. A large part of the perturbation which a free surface introduces is associated with the change in the electrostatic environment of an ion in going from the interior to the surface. If the normally filled valence band is associated with the anions (as is the case with the alkali halides and with certain n-type semiconducting oxides), the surface perturbation acts in the direction of producing a band of surface states with its center lying above the center of the normal anion band. This anion surface band will normally be completely filled. Conversely, for the normally empty cation band (the... 

With the semiconducting oxides, we expect anionic chemisorption to occur over the lattice cations, and our simple molecular orbital theory will be adequate if the conduction band is associated mainly with the cation lattice. This is certainly the case with AI2O3, where there is direct evidence in the soft X-ray emission spectra that the highest filled band is the oxygen 2p band 16). 

Rung HH, Jarrett HS, Sleight AW, Ferretti A (1977) Semiconducting oxide anodes in photoassisted electrolysis of water. J Appl Phys 48 2463-2469... 

Pending further detailed information on the constitution of the surface layer, it is possible neverthelsss to get useful qualitative information on the relationship between defect structure of a given semiconducting oxide and its behavior as an adsorbent or catalyst. Thus a semiconductor can be modified by addition of controlled amounts of impurities. If it is then assumed that the direction of the modification is the same at least qualitatively at the surface and in the bulk, a comparison of oxides respectively unmodified and modified in opposite directions can reveal trends of interest as to the requirements of a given surface reaction. This method was first tried by Wagner (27) and further amplified by one of us (28,28a). 

Catalytic behavior of semiconducting oxides has been modified in opposite directions by the addTtion of impurities which modify their electrical characteristics in opposite directions. Further work is required to put this qualitative correlation on a quantitative basis. 

Schwab and co-workers (5-7) found a parallel between the electron concentration of different phases of certain alloys and the activation energies observed for the decomposition of formic acid into H2 and CO2, with these alloys as catalysts. Suhrmann and Sachtler (8,9,58) found a relation between the work function of gold and platinum and the energy of activation necessary for the decomposition of nitrous oxide on these metals. C. Wagner (10) found a relation between the electrical conductivity of semiconducting oxide catalysts and their activity in the decomposition of N2O. 

---