Photoelectrolysis with Semiconductor Electrodes

Goodenough et have discussed approaches to the design of suitable 

Golstein, S. Jaenicke, and H. Levanon, Ghent. Phys. Lett., 1980, 71, 490. 

Yamase and T. Ikawa, tnorg. Chim. Acta, 1979, 37, L529. 

Neumann-Spallart, K. Kalyanasundaram,C. Gratzel, and M. Gratzel, Helv. Chim. Acta, 1980,63, 

The pressing need for a detailed description of the semiconductor-electrolyte interface is becoming increasingly apparent Gerischer has given an excellent and timely general account of photoassisted interfacial electron transfer, in which particular attention is paid to the role of surface states at the semiconductor-electrolyte interface. Kowalski et al have used the SCF-A -scattered wave method to calculate the position and character of surface states at various characteristic interfaces, and then used these results to develop a model of photoelectrolysis at Ti02 surfaces. 

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Gerischer H (1979) Solar Photoelectrolysis with semiconductor electrodes. In Solar energy conversion Solid-state physics aspects, Seraphin BO (Ed), pp.l 15-172 Springer-Verlag New York... 

Gerischer H (1979) Solar photoelectrolysis with semiconductor electrodes. In Seraphin BO, Aranovich JA (Eds.) Solar energy conversion solid state physics aspects. Springer, Berlin, pp. 114-172... 

Gerischer H. (1979), Solar photoelectrolysis with semiconductor electrodes , in Topics Appl. Phys., Vol. 31, Seraphin B. O., ed.. Springer Verlag, Berlin, pp. 115-172. 

Dye sensitization of semiconductor surfaces is not considered here, nor are issues related to semiconductor particles, photocatalysis and photoelectrolysis per se. These companion topics may be found elsewhere in Volumes I, IV and V. The discussion is phenomenological and is designed to provide an intuitive grasp of the key issues rather than detailed derivations that would have been prohibitive in terms of space constraints in any case. Indeed, the available theoretical framework is only examined in terms of how and with what confidence the pertinent conclusions can be experimentally verified with semiconductor electrodes. 

Two different situations must be considered. One in which photoelectrolysis is done with an externally fixed potential of the semiconductor electrode. In this way, photocurrent voltage curves are normally measured in galvanic cells with semiconductor electrodes. 

The reason for the exponential increase in the electron transfer rate with increasing electrode potential at the ZnO/electrolyte interface must be further explored. A possible explanation is provided in a recent study on water photoelectrolysis which describes the mechanism of water oxidation to molecular oxygen as one of strong molecular interaction with nonisoenergetic electron transfer subject to irreversible thermodynamics.48 Under such conditions, the rate of electron transfer will depend on the thermodynamic force in the semiconductor/electrolyte interface to... 

Ghosh AK, Maruska HP (1977) Photoelectrolysis of water in sunlight with sensitized semiconductor electrodes. J Electrochem Soc 124 1516-1522... 

The possibility of solar photoelectrolysis was demonstrated for the first time with a system in which an n-type Ti02 semiconductor electrode, which was connected through an electrical load to a platinum black counter electrode, was exposed to near-UV light (Fig 2.2).l9) When the surface of the Ti02 electrode was... 

Solar Photoproduction of Hydrogen Review mainly addresses potential and experimental efficiencies for four types of systems of which one comprises photoelectrolysis cells with one or more semiconductor electrodes. 70... 

Photoelectrolysis of Water in Sunlight with Sensitized Semiconductor Electrodes Similar observations as in Ref. 236 for Al3+-doped Ti02. 237... 

The application of semiconductor-liquid junctions is of special interest for the direct production of a chemical fuel. Especially the production of hydrogen by photoelectrolysis of H2O has been studied by many research groups (compare with [114,194]. It has been demonstrated by many authors that H2-formation is rather easy at semiconductor electrodes. The crucial point is the simultaneous oxidation of H2O. So far, photoelectrolysis was only achieved with SrTiOs, a semiconductor of a large bandgap (Eg = 3.1 eV) [206]. Very recently, photocleavage of HjO was also found with some niobates under open... 

High-rate photoelectrolysis of CO2 was conducted in a high pressure CO2 + methanol medium using p-type semiconductor electrodes. Current densities of up to 100 mA cm 2 were achieved, with current efficiencies of up to 93 % for CO production on a p-InP photocathode. The effect of CO2 pressure on the product distributions was examined for p-InP and p-GaAs. 

Considerations similar to those presented above show that illumination of a semiconductor leads to a shift of both the Fermi level and the quasi-levels of holes and electrons, and both the forward and reverse reactions, proceeding according to Eq. (1), are accelerated. In other words, the result of illumination is, above all, the efficient increase of the exchange current in the redox couple but this is not the only result. If a semiconductor under illumination is an electrode in an electrochemical cell and is connected through a load resistor with an auxiliary electrode, the cathodic and anodic reactions become spatially separated, as in the case of water photoelectrolysis (Fig. 11) considered above. The reaction with the minority carriers involved proceeds on the semiconductor surface, and that with the majority carriers involved, on the auxiliary electrode. Thus, the illumination of a semiconductor electrode gives rise to an electric current in the external circuit, so that some power can be drawn from the load resistor. In other words, the energy of light is converted into electricity. This is the way a photoelectrochemical cell, called the liquid junction solar cell, operates. 

Fig. 5 Energy scheme of a cell with one n-type semiconductor electrode for photoelectrolysis of water. A V is stored energy for electrolysis. pEy is Fermi level of photogenerated holes known as quasi-Fermi level, Ef is Fermi level of electron, (after Heinz Gerischer, Pure Appl. Chem. 1980, 52, 2649).

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