Particles, photoelectrolysis

J.S. Curran, D.J. Lamouche, Transport and kinetics in photoelectrolysis by semiconductor particles in suspension, J. Phys. Chem. 87 (1983) 5405-5411. 

Heterogeneous semiconductor systems involve either suspensions or slurries of larger-sized semiconductor powders, or smaller colloids in solution. In principle, these semiconductor particles may act as tiny photoelectrolysis cells, similar to the photoelectrochemical systems discussed above. However, as many of the materials used for bulk electrodes are also described here in particulate form, both similar and new problems may arise, most notably irreproducibility in particle preparation, stability issues, and low C02 reduction rates. 

Hydrogen Evolving Solar Cells Principles in the design of semiconductor electrodes, surface modification strategies, p-n junction cells, and photoelectrolysis by suspended semiconductor particles, discussed. 66... 

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. 

CdS particles or suspensions were the subject of many investigations for a period of time (1980-1985) because Gratzel et al. concluded from their experiments that photoelectrolysis of H2O occurred at CdS particles [42]. The relevant experiments were performed with particles loaded with two kinds of catalysts, namely with Pt for H2 formation and RUO2 for the formation of O2. It was shown, however, that O2 could not be formed at CdS and that corrosion is the only anodic reaction [43]. 

Figure 10. Scheme of water photoelectrolysis on a particle of semiconductor (platinized SrTi03) suspension in an aqueous solution. 

In the latter paper, it was reported on investigations with n-type CdS particles (size 35-45 pm) embedded in a polyurathane membrane of a thickness of 20-25 pm. Each surface of the membrane could be loaded with Pt or RUO2. The photoelectrolysis cell consisted of two compartments separated by the CdS membrane. Electrolytic contact between both compartments was provided by an ion-exchange membrane as illustrated on the left side of Figure 11.24. To get insight into the photoelectrochemical process, the following experiments were performed ... 

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