Bockris and Uosaki

The first step was the evolution away from the Schottky barrier model of photoelectrochemistry caused by the evidence from the late 1970s onward that the rate of photoelectrochemical reactions was heavily dependent on surface effects (Uosaki, 1981 Szklarczyk, 1983). This was followed by the use of both a photocathode and a photoanode in the same cell (Ohashi, 1977). Then the use of nonactive thin protective passive layers of oxides and sulfides allowed photoanodes to operate in potential regions in which they would otherwise have dissolved (Bockris and Uosaki, 1977). The final step was the introduction of electrocatalysis of both hydrogen and oxygen evolution by means of metal islets of appropriate catalytic power (Bockris and Szklarczyk, 1983). 

Photoelectrochemical splitting was discussed extensively in Chapter 10. The key point is the use of trace electrocatalysts added to the surface of both photocathode and photoanode to the appropriate extent (Kainthla, Zelenay, and Bockris, 1987 Turner, 1998). If the electrolyzer is to be entirely solar driven, both electrodes must be irradiated. It is difficult to find photoanodes with the appropriate properties. Most of them dissolve electrochemically ifused as anodes for02 evolution. This can, however, be prevented by using transparent films of nonreactive oxides (Bockris and Uosaki, 1977). 

In the early stages of study of photoelectrochemical kinetics, two extreme models were presented. One is the model of Bockris and Uosaki,93 108,109 in which the charge transfer step was considered to be the rate-determining step and the other is Butler s model,110 in which the semiconductor/electrolyte interface was considered as a Schottky barrier, i.e., the electrochemical kinetics were neglected and all the potential drop occurred only within the semiconductor. 

Bockris and Uosaki calculated photocurrent-potential relations mainly for the hydrogen evolution reaction (HER) at p-type semiconductors with the assumption that the following is the ratedetermining step ... 

A general theory has been proposed by Bockris and Uosaki in... 

Note that in regions II and III, when the electron is accepted by the solvent, solvated electrons are formed which means that Eqs. (70) and (71) are applicable to photoemission of electrons. Calculations by Bockris and Uosaki have given fair agreement with experiment, except the quantum efficiencies were lower than the experimental ones. This is in no way surprising because there is a cumulative set of uncertainties from all parameters about which assumptions had to be made. From a qualitative viewpoint, this theory is the most comprehensive in dealing with the fate of the electron in the solvent. Unfortunately, photocurrent rate expressions are not derived for experimental testing. 

J. O M. Bockris, K. Uosaki, and H. Kita, J. Appl. Phys. 52 808 (1981). Experimental evidence of surface effects in photoelectrochemical kinetics. 

J. O M. Bockris and K. Uosaki, J. Electrochem. Soc. 125 223 (1977). First theoretical treatment of photoelectrochemical kinetics at high surface source case. 

A theory of the photoelectrochemical kinetics of the hydrogen evolution reaction at the metal-solution interface was developed by Bockris, Khan, and Uosaki. This theory takes into account photoemission into the solution, the reflective properties of the electrode material, absorption of light by the electron, and the excitation probability from photon-electron interactions. 

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