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The surface of p-Si has been treated in a number of ways, and the rate of the photoelectrochemical reduction of water to hydrogen measured on each type of surface. Correspondingly, in-situ ellipsometric determinations of thickness and refractive index of the surface films were made; corresponding XPS, ISS and SIMS studies were also carried out. The photoelectrochemical activities of the surfaces, as measured by the positive shift on the potential axis of the mid-current point of the photocurrent/potential curve, differed greatly. In treatments with HF, the chemical structure of the surface remains that of SiO2; in treatments with aquaregia and HF, the surface becomes SiO. After hydrogen evolution, SiOH bonds appear. The degree of dependence of the photoelectrochemical activity on the surface characteristics indicates that a reaction at the semiconductor/solution interface controls the overall (consecutive) photoelectrochemical reaction. The increase in rate with change of surface structure depends on the following factors in increasing order of importance: the presence of band gap surface states, the (established) jump in the order of magnitude of conductance of SiOx at x = 1.8, and the (argued) increasing availability of Si bonds during increasing reduction of the surface, thus causing an increase in the rate constant of a rate-determining proton transfer.

Eight possible explanations for the heat produced in the Fleischmann-Pons effect are examined with the various conservative assumptions concerning the quantities used. No individual explanation is sufficient to explain the heat produced. All of them together can only explain heat as much as 3 W cm −3 .

In most previous treatments of photoelectrochemical kinetics, the focus of attention has been on the hole-electron pair formation by light, transport to the surface and various losses arising from hole-electron recombination. In surfaces of SiO x (2 > x > 0.8), the photoelectrochemical onset potential varies by ca 0.8 V. When the variation of the photoelectrochemical onset potential on metal-decorated p-type semiconductor is plotted against the exchange current density for the dark evolution of hydrogen a slope close to 2RT/F is found. For oxygen evolution on metal decorated n-type semiconductor, there is a dependence of the onset potential on the metal-oxygen bond strength in alkali but zero dependence in acid solution. Work-function dependences are present: there is no correlation with effects of hydrogen on the work-function. The formation of band-gap surface states, recombination and effects of the surface treatment upon work-function are compared with the data but found inconsistent with it. If it is assumed that the surface treatment and metal deposition have a strong effect on the charge-transfer rate constants, several correlations can be rationalized. Implications are drawn regarding the role to be played by electrocatalysis in photoelectrochemistry.

The effect of depositing islets of metals having widely different work functions has been examined by means of the measurement of the relation of photocurrent to potential on p-MoS 2 , containing, respectively, islets of Pt, Au, Co, Pb and Cd. From the exponential sections of the photocurrent-potential curves, the shift, ΔE , caused at constant photocurrent by the presence of the metal was observed. The limiting photocurrent is unaffected by the metal islets. Four models for such effects are examined. The evidence seems strongest for a model in which the rate-determining step of electrochemical charge transfer occurs at the islet-solution interface.

Presentation de deux modeles de la photoelectrocatalyse par des agregats metalliques revetant des photocathodes de p-Si et de donnees experimentales permettant de choisir l'un de ceux-ci