A concept designed to overcome the problems encountered when using photodissociation for the generation of hydrogen is discussed. The problems limiting the efficiency of photodissociation of water are the separation of the photolysis products and the high energy photons necessary for the reaction. It is shown that the dissociation energy of a large number of molecules is catalytically reduced when these molecules are in intimate contact with the surface of certain metals. It is proposed to develop a surface which will take advantage of this catalytic shift in dissociation energies to reduce the photon energy required to produce hydrogen. This same catalytic surface can be used to separate the reaction products if it is made so that one of the dissociations products is soluble in the metal and others are not. This condition is met by many metal systems such as platinum group metals which have been used commercially to separate hydrogen from other gases and liquids.

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Photocatalytic generation of hydrogen from water

D.C. resistivity variation of cold-deposited silver films during gas exposure

Publisher Summary This chapter discusses the resistivity measurements on pure and gas-covered silver films. Electrical resistivity—being an easily monitored property—has been extensively used for the characterization of thin metal films, which may play an important role in such diverse technologies as catalysis, corrosion prevention, microelectronics, optical coatings, and surface treatment. Large-angle grain boundaries—possibly under strains and characterized by built-in foreign molecules stemming from the residual gas—are decisive for conductivity in the films. The induced changes in the electronic density of the states of metal and adsorbate are amenable to measurements by means of high-resolution photoelectron-spectroscopic methods. This can lead to a better theoretical understanding of the influence of gas adsorption on resistivity. The complicated band structure of the adsorbate complex including gas–gas interaction should be an integral part of the description.

Chapter 2: Resistivity Measurements on Pure and Gas Covered Silver Films

The structure of gallium films and the changes in their conductivity during adsorption of oxygen, mercury and water vapours

Thin polycrystalline copper films are deposited in a special UHV cell on glass substrates and are covered step by step with CO2. The optical and electrical properties of the films are studied in-situ by means of ellipsometry and resistivity measurements. The properties of the clean films correspond to literature data. In the case of monolayer adsorption of CO2, the changes in the ellipsometrical angles are δΔ≈+1° and δψ≈+0.1°, similar to the Cu/O and Cu/CO systems. Three-dimensional island growth leads to a drastical increase of δΔ and δψ by several orders of magnitude. The resistivity first quickly decreases and then slowly reapproaches the initial value. This marked kinetics is quantitatively interpreted on the basis of a diffusion model.

B. Rangelov

Papers

The structure of metal films and the changes in their conductivity during adsorption: I. Adsorption of water vapor on copper