On the electrolytic behaviour of thin films. Part II.—The areas of catalytically active surfaces

Abstract

In a previous communication it; was shown that by measurement of the quantity of hydrogen electrolytically deposited on a cathode surface in order to cause a given change in the electrode potential, it was possible to evaluate the accessible area of the surface, this area being defined as the total area accessible to hydrogen atoms and on which they can deposit or be absorbed. This procedure thus provides a third method, in addition to that of the examination of the thickness of oxide films by conductivity or interference methods or of the adsorption of suitable substances, for the determination of the areas of catalytic surfaces. Also, by measurement of the currents required to maintain the plates at a definite potential, the catalytic activities of the metals for the discharge of the hydrogen ions can be compared. In this paper the behaviour of electrolytically deposited and amagamated surfaces is considered in more detail, and the effect of different methods of treatment such as activation, annealing, rolling and electroplating on the area and catalytic activity is studied for a number of metals. The experimental procedure was in all details similar to that described in the previous communication. Silver . The behaviour of a silver cathode under changing surface conditions is shown in fig. 1, in which the logarithm of the apparent current density is plotted against the electrode potential. The electrolyte was oxygen-free N/5 sulphuric acid and the experimental conditions identical with those previously described.