Surface Area Effects on the Sorption of Hydrogen by Palladium

Abstract

Pressure–composition isotherms for dilute solutions of hydrogen in palladium have been measured at temperatures between 100 and 240 °C at pressures of up to 1000 Torr using a conventional volumetric technique. For palladium foil the isotherms are consistent with data over lower temperature ranges and with existing theoretical isotherms. With samples having appreciable surface area, however, a higher sorptive capacity is found which, it is suggested, is due to the formation of a layer of adsorbed hydrogen on the metal surface. It is demonstrated that correction can be made for this effect, to some extent, giving better agreement between the experimental data and the theoretical isotherm.The variation of partial molar enthalpy of absorbed hydrogen with hydrogen content is also affected by this surface phenomenon, although the data available at present are not sufficiently accurate for a detailed discussion.