We have calculated the bonding energy of a hydrogen atom below the surface of Nb(110) and Pd(111) due to the interaction with the surface phonons. Our results show that at room temperature, there is a deep potential well just below the surface of Nb(110) with a much shallower well for Pd(111). Due to this, the kinetics of hydrogen absorption by Nb(110) surface and Pd covered Nb is drastically affected. The kinetic equations, modified to include this subsurface potential well, show that the subsurface-trapped hydrogen acts as a valve for the admission of hydrogen into the bulk. A large variety of experimental facts clearly follow from these considerations.
KeywordsHydrogen Absorption Metal Hydride Absorption Kinetic Hydrogen Impurity Trapping Energy
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