Hydrogen solubility and diffusivity in palladium-rich alloys

Electrochemical hydrogen permeation tests were performed at 40 degreesC, using a 0.1 N NaOH electrolyte, to study the hydrogen diffusivity and solubility in the palladium-rich alloys Pd90Pt10, Pd80Rh20 and Pd50Ni50. Cathodic hydrogen generating currents were varied from 0.1 to 20 mA. A double sigmoidal permeation curve was observed for the highest cathodic currents, indicating the formation of metal hydrides during the test. These hydrides were characterized by x-ray diffraction. It was found that the apparent hydrogen diffusivity decreased in the order Pd90Pt10, Pd80Rh20 and Pd50Ni50, which is also the decreasing order of lattice parameters and effective atomic radius. The Pd90Pt10 alloys presented the greater hydrogen diffusivity and solubility, and hence flux, of all.