Effects of cathodic charging on hydrogen permeation in a Pd80Rh20 alloy

Abstract Samples of Pd 80 Rh 20 alloy were submitted to electrochemical hydrogen permeation tests at 40 °C, using a 0.1N NaOH electrolyte, to study hydrogen permeation in a Pd 80 Rh 20 alloy for different cathodic hydrogen generating currents varying from 0.1 to 20 mA. It was found that the apparent hydrogen diffusivity and the hydrogen flux increased with increasing cathodic charging. For high levels of applied current, equal to or above 5 mA the hydrogen permeation curves present a double sigmoidal shape which corresponds to hydride formation during the test. The hydrides were characterized by X-ray diffraction after exposure of the sample to hydrogen. Phase separation was also observed in the alloy, having been provoked, for high applied currents, by the formation of a PdRhH hydride and a Rh-rich phase.