Electrochemical hydriding in a 6M KOH solution at 20 and 80C for 8h was applied on a series of as-cast binary Mg–Ni and ternary Mg–Ni–Mm alloys (Mm = mischmetal containing 45Ce, 38La, 12Nd and 4%Pr) containing 11 to 24Ni and 0 to 6wt%Mm. The kinetics and mechanism of the hydriding process, as well as hydrogen release temperatures, were studied by glow discharge spectrometry hydrogen profiling, scanning electron microscopy, energy dispersion analysis, X-ray diffraction and mass spectrometry. A maximum hydrogen concentration of 1.1% was achieved in the eutectic MgNi24Mm5 alloy hydrided at 80C. In all cases, the main hydriding product was binary MgH2 hydride. Mass spectrometry revealed its destabilization due to Ni and Mm because its decomposition temperature was lowered by about 100C. Both nickel and mischmetal showed positive effects on hydriding and dehydriding kinetics. These effects were considered in relation to the hydriding mechanism, electronic structure and atomic size of additives and structural variations of the alloys. Based upon the H-concentration profiles, the diffusion coefficients of hydrogen were estimated. For the eutectic MgNi24Mm5 alloy, the H diffusion coefficient at 20C was 4 x 10−10cm2/s.

Study of the Diffusion Kinetics and Mechanism of Electrochemical Hydriding of Mg–Ni–Mm Alloys. D.Vojtěch, V.Knotek: International Journal of Hydrogen Energy, 2011, 36[11], 6689-97