Hysteresis and related irreversible phenomena in CeNi5-based intermetallic hydrides: Effect of substitution of Co for Ni

The phase relationships and thermodynamics of hydride formation and decomposition in the CeNi5−xCox-H2 (x = 1, 1.5, 2.5) systems have been studied by means of pressure-composition isotherm measurement and XRD analysis. Special attention has been paid to the first hydrogenation. A significant reduction of hysteresis, especially within the first cycle, has been observed in all studied alloys as compared with non-substituted CeNi5. The effect of temperature and reaction direction on the isotherm shape and plateau splitting has been revealed for CeNi3.5Co1.5. The CeNi2.5Co2.5-H2 system has demonstrated an exceptional phenomenon of oscillating dynamics of equilibrium achievement within the hydrogen concentration range of 3-5 atoms H per formula unit. Some suggestions on the CeNi5−xCox peculiarities have been proposed.