Enthalpy change (ΔH0) and entropy change (ΔS0) measurement of CeMn1−xAl1−xNi2x (x=0.00, 0.25, 0.50 and 0.75) hydrides by electrochemical P–C–T curve

The thermodynamic properties of CeMn1−xAl1−xNi2x (x=0.00, 0.25, 0.50 and 0.75) hydrides have been investigated in this paper. With increasing Ni substitution content, the hydrogen concentration (H/M) in CeMn1−xAl1−xNi2x (x=0.00, 0.25, 0.50 and 0.75) hydride increases from 0.129 wt% for x=0.00 to 0.421 wt% for x=0.75 at 293 K. The pressure–concentration isotherm (P–C–T) curves show that no hydrogen equilibrium pressure plateau has been observed for CeMnAl hydride while the slope of the plateau become flatter and longer with increasing Ni content. Meanwhile, the enthalpy change (ΔH0) and the entropy change (ΔS0) of the hydrides for dehydrogenization shift from −67.44 kJ mol−1 (x=0.00) to 21.16 kJ mol−1 (x=0.75) and from −0.24 kJ mol−1 K−1 (x=0) to −0.03 kJ mol−1 K−1 (x=0.75), respectively. With increasing Ni content, both ΔH0 and ΔS0 for dehydrogenization shift to the positive direction and make alloy hydrides more stable and hydrogen desorption much easier.