Enthalpy change (ΔH~0) and entropy change (ΔS~0) measurement of CeMn_(1-x)Al_(1-x)Ni_(2x) (x = 0.00, 0.25, 0.50 and 0.75) hydrides by electrochemical P-C-T curve

摘要

The thermodynamic properties of CeMn_(1-x)Al_(1-x)Ni_(2x) (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 CeMn_(1-x)Al_(1-x)Ni_(2x) (x = 0.00, 0.25, 0.50 and 0.75) hydride increases from 0.129wt% for x = 0.00 to 0.421 wt% for x = 0.75 at 293K. 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 (ΔH~0) and the entropy change (ΔS~0) of the hydrides for dehydrogenization shift from -67.44 kjmol~(-1) (x = 0.00) to 21.16kJmol~(-1) (x = 0.75) and from -0.24kJmor~(-1)K~(-1) (x = 0) to -0.03kJmol~(-1)K~(-1) (x = 0.75), respectively. With increasing Ni content, both ΔH~0 and ΔS~0 for dehydrogenization shift to the positive direction and make alloy hydrides more stable and hydrogen desorption much easier.