Temperature-hydrogen pressure phase boundaries and corresponding thermodynamics for ZrCo-H system

The thermodynamically and kinetically stable regions of the temperature-H-2 pressure phase boundaries for the ZrCo-H system were established using the Temperature-ConcentrationIsobar (TCI) method. Based on this, the enthalpy change and entropy change values of dehydrogenation and disproportionation reactions were successfully obtained. The average enthalpy change (Delta H) and entropy change (Delta S) estimated from the phase boundaries for dehydrogenation of ZrCoH3 to ZrCo are respectively 103.07 kJ mol(-1)H(2) and 148.85 J mol(-1) H-2 K-1, which are well agreement with the data reported in literature. The average OH and AS were estimated to be -120.91 kJ mol(-1 )H(2) and -149.32 J mol(-1) H-2 K-1 for the disproportionation of ZrCoH3, whereas the Delta H and Delta S were calculated to be -84.6 kJ mol(-1)H(2) and -92.29 J mol(-1) H-2 K-1 for disproportionation of ZrCo. In addition, it was found from the established phase boundaries that the anti-disproportionation property of ZrCo alloy can be enhanced if the phase boundaries of hydrogenation/dehydrogenation are far away from the phase boundaries of disproportionation by adjusting the thermodynamics. Meanwhile, it is possible to keep ZrCo away from disproportionation even at high temperature of 650 degrees C under hydrogen atmosphere, if the temperature-H-2 pressure trajectory is carefully controlled without crossing the phase boundaries of disproportionation. Therefore, the established phase boundaries can be used as a guide to the eye avoiding disproportionation and improving the anti-disproportionation property of ZrCo alloy. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.