Investigation on hydrogen dissociation pressure, heat of formation and strain energy of metal hydrides

We analyzed the relation among the dissociation pressure, the heat of formation, and the strain energy of metal hydrides, thermodynamically. Logarithm of hydrogen dissociation pressure PMH of alloy-based metal hydrides with different composition ratio linearly increased with the calculated bulk modulus of the hydrogen storage alloys Bc. The heat of formation ΔH0 also linearly increased with the calculated bulk modulus of the hydrogen storage alloys Bc. Those hydrogen dissociation pressure and the heat of formation were analyzed by the thermodynamic relations including strain energy. We obtained the following equation [dΔH0/dBc]/[d(RTln(PMH))/dBc] >1 for metal hydrides having different composition ratio. The value above 1 of this equation was based on the experimental results that the standard entropy change was proportional to the heat of formation of the metal hydride.