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| Title: | NANOSTRUCTURING IMPACT ON THE ENTHALPY OF FORMATION OF METAL HYDRIDES | |
| DOI No: | 10.1142/9789812838025_0008 | |
| Source: | MATERIALS ISSUES IN A HYDROGEN ECONOMY (pp 92-101) | |
| Author(s): | VINCENT BERUBE
Physics Department, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA M. S. DRESSELHAUS Physics Department, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA GANG CHEN Mechanical Engineering Department, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA |
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| Abstract: | Metal and complex hydrides offer very promising prospects for hydrogen storage that reach the DOE targets for storage capacity for 2015. However, the slow sorption kinetics and the high release temperature must be addressed to make automotive applications feasible. Reducing the enthalpy of formation by destabilizing the hydride reduces the heat released during the hydrogenation phase and conversely allows desorption at a lower temperature. High-energy ball milling has been shown to decrease the release temperature, increase the reaction kinetics and lower the enthalpy of formation in certain cases. Increased surface and grain boundary energy could play a role in reducing the enthalpy of formation, but the predicted magnitude is too small to account for experimental observations. Since the particle and grain sizes are reduced considerably under high-energy treatments, structural defects and deformations are introduced. These deformed regions can be characterized by an excess volume due to deformations in the lattice structure, and these deformations have a significant effect on the physical properties of the hydride. We propose the use of two thermodynamic models to characterize the excess energy present in the deformed regions. The equations of state (EOS) provided by the models are used to explain the change in physical properties of metal hydrides. Particularly, the EOSs can predict which hydrides will be the most destabilized (if destabilized at all) by the introduction of excess volume regions. | |
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