Thermodynamic and kinetic studies of hydrogenenation reaction in magnesium/palladium nanostructures
Abstract/Contents
- Abstract
- The factors affecting the formation rate and stability of metal hydride thin films, so crucial for hydrogen storage applications, are not well understood. The low equilibrium hydrogen pressure, hence high stability, of metal hydride inhibits easy charging/discharging for fuel cell applications. The significant increase of equilibrium hydrogen pressure observed in Mg/Pd thin films is encouraging, but has been mistakenly attributed to mechanical and not chemical factors. Our experiments prove that mechanical strain is present only in the Pd layer and cannot significantly affect the hydride stability. However, a simple thermodynamic analysis suggests that an intermixing layer of Mg and Pd will destabilize the hydride enough to account for the observed increase in equilibrium hydrogen pressure. We used TEM and XPS to look for this layer and found it, as expected. We show that the equilibrium pressure increase can be further enhanced by increasing the amount of intermixing. Having determined the effect of intermixing on the hydride thermodynamics, it is still unclear how the diffusion of hydrogen and propagation of the hydride phase boundary occurs in the metal hydride. We next characterize hydride formation from isolated points of nucleation in a simple morphology in order to develop design rules for more complicated hydrogen storage structures. In order to physically control the nucleation, we only permit hydrogen to enter the magnesium through sparsely distributed Pd ``nanoportals.'' Because the Pd nanoportals are far apart, we are able to study hydride nucleation one site at a time. We are able to measure the nucleation time constant and the diffusion constants of hydrogen in the hydride by fitting data to a modified Avrami model. We observe that the morphology of grown hydride and the growth rate of hydride are prominently affected by the crystal structure of the magnesium film. However, continuous oxidation of the Mg film pinches off the Pd portals and slows the hydride formation. Better control of the sample structure and chemical state is needed to extract the kinetic parameters correctly and understand the reaction kinetics. By doing so, we hope to provide new ideas and design rules for future storage materials.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2014 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Chung, Chia-Jung |
|---|---|
| Associated with | Stanford University, Department of Materials Science and Engineering. |
| Primary advisor | Clemens, B. M. (Bruce M.) |
| Thesis advisor | Clemens, B. M. (Bruce M.) |
| Thesis advisor | Cui, Yi, 1976- |
| Thesis advisor | Salleo, Alberto |
| Advisor | Cui, Yi, 1976- |
| Advisor | Salleo, Alberto |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Chia-Jung Chung. |
|---|---|
| Note | Submitted to the Department of Materials Science and Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2014. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2014 by Chia-Jung Chung
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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