| AVS 55th International Symposium & Exhibition | |
| Energy Science and Technology Focus Topic | Monday Sessions |
| Session EN+SE+NS+SS-MoA |
| Session: | Hydrogen Storage |
| Presenter: | D. Mitlin, University of Alberta and NRC National Institute for Nanotechnology, Canada |
| Authors: | D. Mitlin, University of Alberta and NRC National Institute for Nanotechnology, Canada J. Haagsma, University of Alberta and NRC National Institute for Nanotechnology, Canada C. Ophus, University of Alberta and NRC National Institute for Nanotechnology, Canada C.T. Harrower, University of Alberta and NRC National Institute for Nanotechnology, Canada M. Saoudi, National Research Council Canada, SIMS, Canadian Neutron Beam Centre, Chalk River Laboratories H. Fritzsche, National Research Council Canada, SIMS, Canadian Neutron Beam Centre, Chalk River Laboratories |
| Correspondent: | Click to Email |
The key for achieving 100 °C - range hydrogen sorption is to have favorable thermodynamics, i.e. a hydrogen binding energy near 30 kJ/mol. Metallic magnesium possesses sufficient gravimetric and volumetric sorption capacity, but has unfavorable thermodynamics (-77 kJ/mol α-MgH2 formation energy) and poor kinetics. In this presentation I will discuss our general methodology for tuning the hydrogen sorption thermodynamics of magnesium, through alloy design. We use a thin films approach to create a range of destabilized magnesium-based alloys and of accompanying catalytic layers. Thin films make for ideal “model” systems that may be used for accurately and rapidly screening a variety of matrix and catalyst formulations. Because of the small diffusion distances, films also allow for better separation of system thermodynamics from the kinetics. The synthesized films were tested volumetrically through multiple adsorption-desorption cycles. The microstructures were characterized by neutron reflectometry and x-ray diffraction. We show that alloying magnesium with light elements that have weak hydrogen interaction, such as aluminum, is a very effective method for lowering the sorption temperature to near ambient. At certain compositions, the addition of aluminum promotes the high-pressure γ-MgH2 phase at the expense of the equilibrium α-MgH2. At other compositions, the sorbed microstructure is a composite of α-MgH2 intermixed with α-AlH3. We also demonstrate that there is critical temperature above which the palladium catalyst caps are not stable, reacting with the underlying material and losing their efficacy. Additionally, there will be a discussion of the processing and sorption kinetics of MgH2 - metal catalyst - carbon nanotube (CNT) powder composites, and of direct TEM characterization of milled MgH2.