Figure 1
Theoretical and Experimental Studies of Designed Defects in Carbon Nanotubes for Hydrogen Storage
Hydrogen represents a clean alternative fuel to hydrocarbons, but the successful launching of the fuel for mass use depends on an efficient storage technology. Carbon nanotube materials are among the most promising candidates for storage of hydrogen, however substantial developments need to be made before the storage capacity targets of the U.S. Dept of Energy are met. This project will explore, using the state-of-the-art computational facilities at the APAC National Facility, the possibility of designing new nanotube architectures with superior hydrogen uptake, storage and release properties. Specifically this project will develop a quantitative understanding of the defect sites in nanotube walls using state-of-the-art computational chemistry.
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Principal Investigator Justin FinnertyEngineering, Physcial Sciences and Architecture University of Queensland |
Project f26 |
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Co-Investigators Sean SmithChemistry University of Queensland Max Lu Engineering, Physcial Sciences and Architecture University of Queensland |
RFCD Codes 291804 |
Significant Achievements, Anticipated Outcomes and Future Work
2003 has seen significant advances in two areas of this project. The installation of the Gaussian G03 program mid-way through the year has been a major factor in allowing this progress to occur.
The first major development has been the refinement of the methodology we intend to use to study models of carbon nanotubes. The method involves quantum mechanical calculations using the ONIOM approach (see below), which treats sub-domains of the model at different computational levels.
Several interesting observations have come out of our calculations so far with selection of the computational levels to use for each domain not being a trivial task. We have found that molecular mechanics methods are not suitable for non-bonding systems and that the density functional theory method B3LYP does not perform well for long-range interactions. We have also found that choosing a more expensive method for the lowest level did not mean the calculation would take longer. These calculations use an iterative process to find an optimum structure and using the more expensive HF/3-21G* for the outer domain used less time than AM1 or PM3 as it required fewer iterations. We expect to publish the findings of these calculations in the first half of 2004.
The next phase of the project will be to extend the model in three directions. Firstly we want to look at a defect sites in a graphite lattice. We have already completed working on a range of oxygen containing benzenoid sub-models of the inner domain. During 2004 we will be combining these sub-models into the graphite model to look at oxygen containing graphite defect sites. Secondly, we are interested in the effect light metals have on hydrogen adsorption so we are planning to perform a series of calculations which include these. The last area of interest is extending the model to carbon nanotubes (see Figure 1). So far the models we have investigated use a planar graphite structure. We are interested in extending our model to include the curvature of a carbon nanotube.
Developing the initial model has been a major step forward in this project. This model will form a valuable foundation for the next phases of the project.
Figure 1
Computational Techniques Used
As stated earlier, the methodology we have used to study carbon nanotubes involves quantum mechanical calculations using the ONIOM approach, as implemented in the Gaussian 03 program suite. The ONIOM method allows a chemical structure to be divided into several sub-domains. These domains are then treated at different levels of theory. This allows the key areas of the structure to be treated at the computationally intensive levels of theory required to provide the desired accuracy while still incorporating effects of the larger structure. Figure 2 shows a model graphite structure and hydrogen molecule divided into three domains. The atoms in the area of the light background are treated with the high level method. The atoms in the medium and light backgrounds are treated with a middle level method and the entire molecule with a low level method.
Figure 2
Publications, Awards and External Funding
External Funding and Awards
None.
Publications
None.