| Summary: | Hydrogen has been viewed as a clean synthetic energy carrier that could replace fossil fuels, especially for transport applications. One bottleneck in developing a hydrogen economy is to find feasible and safe storage materials that can store hydrogen with high gravimetric and volumetric densities at ambient conditions. The U.S. depart ment of energy has set a system target of 6 wt.% hydrogen storage density by 2010 and 9 wt.% by 2015, which has not been met yet. In this thesis, hydrogen adsorption and storage in calcium-decorated boron-doped graphene is studied by ab initio calculations using density functional theory (DFT).
We first consider pure graphene coated with calcium atoms on both sides, supposing that metal atoms are dispersed uniformly on the surface with a calcium coverage of 25%. We find that up to four hydrogen molecules can bind to a Ca atom, which results in a storage capacity of 8.32 wt.%. Then, we address the issue of metal adsorbate clustering. Our calculations show that Ca clustering takes place on pristine graphene because of the small binding energy of Ca to graphene. One way to enhance the metal adsorption strength on the graphene plane is to dope graphene with acceptors such as boron atoms. We show that upon boron doping with a concentration of 12 at.%, the clustering problem could be prevented and the resulting gravimetric capacity is 8.38 wt.% hydrogen.
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