Hydrogenation Energies and Vibration Frequencies of Hydrogenated Carbon Nanotubes

45 Alternative energy sources are becoming increasingly important to investigate as world energy consumption rises and fossil fuels become depleted. Hydrogen is a strong candidate for a renewable, non-toxic, and plentiful energy source, and much research has been done to harness its energy [1, 2]. Yet, for hydrogen energy to become a reality, a suitable means for storage must be developed. Storage of hydrogen as a pressurized gas and cryogenic storage as a liquid can be dangerous [3]. Weight becomes an issue when considering storage in solid materials. The U.S. Department of Energy (DOE) has set a goal for hydrogen storage materials to have a fuel density of 6.5 mass % (mass % is a measure of the relative mass of the stored material to the total mass of the storage material) [3]. Carbon nanotubes (CNTs) have been proposed as a possible hydrogen storage material. With a high surface area to volume ratio, CNTs could store a high hydrogen content per volume if hydrogen atoms were to bond to the carbon atoms of CNTs. Carbon is also a relatively light element. If every carbon site in a single-walled CNT were hydrogenated, 7.7 mass% hydrogen storage could be achieved. However, great controversy surrounds the actual storage capability of CNTs. Experimental results vary greatly, with some groups claiming that hydrogen storage in CNTs is not a viable option while others remain optimistic that the high theoretical mass% estimates can be achieved [4,5]. Part of the problem in comparing experimental results to theoretical predictions lies in the current limitations of CNT fabrication. Hydrogenation Energies and Vibration Frequencies of Hydrogenated Carbon Nanotubes