Thursday, November 22, 2012

Is graphene the key to solving hydrogen storage issue?

There has been plenty of talk about hydrogen as future energy source No.1 primarily because hydrogen is by far the most abundant element in universe. Hydrogen is environmentally friendly source of energy because when hydrogen burns in air it produces only water vapor. Still, in order for hydrogen to become one of the top energy sources several important issues need to be resolved, and one of the most important issues is definitely a hydrogen storage issue.

There have been many interesting theories about hydrogen storage methods and one of the most interesting proposals comes from the researchers at the National Institute of Standards and Technology (NIST) and the University of Pennsylvania. They believe that the solution for hydrogen storage issue can be found in form of the layered graphene sheets. Can these graphene sheets really solve this issue?

Graphene, an allotrope of carbon, is recently attracting plenty of scientific research, primarily because of its excellent conductive, optical, and thermal properties, all of which make graphene very favorable choice for use in sensors and semiconductor devices.

The graphene in its original form cannot lead to successful hydrogen storage solution because original graphene form means largely reduced hydrogen storage ability. To bypass this, oxidized graphene sheets are stacked atop one another, and connected by molecules that both link the layers to one another and maintain space between them. The resulting layered graphene sheet can store hydrogen in large quantities.

The scientists have found out that layered graphene sheets can hold at least a hundred times more hydrogen molecules than ordinary graphene oxide does. The benefits of using this hydrogen storage method include easy synthesis, relatively low costs and the fact that graphene is non toxic material.

Another discovery that could be of great significance for solving hydrogen storage issue was also a rather unusual relationship that layered graphene sheets exhibit between temperature and hydrogen absorption.

In most storage materials, the lower temperature normally means the bigger uptake of hydrogen. The layered graphene sheets act differently than that, and although they can absorb hydrogen, they do not uptake the significant amounts at below 50 Kelvin (-223 degrees Celsius). Even more importantly, it does not release any hydrogen below this temperature meaning that, with further research, layered graphene sheets might be used to not only store hydrogen but also to release it when it is needed, which can be of vital importance in fuel cell applications.