Hydrogen storage by carbon materials

In order for fuel cells to become a practical means of supplying power for road vehicles it will be necessary for a viable method of on-board hydrogen storage to be identified and implemented. Target values that must be achieved for the critical parameters in such a system have been drawn up by the US Department of Energy. It is quite clear that these targets cannot be met by systems that store hydrogen at high pressure or as a liquid at cryogenic temperatures. Attention has thus been focused on methods of storing hydrogen in, or on, a solid phase. In such schemes it is obviously desirable to make use of elements from the early part of the periodic table and there has been much interest in the possible use of carbon as a hydrogen host. This paper provides an overview of experimental work on such systems together with an outline of theoretical studies that have been undertaken to estimate the practical limits to the amount of hydrogen that could be stored per unit weight.