Towards efficient hydrogen storage

Hydrogen is difficult to store or transport with current technology. Hydrogen gas has good energy density by weight, but poor energy density by volume compared to the hydrocarbons used currently to power cars. In principle, hydrogen requires a larger tank than petrol to store the same energy, making it a less practical alternative in volumetric terms. One approach to improve the energy density of gaseous hydrogen is by storing the gas at higher pressures. This requires material and design improvements in order to ensure tank integrity. Advances in compression technologies are also required to improve efficiencies and reduce the cost of producing high-pressure hydrogen.

A team from the University of Nottingham, led by Professors Schröder, Champness and Blake from the School of Chemistry, are currently looking at developing new materials as a basis for hydrogen storage for application in transport. The new materials allow hydrogen to be stored at relatively low pressures leading to cost and weight savings in storage tanks. Accurate structural characterisation is key to the new metal-organic frameworks they have developed.

Different cages in the crystal structure of one of the Nottingham team’s new polyhedral framework materials with high hydrogen storage capacity. Cages A, B and C have internal spherical diameters of 13.0, 13.9 and 20.0 Å, respectively, with the volumes shown as large purple, orange or blue spheres. For the atoms, copper is shown as turquoise, carbon as grey and oxygen in red.

Such detailed analysis needs to use the intense X-rays produced at Diamond to look at tiny single crystals and volatile solvent molecules within these new metal-organic frameworks.

The structural analysis carried out has given invaluable information on the structural characteristics of the metal-organic frameworks leading to improvements in the design of the materials. Prof. Sandy Blake from the University of Nottingham leads the structural characterisation of these materials at Diamond.