Hydrogen storage remains one of the most challenging areas in materials science. The goal is to pack as much hydrogen as possible into a given volume with minimum excess weight.
The US Department of Energy is the most commonly used international standard in this area and has set ultimate system goals of 7.5 wt% and 70 kg/m3 at or near room temperature, but to date no material has come close to meeting these specifications.
The two main classes of hydrogen storage materials are hydrides, which generally possess high hydrogen binding enthalpies that require exotic engineering solutions to deal with the excess heat absorbed and released on cycling, and physisorption materials, which use high surface area porous solids to bind hydrogen at very low enthalpies necessitating extreme levels of cooling at elevated pressures in order to function. For this reason new classes of materials must be developed.
The research in our group involves the design and synthesis of specifically tailored transition metal polymers and gels for applications in a new type of hydrogen storage, in which Kubas-type binding (a type of weak chemisorption of hydrogen with enthalpies in the 20-30 kJ/mol range predicted to be ideal for room temperature application) is the principal storage mechanism, making them distinct from traditional hydrides and physisorption materials.
The materials were first discovered in 2009 by the Antonelli group and show remarkable storage properties with volumetric storage capacities that already are comparable to many of the 2015 DOE system targets without the drawbacks of physisorption materials or hydrides. These materials possess linear isotherms, enthalpies that rise with surface coverage, have no kinetic or thermodynamic barriers to storage at 298 K, and operate using pressures as the toggle for instantaneous uptake and release of hydrogen. Computational studies suggest performances as high as 9.9 wt% in some cases, such that the potential of these materials in commercial applications appears exceptional at this early stage.
Major Research Outputs & Research Impacts
SERC is the UK representation on MPNS COST Action MP1103: Nanostructured materials for solid-state hydrogen storage