Exploration of Metal Hydride Systems with High Adsorption/Desorption Pressure

• Applicants: Dr. Michael Felderhoff; Professor Dr. Florian Mertens
• Subject Area: Solid State and Surface Chemistry, Material Synthesis ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449160425

Hydrogen PEM fuel cell technology for the transport sector has reached a degree of maturity that we currently see the first introduction of fuel cell vehicles (Toyota Mirai) to the general consumer market. One of the main factors that prevents the wide scale dissemination of this technology is the lack of an effective, large capacity, and economic hydrogen storage system. After intensive exploration of possible alternatives, high pressure compressed gas was selected as the storage option that fulfills the many requirements for the transport sector best, although the storage capacity remains a challenge. Accepting this choice and the necessary pressure level of 30 to 70 MPa, new hydrogen storage materials with special properties to further improve the storage capacity by using a combination of high pressure gas storage and solid state hydrogen storage in one system can be defined. The US Department of Energy (DoE) and Industry have evaluated requirements for such materials and published a set of parameter that these materials need to fulfill, among which the value for the hydrogen absorption enthalpy of about |Delta H| = 20 kJ/mole H2 is the most important one, because it defines the pressure and temperature level of operation. The published parameter values generally define materials that are scientifically fully unexplored, yet not even discovered, because the standard laboratory equipment for metal hydride investigations is usually limited to pressures up to 20 MPa. It is therefore, the goal of the proposed project to discover new metal hydride systems that display the desired plateau pressures and to characterize them in respect to their crystal structures, decomposition pathways, energetics and kinetics. The project partners have specific expertise in the field of metal hydrides and can provide necessary and complementary equipment that allows the synthesis of high pressure metal hydrides (called "unstable Hydrides") and/or high pressure characterization. The Mertens group has recently built a high pressure Sieverts apparatus (pressures limit 100 MPa) and can perform high pressure calorimetry, the Felderhoff group possesses high pressure synthesis equipment and has access to a high pressure XRD facility. In respect to the materials synthesis and the materials to be investigated the both groups complement one another in an almost ideal way. The materials types will range from transition metal complex hydrides and rare earth metal complex hydrides all the way to metal hydride mixtures allowing to apply the concept of thermodynamic tuning. The high pressure ball milling based synthesis provides a specific synthesis method for unstable hydrides that is unique to the project.

• DFG Programme: Research Grants