The research in the division aims at developing new carrier materials for hydrogen mobile and stationary storage, as well as for hydrogen delivery. For mobile hydrogen storage, the material based storage system must meet the needs of hydrogen fuel cell vehicles in terms of volume, weight percent hydrogen, cost, fast charging and discharging, and durability with high well-to-wheel energy efficiency. Hydrogen delivery systems based on hydrogen-absorbing materials are focused on cost effective truck transport of large amounts of hydrogen. Material based stationary hydrogen storage applications must be more cost effective and energy efficient than conventional pressurized gaseous hydrogen storage or uniquely meet particular requirements of specific stationary applications.
The unique, important accomplishments of this division are: demonstration of the microscopic degradation mechanisms in certain hydrogen storage materials; development of advanced materials synthesis methods to advance the performance of other hydrogen storage materials; and the discovery of a method that greatly enhances the performance of a third hydrogen storage material and opens an entirely new range of materials and approaches to hydrogen storage.
● RESEARCH HIGHLIGHTS
TiFe is a low price ideal hydrogen storage material for stationary storage. It absorbs and desorbs hydrogen at room temperature under ambient hydrogen pressure in a more compact form than liquefied hydrogen. Although it has been reported as a storage system in late 1970s, it was abandoned for decades because activation (hydrogen absorption/desorption) requires heating at temperatures higher than 400°C under 30 bar (or higher) of hydrogen. In an ongoing collaboration, PIs Akiba and Horita targeted this issue of activation by using high-pressure torsion (HPT) techniques. Surprisingly, it was found that severely strained TiFe readily absorbs and desorbs hydrogen without activation.
For the study of Ti-based BCC systems, the microstructural changes of V-Ti alloys after hydrogenation were identified; twin boundaries introduced into the hydrogenated V-Ti alloys result in degradation of the effective absorbing capacity. Hydrogenation/dehydrogenation properties and microstructure of other Ti-based BCC alloys, which are one of the most promising candidates for hydrogen tanks in fuel cell vehicles, have also been investigated.
An important research focus point of the Division is to elucidate the hydrogenation mechanism of Mg/Ni films in order to improve kinetics and thermodynamics of Mg-based materials. Optimizing the composition of these films will help develop materials with higher performance. The relationship between microstructure and Mg/Ni ratio in Mg-Ni films has been elucidated by means of TEM.
● FUTURE DIRECTIONS
Advanced materials for on board application will be developed under a NEDO funded project (proposal under review) with three major Japanese carmakers and other stakeholders.
Hydrogen storage in severely deformed TiFe using the HPT (High Pressure Torsion) technique will be pursued further for mass production development and applications.
As the road-map indicates, first generation materials for on board storage are aimed for late real application in 2020s to 2030s. For early application they Division will also focus on high performance storage systems. Borohydrides have hydrogen capacity of over 10 wt %, but reaction speed and hydrogen release temperature are serious roadblocks at present. To control the kinetics and thermodynamics of borohydrides work will be carried out on intermediates of hydrogen release/uptake process.
Hydrogenation properties are heavily influenced by morphology, in other words nanostructures. TEM (Transmission Electron Microscopy) is one of the most powerful tools to observe nanostructures. This technique provides shape of nano-grains, crystal structures, interfacial structure and chemical analysis. Professor Matsuda introduces in-situ hydrogen cell to her TEM to observe dynamic behavior of hydrides using TEM. The materials to be observed are along the targets both for mobile and stationary applications as well as model materials for deeper understanding of phenomena.