Zenji Horita

Abstract:

High performance of hydrogen storage requires not only fast absorption/desorption kinetics but also lower operating temperature near ambient pressure. A process of severe plastic deformation through high-pressure torsion (HPT) was applied to two major hydrogen storage metallic materials such as Ti-based and Mg-based systems. Microstructures were well refined by the HPT process, so that nanograins were formed in the materials. For the Ti-based system, an HPT-processed TiFe intermetallic no longer requires pre-activation that limits practical use, as it involves exposure to hydrogen atmosphere under high pressures (>3 MPa) at high temperatures (~700 K). The lack of requirement for pre-activation is because hydrogen diffusion is enhanced through introduction of high densities of lattice defects such as grain boundaries [1]. Furthermore, the HPT-processed TiFe was not deactivated even after storage in air [2]. Application of the HPT process to Mg₂Ni made its hydrogen storage performance improved so that hydrogen absorption is feasible at a reduced temperature of 423 K with faster hydrogen kinetics. This was due to the introduction of high densities of planar lattice defects such as grain boundaries and stacking faults [3].