In-situ TEM Observation for Reaction Mechanism in MgH₂ Hydrogen Storage Material

Abstract

In-situ observation on the catalytic effect of Nb₂O₅ in MgH₂ was carried out by using transmission electron microscopy (TEM). We prepared two kinds of samples, because we tried to observe the reaction from two kinds of viewpoints. MgH₂ catalyzed with 1 mol% of Nb₂O₅ was prepared for an overall viewpoint on the desorption process of MgH₂ with catalyst by conventional TEM. The dehydrogenation of the 1 mol% sample started at 150 °C and Mg nano-size particles were formed. However, Nb₂O₅ was not confirmed in diffraction patterns and images, because it was highly dispersed by ball-milled. So MgH₂ catalyzed with 10 mol% of Nb₂O₅ was prepared for local viewpoint to focus the boundary between the catalyst and the Mg phase by high voltage electron micro scope (HVEM). The sample mixed in mortar was prepared for this, because it was difficult to find the boundary in the sample ball-milled. The high resolution images of the 10 mol% sample revealed that the dehydrogenation started from the interface of MgH₂ and Nb₂O₅. The result suggested that the dehydrogenation could proceed with hydrogen diffusion from MgH2 phase to the interface between Mg and Nb2O5.