In-situ TEM Observation for Reaction of LiH with NH 3 by Means of Environmental Cell
- PDF / 88,709 Bytes
- 2 Pages / 612 x 792 pts (letter) Page_size
- 28 Downloads / 211 Views
1216-W03-34
In-situ TEM observation for reaction of LiH with NH3 by means of environmental cell Hiroko Hirasawa†*, Shigehito Isobe†, Yongming Wang†, Hikaru Yamamoto‡, Hiroki Miyaoka‡, Naoyuki Hashimoto†, Somei Ohnuki†, Takayuki Ichikawa‡, Yoshitsugu Kojima‡ † Graduate School of Engineering, Hokkaido University, N-13, W-8, Sapporo 060-8278, Japan ‡ Institute for Advanced Materials Research, Hiroshima University, 1-3-1, Kagamiyama, Higashi-Hiroshima, 739-8530, Japan ABSTRACT Nowadays, light weight hydrides, such as LiH and NaH, have been studied as promising hydrogen storage materials for onboard fuel cell vehicle. LiH and NaH can be reacted with NH3 to produce H2, LiNH2 and NaNH2, respectively. The reaction formulae are “LiH + NH3 ↔ H2 + LiNH2”, “NaH + NH3 ↔ H2 + NaNH2”. In this work, we performed in-situ TEM (Transmission Electron Microscopy) with an environmental cell, which is especially designed to control the “in-situ” condition such as temperature and gas atmospohere, in order to microscopically examine the reactions. With the environmental cell, we can observe the reaction in 0 ~ 0.2 MPa gas atmosphere and 20 ~ 150 °C. We observed LiH under NH3 gas of 0.1 and 0.01 MPa at room temperature by TEM. It has been confirmed that LiH reacted with NH3 to generate LiNH2 with volume expansion of the particles. Moreover, we obtained the results, that is, LiNH2 was generated at the surface of LiH particle in first process of the reactions. Keywords; hydrogen storage materials, in-situ TEM, environmental cell *Corresponding author; [email protected] INTRODUCTION Recently, hydrogen energy systems have been proposed as a means to reduce greenhouse gas and other harmful emissions from stationary and mobile sources. For realizing hydrogen energy systems in the near future, we have to establish suitable energy storage and transportation technologies. One of the key technologies is in the development of high-performance hydrogen storage materials [1]. Some materials composed of light elements such as borohydrides, alanates and amide/imide systems can store a gravimetrically large amount of hydrogen [2-5]. Recently, Kojima et al. proposed “M-H + NH3” hydrogen storage system [6, 7]. That is, LiH and NH3 react to form LiNH2 and desorb H2, as following reaction, LiH + NH3 → LiNH2 + H2 (1) By this system, large amount of hydrogen at relatively lower temperature can be reversively stored. So far, almost no information about microscopic morphology and mechanism of this reaction has been reported yet. In this work, we have studied microscopic morphology and the reacion mechanism by in-situ and ex-situ observation with Transmission Electron Microscope (TEM). EXPERIMENT Starting materials are powders of LiH purchased from a company. For in-situ observation on dehydrogenation reaction by TEM (JEOL-2010, 200keV), we prepared samples by ball-milling LiH under 1.0 MPa of H2 atmosphere for 10 hours [6, 7], then, we used Environmental Cell (EC: Figure 1), by which we can control temperature (R.T. ~ 150 C) and gas atmosphere (~ 0.2 MPa) o
Data Loading...
