In-situ Kinetics Studies on Hydrogenation of Transition Metal (=Ti, Fe) Doped Mg Films
- PDF / 287,317 Bytes
- 5 Pages / 595 x 841 pts Page_size
- 54 Downloads / 238 Views
1216-W04-04
In-situ Kinetics Studies on Hydrogenation of Transition Metal (=Ti, Fe) Doped Mg Films Zhuopeng Tan1,2, Edwin J. Heilweil3,, Leonid A. Bendersky1 1
. Materials Science and Engineering Laboratory, National Institute of Standards and Technology,
Gaithersburg, MD, 20899, USA 2
. Department of Materials Science and Engineering, University of Maryland, College Park, MD,
20742, USA 3
Physics Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, 20899,
USA ABSTRACT In this paper we report on kinetics studies of the growth rates of a hydride phase during the metal-hydride phase transformation of Mg films doped with transition metals (=Ti, Fe). Infrared emission imaging of wedge-shaped thin films during hydrogen loading reveals different effects of Ti and Fe additives on Mg hydride growth rates. Compared to hydrogenation of pure Mg, Ti addition (atomic fraction 1.6 % and 2.3 %) does not increase the Mg hydride growth rate. However, this doping results in the formation of a thicker hydride layer residing on top of the films. The hydrogenation rate is increased by an order of magnitude for addition of atomic fraction 3.1 % of Fe and the thickness of Mg hydride layer is more than twice that of the hydride layer during hydrogenation of pure Mg. Results obtained here can be used to guide powder design for hydrogen storage applications. INTRODUCTION Development of hydrogen storage materials with fast absorption/desorption cycling is essential for advancing a zero emission hydrogen fuel-based economy, especially for the transportation sector [1, 2, 3].One of the main challenges faced by the development of hydrogen storage materials is the capability of storing hydrogen safely and efficiently. Magnesium hydride, MgH2, has attracted extensive attention because it is inexpensive, satisfies most safety requirements, has high gravimetric hydrogen capacity (mass fraction 7.6 %), high volumetric density, and good cyclability [4]. However, it suffers from high hydrogen desorption temperature (~552 K) and slow kinetics for on-board hydrogen storage applications under ambient conditions [5]. The influence of transition metals Ti, V, Mn, Fe, Ni, Cu, Zn, Zr etc. on the hydrogenation properties of Mg has been studied extensively [6, 7, 8, 9, 10, 11, 12]. Milanese et al. reported that among nine metals (Al, Cu, Fe, Mn, Mo, Sn, Ti, Zn and Zr), Cu, Al and Zn actively participated in Mg hydrogenation/dehydrogenation, while Cu was the most effective additive for destabilizing MgH2 [8]. However, after studying the effects of Ti, Mn, Fe and Ni additives on MgH2 on its thermal stability and decomposition temperature, Ershova et al. concluded that Ti had the largest influence on destabilizing the MgH2 phase [12]. Fe was not identified to be a promising additive in either study, but theoretical calculations based on first principles performed by Larsson et al indicate that Fe can be a good catalyst for both hydrogen absorption
and desorption [13]. In spite of the large effort made in the past decade to study t
Data Loading...
