Microstructure of MmM₅/Mg multi‐layer hydrogen storage films prepared by magnetron sputtering

Abstract

KEY WORDStransmission electron microscopy; hydrogen storage alloys; thin films; magnetron sputtering ABSTRACT Multi-layer hydrogen storage thin films with Mg and MmNi 3.5 (CoAlMn) 1.5 (here Mm denotes La-rich mischmetal) as alternative layers were prepared by direct current magnetron sputtering. Transmission electron microscopy investigation shows that the microstructure of the MmNi 3.5 (CoAlMn) 1.5 and Mg layers are significantly different although their deposition conditions are the same. The MmNi 3.5 (CoAlMn) 1.5 layer is composed of two regions: one is an amorphous region approximately 4 nm thick at the bottom of the layer and the other is a nanocrystalline region on top of the amorphous region. The Mg layer is also composed of two regions: one is a randomly orientated nanocrystalline region 50 nm thick at the bottom of the layer and the other is a columnar crystallite region on top of the nanocrystalline region. These Mg columnar crystallites have their [001] directions parallel to the growth direction and the average lateral size of these columnar crystallites is about 100 nm. A growth mechanism of the multi-layer thin films is discussed based on the experiment results.

MgNi/Pd multilayer hydrogen storage thin films prepared by dc magnetron sputtering

“…Previous researches have demonstrated that the nanocrystalline MgNi thin film fabricated by direct current magnetron sputtering exhibited better kinetic performances than the usual polycrystalline phases, for which the hydrogen absorption and desorption temperatures decreased as reported before [19]. Previous studies also show that the thin MmM 5 layer acts as a catalyst to accelerate the hydrogenation/dehydrogenation process of the MgNi layer in MgNi/MmM 5 multilayer films [18]. Here, the presence of a uniform Pd layer catalyst, typically in form of nanoclusters on the MgNi surface, stimulates the surface reaction leading to the dissociation and recombination of the H 2 molecules and accelerates the hydrogenation/dehydrogenation process of the MgNi layer.…”

“…It was reported, for example, that Pd/Mg/Pd films can absorb and desorb hydrogen at 373 K and its hydrogen storage capacity reach the value as high as 5 mass% [17]. It has also been revealed that incorporation of LaNi 5 type alloys into Mg-base alloys by MA or sputtering can improve the hydriding kinetics of Mg-base alloys by an auto-catalysis reaction mechanism [2,18]. The reported work demonstrate obviously that good hydrogen storage performance (high hydrogen capacity and moderate absorption/desorption temperature) of Mg-base alloys can be achieved by forming nano-composite of Mg-base hydrogen storage alloys and proper catalyst [15][16][17][18].…”

“…It has also been revealed that incorporation of LaNi 5 type alloys into Mg-base alloys by MA or sputtering can improve the hydriding kinetics of Mg-base alloys by an auto-catalysis reaction mechanism [2,18]. The reported work demonstrate obviously that good hydrogen storage performance (high hydrogen capacity and moderate absorption/desorption temperature) of Mg-base alloys can be achieved by forming nano-composite of Mg-base hydrogen storage alloys and proper catalyst [15][16][17][18]. A proper way to make suitable nano-composite for hydrogen storage is to form thin films by sputtering or evaporation methods because it is easy to control the thickness of the film layers in nano-meter scales.…”

Thermodynamic Tuning of Mg-Based Hydrogen Storage Alloys: A Review

“…To improve the hydrogenation properties of Mg, Wang and Ouyang et al prepared Mg–Ni thin films, and Mg/MmM x and Mg-Ni/MmM 5 multi-layer films [69,70,71,72,73,74]. They prepared the Mg/MmM 5 multi-layer film via magnetron sputtering, and X-ray diffraction (XRD) analysis showed that most of the Mg was hydrogenated and dehydrogenated at about 523 K, which is about 100 K lower than the dehydrogenation temperature of pure Mg film.…”

Electrochemical characteristics of La–Ni–Al thin films

“…Devi et al [2] found that the change in resistance for LaNi 5 thin film due to hydrogen absorption increases with the angle of deposition and resistance decreases with desorption. Recently, the microstructure of the Mg and MmNi 3.5 (CoAlMn) 1.5 multi-layered thin films was reported to be affected by the substrate temperature and the composition of the deposited layer [16]. Only limited reports were focused on the electrochemical hydrogen storage properties, no detailed analysis was associated to the microstructure of LaNi 5 based thin films.…”