Electrochemical Hydrogen Storage Characteristics of Thin Film MgX (X=Sc, Ti, V, Cr) Compounds

Niessen, Rah Rogier; Notten, Phl Peter

doi:10.1149/1.2012238

Cited by 130 publications

(115 citation statements)

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“…Moreover, the fast switching together with the high optical contrast between the reflective and the absorbing states make Mg-Ti-H films also interesting for hydrogen sensor applications. The solar collector and sensor applications of Mg-Ti-H thin films described in this letter combined with the very large reversible hydrogen storage capacity of Mg-Ti-H thin film battery electrodes reported earlier by Notten and co-workers 8,9 …”

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confidence: 67%

“…8,9 We observe a similar crystalline Mg-Ti alloy phase ͑hexago-nal structure͒ when co-sputtering Mg and Ti. In hydrogenated films the formation of a MgH 2 -like rutile phase is observed for low Ti contents ͑y = 0.90͒, whereas in Mg y Ti 1−y with y = 0.80 and y = 0.70, a fluorite-like Mg-Ti-H phase is formed, similar to that identified by Kyoi et al 10 in bulk samples.…”

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Mg–Ti–H thin films for smart solar collectors

Borsa

Baldi

Pasturel

et al. 2006

Applied Physics Letters

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108

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Mg-Ti-H thin films are found to have very attractive optical properties: they absorb 87% of the solar radiation in the hydrogenated state and only 32% in the metallic state. Furthermore, in the absorbing state Mg-Ti-H has a low emissivity; at 400 K only 10% of blackbody radiation is emitted. The transition between both optical states is fast, robust, and reversible. The sum of these properties highlights the applicability of such materials as switchable smart coatings in solar collectors. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2212287͔ Many metal hydrides behave as switchable mirrors ͑i.e., their optical properties switch from reflective in the metallic state to transparent in the hydrogenated state͒. [1][2][3][4] In addition, magnesium-rare-earth ͑Mg-RE͒ and magnesium-transitionmetal ͑Mg-TM͒ switchable mirrors also exhibit an intermediate highly absorbing optical state on hydrogenation. The possibility to switch a film from a reflective state to an absorbing state suggests that such materials might be interesting for smart solar collectors, which absorb light in normal operation condition and switch to a reflective state to avoid overheating. Limiting the stagnation temperature of the solar collector makes it possible to use cheap materials such as plastics ͑generally not designed for high temperatures͒.In this letter we show that Mg y Ti 1−y thin films prepared by dc magnetron co-sputtering of Mg and Ti at room temperature ͑on quartz and CaF 2 ͒ satisfy the following requirements for a smart solar coating: ͑i͒ high absorption in the solar regime ͑0.5Ͻប Ͻ 4 eV͒, ͑ii͒ low emissivity in the thermal regime ͑ប Ͻ 0.5 eV͒, and ͑iii͒ reversibility. Three compositions are studied in detail: y = 0.70, y = 0.80, and y = 0.90. Typical deposition rates are 2 Å / s for Mg ͑150 W rf power͒, 0.1-1 Å / s for Ti ͑25-160 W dc power͒, and 1.3 Å / s for Pd ͑50 W dc power͒. All the films are covered with a Pd layer ͑10-50 nm͒ to promote dissociation of H 2 and to prevent oxidation of the underlying film.Reflection ͑R͒ and transmission ͑T͒ spectra are measured simultaneously during hydrogenation ͑pressures up to 1 bar H 2 ͒ in a Perkin Elmer Lambda 900 diffraction grating spectrometer ͑0.495Ͻប Ͻ 6.51 eV͒ and a Bruker IFS 66 Fourier transform infrared spectrometer ͑0.2Ͻប Ͻ 1.1 eV͒. The R-T spectra are measured through the transparent substrate at near normal incidence of the incoming beam. Figures 1͑a͒ and 1͑b͒ show the reflection and transmission spectra measured for 200 nm Mg y Ti 1−y / 10 nm Pd films ͑y = 0.90, 0.80, and 0.70͒ in the as-prepared and hydrogenated states ͑in 1 bar H 2 at room temperature͒. In the metallic state ͓Fig. 1͑a͔͒ all the films have a relatively high and featureless reflection that decreases with increasing Ti content.After hydrogen absorption, the reflection is low for all compositions, whereas significant transmission is observed only for the y = 0.90 sample. The combination of low reflection and low transmission in the hydrogenated state ͑y = 0.80 and 0.70 samples͒ gives rise to a highly a...

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confidence: 67%

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confidence: 73%

Mg–Ti–H thin films for smart solar collectors

Borsa

Baldi

Pasturel

et al. 2006

Applied Physics Letters

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108

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“…Various transition metals were investigated in order to control the kinetics of the (de)hydrogenation reaction. Niessen et al showed that meta-stable alloys can be prepared in thin film form by depositing Mg with Ti, V or Cr, though they are immiscible elements from a thermodynamic point of view, [20]. The hydrogen content of these materials also strongly affects the optical properties, which can be used in hydrogen sensors, smart solar collectors and switchable mirrors.…”

Section: Electrochromic Applicationsmentioning

confidence: 99%

Electrochemical and Optical Properties of Magnesium-Alloy Hydrides Reviewed

2012

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Abstract:As potential hydrogen storage media, magnesium based hydrides have been systematically studied in order to improve reversibility, storage capacity, kinetics and thermodynamics. The present article deals with the electrochemical and optical properties of Mg alloy hydrides. Electrochemical hydrogenation, compared to conventional gas phase hydrogen loading, provides precise control with only moderate reaction conditions. Interestingly, the alloy composition determines the crystallographic nature of the metalhydride: a structural change is induced from rutile to fluorite at 80 at.% of Mg in Mg-TM alloy, with ensuing improved hydrogen mobility and storage capacity. So far, 6 wt.% (equivalent to 1600 mAh/g) of reversibly stored hydrogen in Mg y TM (1-y) H x (TM: Sc, Ti) has been reported. Thin film forms of these metal-hydrides reveal interesting electrochromic properties as a function of hydrogen content. Optical switching occurs during (de)hydrogenation between the reflective metal and the transparent metal hydride states. The chronological sequence of the optical improvements in optically active metal hydrides starts with the rare earth systems (YH x ), followed by Mg rare earth alloy hydrides (Mg y Gd (1-y) H x ) and concludes with Mg transition metal hydrides (Mg y TM (1-y) H x ). In-situ optical characterization of gradient thin films during (de)hydrogenation, denoted as hydrogenography, enables the monitoring of alloy composition gradients simultaneously.

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“…The equality of the molar volumes of TiH 2 and Mg has been used to explain the structural stability of these metastable thin film alloys. 15,16 Notten and co-workers [20][21][22] and Borsa et al 6,15 showed that for a high titanium content, x Շ 0.8, the structure of the hydrides is fluoritelike. Hydrides with a lower titanium content adopt a rutilelike structure, similar to that of ␣-MgH 2 .…”

Section: Introductionmentioning

confidence: 99%