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HYDROGEN STORAGE IN Mg-In-C ALLOYS: EFFECT OF COMPOSITION AND AGEING
Čermák, Jiří ; Král, Lubomír
Hydrogen storage in two Mg-In-C alloys with different In concentration, c In , was studied in the temperature range from 250°C to 350°C after five-years-ageing at room temperature. The both alloys show acceptable cycling stability, however, the storage capacity of the alloys decreased from about 5 wt. % H2 to about 2,5 and 3.1 wt. % H 2 by higher c In and lower c In , respectively after 5 years. The sorption kinetics degraded much more by high c In than by c In . PCT isotherms, TPS and DSC patterns were measured for both materials. It was found that the hydrides responsible for hydrogen storage in alloy with higher c In are slightly more stable.
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Hydrogen Storage Capacity of Mg/Mg2Ni Eutectic Doped with Elements from Groups XIII and XIV
Čermák, Jiří ; Král, Lubomír
In the present paper, the chemical composition of Mg-8.5 at.% Ni-2.7at.%X alloys (X – elements of the 13th and 14th groups) as prospective hydrogen storage was investigated. Experimental alloys were studied in three states: (i) after stabilization anneal, (ii) after stabilization anneal and hydrogen charging, and (iii) after stabilization anneal, hydrogen charging and hydrogen desorption. It was ascertained that a ratio of concentration of X in two principal phases – Mg2NiH4(-X) and MgH2(-X) – was a decreasing function of the ionization potential of X. The stronger the preference of X for Mg2NiH4-X phase, the higher the hydrogen storage capacity of Mg-Ni-X alloy was. For X = In, the hydrogen storage capacity was slightly higher than the capacity of an un-alloyed binary eutectic Mg-Ni alloy.
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Improvement of Hydrogen Desorption Characteristics of Eutectic Mg/Mg2NiH4 and Mg2NiH4 by In addition
Čermák, Jiří ; Král, Lubomír
Mg-xNi alloys are known as perspective hydrogen storage materials [1,2]. Hydrogen storage capacity and hydrogen desorption rate of binary alloys Mg-Ni are, however, still unsatisfactory and therefore, improvements are sought, e.g., by introduction of a proper catalyst [3]. As candidate elements, transition metals [4] are often used that attract bonding valence electrons and, hence, destabilize the hydrides. However, also elements with weaker bond to H than that of Mg, or even non-hydride forming elements show a beneficial effect upon the hydrogen desorption rate [5,6]. The present investigation continues our previous work [7,8]. Here we investigate the resistance of eutectic Mg/Mg2Ni against the poisoning by residual air and possible ways how to improve the hydrogen desorption kinetics of Mg2NiH4 by doping. As dopants, elements of the 13th and the 14th group were tested that do not form stable hydrides.
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Kovové materiály pro přechovávání vodíku
Soukup, Karel ; Rogut, J. ; Ludwik-Pardala, M. ; Wiatkowski, M. ; Šolcová, Olga
Another alternative is the redox cycle of iron/iron oxides which is presented here. Hydrogen storage is described as a reduction of iron oxides to metallic iron by hydrogen. Hydrogen production is achieved through the oxidation of iron with water steam. This contribution describes textural and transport properties of solid materials composed of iron and aluminium oxide phases which are believed to be promising for the hydrogen storage process.
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Kinetika vodíku v Mg2Ni a v hydrogenovaném eutektiku Mg-Mg2Ni
Čermák, Jiří ; Král, Lubomír ; Stloukal, Ivo
Time dependence of total amount of hydrogen desorbed from hydrogen-charged Mg and eutectic Mg-Mg2Ni (23.5 wt. % Ni) alloy was measured at temperatures from interval 552 – 723 K. Experiments were carried out well below the equilibrium pressure, where these hydrides – perspective as solid hydrogen storage media – are unstable and the desorption process is controlled mainly by diffusion of hydrogen in respective hydride (MgH2 and/or Mg2NiH4). Hydrogen diffusion coefficients were evaluated from desorption curves and hydrogen diffusion coefficient along interphase boundary MgH2/Mg2NiH4 was estimated from results obtained with the eutectic alloy.
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Strukturní změny ve slitinách Mg-Ni po absorpci a desorpci vodíku
Král, Lubomír ; Čermák, Jiří
This paper deals with changes of structure in Mg-Ni alloys after absorption and desorption of hydrogen. Experimental materials were prepared by two techniques – by casting and by ball milling and subsequent compacting to pellets. These materials were hydrogen-charged at elevated temperature and pressure. Materials were studied using the SEM Jeol JSM 6460 equipped with EDS/WDS analyzers. Formation of rectangular particles of MgNi2, nucleation of MgH2 at grain boundaries, and changes of Mg2Ni were observed. The so-called activation of hydrogen storage alloy is most likely due to fine particles that appear after the first hydrogen charging.
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Vlastnosti nanokrysltalického Zr-Fe-H
Roupcová, Pavla ; Schneeweiss, Oldřich
In this paper, we describe some results obtained by synthesis of Fe-Zr alloys and the study of the phase transformations in these materials induced by hydrogen. Mossbauer spectroscopy was used as the most sensitive method for determination of Fe-Zr based phases in a nanocrystalline form.
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