Development of melt-spun Ni–Nb–Zr–Co amorphous alloy for high-performance hydrogen separating membrane
Introduction
Pd-based alloy membranes are adopted in the current designs of fuel reformers in fuel cell systems due to their ability for catalyzing hydrogen dissociation and selective permeation of hydrogen without suffering from hydrogen embrittlement [1], [2]. However, the use of the novel metals makes the cost of such membranes unacceptably high for many fuel cell applications. It is therefore desired that alternative membrane alloys with low-cost metals should be developed to replace the Pd-based alloys and to improve hydrogen permeability while reducing the material cost. Recently, many alloy candidates such as amorphous [3], [4], [5], [6], [7], [8], V-based [9], [10], Ti–Ni–Nb [11] and Ta [12] alloys have been developed as hydrogen permeable membranes.
We have been developing economical high-performance alloys for hydrogen separating membranes. Previously, we investigated the formability, mechanical properties and thermal stability of the Ni–Nb–Zr amorphous alloys [13]. It was found that the hydrogen permeability of the Ni–Nb–Zr amorphous alloy is strongly dependent on the composition of the alloy and increased with increasing Zr content in our previous work [14]. The hydrogen permeability of the melt-spun Ni–Nb–Zr amorphous alloy ribbons was higher than that of pure Pd metal. However, it was difficult to investigate the hydrogen permeability of the amorphous alloys having high Zr content due to severe hydrogen embrittlement during the measurement. Therefore, we produced the Ni–Nb–Zr–Co amorphous alloys and investigated the effect of Co addition to the Ni–Nb–Zr alloys on the suppression of hydrogen embrittlement. As the result, it was found that the Co addition is effective for the suppression of hydrogen embrittlement [15]. In this work, we performed long-time permeation tests to examine the hydrogen permeability and the durability of the Ni–Nb–Zr–Co amorphous alloys.
Section snippets
Experimental
Ni–Nb–Zr–Co alloy ingots were prepared by arc-melting the mixture of pure metals with desired compositions in an Ar atmosphere. Melt-spun ribbons were produced by a single-roller melt-spinning technique in an Ar atmosphere. The ribbons for hydrogen permeation measurement were about 20 mm in width and about 50 μm in thickness.
Pd thin film was deposited on both sides of the specimens by sputtering technique (ULVAC SH-350) to obtain an active catalyst for hydrogen dissociation and recombination
Results and discussion
Fig. 1 shows the Arrhenius plots of the hydrogen permeability of (Ni0.6Nb0.4)45Zr50Co5 amorphous alloy prepared in this work together with our previous data of Ni–Nb–Zr amorphous alloys. The permeabilities shown in Fig. 1 were measured with pure hydrogen gas. The hydrogen permeability of the Ni–Nb–Zr–Co amorphous alloys increased with increasing test temperature like the Ni–Nb–Zr amorphous alloys. The hydrogen permeability of the (Ni0.6Nb0.4)45Zr50Co5 amorphous alloys was as high as that of the
Summary
We examined the hydrogen permeability and the durability of the Ni–Nb–Zr–Co amorphous membranes which were produced by single-roller melt-spinning technique. The results obtained are summarized as follows:
- (1)
The hydrogen permeability of the (Ni0.6Nb0.4)45Zr50Co5 amorphous alloy increased with increasing test temperature and was much larger than that of the conventional Pd–Ag alloy.
- (2)
The permeability of the (Ni0.6Nb0.4)55Zr40Co5 and the (Ni0.6Nb0.4)45Zr50Co5 amorphous alloys did not almost decrease
Acknowledgements
This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan under the Research program, “Development for Safe Utilization and Infrastructure of Hydrogen”.
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