dc.description.abstract | The present study focuses on hydrogen storage alloys, with particular emphasis on Ti-V-based bcc and Mg-Co-based alloys, as they have the potential to be some of the most promising clean hydrogen sources for use in fuel cell vehicles or hydrogen storage applications.
The main purpose of this research is to investigate the micro-alloying effects on the hydrogen storage properties of Ti-V-Cr and Ti-V-Cr-Mn bcc alloys; develop a novel route for synthesizing Mg2CoH5 hydride by mechanical alloying (MA) without leaving residual Co, and enhance the absorption-desorption properties of Mg-Co alloy by adding Ni and Mg2Ni, combining the effects of alloying and grain-refining on hydrogen storage properties.
Ti33V33Cr34 ingots with 0-3 at% Pd were prepared by argon arc melting. X-ray diffraction results reveal that all of these alloys are single bcc phases, and vary only slightly in their lattice parameters, which range from 3.0297 to 3.0726Å. Ti-V-Cr alloy that contains 0.5 at% Pd exhibits a high hydrogen absorption capacity of up to 3.42 mass% at 80℃. Pd-containing (0.05-3 at% Pd) alloys have a higher rate of absorption than alloy that does not contain Pd. The plateau pressure increased slightly with Pd content in the range 0.05 to 0.5 at%; in particular, the desorption plateau pressure of the (Ti33V33Cr34)99.5Pd0.5 alloy increased significantly after the 50th absorption-desorption cycling test.
Ti-V-based alloys typically exhibit a low desorption plateau pressure under ambient conditions. Therefore, various amounts of Al, Cu and Al-20wt%Sc master alloy are added to Ti-V-Cr based alloys, and the structural characteristics, hydrogen absorption-desorption properties and cycling properties of Ti-V-Cr-Mn alloy are investigated. The addition of trace Al, Cu and Al-20wt%Sc to Ti-V-Cr alloy improves its absorption and desorption properties. The addition of Al-20wt%Sc (< 2 at%) to Ti-V-Cr alloy apparently increases the desorption plateau pressure without reducing its hydrogen storage capacity. Furthermore, the fine-grain (Ti33V33Cr24Mn10)99 (Al-20wt%Sc)1 alloy produced by rapid solidification exhibits a low decline of reversible desorption capacity after cycling test.
The authors’ group proposed a novel method for producing Mg2CoH5 hydride by comparative short-term mechanical alloying (MA), using 3Mg-MgCo2 mixture as the starting material. 2Mg-Co and 3Mg-MgCo2 mixtures are prepared by MA, and their hydrogen storage properties are examined. X-ray diffraction (XRD) reveals that the main phase Mg2CoH5 can be synthesized from a 3Mg-MgCo2 mixture by 50h ball milling and hydrogenation under 5 MPa hydrogen atmosphere at 400℃ for 15h. An ball-milled 3Mg-MgCo2 mixture has an absorption capacity of up to 1.5 mass% at 115℃, and a desorption capacity of over 2.0 mass% hydrogen in 20 min at temperatures from 300 to 350℃, which represents a higher desorption rate than that achieved, according to the literature, by preparation using a combined milling and sintering procedure.
Pure Ni and Mg2Ni catalysts are added to 3Mg-MgCo2 mixture to enhance its hydrogen storage capacity and improve its kinetics of hydrogen absorption and desorption. A novel route was utilized to synthesize Mg-Co-based alloys by mechanical alloying, using 3Mg-MgCo2, 3Mg-MgCo2-10wt%Ni, 3Mg-MgCo2-10wt%Mg2Ni and 3Mg-MgCo2-20wt%Mg2Ni mixtures as the starting materials. X-ray diffraction of the hydride products reveals that Mg2CoH5 was the dominant hydride phase in all of these alloys. The results of temperature-programmed decomposition (TPD) reveal that the de-hydriding temperature of 10wt%Ni-containing 3Mg-MgCo2 mixture was around 35℃ lower than that of the ball-milled 3Mg-MgCo2 mixture. Additionally, adding 10wt% Mg2Ni to the 3Mg-MgCo2 mixture significantly improved both the hydrogen absorption capacity and the hydrogen absorption rate; the latter was especially improved at low temperature (115 ℃). The absorption capacity and absorption rate of the alloy 3Mg-MgCo2-10wt% Mg2Ni at 350℃ were 3.0 mass% and over 2.5 mass% in 5min, respectively. TEM analysis indicates that the ball-milled 3Mg-MgCo2-10wt%Mg2Ni mixture had a body centered cubic (BCC) structure.
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