Effects of rare-earth element additions to Laves phase-related body-centered-cubic solid solution metal hydride alloys: Thermodynamic and electrochemical properties

Abstract The influences of rare-earth element additions on the structural, gaseous phase hydrogen storage, and electrochemical properties of Laves phase-related body centered cubic (BCC) metal hydride alloys were studied using a series of alloys with the design composition of Ti 14.6 Zr 2.1 V 44.1 Cr 12.2 Mn 6.9 Fe 2.7 Co 1.4 Ni 14.7 Al 0.3 RE 1.0 , where RE (rare earth) = Y, La, Ce, Nd. Samples were prepared by induction melting and then annealed, and only 0.2 to 0.3 at% of the rare-earth element was included in the final samples in the elemental form, which varies from the RENi phase formed in the C14-predominated metal hydride alloy. The Al-content in the final alloy is about 1 at% because of a small reaction to the crucible material. The beneficial effects of rare-earth element addition on the low-temperature performance of the C14-predominated alloy was not observed in this group of BCC/C14 alloys. The gaseous phase and electrochemical hydrogen characteristics were influenced by the rare-earth elements addition mainly through changes in both compositions and abundances of the constituent phase. Y increased reversibility of gaseous phase hydrogen storage. La raised plateau pressure, decreased discharge capacity, and hindered activation and surface electrochemical reaction. Ce increased BCC phase abundance and discharge capacity with reduced room temperature surface charge-transfer resistance. Nd increased C14 phase abundance, decreased the plateau pressure, increased gaseous phase hydrogen storage capacities, and increased discharge capacity and bulk hydrogen diffusion.