Hydrogen storage and electrochemical properties of annealed low-Co AB5 type intermetallic compounds

The structure, hydrogen storage and electrochemical properties of annealed low-Co AB5- type intermetallic compounds have been investigated. La-alloy, Nd-alloy and Cr-alloy are used to represent La0.8Ce0.2Ni4Co0.4Mn0.3Al0.3, La0.6Ce0.2Nd0.2Ni4Co0.4Mn0.3Al0.3 and La-0.6-Ce0.2Nd0.2Ni3.8Co0.4Mn0.3Al0.3Cr0.2, respectively. The XRD results indicated that annealed samples are all single-phase alloys with CaCu5 type structure. The maximum of both hydrogen content and discharge capacity is obtained for La-alloy 1.23 wt%H-2 and 321.1 mA h/g, respectively. All the investigated alloys are quiet stable with DH of hydrogen desorption about 36-38 kJ/mol H-2. Cycle life of alloy electrode has been improved by partial substitution of La for Nd and Ni for Cr. The highest capacity retention of 92.2% after 100 charge/discharge cycles at 1C has been observed for Nd-alloy. The hydrogen diffusion coefficient measured by PITT is higher at the start of charging process and dramatically reduces by 2-3 order of magnitude with saturation of b-hydride. The highest value 6.9 x 10(-13) cm(2)/s is observed for La alloy at 100% SOC. Partial substitution La for Nd and Cr for Ni in low-Co AB5 metal hydride alloys slightly reduces maximum discharge capacity, HRD performance and hydrogen diffusion kinetics. Low-Co alloys show good overall electrochemical properties compared to high-Co alloys and might be perspective materials for various electrochemical applications. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

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The study investigated the structure, hydrogen storage, and electrochemical properties of annealed low-Co AB5-type intermetallic compounds. Partial substitution of metals could improve the cycle life and capacity retention of the alloys, while low-Co alloys show better overall electrochemical properties compared to high-Co alloys.