Solid gas and electrochemical hydrogenation properties of the R1-xR’xMgNi4-yCoy (R, R’ = Y, La, Ce) alloys

Yu V Verbovytskyy,I Yu Zavaliy,V V Berezovets,P Ya Lyutyy

doi:10.15330/pcss.21.3.503-509

Abstract

New R1-xR’xMgNi4-yCoy (R, R’ = Y, La, Ce; x = 0.5; y = 0, 1, 2) alloys have been synthesized by powder sintering method, and their crystal structure and hydrogen storage properties have been studied. X-ray diffraction analysis showed that R1-xR’xMgNi4-yCo alloys belong to the MgCu4Sn-type structure. The synthesized alloys absorb hydrogen at room temperature and hydrogen pressure 0.1-10 bar. For some of the studied compounds, the formation of hydrides with cubic and orthorhombic structures was found. Highest hydrogen content is found for the Co-rich compounds: La0.5Y0.5MgNi2Co2H5.18 and La0.5Ce0.5MgNi2Co2H6.48. Electrochemical studies showed that Y-based electrode materials exhibit better electrochemical performance comparing with Ce-doped ones. Highest discharge capacity of 292 mА∙h/g was observed for La0.5Y0.5MgNi3Co, but the best cyclic stability after 50th cycle of 92% was seen for La0.5Y0.5MgNi2Co2. Additionally, obtained results of the electrochemical properties were compared with related compounds. High rate dischargeability of Co-free alloys at I = 1 A/g were twice higher than ones containing cobalt.

Highlights

Rare earth - magnesium - nickel based hydrogen storage alloys have gained increasing interest as one of the most promising materials for negative electrodes in Ni-metal hydride (MH) batteries
Electrochemical discharge capacity of the electrode materials based on the La-Mg-Ni-Co alloy reached 400 mAh/g [1, 2], which is 30 % higher than the capacity of commercial LaNi5-based electrodes
Alloys with the composition with y = 3 and 4 were not prepared and studied in the present paper; we did not exclude that above mentioned alloys can be formed as the single phase and belong to certain continues solid solutions

Summary

Vasyl Stefanyk Precarpathian National University

Solid Gas and Electrochemical Hydrogenation Properties of the R1-xR’xMgNi4-yCoy (R, R’ = Y, La, Ce) Alloys. New R1-xR’xMgNi4-yCoy (R, R’ = Y, La, Ce; x = 0.5; y = 0, 1, 2) alloys have been synthesized by powder sintering method, and their crystal structure and hydrogen storage properties have been studied. X-ray diffraction analysis showed that R1-xR’xMgNi4-yCo alloys belong to the MgCu4Sn-type structure. For some of the studied compounds, the formation of hydrides with cubic and orthorhombic structures was found. Highest hydrogen content is found for the Co-rich compounds: La0.5Y0.5MgNi2Co2H5.18 and La0.5Ce0.5MgNi2Co2H6.48. Electrochemical studies showed that Y-based electrode materials exhibit better electrochemical performance comparing with Ce-doped ones. Obtained results of the electrochemical properties were compared with related compounds. High rate dischargeability of Co-free alloys at I = 1 A/g were twice higher than ones containing cobalt.

Introduction

Sample synthesis and crystal structure of parent alloys

Summarized electrochemical properties for the electrodes

Conclusion