Effect of Mn Element on the Structures and Properties of A2B7-Type La–Y–Ni-Based Hydrogen Storage Alloys
Anqiang Deng, Yong‐Chun Luo, Jianfei Zhou, Yunding Xie, Yuan Yuan, Xiaoyan Kang, Bingjin Shen, Haimin Zhang
Abstract
The structures, hydrogen storage behaviors and electrochemical properties of Y0.75La0.25Ni3.5−xMnx (x = 0–0.3) alloys were analyzed by X-ray diffraction, Neutron powder diffraction, pressure–composition isotherms and electrochemical tests. All alloys have a multiphase structure. With the increase in Mn content, the Gd2Co7-type phase of the alloys gradually transforms into the Ce2Ni7-type phase; the Mn atom mainly occupies the Ni sites in the [AB5] subunit and the interface between the [AB5] and [A2B4] subunits; the V[A2B4]/V[AB5] continuously decreases from 1.045 (x = 0) to 1.019 (x = 0.3), which reduces the volume mismatch between [A2B4] and [AB5] subunits. The maximum hydrogen absorption of the series alloys increases first and then decreases, and the addition of Mn effectively promotes the hydrogen absorption/desorption performance of the alloys. The maximum discharge capacity of the alloy electrodes is closely related to their hydrogen storage capacity at 0.1 MPa and hydrogen absorption/desorption plateau pressure. The cyclic stability of all the Mn-containing alloy electrodes is improved clearly compared to that of Mn-free alloy electrodes, because the volume mismatch between the [AB5] and [A2B4] subunits of the alloys becomes smaller after the addition of Mn, which can improve the structural stability and reduce the corrosion of alloys during hydrogen absorption/desorption cycles. When the Mn content is between 0.1 and 0.15, the Ce2Ni7-type phase of the alloys has high abundance and the alloy electrodes exhibit excellent overall performance.