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The structures, hydrogen storage behaviors and electrochemical properties of Y_0.75La_0.25Ni_{3.5−<i>x</i>}Mn<i>_x</i> (<i>x</i> = 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 <i>V</i>_[A2B4]/<i>V</i>_[AB5] continuously decreases from 1.045 (<i>x</i> = 0) to 1.019 (<i>x</i> = 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.