Effect of magnetic field on the microstructure and electrochemical performance of rapidly quenched La0.1Nd0.075Mg0.04Ni0.65Co0.12 alloy

Rare earth-Mg-Ni-based (RE-Mg-Ni-based) La0.1Nd0.075Mg0.04Ni0.65Co0.12 hydrogen storage alloys were rapidly quenched with and without exerting a 0.18 T static magnetic field and investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) studies and various electrochemical measurements. The results show that all samples hold a two-phase structure consisting of La2Ni7 phase and LaNi5 phase, suggesting that the structure remains unchanged after treatment. Grain refinement, homogeneous composition and increase in La2Ni7 phase abundance are achieved when magnetic field is applied. In comparison to quenched alloys, higher discharge capacities are obtained for the alloys prepared with the aid of magnetic field mainly due to the larger La2Ni7 phase abundance. Cycling stability is improved with increasing quenching rate probably owing to better anti-pulverization ability resulted from refined grain size. Ameliorated electrochemical kinetics of the magnetic field assisted rapidly quenched alloys has been confirmed by potential-step measurements and electrochemical impedance spectroscopy (EIS) tests in accordance with the enhanced electrochemical properties. (C) 2014 Elsevier B.V. All rights reserved.