Microstructures and electrochemical properties of LaNi3.8−xMnx hydrogen storage alloys

In this paper, the microstructures, hydrogen storage and electrochemical properties of LaNi3.8−xMnx (x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) have been studied systematically. The microstructures were identified by X-ray diffraction (XRD) and scanning electronic microscope (SEM). The results showed that all the alloys were mainly composed of two different phases with the same composition, including the hexagonal Pr5Co19-type phase (P63/mmc) and the rhombohedral Ce5Co19-type phase (R-3m), respectively, but minor phases appeared when x ≥ 0.4. With Mn content increasing, the cell volume increased and the relative abundances of Pr5Co19-type phase and Ce5Co19-type phase were changed, the equilibrium pressure declined gradually and the hydrogen storage capacity increased first and then decreased, and the maximum discharge capacity increased from 209.4 mAh g−1 (x = 0.0) to 268.8 mAh g−1 (x = 0.4) and then decreased to 230.3 mAh g−1 (x = 0.5). Meanwhile, the exchange current density (I0) and the diffusion coefficient (D) were also improved with the addition of Mn, reaching a maximum at x = 0.4.