Mn in misch-metal based superlattice metal hydride alloy – Part 1 structural, hydrogen storage and electrochemical properties

• The various properties of misch-metal superlattice alloys were studied.
• Mn partially substituting Ni promotes formation of AB5 phase.
• Mn decreases hydrogen storage capacities and degrade the surface catalytic ability.
• Mn adversely affects the cycle stability and high rate dischargeability.
• Magnetic susceptibility confirmed the Ni in the surface oxide as catalyst.

The structural, gaseous phase hydrogen storage, and electrochemical properties of a series of Mn-modified misch-metal based superlattice metal hydride alloys were investigated in part one of this two-part series of papers. X-ray diffraction analysis showed that these alloys are all multi-phased compositions with different abundances of AB2, AB3, A2B7, AB4, and AB5 phases. Substitution of Ni in the B-site by Mn promotes AB5 phase formation and decreases both gaseous phase and electrochemical capacities due to the reduction in the abundance of main hexagonal A2B7 phase. AC impedance and magnetic susceptibility measurement were employed to characterize the surface of Mn-free and Mn-modified alloys and show deterioration in surface catalytic ability as the Mn-content increases. Mn-modification adversely affected misch-metal based superlattice metal hydride alloy properties such as phase homogeneity, capacity, cycle stability, high-rate performance, and surface reaction.