Effects of Co Substitution for Ni on Microstructures and Electrochemical Properties of LaNi3.8 Hydrogen Storage Alloys

The effects of Co partial substitution for Ni on the microstructures and the electrochemical properties of the LaNi3.8-type phase LaNi3.8-xCox (x=0.0, 0.2, 0.4, 0.6) alloys were systematically studied. All the alloys mainly consist of LaNi5-type phase, rhombohedral Ce5Co19-type phase and hexagonal Pr5Co19-type phase. With increasing Co content, the relative abundance of each phase changes while the cell volume increases monotonously, which lower the hydrogen desorption pressure down to the desirable range (0.01~0.1 MPa) for hydride electrode of Ni/MH battery. All the Co-containing alloys display an enhanced cycle ability compared to LaNi3.8 alloy. The LaNi3.4Co0.4 alloy has the biggest discharge capacity, which is consistence with the solid hydrogen desorption capacity of the alloy. The LaNi3.6Co0.2 alloy exhibits the best rate performance corresponding to its maximum exchange current density (Io) and minimum charge transfer resistance (Rct).