Chaoling Wu

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).

Differential thermo-analysis (DTA) method in strip casting AB5-type hydrogen storage alloys

Abstract In this work, strip casting was introduced, and the necessity of heat treatment was explained from the viewpoint of DTA thermo-analysis. The results showed that: Five exothermic peaks appeared in the DTA curves of LPCNi3.55Co0.75Mn0.4Al0.3 alloy in which the intensity of the second and third peak decreased strikingly with the decrease of cooling rate. It was sensitive to the grain sizes. The intensity of the fourth and fifth peak showed less correlation with cooling rate, and they located in the range of theoretical recrystallization temperature. It was possibly introduced by recrystallization. In addition, segregation and internal stress also contributed to exothermic peaks. All heat variation had finished during the first temperature-rising period of DTA test, which implied that there was no irreversible phase transformation in the hydrogen storage alloys during the whole heated-cooled process. Four kinds of AB5-type hydrogen storage alloys in our work showed similar exothermic characteristics.