Gas phase hydrogen absorption and electrochemical performance of La2(Ni,Co,Mg,M)10 based alloys

The effect of M = In or Al on the hydrogenation behavior of the La2(Ni,Co,Mg,M)10 alloys at room temperature is presented. The ceramic like samples have been prepared by powder metallurgy route using pure Mg- and the La2Ni9−xMx alloy powder precursors. XRD analysis revealed predominantly the CaCu5-type structure for all final alloys. Partial substitution of Co by In in La2Ni8MgCo causes a slight decrease of hydrogen concentration whereas Al addition increases this parameter. The highest hydrogen concentration of 1.87 wt.% has been reached for La2(Ni8Co0.8Al0.2)Mg composition at hydrogen pressure of 10 bar. Indium addition dramatically decreases the middle-plateau hydrogen equilibrium pressure from peq = 0.37 bar (In-free alloy) to peq = 0.06 bar (1.7 at.% In). The electrochemical performance of the studied materials has been characterized using chronoamperometric and chronopotentiometric techniques. The galvanostatic hydrogenation experiments at 185 mA/g discharge rate revealed the largest discharge current capacity of 355 mAh/g for La2(Ni8Co0.8Al0.2)Mg alloy. The relative diffusivity factor of hydrogen (D¯H/a2) varies for the tested materials in the range of (2.0-5.4)·10−5 s−1.