Effect of vanadium content on electrochemical properties of la-based AB 5-type metal hydride electrodes

Abstract

Commercial La–Ni–Al–Co–Mn–V hydrogen storage alloys have been investigated to examine the effect of non-stoichiometry on the microstructure and electrochemical properties. It is found that for the stoichiometric ‘B’-rich compound, single phase with CaCu 5-type exists. However, for B-poor compounds, there is principally a CaCu 5-type phase with a small amount of V-rich type phase and the amount of V-rich phase reduces with vanadium. With the increase of V y⩽0.1 content, hydrogen storage capacity is enhanced, whereas when y=0.2–0.3 it is decreased. The discharge capacity and cyclability are increased considerably by addition of vanadium in the range 0.02–0.1 with a maximum value at about 0.02%. The decrease of capacity for high V content was also correlated with the amount of V-rich phase. The V-rich phase is consisted of La 0.1Ni 2.6Al 0.2Co 2.0Mn 0.6V 1.3. The improvement of kinetics is due to the catalytic effect, grain boundary diffusion effect or more pronounced alloy pulverization upon cycling. This can be explained because the improvement of capacity for alloys with low V content is due to better kinetics. These alloys have been subjected to analysis by EDS, SEM and XRD. In order to determine the hydrogen storage capacity, the pressure composition isotherms (PCT curves) have been used. The metal hydride electrodes were characterized by galvanostatic cycling test.