Effect of Co substitution for Ni on the structural and electrochemical properties of La2Mg(Ni1−xCox)9 (x = 0.1–0.5) hydrogen storage electrode alloys

• DOI: 10.1016/j.electacta.2004.08.004
• Publication Date: 2004-09-14T13:15:35Z
• Authors: B. Liao; Y.Q. Lei; L.X. Chen; G.L. Lu; H.G. Pan; Q.D. Wang
• Keywords: 01 natural sciences; 0104 chemical sciences

Abstract The effect of partial substitution of Co for Ni on the structure and electrochemical properties of the thus formed La 2 Mg(Ni 1− x Co x ) 9 ( x = 0.1–0.5) quaternary alloys was investigated. All alloys are consisted of a main phase with hexagonal PuNi 3 -type structure and a few impurity phases (mainly La 2 Ni 7 and LaNi). The increase of Co content in the alloys leads to an increase in both the cell volume and the hydride stability, and leads to a noticeable decrease in cell volume expansion rate (Δ V / V ) on hydriding. The discharge capacity of the alloys at 50 mA/g increases slightly with the increase of Co content and passes though a maximum of 404.5 mAh/g at x = 0.2. As the Co content increases, the high-rate dischargeability of the alloy electrodes at 800 mA/g (HRD 800 ) decreases sharply from 72.8 ( x = 0) to 24.5% ( x = 0.5), yet the decrease of HRD 800 of the alloy electrodes with lower Co substitution (with x ≤ 0.2) is much milder. The slower decrease of HRD 800 (from 72.8 to 64.2%) of the alloys with x from 0 to 0.2 is mainly attributed to the decrease of eletrocatalytic activity for charge-transfer reaction, the more rapid decrease of the alloys with x > 0.2 is mainly attributed to the lowering of the hydrogen diffusion rate in the bulk of alloy. The cycling capacity retention rate ( S 100 ) of the alloys increase greatly with increasing of Co content, increasing from 60.2% for the alloy with x = 0 to a much higher value of 87.9% for the alloy with x = 0.5. The improvement in cycling stability is attributed to the lower cell volume expansion on hydriding.