Investigation of Electrochemical Hydrogen Storage Kinetics of Melt Spun Nanocrystalline and Amorphous Mg2Ni-type Alloy

摘要:

用快淬工艺制备了Mg2Ni型合金，其名义成分为 Mg2Ni1-xCox (x = 0, 0.1, 0.2, 0.3, 0.4)。以XRD、SEM、TEM分析了铸态及快淬合金的结构。用程控模拟电池测试仪测试了合金的电化学贮氢动力学。用电位跃迁法计算了氢在合金中的扩散系数。用电化学工作站测试了合金的电化学交流阻抗谱 (EIS) 和Tafel极化曲线。结果表明，快淬态无Co合金具有典型的纳米晶结构，而Co含量为0.4的快淬态合金具有纳米晶/非晶结构，表明Co 替代Ni可以提高Mg2Ni型合金的非晶形成能力，且快淬态合金的非晶化程度随Co替代量的增加而增加。Co替代Ni显著地提高了合金电化学贮氢动力学。当Co含量从0增加到0.4时，淬速为25 m/s的快淬态合金的高倍率放电能力 (HRD) 从65.3% 增加到75.3%，氢扩撒系数 (D) 从2.22 cm2/s增加到3.34 cm2/s，极限电流密度 (IL) 从247.8 mA/g增加到712.4 mA/g

Abstract:

The Mg2Ni-type Mg2Ni1-xCox (x=0, 0.1, 0.2, 0.3, 0.4) alloys were prepared by melt-spinning technique. The structures of the as-cast and spun alloys were characterized by XRD, SEM and TEM. The electrochemical hydrogen storage kinetics of the as-spun alloy ribbons was tested by an automatic galvanostatic system. The hydrogen diffusion coefficients in the alloys were calculated by virtue of potential-step method. The electrochemical impedance spectrums (EIS) and the Tafel polarization curves were plotted by an electrochemical workstation. The results show that the as-spun Co-free alloy exhibits a typical nanocrystalline structure, while the as-spun (x=0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni facilitates the glass formation in the Mg2Ni-type alloy. The amorphization degree of the as-spun alloys substituted by Co visibly increases with the increase in the amount of Co replacement. The Co replacement for Ni notably improves the electrochemical hydrogen storage kinetics of the alloys. With a growth in the amount of Co replacement from 0 to 0.4, the high rate discharge ability of the as-spun (25 m/s) alloy increases from 65.3% to 75.3%, the hydrogen diffusion coefficient (D) from 2.22 to 3.34 cm2/s and the limiting current density IL from 247.8 to 712.4 mA/g, respectively