Abstract
In this paper, the electrochemical properties of the MmNi
3.55Mn
0.4Al
0.3Co
0.75 compound, used as negative electrode of Ni–MH accumulator, have been studied and compared to those of the LaNi
3.55Mn
0.4Al
0.3Co
0.75 electrode. Several methods, such as, the chronopotentiometry, the cyclic voltammetry (CV), the chronoamperometry and the electrochemical impedance spectroscopy (EIS) were applied to characterize these electrochemical properties. The discharge capacity of the MmNi
3.55Mn
0.4Al
0.3Co
0.75 compound increases to reach 270
mAh/g after 12 cycles and then decreases to 200
mAh/g after 20 cycles. However, the electrochemical discharge capacity of the LaNi
3.55Mn
0.4Al
0.3Co
0.75 compound reaches its maximum value of 335
mAh/g after 7 cycles and then decreases to 180
mAh/g after 50 cycles. The decrease of the discharge capacity for the two alloys was attributed to the corrosion and the deprecipitation of the alloys in the KOH aqueous solution. A good stability of the discharge capacity can be observed after a number of cycles bigger than 20 and 50, respectively, for the Mm and the La alloys. The charge transfer coefficient and the average hydrogen diffusion coefficient determined by the cyclic voltammetry are 0.35, 0.221, 5.86
×
10
−10 and 2.1
×
10
−10
cm
2
s
−1, respectively, for the MmNi
3.55Mn
0.4Al
0.3Co
0.75 and LaNi
3.55Mn
0.4Al
0.3Co
0.75 alloys. The obtained values of the hydrogen diffusion coefficient
D
H, at 10% of charge of MmNi
3.55Mn
0.4Al
0.3Co
0.75 and LaNi
3.55Mn
0.4Al
0.3Co
0.75 compounds are 6.64
×
10
−10 and 2.7
×
10
−11
cm
2
s
−1, respectively. The chronoamperometry method shows that the size of the particles participating in the electrochemical reaction is about 12 and 31
μm, respectively, for the MmNi
3.55Mn
0.4Al
0.3Co
0.75 and LaNi
3.55Mn
0.4Al
0.3Co
0.75 alloys.