Investigation of the cycle stability and diffusivity of hydrogen in the MmNi3.55Mn0.4Al0.3Co0.6Fe0.15 compound

The hydrogen storage alloy MmNi3.55Mn0.4Al0.3Co0.6Fe0.15 was used as a negative electrode in Ni-MH accumulators. The chronopotentiometry, the cyclic voltammetry and the chronoamperometry were applied to characterize the electrochemical properties of this alloy. The obtained results showed that the maximum discharge capacity reaches its maximum of 266 mAh/g after 16 cycles, and then decreases to 220 mAh/g after 40 charge–discharge cycles. The hydrogen diffusion behaviour in this alloy was characterized by a cyclic voltammetry after activation. The value of the hydrogen diffusion coefficient in the MmNi3.55Mn0.4Al0.3Co0.6Fe0.15 compound is equal to 1.95 × 10−9 cm2 s−1, and the value of the charge-transfer coefficient in this alloy is about 0.6. These results showed that compared to the LaNi5 compound, this alloy has a better stability in the alkaline solution, a good reversibility and a good kinetic of the electrochemical reaction. The chronoamperometry shows that the average size of the particles concerned by the electrochemical reaction is about 12 μm.