Effect of electrolytes on electrochemical properties of MmNi(5)-based hydrogen storage alloy

Abstract

The effect of electrolytes on the electrochemical properties of MmNi(3.68)Co(0.72)Mn(0.43)Al(0.17) hydrogen storage alloy electrodes has been investigated at 303 K and 273 K. Three electrolytes (EL1, EL2, EL3) were obtained by adding 2 wt%, 4 wt% and 6 wt% LiOH into the original electrolyte EO (6 M/ L KOH), respectively. The results indicate that the addition of LiOH improves the discharge capacity and cycle life at 303 K and 273 K. The highest maximum capacity and capacity retention (after 50th cycles) have been observed in electrolyte EL2. However, the high-rate dischargeability (HRD) decreases gradually from EO to EL3 at the two temperatures because of the addition of LiOH. The corrosion current I-corr from Tafel Polarization curves (TP) and the resistance of the oxide layer R-ol from electrochemical impedance spectroscopy (EIS) indicates that the alloy electrode worked in EL1 has a better anti-corrosion ability. The real surface area of the electrodes estimated with EIS analysis, decrease from 51.95 cm(2) in EO to 15.6 cm(2) in EL2, but increase to 31.59 cm(2) in EL3 after being fully activated. The additional LiOH improves the anti-pulverization ability of alloy powders, delay the loss of active elements within the alloy electrode, resulting in an inproved capacity retention of alloy electrode. Meanwhile, the electrochemical kinetics analysis suggests that the charge-transfer reaction at the interface of electrode surface and electrolyte is the rate-determining step when tested at 303 K and 273 K.