Electrochemical Performances Research Of Mg-Li-Al-La Alloy As The Anode Material

Magnesium lithium alloys systems have the advantages of negative standard electroreduction potentials, high discharge activity, high energy desity,environmentally acceptability, safety in the seawater and lower price, therefore,magnesium lithium alloys show excellent performances as ideal anode materials for chemical power sources. Magnesium lithium alloys have been widely used in many areas, for example, they can be used as anodes of magnesium-hydrogen peroxide semi-fuel cell. However, as the anode materials, magnesium lithium alloys also show some drawbacks which lead to the limits for their application. Such as, magnesium lithium alloys undergo parasitic corrosion reactions or self-discharge, resulting in the reactive power consumption of the electrode, and thus the utilization rate of the anodes is decreased. Besides, magnesium lithium alloy electrodes are easier to cause"negative difference effect", as the hydrogen evolution rate increase with the increase of discharge voltage, resulting in a loss of efficiency of anodes less. The discharge activity of the anodes declines because of the formation of the passive oxide films on the alloy surface. In order to enhance the electrochemical behaviors of magnesium lithium alloy anodes,there are two methods to improve their electrochemical performance. One is to raise the content of the element of Li, the second is to add the additive to the electrolyte. Both methods can inhabit the fonnation and accelerate the elimination of oxide layers and improve the corrosion resistance. The obtained results provide useful information for the development of high performance magnesium based alloy anodes.The electrochemical performances of Mg-5Li-3Al-1La and Mg-8Li-3Al-1 La alloy electrodes were investigated in the 0.7 mol L-1 NaCl solution. The main test methods include potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), potentiostatic oxidation, scanning electron microscopy (SEM)and X-ray diffraction (XRD). The results show that Li activated Mg-Li-Al-La alloy and obviously improved its discharge activity. At the same time, the current efficiency is also improved, which means that the using rate of alloys is enhanced.This paper also studied the effects of the additives of sodium fluoride and hexamethylenetetramine on the electrochemical performances of the electrodes, and chose the best concentration of additive to make the electrodes to achieve exceedingly good discharge performance. For the Mg-5Li-3Al-1La electrode, the optimal concentration of NaF is 1.0 mmol L-1, and the optimal concentration of hexamethylenetetramine is 0.8 mmol L-1. For the Mg-8Li-3Al-1La electrode,the optimal concentration of NaF is 2.0 mmol L-1, and the optimal concentration of hexamethylenetetramine is 1.0 mmol L-1. When sodium fluoride and hexamethylenetetramine were added as the electrolyte additives, the electro-oxidation behaviors of the electrode were improved, and they may play the "activation"function on the electrode. At the same time, the corrosion rate of the electrode was lowered, and they may also play a "corrosion resistant" function on the electrode.