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

Mg-H₂O₂ semi-fuel cell is a kind of battery with the negative electrode as magnesium metal and the positive electrode as hydrogen peroxide,which is widely used in ocean exploration and energy development.Magnesium electrode has many advantages,such as negative electrode potential,high discharge activity,high energy density,safety,environmental protection,low cost,etc..But in the process of using,pure magnesium is easy to corrosion,hydrogen evolution,lagging effect,negative difference effect and other problems,resulting in a decrease of the utilization rate of the electrode.In addition,the surface of magnesium electrode is easy to form passivation film,so that the activity of anodic discharge decreases.In order to improve the performance of magnesium electrode,the first step is to incorporate an alloying element.Firstly,Li is an active anode material,whose equilibrium electrode potential is more negative than Mg and energy density is higher than Mg.Therefore,Li and Mg are combined to form Mg-Li alloy.Secondly,the size and electronegativity of atoms La and Mg are similar,and La is highly soluble in Mg.Then,the tafel polarization curve of oxidation curve,constant current and constant voltage oxidation curve,AC impedance spectroscopy and corrosion weight-loss method for Mg-8Li,Mg-8Li-0.5La and Mg-8Li-1La alloy anode in simulated seawater?0.7 mol?L^-11 NaCl?solution for performance study,and comparing with Mg.The surface of the electrodes is characterized by scanning electron microscopy?SEM?and the composition of the discharge products is analyzed by x-ray diffraction?XRD?.The results show that the active order of the electrode in 0.7 mol?L^-1NaCl solution:Mg<Mg-8Li<Mg-8Li-0.5La<Mg-8Li-1La,and Li and La also improve the current efficiency of the Mg electrode.In order to improve the performance of the magnesium and magnesium alloy electrodes further,a method of adding an additive to the electrolyte is employed.Using the same method to explore the electrochemical performance of electrodes in 0.7 mol?L^-11 NaCl solution with additive of hexamethylenetetramine(C₆H₁₂N₄)and sodium dodecyl benzene sulfonate(C₁₈H₂₉NaO₃S),respectively.It was found that for the Mg electrode,the optimum concentration of hexamethylenetetramine and sodium dodecyl benzene sulfonate is 0.8mmol?L^-1;For Mg-8Li,Mg-8Li-0.5La and Mg-8Li-1La alloy electrode,the optimum concentration of hexamethylenetetramine is 1.0 mmol?L^-1,and the optimum concentration of sodium dodecyl benzene sulfonate is 0.5 mmol?L^-1.After adding two kinds of additives in electrolyte,the discharge current densities of Mg,Mg-8Li,Mg-8Li-0.5La and Mg-8Li-1La electrodes increase,the self-corrosion rate decrease,and the"lag effect"is improved.Therefore,it means that both hexamethylenetetramine and sodium dodecylbenzene sulfonate play a benefical role both in the process of discharging to have the effect of the"activation",and in the process of corrosion for a long time to have the"corrosion"effect.