Electrochemical Behavior Of Magnesium-Germanium Based Alloy In Sodium Chloride Solution

Electrochemical oxidation reactions of magnesium are prone to occur because the standard electrode potentials of magnesium in acidic and alkaline media are-2.37 V and-2.69 V respectively.As an ideal anode material for chemical power sources,Mg has an appropriate electrochemical equivalent(2.20 Ah·g^-1).However,magnesium anodes also have some problems.Self-corrosion hydrogen evolution reactions during discharge result in the low utilization of anodic materials and a"hysteresis effect"during the initial discharge,which leads to the battery starting slowly.The addition of alloying elements to the magnesium and corrosion inhibitors to the electrolyte can effectively reduce the self-corrosion rate of the anode while increase its overall discharge performance.Germanium can form Mg₂Ge intermetallic compounds with magnesium.In contrast,germanium can increase the hydrogen overpotential and reduce the self-corrosion hydrogen evolution reaction.The energy density of germanium in magnesium alloys is 7.382 Wh cm^-3which is only prior to Pb in the same family,so the addition of germanium element is very suitable when magnesium alloys act as the anodic materialIn this dissertation,open-circuit potential,potentiodynamic scanning,electrochemical impedance spectroscopy,chronopotentiometry and other electrochemical testing techniques were used,as well as weightlessness method,hydrogen evolution test combined with X-ray diffraction?XRD?and scanning electron microscopy?SEM?to characterize the microstructure of alloy elements.The electrochemical behavior of Mg-Ge binary alloy and Mg-Al-Ge ternary alloy in sodium chloride solution was studied by element action,solid solution treatment and adding corrosion inhibitor in the electrolyte.Mg-Al-Ge ternary alloy was used as anode,MnO₂ as cathode,octyldecyl glucoside+sodium silicate as corrosion inhibitor.The electrolyte was assembled into a magnesium air battery to test its comprehensive discharge performance.The main findings of this paper are as follows:The microstructure and electrochemical properties of Mg-xGe?x=0.1,0.3,0.5,0.7,1,3 wt%?binary alloys were studied.The results show that as-cast Mg-Ge binary alloys mainly consist of a-Mg and eutectic structure?a-Mg+Mg₂Ge?.With the increase of Ge content,the distribution of Mg₂Ge phase in the alloy gradually changes from point-like or band-like dispersion to band-like network distribution.The results of constant current hydrogen evolution test show that the corrosion of Mg-0.7Ge alloy can be effectively inhibited by adding Ge element to form a network precipitate phase,but the galvanic corrosion of Mg-0.7Ge alloy will increase with the increase of Ge content,so the corrosion resistance of Mg-0.7Ge alloy is the best.The open-circuit potential and discharge potential of Mg-Ge binary alloys become negative gradually with the increase of Ge content,which indicates that the electrochemical activity of Mg-Ge binary alloys can be improved with the increase of Ge content.Among them,Mg-3Ge alloy has the best comprehensive discharge performance.Its discharge curves are smooth at current densities of 5and 10 mA cm^-2,but oscillate at current densities of 20,30 mA cm^-2 due to the formation and spalling of discharge corrosion products.The microstructure and electrochemical properties of Mg-xAl-yGe?x=3,6wt%,y=1,3,5wt%?alloys were studied.The results show that as-cast Mg-Al-Ge ternary alloys consist of a-Mg,Mg₁₇Al₁₂ and Mg₂Ge phases.With the increase of Ge content,the morphology of Mg₂Ge phase changes from banded to"alien writing"and finally to regular block.Solid solution Mg-Al-Ge three alloy consists of alpha-Mg and Mg₂Ge phase.Solid solution treatment did not change the morphology of Mg₂Ge phase.The corrosion test results show that the corrosion resistance of as-cast alloy is better than that of solid solution alloy,because the dissolution of Al element after solid solution treatment promotes the precipitation of Ge element and reduces the corrosion resistance of matrix.When the current density is 5,10,20 mA cm^-2,the discharge potential of as-cast alloy is close to that of as-cast alloy.When the current density is 30 mA cm^-2,the discharge potential of as-cast alloy is negative to that of as-cast alloy,which is related to the change of matrix elements and precipitated phase composition after solution treatment.The addition of Al element can improve the discharge efficiency of Mg-6Al-1Ge alloy,because the addition of Al element can improve the corrosion resistance and reduce the self-corrosion hydrogen evolution of the alloy.The effects of corrosion inhibitors?octdecyl glucoside,octdecyl glucoside+sodium tungstate,octdecyl glucoside+sodium silicate?on the electrochemical properties of Mg-6Al-1Ge?AG61?alloy were investigated.The results showed that the corrosion resistance of AG61 alloy was improved by the three inhibitors.The inhibition efficiency of octdecyl glucoside and sodium silicate was 95.88%.At the current densities of 5,10,20,30 mA cm^-2,octdecyl glucoside decreased the discharge activity of the alloy.Octdecyl glucoside+sodium silicate and octdecyl glucoside+sodium tungstate all increased the discharge activity of the alloy.Especially,octyl decyl glucoside+sodium silicate could effectively reduce the discharge potential of the alloy by about 50 mV and 4 mV.The discharge efficiency of different current densities was 20.58%,11.88%,8.26%and 16.59%higher than that without corrosion inhibitor.Octdecyl glucoside+sodium silicate can not only improve the corrosion resistance of AG61 alloy,but also improve its discharge efficiency.It is a green and efficient corrosion inhibitor.MnO₂ air electrode was prepared.As-cast AG61 alloy was used as anode,3.5wt.%NaCl solution was added as electrolyte,AZ31 as anode,and 3.5wt.%NaCl solution was used as electrolyte.The results show that as-cast AG61 alloy and octdecyl glucoside+sodium silicate are good anode materials and corrosion inhibitors for magnesium-air batteries.The peak power of the battery can reach83 mW cm^-2,and the charging time can reach 32.7 h and 9.6 h at 10,30 mA cm^-2current densities,respectively.