The Electrochemical Behavior Of AZ31B Magnesium Alloy In Composite Electrolyte

Magnesium is an active light metal, it has many advantages such as being non-toxic, pollution-free, extensively sourced and so on, as a kind of electrode material, it is advantaged in high theoretical capacity, stable discharge potential, wide operating temperature range and so on, which makes the magnesium alloy material highly potential in the domain of battery. However, the drawbacks of magnesium electrode material such as the self-corrosion and negative difference effect induced in aqueous solution, and the occurrence of hysteresis phenomenon during the discharge of electrode, disable it to meet the practical application, which restricts the wide use of magnesium battery in the market, so far, the studies on magnesium battery mainly focus on the electrode material itself and one-component electrolyte, while the electrochemical behavior of negative electrode material of magnesium alloy in the complex electrolyte is rarely reported, thus, the study on the effect of complex electrolyte and addictives on electrochemical behavior of negative electrode material of magnesium alloy is of great importance and practical value.This dissertation firstly compared the electrochemical behavior of negative electrode material of magnesium alloy in the one-component and two-component complex electrolyte, in order to seek the complex electrolyte which has an optimal electrochemical performance. By the use of open circuit potential, linear potential scan, AC impedance test, Tafel polarization curve, constant-current discharge, weight-loss method, scanning electron microscope and other methods, the electrochemical performance of magnesium electrode alloy in the complex electrolyte had been studied, the electrochemical behavior of magnesium electrode alloy in the complex electrolyte and the effect of immersion time on the change of morphology had been investigated. The following findings had been obtained: AZ31 B had been exposed to the electrolyte of MgSO₄-Mg（NO₃）₂ with different molar ratio, the increase in concentration of MgSO₄ drove the open circuit potential to shift towards negative, the complex electrolyte with a molar ratio of 0.7:9.3 had the most negative activated potential and the lowest degree of polarization; the discharge and anti-corrosion of negative electrode material of magnesium alloy can be remarkably enhanced when NaF concentration was 30mmol/L, corrosion rate was reduced by 4.8 times, discharge potential was shifted towards negative by 190 mV, and the delay time was shortened to 0.72 s, when the concentration of sodium hexametaphosphate was 30mmol/L, the density of galvanic corrosion was reduced, which inhibited the corrosion, and when the concentration was 0.1mol/L, the most negative discharge potential was-1.70 V with the minimal potential drop and delay time. The corrosion current density increased when the concentration of sodium dodecyl benzene sulfonate was 0.05mmol/L, it decreased when the concentration increased to 0.15mmol/L, it had a repeated changing effect on the corrosion-resistance of electrode. The addictive NaHCO₃ had a poor effect on the corrosion-inhibition in the single MgSO₄ solution, while in the complex electrolyte, its effect on the corrosion-inhibition had been markedly improved, and when the concentration was 20mmol/L, the corrosion current density was the lowest, which was lowered by five times to 0.47×10^-5·A·cm^-2,the delay time was shortened to below 0.7s.This dissertation finally discussed the effect of binary complex addition on the electrochemical performance of the electrode, it was shown by the result that, the binary complex additives compounded with NaF-NaHCO₃ had the most positive activated potential, the magnesium electrode was extended in its passivation range, the polarized current was reduced, having a greater impedance as compared with the impedance generated when either of them was added, thus, it can be regarded as an ideal binary compound corrosion inhibitor; the compounded NaF-SHMP CP curve had the most negative discharge potential and the lowest potential drop, and with a short delay time, the overall electrochemical performance had been improved.