Effect Of The Microstructures Of Mg Anode And Oxygen Anion Corrosion Inhibitor On The Performance Of Mg-air Battery

Energy is an important material base of safeguarding the human survival and society development.However,the traditional energy,such as natural gas,the petroleum and coal,are greatly consumed in the last century,and the problem of lacking of energy cannot be avoided any more in today’s world.Meanwhile,the use of traditional energy results in serious environmental pollution,so the developing of new green energy is looming ahead.Metal-air battery is considered as an ideal substitution of traditional energy because of its numerous advantages,such as low cost,no poisonous,no pollution,high theoretical voltage and high specific energy.Mg is the eighth element on earth reserves.Because of the low density(1.74 gmL^-1),high electrochemical activity and high electrochemical equivalent(2.20 Ahg^-1),Mg is an ideal anode material for metal-air battery.But Mg alloys are very easy to corrosion in neutral salt solution due to the high electrochemical activity of Mg,and the anode efficiency of Mg-air battery is very low.Moreover,a discharge product film which mainly consist of magnesium hydroxide would be produced on the surface of the Mg anode during the discharge process of Mg-air battery.And serious voltage delay phenomenon would appear during the intermittent discharge process.In this paper,the effect of microstructure and oxygen anion corrosion inhibitor on the electrochemical performance of Mg alloy were investigated by polarization curve,electrochemical impedance spectroscopy（EIS）and hydrogen evolution test.The effect of Mg anode microstructure and using oxygen anion corrosion inhibitor as electrolyte additive on the discharge performance of Mg-air battery were investigated by continuous discharge and intermittent discharge test.The morphology and composition of discharge product film on the Mg anode surface were investigated by scanning electron microscope（SEM）,laser scanning confocal microscopy（LSCM）and energy disperse spectroscopy（EDS）.The main research contents of this paper are shown as follows:（1）AZ31 Mg alloy sheets with different grain sizes were obtained through cold rolling and the followed annealing process,and the performance of the Mg-air battery based on the processed AZ31 alloys was also investigated.With the increasing density of twins,the electrochemical activity of the Mg anode and the discharge voltage of the battery increased gradually,and the voltage delay time decreased gradually.（2）The effect of texture on the corrosion behavior of Mg alloy and the performance of Mg-air battery were investigated.The TD-ND plane exhibited a better corrosion resistance than the TD-ND plane when the alloy had a surface with mechanical roughening.The Mg-air battery based on the TD-ND anode had a higher anode efficiency compared with that of the Mg-air battery based on the RD-TD anode.（3）AZ31 Mg alloy sheets with different grain sizes were obtained through cold rolling and a subsequent annealing process,and the performance of the Mg-air batteries based on the processed AZ31 alloy sheets were also investigated.The electrochemical activity and corrosion resistance of AZ31 Mg alloy increased with the decreasing grain size.The discharge voltage and anodic efficiency of the Mg-air batteries also increased with the decreased grain size.（4）The addition of Li₂CrO₄ could effectively improve the corrosion resistance of AZ31 Mg alloy in 3.5 wt% NaCl solution,and the corrosion current density of the AZ31 Mg alloy in 3.5 wt% NaCl +0.1 wt% Li₂CrO₄ solution was only about 1/7 times of that in 3.5 wt% NaCl solution.The addition of Li₂CrO₄ could improve the anode efficiency and the morphology of discharge product on the Mg anode surface effectively.（5）Both phosphate and vanadate enhanced remarkably the corrosion resistance of AZ31 Mg alloy in 0.6 M NaCl solution.A phosphate and vanadate protect film would be produced on the alloy surface after adding Na₃PO₄?12H₂O and NaVO₃ which improved the corrosion resistance of the alloy.But the phosphate protect film was more complete,so phosphate showed a better inhibitting effect than vanadate.Both phosphate and vanadate had a better effect in improving the anodic efficiencies under intermittent discharge compared with those under continuous discharge.This indicates that the addition of phosphate and vanadate reduced the anodic efficiency loss in the no-discharge periods of the intermittent discharge tests.Compared with NaVO₃,Na₃PO₄?12H₂O had a more significantly effect on the anodic efficiency.