Corrosion And Electrochemical Behaviors Of Aluminum In Alkaline Methanol-water Mixed Solutions

Aluminum is a very attractive anode material for energy storage and conversion because of its negative standard electrode potential,high theoretical capacity, abundance in nature and low price.However,in neutral solutions,the surface of aluminum tends to form passive film and become inactive.In acid or alkaline solutions,aluminum is an active anode,but undergoes serious self-corrosion with the evolution of large amounts of hydrogen gases.The above problems must be solved for aluminum to be commercially used in batteries.There are two ways to solve the problem.One is to dope aluminum with other elements.The second is to modify the electrolyte by adding inhibitors,additives or complexing agents in order to make the electrolyte less corrosive.In this dissertation,the history of the usage of aluminum in electrochemical batteries as well as the development situation of various kinds of aluminum batteries was reviewed.Then,the author introduced a new electrolyte system based on potassium hydroxide methanol solutions.In this medium,aluminum is electrochemically active due to the use of alkali and hydrogen evolution is inhibited because of the substitution of methanol for solvent water.However,aluminum still displays larger corrosion rates in the potassium hydroxide methanol solutions with relatively high water contents,and the passive phenomenon occurs for the aluminum anode discharged at relatively large current density.In this work,the effects of different inhibitors were investigated.In the third chapter,the effects of Na₂SnO₃ on the corrosion and anodic dissolution behaviors of pure aluminum in 4 mol·L^-1KOH methanol-water mixed solutions with various methanol/water volume ratios were investigated.The experimental results indicated that the addition of stannate greatly inhibited the corrosion of aluminum in the 4 mol·L^-1KOH methanol-water solution by the deposition of tin with a higher hydrogen evolution potential on the electrode surface, and in the electrolytes with higher stannate contents the inhibition effect decreased due to the occurrence of some cracks on the tin deposition film.In the 4 mol·L^-1KOH methanol-water solution with 20%water the electrolyte system with 0.0015 mol·L^-1 stannate provided larger inhibition efficiency.The results of galvanostatic discharge showed that the discharge of aluminum in the Na₂SnO₃-containing 4 mol·L^-1KOH methanol-water solutions was obviously improved,and the improvement effect enhanced with the increase of stannate content.It was noted that the aluminum anode stably discharged for more than 50 h at 30 mA·cm^-2in the 4 mol·L^-1KOH methanol-water solution with 30%water and 0.02 mol·L^-1Na₂SnO₃.In the fourth chapter,the effects of ZnO and hydroxytryptamine(HT)on the electrochemical behavior of aluminum in the 4 mol·L^-1KOH methanol-water mixed solution with 40%water were investigated.The addition of ZnO could obviously inhibit the corrosion of aluminum in the 4 mol·L^-1KOH methanol-water solution,and its inhibition effect was enhanced in the HT-containing KOH solution.The results of EIS and SEM revealed that ZnO produced the inhibition effect by the formation of a zinc deposit layer on the surface of aluminum,and the cooperative effect of ZnO and HT improved the deposit of zinc.