Corrosion And Electrochemical Behaviors Of Aluminum In Alkaline Media

Aluminum is an attractive anode material for electrochemical energy storage and conversion because of its high specific capacity,very negative standard electrode potential,environmentally benign characteristics and almost unlimited reserves. Among several investigated aluminum batteries systems,alkaline aluminum batteries display excellent discharge performance especially at high discharge rates. However,in alkaline solutions aluminum anode undergoes self discharge with the production of large amount of hydrogen gas.This destructive self corrosion results in unacceptably high-energy loss during standby and gives rise to the safety problem in the use of batteries.The mentioned problem must be solved to make alkaline aluminum batteries commercially available.In this dissertation,the corrosion and electrochemical behaviors of aluminum have been investigated in a new electrolyte system based on potassium hydroxide methanol solutions with or without additives in detail.In addition,the electrochemical behavior of aluminum anode was also probed in a novel KOH-ionic liquid-water electrolyte.In the first and second chapters of 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 firstly reviewed.Then,the author introduced the research development on the corrosion electrochemistry of pure aluminum and aluminum alloy anodes,including corrosion mechanism and solution phase inhibitors.The general research ideas and experimental details of this dissertation were subsequently described.In the third chapter,the corrosion and electrochemical behaviors of pure aluminium in alkaline methanol solutions have been investigated.The results of hydrogen collection experiments showed that aluminium has a lower corrosion rate in alkaline methanol solutions compared to water based solutions and that the corrosion rate increases with increasing water content of the solution.Polarization and galvanostatic discharge experiments showed that there is a wide potential window of electrochemical activity and a better discharge performance in the alkaline methanol solutions with certain amount of water.Scanning electron microscopy(SEM) and energy dispersive analysis of X-ray(EDAX) showed that the passivation in the later stages of discharge in alkaline methanol solutions at relatively high current densities is due to the formation of a dense Al(OH)₃ layer on the surface of the anode.In the fourth chapter,the electrochemical dissolution of pure aluminum in alkaline KOH methanol solution was investigated by electrochemical impedance spectroscopy(EIS).Models of EIS were proposed based on the circuit model and the electrochemical kinetics,respectively.Then the Faradic admittance was expressed by the equivalent circuit elements and the partial differentials of state variables in the electrode reactions,respectively.The values of state variables and kinetic parameters of the element reaction steps were solved from the experimental data.Finally,the electrochemical kinetic mechanism on the anodic dissolution of aluminum was discussed according to the above experimental results.In the fifth chapter,the corrosion and electrochemical behaviors of aluminum in inhibited and uninhibited 4 mol dm^-3 KOH methanol solutions with 40%water content were investigated by means of hydrogen collection,polarization curve, galvanostatic discharge and EIS.The results of hydrogen collection and electrochemical experiments showed that the addition of ZnO can obviously inhibit the corrosion of aluminum in the 4 mol dm^-3 KOH methanol solution,and its inhibition effect can be enhanced in the hydroxytryptamine(HT)-containing KOH solution.The results of SEM and EDAX revealed that ZnO produces the inhibition effect by the formation of a zinc deposit layer on the surface of aluminum,and the cooperative effect of ZnO and HT may improve the deposit of zinc.The results of galvanostatic discharge indicated that aluminum can present good electrochemical activity in the 4 mol dm^-3 KOH methanol-water solution with 0.2 mol dm^-3 ZnO and 1.0 mL L^-1 HT.In the sixth chapter,the corrosion and anodic dissolution behaviors of aluminum in Na₂SnO₃-containing 4 tool dm^-3 KOH methanol solutions with 20% water content were investigated by means of hydrogen collection,polarization curve, galvanostatic discharge,SEM and EDAX.The experimental results indicated that the addition of stannate greatly inhibits the corrosion of aluminum in the 4 mol dm^-3 KOH 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 decreases due to the occurrence of some cracks on the tin deposition film.The results of galvanostatic discharge showed that the discharge of aluminum in the Na₂SnO₃-containing 4 mol dm^-3 KOH methanol-water solutions is obviously improved,and the improvement effect enhances with the increase of stannate content.It was noted that the aluminum anode presents a very flat discharge plateau at relatively low potentials in the electrolyte with 0.01 mol dm^-3 Na₂SnO₃ at 20 mA cm^-2.In the last part of this dissertation,the electrochemical behaviors of aluminum in KOH-ionic liquid-water solutions with variable volume ratios of water and the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate(BMIMBF₄) were for the first time investigated by means of hydrogen collection,polarization curve, galvanostatic discharge and EIS.The results of hydrogen collection experiments showed that aluminum has low corrosion rate in KOH-BMIMBF₄-H₂O solutions, and the corrosion rate decreases with increase in BMIMBF₄ content in the electrolytes.The results of electrochemical experiments revealed that aluminum is electrochemically active over a very wide potential window in the KOH-BMIMBF₄-H₂O solutions,and its electrochemically kinetic mechanism is similar to that in the corresponding aqueous solution;the increase in KOH and water contents in the electrolytes may improve the anodic dissolution performance of aluminum.It was found that aluminum presents excellent galvanostatic discharge performance in the 2.0 mol dm^-3 KOH BMIMBF₄-H₂O mixed solution with 60% water.