Aluminum corrosion and dissolution behavior as anode in aluminum – air battery

The self-corrosion of aluminum anodes is one of the key issues that hinder the development and application of low cost and high-energy-density Al-air batteries. Generally, the aluminum metal anode in Al-air battery is continuously consumed during the discharge process. [1] Based on this consideration, the design principle of aluminum anode materials should be to homogenize the material composition and entirety morphology to keep functioning during aluminum stripping rather than ordinary interfacial modification. The negative effects of passivation on the aluminum anode interface are amplified in solid and non-aqueous electrolyte systems. For micro and flexible Al-air batteries, low anodic polarization can be achieved by modifying the micro-morphology of aluminum-based materials to improve the electrical contacting area. [2] The modification of electrolyte plays an important role in eliminating anodic passivation and inhibiting of self-corrosion, as most reactions take place at the solid-liquid interface of aluminum electrolyte. Generally, adding additives to the electrolyte is the most common method. And the frequently-used additives can be classified into inorganic additives and organic additives based on different working mechanisms. Hybrid additives containing both inorganic and organic additives are more effective to synergistically suppress the passivation and self-corrosion by dynamically constructing complex films to active and isolate the interface between aluminum and electrolyte. [3] It has been manufactured for over 60 years and is also readily available. The commercially available grades of Al, 2N5 (99.5% purity) and 4N (99.99% purity) have both been used as an anode. The impurities present in Al anode and the products formed during anode reactions constitute layers that impede the battery performance. [4] However, the 2N5 grade Al is a suitable anode for high power discharge conditions. It has been observed [5] that these commercially available 2N5 and 4N grade Al suffer, in different degrees, with the problems of (i) corrosion yielding the products Al(OH)4− and Al(OH)3, (ii) hydrogen evolution due to these parasitic reactions as given by the equation, Al + H2O + e- → H2 and, (iii) passivation by the formation of an oxide film almost instantaneously when introduced to air or water. Pure aluminum, when used as an anode in the presence of an aqueous electrolyte, corrodes rapidly and undergoes a vigorous reaction to yield hydrogen Zinc is commonly used to reduce the corrosion of the anode by increasing the hydrogen evolution potential. tested Al–Zn alloys as anode and noted that this alloy gave a shorter voltage stabilization time than pure 4N Al.[6] Figure 1. EIS at OCV and discharge at 1mA in different electrolyte concentration. With the increase in the concentration of the electrolyte, the reduction potential of the aluminum oxidation reaction becomes more intense and its chemical corrosion increases. Since pure aluminum is unstable when used as an anode for Al-air batteries, the most common way to extend battery life and reduce corrosion rates is to use Al alloys. A significant number of alloying elements such as Ga, Tl, In, Sn, Zn, Bi, Mn and Mg have been investigated. The outstanding performance of Al alloys in Al-air batteries can be attributed to the comprehensive effect of each individual alloy component. For example, zinc metal (Zn), by increasing the HER potential and reducing hydrogen production, reduces anode destruction, which is a well-known phenomenon. Indium (In) is responsible for the positive change of the anode potential and the increase of the excess hydrogen production potential. In addition, tin (Sn) can increase the dissolution rate of Al in aqueous solutions and reduce the corrosion rate.