| Facing the shortage of energy and environmental pollution,mankind urgently needs to develop a new green energy resource.Being high energy density,safe,no pollution,and low cost,Al-air batteries have a great commercial potential value as an energy storage power source.However,both the low electrochemical activity and poor corrosion resistance of Al anode during the discharge are one of the bottleneck problems that restrict the large-scale commercial application of Al-air batteries.In this paper,the effects of Al anode purity,microalloy elements(Mg,Zn,Mn,Ga,and Sn)addition and the modification of waste cans on Al anode on the corrosion resistance,electrochemistry,and discharge behavior are investigated,aiming to solve the bottleneck problem of Al anode with poor corrosion resistance and low electrochemical activity during the discharge.The Al anodes were prepared by melting and casting.The microstructures of Al anode were characterized by SEM,EDS and XRD.The corrosion resistance of Al anode in 4M Na OH solution was studied by the drainage and weight-loss methods.The electrochemical activity of Al anodes was analyzed by open circuit potential(OCP),polarization curve and electrochemical impedance spectroscopy(EIS).The discharge behavior of Al anode was studied by the constant current discharge of Al-air batteries.The experimental results are followed as:(1)Al anodes with different purity exhibit a large difference in the corrosion resistance,electrochemical activity and discharge performance.With the increase in purity,the hydrogen evolution and weight-loss of Al anode are significantly reduced.The Fe/Si impurity content is reduced with the purity of Al anode,leading to a decrease in the amount of the second phase particles containing Fe/Si impurity elements.As a result,the hydrogen evolution decreases with the increase of Al purity because the second phase particles play a role of active sites for hydrogen evolution.In addition,the weight-loss of Al anode decreases with the increase of Al purity.It attributes to a decrease in the number of micro cell corrosion reactions between the second phase particles and the Al matrix.With the decrease of the Al purity,the electrochemical activity is significantly improved,due to the depolarization effect of the second phase containing Fe/Si impurity elements.As a comparison,the discharge efficiency is significantly improved with the increase of Al purity.It results from the improvement of the corrosion resistance of Al anode.(2)Within the content range of microalloy elements studied(Mg: 0.1-1 wt.%,Zn:0.1-1 wt.% and Mn: 0.1-2 wt.%),the microalloy elements Mg,Zn and Mn can effectively reduce the amount of hydrogen evolution of Al anode.The introduction of Mg and Mn elements suppress hydrogen evolution due to their modification effect on the second particles containing Fe/Si impurities.The hydrogen evolution inhibited by Zn element addition attributes to the fact that Zn element dissolves into the Al matrix and reduces the potential difference between the phase and the Al matrix.The weight loss of Al anodes containing Mg and Zn element increases may be related to the accelerated peeling of corrosion product.On the contrary,the Mn addition effectively reduces the weight loss of Al anodes.It attributes to two factors: one is the dissolution of Mn element into the Al matrix increases the electrode potential of the matrix;the other is the modification of the Fe/Si impurity phase by the Mn element reduces the electrode potential of the impurity phase.The combined effect of the two factors reduces the potential difference between the matrix and the impurity phase.,thereby improves the corrosion resistance of Al anodes.Mg,Zn and Mn elements addition can improve the electrochemical activity of the Al anodes,attributing to the fact that Mg,Zn and Mn elements are dissolved into Al matrix and destroy the dense oxide film on the surface of Al anode.Based on the analysis of hydrogen evolution,corrosion resistance and the electrochemical activity,the appropriate addition of Mg,Zn and Mn in Al anode(e.g.0.1 wt.%)exhibit the best discharge efficiency is the best.Compared to pure Al anode,the addition of Ga and Sn elements deteriorates the hydrogen evolution and weight-loss,but significantly improve the electrochemical activity of Al anode.it is attributed to the activation effect on the oxide film by the dissolution of Ga element into Al matrix and undissolved Sn particles,respectively.Considering the comprehensive effects of corrosion resistance and electrochemical activity,Ga and Sn addition can improve the discharge efficiency of the battery to a certain extent.(3)The Al anode prepared by the recycled Al beverage has ability to discharge,accompanying with the fluctuant discharge voltage,much hydrogen evolution and severe weight loss.When Zn element is added into the recycled Al beverage acted as Al anode,the hydrogen evolution can be effectively suppressed and the weight loss decreases.Furthermore,the electrochemical activity of Al alloy is greatly improved.beverage-0.1Zn as Al anode exhibits more stable discharge voltage and higher discharge efficiency than beverage anode. |
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