Preparation And Electrochemical Performance Of Magnesium-Rare Earth(Ce,Dy) Binary Alloys

Magnesium（Mg）has the characteristics of negative electrode potential,high specific capacity,abundant reserves in the earth’s crust,low cost,and safety and environmental protection.It is one of the most attractive anode materials for chemical power sources such as metal/seawater fuel cells.However,when applied to neutral electrolytes such as seawater,magnesium anodes have serious hydrogen evolution corrosion and polarization problems,resulting in their actual specific capacity and the electrode potential far lower than the theoretical values.Rare-earth element alloying is one of the ways known to effectively alleviate the above-mentioned problems.Researchers have conducted rare-earth alloys on commercial magnesium alloys such as AZ（Mg-Al-Zn）and AM（Mg-Al-Mn）.Its electrochemical performance is significantly improved,but the research is carried out in a multi-element alloy system,so it is difficult to reveal the special mechanism of rare earth elements on magnesium alloy anodes.For this reason,this thesis prepared series of magnesium-cerium（Mg-Ce）and magnesium-dysprosium（Mg-Dy）binary alloys.We researched the effects of cerium and dysprosium on the microstructure,electrochemical performance,and discharge product morphology of magnesium anodes through spectroscopic microanalysis and electrochemical characterization,aiming to provide theoretical support for the design and development of high-performance magnesium alloy anodes for magnesium/seawater fuel cells.The main findings are as follows:Adding an appropriate amount of cerium（0.034～0.174 wt.%）not only improves the utilization rate of the magnesium anode,but also causes the electrode potential to shift negatively.The mechanism of cerium improving the electrochemical performance of magnesium alloys includes:（1）cerium would refine the grains,thereby improving the electrochemical activity of magnesium alloys and reducing the capacity loss caused by the block effect;（2）the addition of cerium is inclined to form a dense product layer on the surface of the alloy,thereby inhibiting the self-corrosion of the magnesium alloy and improving its utilization;（3）The micro-precipitated phase Mg₁₂Ce with uniform distribution is anodic relative to the magnesium matrix,thus the magnesium alloy is effectively activated and the electrode potential is negatively shifted.（4）When the cerium content reaches 0.241～0.542 wt.%,the large-size Mg₄₁Ce₅ precipitates formed in the magnesium matrix as the cathode phase would aggravate the micro-galvanic corrosion of magnesium alloys.And the shedding of the precipitated phases will cause blocky effects,which will reduce the utilization rate of the magnesium anode.Dysprosium can also significantly improve the electrochemical performance of magnesium alloys,and its optimal addition amount is 0.509 wt.%.The reasons for the performance improvement are as follows:（1）Because of the precipitated phase of magnesium-dysprosium alloy is the anode phase compared to the magnesium matrix,it reacts preferentially,forming a multi-layer parallel stacked structure.The product layer has an inducing effect,causing it to cover the entire alloy surface,thereby effectively inhibiting the spread of corrosion and improving the electrochemical performance of the magnesium alloy;（2）Higher valence dysprosium in the oxide layer of the magnesium alloy surface makes it more difficult for electrons to escape from the alloy surface,and inhibits the self-corrosion of the alloy surface;（3）When the addition amount of dysprosium is too high,the content of high-valence dysprosium on the alloy surface will decrease,causing the magnesium alloy’s self-corrosion rate to increase.