| The La0.64Gd0.2Mgo.16Ni3.1Coo.3Alo.1alloy was selected to research and synthesized by vacuum induction melting,then treated by hot alkaline etching and additive.The effects of hot alkaline etching in different times (0～60min) on the microstructure、surface elements and the state、bulk phase chemical components and the electrochemical properties of alloy electrodes were studied by means of SEM、EDS、VSM、XPS、ICP and electrochemical methods. This paper investigated the effects of the particle size of alloy、process time and additive of Yb2O3on the perperties of alloy electrodes.The particle size of alloy had a significant effect on the maximum discharge capacity (Cmax) of alloy electrodes,especially the high rate discharge ability (HRD). The HRD increased with the decrease of particle size, whereas the discharge capacity retention(S100) increased with the increase of the particle size. For original alloy powers, the smaller particle size,the larger specific surface area of the alloy electrodes and more chemical reactions,further leading to the corrosion on the alloy surface.With the decrease of particle size,the Icorr increased,which mean poor corrosion resistance.The results revealed the Io decreased and the polarization resistance increased with the decrease of particle size,and.It has been showed that the optimum particle size is300-500mesh according to the performaces of alloy electrodes.On the above result, the effect of hot alkaline etching on the performance of alloy electrodes was researched. The results showed that Mg、Al、La and Ni elements on the surface of alloy were dissolved or oxidized in different levels through the hot alkaline treatment. And with the increase of process time, the saturation magnetization intensity of alloy increased first and then decreased. When the process time was15min, the saturation magnetization intensity could reach the maximum value of0.808emu/g, which due to the formation of enriched Ni element layers on the surface of the alloy. When the process time was longer than15min, the tendency which the enriched Ni element layers were oxidized and rare earth oxides formed on the surface increased gradually. That led to the gradual decreased of the saturation magnetization intensity of alloy. The electrochemical performance test result showed that with the increase of the hot alkaline treatment time, the Cmax,the S100and the HRD900of alloy electrodes increased first and then decreased, respectively. The alloy electrodes which was processed for15min had the best electrochemical performance, and its cyclic stability increased from83.67%(blank) to93.09%(treated).The alloy electrodes performances which changed with the hot alkali processing time was related to the formation of enriched Ni element layers and their subsequent oxidation tendency as well as the precipitation of rare earth oxides on the alloy surface.The best condition of hot alkaline etching was30wt.%NaOH solution in90℃by15minFinally,the effects of Yb2O3on the electrochemical performance of electrodes were studied after the hot alkaline treatment of alloy.The activation performance of the electrodes was integrally deteriorated by the addition of Yb2O3compared the without. The Cmax of all electrodes decreased beside the electrode added0.5%Yb2O3. The more addition of Yb2O3,the more times of activation.It was investigated that electrode with7%Yb2O3was not completely activated until the16th cycle.The HRD was drastically deteriorated after hot alkaline treatment and following addition of Yb2O3.The HRD of electrode which was only hot alkaline treated, was86.35%. When the additive of Yb2O3up to7%, the HRD was21.04%.The S100of treated alloy electrode with0.5%Yb2O3was slightly improved.The channel of the porous enriched Ni layers will be blocked by Yb2O3when the amount of Yb2O3was beyond0.5%, which lead to the decrease of hydrogen diffusion、corrosion resistance and comprehensive properties. |
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