Effect of Chloride Ions on the Sparking Voltage of Working Electrolytes and Its Restraint Method

As we all know, chloride ions (Cl-)are majorimpurities that significantly influence the lifetime and degradationof the dielectric properties of working electrolytes in aluminum electrolyticcapacitors. However, the exact destructive mechanism of Cl- on the working electrolytes remains unstudied. In this work, ppmNH(4)Cl is added to the working electrolytes to study theformation process of dense films of anodic alumina and the sparkingvoltage of electrolytes. As a result, nanopores and hemisphericalshapes similar to the morphologies of the porous alumina film arefound in the originally dense films of anodic alumina and the sparkingvoltage of electrolytes also decreases. The presence of Cl- leads to the generation of electronic current (J (e)) and oxygen gas evolution in the anodizing process,which could decrease the sparking voltage. The oxygen bubbles insidethe dense films of anodic alumina result in the generation of nanoporesand hemispherical shapes within them. When 1 wt % ethylene glycolborate polyester (BPE) is added to the NH4Cl electrolytes,the morphologies of nanopores and hemispherical shapes in the densefilms disappear, which proves that BPE can not only restrain the generationof J (e) and oxygen gas evolution but alsoimprove the sparking voltage.