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

Abstract

As we all know, chloride ions (Cl–) are major impurities that significantly influence the lifetime and degradation of the dielectric properties of working electrolytes in aluminum electrolytic capacitors. However, the exact destructive mechanism of Cl– on the working electrolytes remains unstudied. In this work, ppm NH4Cl is added to the working electrolytes to study the formation process of dense films of anodic alumina and the sparking voltage of electrolytes. As a result, nanopores and hemispherical shapes similar to the morphologies of the porous alumina film are found in the originally dense films of anodic alumina and the sparking voltage 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 inside the dense films of anodic alumina result in the generation of nanopores and hemispherical shapes within them. When 1 wt % ethylene glycol borate polyester (BPE) is added to the NH4Cl electrolytes, the morphologies of nanopores and hemispherical shapes in the dense films disappear, which proves that BPE can not only restrain the generation of J e and oxygen gas evolution but also improve the sparking voltage.

Relationship between the Growth Rate of Nanotubes and the Current–Time Curve of the Anodizing Process

“…The porosity of the surface is basically positively correlated to the amount of charge transferred by the electronic current, as shown in Figure . The surface morphology in Figure a–c also proves that the influence of the dissolution reaction involving fluoride ions on the surface pores is very weak. − Figure c,d shows the morphology of titanium oxide nanotubes produced by anodic oxidation in the EG + T-07 electrolyte. It can be seen from Figure c that there are holes in the oxide surface layer, and the diameter of the holes is very small, much smaller than that of the nanotubes shown in Figure d.…”

Optimization of Photoelectrochemical Response on TiO2 Nanotube Arrays Treated by H3PO4 and Mechanism Analysis of the Slowing Down Effect during Preparation

“…Owing to the limited space on the anode surface, ions with a high charge-to-volume ratio are easier to accumulate on the electrode surface to form ACL, such as fluoride ions and chloride ions, while ions with a low charge-to-volume ratio are difficult to cross the ion layer and stay outside the ACL.…”

“…This finding proved that we can control the anodization process by introducing heterogeneous anions into the electrolyte to change the ion distribution at the anode interface. According to existing studies, chloride ions may lead to a decline in sample stability, and compounds with reducibility may lead to the introduction of impurities in the side reaction during anodization. , Therefore, the selection of anions needs to be carefully considered when anion-specific changes are introduced to the ACL composition. On the one hand, the introduced anions reduce the fluoride ion concentration at the reaction interface, which reduces the reaction rate.…”

“…With the development of society, the demand for high-performance energy materials is increasing. − Owing to the wide application in photoelectrocatalysis, biosensors, supercapacitors, and so on, the preparation of TiO 2 has been a research hot spot for a long time. ,− Owing to the optical, structured, and electronic advantages, nanostructured TiO 2 -based photoelectrodes are promising for application as photoelectrochemical (PEC) devices, and photoelectrodes based on nanowire, nanorod, and nanoparticle structure have been widely studied. − Nowadays, many researchers focus on the catalysts, such as TiO 2 /Ti 3 C 2 , Bi/BiOBr, and N-graphyne/BiOCl 0.5 Br 0.5 , but a few focus on its carrier. However, the photoelectrochemical properties of anodic TiO 2 nanotubes (ATNTs), one of its important carriers, have been studied less. − It is worth mentioning that the ATNT array is usually formed in the electrolyte containing halogen ions typically, whereas the dense film in the electrolyte without halogen ions. − Some researchers attributed the formation of porous film to an electrochemical dissolution reaction (i.e., TiO 2 + 6F – + 4H + → [TiF 6 ] 2– + 2H 2 O), − and some other researchers suggested that the mechanism of porous film formation is related to the contamination layer formed by halogen ions. − In summary, all of these studies supported the conclusion that the anion is indispensable for the formation of anodic TiO 2 nanotubes. Unlike other forms of TiO 2 , ATNT arrays may have defects in strength due to corrosion by fluoride ions during rapid growth. − Therefore, it is crucial to slow down or prevent the corrosion of fluoride ions on the nanostructure during anodization to improve the stability of the nanotube array performance.…”

Real Role of Fluoride Ions in the Growth of Anodic TiO2 Nanotubes

“…However, the oxide near the metal substrate still constitutes the barrier oxide layer. When the barrier oxide layer reaches a critical thickness, the violent collision of ions generates the initial avalanche electronic current. − This sudden increase in the total current creates an inflection point on the current–time curve. With the increase in electronic current, the oxygen bubble generation reaction triggered by the electronic current intensifies and oxygen bubbles are generated at the interface between the anionic contaminated layer and the barrier oxide layer.…”