Extension of the Service Life of IrO_2 Anodes by the Addition of Colloidal Silica

由于电解工艺的显着进步，氧化铱电极作为析氧反应的工业金属阳极变得越来越重要。铸铅合金通常用作不溶性阳极，但具有一些缺点，例如析氧反应的过电位高、产品的铅污染以及变形引起的短路。然而，这些困难可以通过使用氧化铱电极来克服。金属电极的缺点之一是由于溶解在镀液中的有机物质的侵蚀而导致催化剂损失。为了提高金属电极的稳定性，将胶体尺寸的二氧化硅颗粒分散在电催化剂中，结果表明，电极的使用寿命随着涂层总数的平方次方而增加。因此可以制备具有减少的涂层数量的耐用电极。描述胶体二氧化硅对使用寿命影响的特殊关系促进了对层状催化剂的深入剖析研究。电子探针显微分析仪和扫描电镜实验观察表明，催化剂薄膜由三层结构组成，外部富集IrO_2，内部富集SiO_2，中间部分为两种氧化物互穿。因此，在薄膜表面提供的胶体二氧化硅很容易穿过层向内形成进一步的SiO_2富集层。换句话说，二氧化硅梯度浓度内置于薄膜中；这种梯度浓度导致损耗率降低，并且似乎使阳极薄膜具有较长的使用寿命。

Iridium oxide electrodes have become increasingly important as industrial metal anodes for oxygen evolution reaction owing to the significant advances in electrolytic processes. Cast lead alloys have been commonly used as insoluble anodes but have some drawbacks such as a high overpotential for the oxygen evolution reaction, lead contamination of products and short circuiting by deformations. These difficulties can be however overcome by the use of iridium oxide electrodes. One shortcoming of the metal electrodes is undesirable catalyst loss due to attack by organic substances dissolved in baths.To promote the stability of the metal electrodes, silica particles of colloidal size were dispersed in the electrocatalysts and it was shown that the service life of the electrodes was increased with the square power of the total number of coating. It has thus become possible to prepare the durable electrodes with reduced number of coating. The peculiar relation describing the effect of colloidal silica on the service life prompted the depth profiling study of the layred catalysts. Experimental observation with an electron probe microanalyzer and scanning electron microscope has shown that the catalyst films consisted of triplex layrs with an IrO_2-enriched outside, an SiO_2-enriched inside, and an intermediate section where the two oxides interpenerated. Colloidal silica supplied at the surface of films thus easily through the layrs inward to form further SiO_2-enriched layrs. In order words, silica gradient concentrations are built into films ; such gradient concentrations result in the reduction in the loss rate and appear to give anode films their long service life.