Electrochemical Behavior of the Oxide‐Coated Metal Anodes

Abstract

Polarization measurement and an accelerated life test of the oxide-coated titanium anodes in relatively dilute solutions of NaCl and in HClO4 solution were conducted. The OCTA failed at potentials higher than 1.3V vs. SCE, probably due to anodic oxidation of RuO2 and passivation of Ti substrate. An accelerated life test based on those results has been investigated to estimate the OCTA. The polarizing current decreases quickly when the OCTA becomes inactive, and the service life of material is evaluated by the time-to-failure from the start-up.A n u m b e r of the oxide-coated titanium anodes (OCTA) consisting of RuO2 and TiO~ are being used because of durability and low chlorine overvoltage in chlor-alkali cells. But eventually the OCTA becomes inactive and a part of the oxide drops out (arrow in Fig. 1). Low oxygen overvoltage is another problem for this oxide anode in chlorine cells.The OCTA is stable and its chlorine overvoltage is p r e f e r a b l y low in concentrated NaC1 solutions even a t high current densities, whereas it is attacked g r a d u a l l y and the anode potential becomes high in dilute N a C 1 solutions.Since the OCTA has come into the m a r k e t in early 1970's, m a n y articles on its preparation, modification, physico-chemical properties, electrochemical characteristics, and applications have been published. Degradation and deactivation of its unique material have also been discussed. With those articles and patents, degradation of the OCTA in chlor-alkali cells can be classified into three types: (i) coating dissolution, (ii) substrate a t t a c k , and (iii) substrate oxidation leading to electrical insulation, as stated by W a r r e n et al., who have studied the P t -I r alloy coated anodes for chlorate cells (1, 2).Extensive studies on the OCTA as well as the solid Ru metal anodes in sulfuric acid solution and solid p o l y m e r electrolyte have been conducted as a part of new developments in high-performance water electrolysis. Low oxygen overvoltage of those materials is a reason. However, dissolution a n d / o r degradation of the anode material at high potential ranges, and hence at high current densities, is a problem (3).Experiment of the OCTA under the operating conditions of chlorine cells are time-consuming, about one y e a r or more for only one run. Consequently, this paper deals mainly~with an accelerated life test and its procedure for the OCTA. The procedure is simple and requires minimum labor even for a prolonged period. The test specimen of the OCTA is electrolyzed in a mixed solution of HC104 and NaCI or in HC104 single solution under a constant terminal voltage, and the current is recorded until the test specimen breaks down. The concept is based on gradual degradation of the active material due to oxygen evolution. ExperimentsTest specimen.--Titanium sheet of 5 m m wide, about 150 m m long, and 0.5 m m thick was pickled with 10% oxalic acid at about 80~ for about 3 hr, rinsed Fig. I. SEM photograph ot degraded surface of OCTA 1439 ) unless CC License in place (s...

Electrooxidation of urea at the ruthenium titanium oxide electrode

“…While ruthenium titanium oxide electrodes are stable in concentrated chloride solutions, they are reported to be of limited stability in dilute chloride solutions or solutions devoid of chloride (Hine et al, 1979;Yeo et al, 1981). In the present investigation, electrode lifetime appeared to be at least six months, but further investigation would be warranted.…”

Synthesis and Stabilization of Blue-Black TiO2 Nanotube Arrays for Electrochemical Oxidant Generation and Wastewater Treatment

“…An empirical equation for the prediction of lifetime of water oxidation electrode has been proposed previously 13,14 …”

“…According to equation S4, One must notice that these tests are not the typical accelerated life time tests, in which i 1 could be as high as 1 A/cm 2 . 13,14 Because BNTA is inactive for water oxidation, thus operating it at 1 A/cm 2 will instantly leads to an extremely high anodic potential, which consequently results in the corrosion of Ti metal substrate.…”

Effects of the geometry and operating temperature on the stability of Ti/IrO2–SnO2–Sb2O5 electrodes for O2 evolution

“…However, the rod shaped electrode of a mean curvature of 200 m -1 operated 263 h before its failure. This value would mean a working life to be over 10 years when the current density is lowered to 300 A m -2 in a neutral solution for O 2 [20,21].…”