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Electrochemical Behaviors of RuO2-TiO2 Mixed Metal Oxide Coated on Titanium Anodes in Chlor-Alkali Electrolysis

Paryani, Kasra | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: English
  3. Document No: 39677 (57)
  4. University: Sharif University of Technology, International Campus, Kish Island
  5. Department: Science and Engineering
  6. Advisor(s): Ghorbani, Mohammad
  7. Abstract:
  8. Titanium anodes activated by noble metal oxides under the trade name of dimensionally stable anodes (DSAs) are widely used in the electrolytic industry, particularly in chlor – alkali electrolysis. Over 20 years of use, the fundamental aspects of their long – lasting performance are not fully understand and the corrosion mechanisms are still the subject of many investigations. RuO2 – TiO2 coatings on titanium substrate, due to proper electrochemical characteristics and good corrosion resistance, is most applicable as an anode in chlor – alkali systems. In the present investigation, the first layer of Pt – Ir coating is applied via electrodeposition method on the pretreated titanium substrate and then RuO2 – TiO2 coatings are obtained via thermal decomposition of soluble salts in different applied coated from (2, 4, 6 and 8 layers) on this layer. Moreover, the other anodes that prepared commercially (Anode 1 and 2) are examined. The electrochemical behaviors of these coatings were assessed by electrochemical techniques such as, Cyclic Voltammetry (CV), Polarization measurements and galvanostatic methods. Scanning Electron Microscopy (SEM) and Energy dispersive x-ray (EDX) techniques were used before and after accelerated life tests in order to investigate the surface morphology and elemental analysis. Polarization measurements show that with enhancement in the number of coated layers from 2 to 8, tafel slopes are constant about 30 mV/decade which show that chlorine evolution reaction (CER) proceed in according to Volmer – Tafel mechanism and independent of coating mass, but exchange current densities for chlorine evolution are increased which show that anodes become better in the electrochemical properties aspects. Cyclic voltammetry measurements were done in the potential range between H2 and O2 evolution. The shape of the voltammetric curves is characteristic of RuO2 electrode with a broad peak in about 500mV (SCE) which related to Ru/Ru3+ redox couple. By integration of anodic part of CV curves in the potential range 0.05 – 1 V (SCE), another important parameter i.e. voltammetric charge was obtained that shows the electrochemical real surface area which is strongly depend on scan rate for inner and outer voltammetric charge investigations. The results obtained here indicate that the commercial electrode 2 presents a greater internal area. Repeated potential cycling between O2 and H2 evolution was not affected the shape of the curve which shows that the qualitative and quantitative reproducibility of the (i/E) curve of RuO2 are excellent. An accelerated life test (ALT) was performed in more dilute NaCl solutions (0.3M). From these data, failure times of the anodes were increased with increment number of applied coated from 2 to 8 and commercial anode number 2 has a longest life time. ALT follow by SEM and EDX experiments shows that, TiO2 formation at the substrate – coating interface was dominate mechanism in the anode deactivation process. And also existence of Ti, Ru, Pt and a little Ir were confirmed by EDX results. SEM images shows the typical cracked- mud morphology containing a continuous network of microcracks that facilitates gas evolution on the surface and also shows that with increasing number of applied coated from 2 to 8, the crack density per unit area was increased and protective structures were obtained
  9. Keywords:
  10. Ruthenium Dioxide ; Thermal Decomposition ; Chlor-Alkali ; Dimensionally Stable Anodes ; Chlorine Evolution ; Electrocatalysis Electrods ; Electrodes Corrosion Stability

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