Nanoscaled Structures in Ruthenium Dioxide Coatings
Sammanfattning: An essential ingredient in the generation of environmentally compatible pulp bleaching chemicals is sodium chlorate. Chlorate is produced in electrochemical cells, where the electrodes are the key components. In Sweden the so-called DSA !R electrodes with catalytic coatings have been produced for more than 35 years. The production of chlorate uses a large amount of electric energy, and a decrease of just five percent of this consumption would, globally, decrease the consumption of electrical energy corresponding to half a nuclear power reactor. The aim of this project is to improve the electrode design on the nanoscale to decrease the energy consumption. The success of the DSA!R depends on the large catalytic area of the coating, however, little is known about the actual structure at the nanometer level. To increase the understanding of the nanostructure of these coatings, we used a number of methods, including atomic force microscopy, transmission electron microscopy, X-ray diffraction, porosimetry, and voltammetric charge. We found that the entire coating is built up of loosely packed rutile mono-crystalline 20 − 30 nm sized grains. The small grain sizes give a the large area, and consequently, lower cell-voltage and reduced energy consumption. A method to control the grain size would thus be a way to control the electrode efficiency. To alter the catalytically active area, we made changes in the coating process parameters. We found a dependency of the crystal-grain sizes on the choice of ruthenium precursor and processing temperature. The use of ruthenium nitrosyl nitrate resulted in smaller grains than ruthenium chloride and lowering the temperature tended to favour smaller grains. A more radical way would be to create a totally different type of electrode, manufactured in another way than using the 1965 DSA !R recipe. Such new types of electrodes based on, for example, nanowires or nanoimprint lithography, are discussed as future directions.
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