Structural, Electrocatalytic and Capacitive Properties of Ruthenium/Titanium-Oxide Based Electrodes Synthesized by Novel Methods

Abstract

Activated titanium anodes, commercially known as dimensionally stable anodes (DSA®), are one of the most important discoveries in the field of applied electrochemistry of the 20th Century. These anodes are widely used for chlorine production in chlor-alkali industry, oxygen evolution reaction in electrowinnung processes and in electrochemical remediation of water and soil. DSAs consist of the mixed ruthenium−titanium oxide (RuO2–TiO2) coatings, oftenly doped with additional noble and/or transition metal oxides, deposited onto Ti surface. Structural, electocatlytic and capacitive properties of activated titanium anodes, prepared from oxides obtained by various synthesis methods, are investigated. These methods include sol–gel procedure, MW-assisted synthesis of the oxide from aqueous chloride solution and ultrasonic spray pyrolysis (USP). Microscopic investigations of the oxide sols and coatings showed that the aging time of the sols defines the coating morphology and, consequently, the electrochemical behavior of a coating. Better electrochemical characteristics, including anode stability in electrolysis, were registered for a combination of small RuO2 and large TiO2 sol–gel processed particles. Deactivation of an anode is manifested by an increased coating resistance and decreased electrochemically active surface area. The increase in the coating resistance is more pronounced for traditional coatings prepared by pyrolysis of metal chlorides, while sol–gel prepared coatings show more pronounced decrease in the electrochemically active surface area. The initial increase in coating resistance is caused by the dissolution of Ru species from the coating surface facing the electrolyte, which restricts the coating activity to the active sites from the interior of the coating (within the porous structure). It is shown that spray pyrolytic synthesis methods, e.g., ultrasonic spray pyrolysis, are versatile and applicable synthetic techniques for creating novel, rationally designed, RuO2–TiO2 material structures. Synthesized USP powders consisted of separated anatase and rutile phases, with anatase structure preserved even at 800 °C in the core of spherical particles onto which crystalline RuO2 preferentially grows.