Innovative Approaches Toward the Synthesis of Electroactive RuO2-based Materials of Intrinsic Structures

Abstract

Supercapacitors are one of the most promising devices for energy storage, which can, in the highest extent, bridge the batteries/capacitors energy/power gap. Ruthenium oxide is one of the most powerful, with superior pseudocapacitive properties and high theoretical specific capacitance, depending on its structure. It has widespread application in many fields, one of which is as a coating of dimensionally stable anodes (DSA). Different methods for the synthesis of RuO2 are presented, such as the thermal decomposition of RuCl3, the sol-gel process, the polyol process, the silar method, hydrothermal synthesis, spray pyrolysis, the evaporation-induced self-assembly (EISA) method, electrochemical deposition, chemical deposition from the vapor phase, etc. In recent years, microwave (MW)-assisted procedures were shown to be powerful techniques for the synthesis of a variety of materials, especially metal oxides, through hydrothermal routes. Highly active RuO2 coatings on Ti could be prepared from colloidal suspensions of the oxide synthesized under the rigorous heating conditions induced by microwave irradiation. Intensification of the heating conditions by increased reaction temperatures and pressures produced small particles and increased the surface energy. The most rapid heating conditions generated the smallest high-energy oxide particles, which were able to form compact RuO2 coatings with high electrochemical activity. The coating capacitive performances and the activity for oxygen evolution seemed considerably improved with respect to those of the coating prepared by the traditional thermal decomposition of chloride or usual hydrothermal processing routes. The synthesised material is of highly accessible inner structure, and is an excellent candidate for both low and high power applications.