Toward a reliable synthesis of strontium ruthenate: Parameter control and property investigation of submicrometer-sized structures

SrRuO₃ (SRO) has been studied extensively at the bulk and thin film scales for a variety of applications, such as multilayer devices, field-effect devices, multiferroics, and even ferroelectric random access memory (FeRAM). Conversely, the exploration of SRO nanoscale and submicrometer scale structures in terms of both synthesis and applications has been significantly limited. Herein, we are the first to report on the synthesis of SRO submicrometer-sized particles via a molten-salt method. We have accomplished this by systematically probing experimental parameters such as precursors, type of salt, annealing time, annealing temperature, surfactant, cooling rate, and reaction atmosphere in an effort to predictably control the resulting size, shape, and morphology of the SRO product particles. In particular, by quenching the reaction at a cooling rate of 100 A'A C/min, we can produce rounded SRO particles averaging 149 100 nm in size. Moreover, with the addition of a mixture of mineral oil in Triton X-100, the final SRO particles are highly faceted, single-crystalline octahedra, averaging 126 A 45 nm in size. Apart from the choice of molten salt which primarily controls chemical composition of SRO, we have determined the most important experimental parameter for shape and aggregation control is the surfactant, because of a combination of its hydrophobic and hydrophilic characteristics. We have found that the decomposition of the surfactant promotes the formation of SrCO₃, which is consistent with the generation of SRO through the reaction of SrCO ₃ with RuO₂. Our successful syntheses have allowed us to explore physical properties, that is, magnetic and electronic, of these submicrometer-sized SRO particles, which are in good agreement with bulk SRO. Furthermore, we have also explored the potential of our as-synthesized particles as effective methanol oxidation reaction (MOR) catalysts for direct methanol fuel cells (DMFCs). Not only are our as-synthesized SRO particles MOR active but also our well-defined faceted octahedra exhibit a 4-fold increase in mass-activity and a 4-fold increase in surface area by comparison with the rounded particles, thereby emphasizing a clear advantage of faceted submicrometer SRO for electrochemical applications.