Title : Size control of Ruthenium nanoparticles in Ruthenium/Carbon composites derived from metal-organic frameworks
In order to utilize catalytic activities efficiently, while using minimum amount of catalysts, various synthetic methods have been attempted by deposition of catalytic nanoparticles onto a porous or/and conductive support. In the case of platinum, which is the most commonly used electrocatalyst, platinum is deposited by wet chemical method, vacuum deposition, or atomic layer. However, these synthetic methods have obstacles regarding effective dispersion and utilization of Pt catalyst. In addition, heterogeneous particle size and broad size distribution of Pt catalyst can be another obstacle exhibiting efficient catalytic properties. These days, many efforts have been implemented as a way to create composites materials by incorporating metal or metal oxide nanoparticles into various host materials. Among these candidates, carbonaceous materials using metal-organic frameworks (MOFs) as precursors have already enormous attentions. In this study, we report a successful synthesis of ruthenium/carbon composites via simple carbonization process of Ru-MOF under inert atmosphere. For the investigation of the effects of temperature on the microstructural development, Ru-MOF samples have been carbonized at different temperatures from 300, 500, 700, and 900 ? in a horizontal quart tube furnace. The microstucture of the composites was observed by field-emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). It was founded that the Ru-MOF have the cubic morphology covered with particles which are considered to be ruthenium nanoparticles that have not been synthesized in the form of Ru-MOF. As the carbonization temperature increases, the size of the ruthenium particles increases with the sizes of 2-3 nm, 3-4 nm and 5-7 nm for the carbonization temperatures of 500, 700, and 900 ?, respectively and the shape becomes uneven with an agglomeration. The growth of the nanoparticles phenomenon is explained by a particle migration and coalescence (PMC) or Ostwald ripening mechanism. Structural and electrochemical characterizations reveal that carbonization temperature plays a critical role for the determination of the degree of graphitization and Ru particle size. This study suggests a simple and effective way to control the size of the metal obtained by carbonization of MOF, which provides a perspective in many fields of chemical or energy applications of Ru-MOF and others.