Abstract
The aim of this study is to utilize chemical oxidation precipitation method accompanied by the post thermal conditioning for the synthesis of porous ruthenium-based oxides with tunable microstructure. Here, we provide a systematic platform to meet our experimental concepts for the better understanding of dependency between structure, surface morphology and electrochemical charge-discharge mechanism. Hence, our spotlights focus on the investigation of RuO2 electrochemical performance enhancement by the incorporation of second Ti dopants and the modification by templating surfactants. In the 1st part, a binary ruthenium-titanium (Ru-Ti) oxide nanocomposite has been synthesized through chemically oxidative precipitation method, followed by the thermal annealing treatment at different temperatures ranging from 150 to 300oC. X-ray absorption spectroscopy (XAS) demonstrates that a minor amount of Ti atoms are incorporated into crystalline RuO2, which partially occupy Ru sites in the octahedral RuO6 structure. This would induce the distortion of original RuO2 lattice and generate additional electrochemically active sites. Therefore, it is found that Ru-Ti oxides annealed at 200oC exhibits much higher specific capacitance (near 1.5 fold improvement) and better capacitance retention relative to pure RuO2. On the other hand, the growth of RuO2 nanorods has been thermally induced from binary Ru-Ti oxides at a higher annealing temperature region (> 250oC) since the presence of incorporated Ti dopants provide an inhomogeneous interface for facilitating the crystallization and growth of RuO2 along c-aixs to form Ru1-TiO2 nanorods. In the 2nd part, we demonstrates that the combination of different surfactants containing Pluronic F127 along with cetyltrimethylammonium bromide (CTAB), and post annealing treatment can prepare well-crystalline RuO2 with the preferential orientation growth of facet {101}. Based on the heterogeneous surface chemistry viewpoints, the preferential orientation growth along the {101} facet of RuO2 is due to the adsorption of ligands of surfactants on the higher surface energy facets and it is proposed to promote the prosperous crystal growth along the {101} plane. Apparently, in F127 system, the specific capacitance and capacitance rate-retention are promoted substantially since the topmost surface of facet {101} is occupied by Ru atoms, probably favoring the construction of the electron pathways. Besides, in the case of CTAB system, the electrochemical performance enhancement is owing to the transformation of residue polymer into ionic and electronic conducting buffer layer on the topmost surface of RuO2 nanoparticles or locally robustness formation of RuO2 nanocrystallites. In order to further promote the capacitive property, the synergy combination of Ti intercalation and surfactants introduction has been executed. As a consequence, the synthesis of Ru-Ti oxides trapped with Pluronic F127 or CTAB has been prepared by virtue of the identical approach. It is suggested that the specific capacitance of Ru-Ti oxides modified with F127 or CTAB is considerably enhanced because of the synergistic effects from Ti incorporation to create more electrochemical sites and surfactant assistance to promote the anisotropic crystal growth along with well dispersion of oxide nanoparticles.