Temperature-Dependent Structure and Electrochemical Behavior of RuO₂/Carbon Nanocomposites

RuO2/carbon nanocomposites are promising materials for supercapacitor electrodes because of their high power and energy capabilities. Understanding their structural change against temperature and electrochemical potential is crucial for better supercapacitor performance of these nanocomposites. The present work involves the preparation of RuO2 nanoparticles in mesoporous carbon substrates using a consecutive impregnation method and subsequent annealing of the composites from 25 to 600 °C. X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Ru K- and L-edge X-ray absorption spectroscopy (XAS), ab initio calculations, cyclic voltammetry, and in situ electrochemical XAS are used to investigate the structural changes of RuO2 in the nanocomposite. The data show that the RuO2 transitions from a heavily hydrated to slightly hydrated form and then reduces to metallic Ru as temperature increases. The latter reduction of RuO2 occurs at much lower temperatures than those for bulk RuO2. Electrochemical analysis indicates that the specific capacitance of the nano-RuO2 in the nanocomposite is significantly lower than that of bulk RuO2, implying that only a small amount of nano-RuO2 present is electroactive. This finding coincides with the in situ electrochemical XAS study, in which nearly no change in the Ru K-edge XAS is observed for the nanocomposite electrode under varied potentials, differing from the bulk RuO2. This work presents a comprehensive picture of the structural changes of RuO2/carbon nanocomposites against temperature and electrochemical potential.

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