Structural electrodes of anhydrous RuO2 vertical nanorods encased in hydrous RuO2 have been prepared via chemical vapor deposition (CVD) followed by electrochemical deposition and arranged in parallel-plate configurations. The composite structures are studied using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The capacitive properties are measured using cyclic voltammetry and impedance spectroscopy. In a miniaturized configuration, the CVD grown structure provides a connecting backbone of electron paths and open channels for ion migration to facilitate the charge delivery or acceptance from the electrodeposited hydrous RuO2 of high pseudocapacitance. The sample of thermally reduced nanorods encased in RuO2•0.46H2O (RuRuO2NR-H2) exhibits a total capacitance of 侧520 Fg-1 (870 mFcm-2) at 5 mVs-1, superior to that of the RuO2•0.46H2O coated as-grown nanorods (RuO2NR-H) 侧260 Fg-1 (300 mFcm-2). Despite the twice charge storage capability, RuRuO2NR-H2 demonstrates a similar capacitor response time as RuO2NR-H, because of its low internal resistance. Two important features of RuRuO2NR-H2 are identified, including an open structure for hydrous RuO2 accommodation and a fast electron path for charge delivery and retrieval.
Besides the parallel-plate configuration, the capacitor electrodes are configured in interdigital single-chip capacitors via photolithography and reactive sputtering techniques. Briefly, the anhydrous RuO2 nanorods are grown on finger-like patterned of TiO2/Ti/Au/SiO2/Si substrates with various finger spacing of d = 20, 30, and 40 μm. The hydrous RuO2 is electrochemically deposited on the anhydrous RuO2 samples to increase the specific capacitance. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction are used to study the structures of the composites. The capacitive properties are measured using cyclic voltammetry, charging-discharging and impedance spectroscopy analysis. The specific capacitances of d=20 μm are larger than those of d=30 μm and those of d=30 μm are larger than those of d=40 μm. The mass-specific capacitance of d=20 μm is 105.5 F.g-1, that of d=30 μm is 77 F.g-1 and that of d=40 μm is 68.4 F.g-1 measured by cyclic voltammetry at 2 mV.s-1 sweep rate. Besides, the sample of d=20 μm also performs the fastest capacitive response among the other two samples. Although the specific capacitances of the finger-like electrodes are smaller than those of the parallel-plate electrodes, this design offers practicality in integrating the electrode in a single chip and fast capacitive response.

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