Structures and electrochemical capacitive properties of RuO₂ vertical nanorods encased in hydrous RuO₂

Structural electrodes of anhydrous RUO₂ vertical nanorods encased in hydrous RUO₂ have been prepared via chemical vapor deposition (CVD) followed by electrochemical deposition. 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 (RuRuO ₂VR-H2) exhibits a total capacitance of ∼520 F g^-1 (870 mF cm^-2) at 5 mV s^-1, superior to that of the RuO₂·0.46H₂O coated as-grown nanorods (RuO ₂VR-H) ∼260 F g^-1 (300 mF cm^-2). Despite having twice the charge storage capability, RuRuO₂·0.46H ₂O demonstrates a capacitor response time similar to that of RUO ₂VR-H because of its low internal resistance. Two important features of RuRuO₂VR-H2 are identified, including an open structure for hydrous RuO₂ accommodation and a fast electron path for charge delivery and retrieval.