(163az) Electrochemical Capacitor Behavior of Ruo2 Vertically Aligned Rods Filled with Ruo2•Xh2o

An electrochemical mini-capacitor of a designed microstructure, which allows proton insertion and migration in hydrous RuO2 interspersed between an assembly of anhydrous RuO2 vertical rods, was prepared and its capacitive behavior was studied using cyclic voltammetry and impedance spectroscopy. The anhydrous RuO2 rods of 110-200 nm in diameter, 2000-3000 nm in length are vertically grown on LiNbO3(100) substrates using chemical vapor deposition. The porous space among densely packed rods can be filled with RuO2?0.46H2O using electrodeposition. The anhydrous RuO2 rods provide the electron conducting path for charging and discharging the capacitor, while the hydrated RuO2?0.46H2O offer the proton storage for pseduocapacitance. The sample of anhydrous RuO2 rods without hydrous RuO2 is denoted as RuO2VR, the composite of anhydrous and hydrous RuO2 is denoted RuO2VR-H. The capacitance of RuO2VR is 11-16 mFcm-2 (16-23 Fg-1). While the capacitance of RuO2VR-H rises to 300-400 mFcm-2 (300-350 Fg-1). The Nyquist plots of RuO2VR and RuO2VR-H are characterized with depressed semicircles in the high frequency range, and nearly vertical lines in the low frequency range when the bias > 0.4V, while systematic deviation from the vertical line when the bias < 0.4V. The systematic deviation from 90o is attributed to the slower kinetics of redox reactions related to pseudocapacitance. Since RuO2?0.46H2O possesses a large pseudocapacitance, RuO2VR-H exhibits more prominent deviation in the low frequency range. Additionally, comparison of RuO2VR and RuO2VR-H Bode plots indicates that the replacement of acid electrolyte with RuO2?0.46H2O reduces the impedance by one order of magnitude in the intermediate and low frequency ranges. An equivalent circuit for modeling the impedance is proposed and the results will be discussed.