Electrochemical capacitors of RuO2 nanophase grown on LiNbO3(100) and sapphire(0001) substrates

The electrochemical properties of RuO2/LNO and RuO2/SA electrodes made of RuO2 rods and plates of nanometre size on LiNbO3(100) and sapphire(0001) substrates are investigated. Both rods and plates are grown vertically using chemical vapor deposition. The RuO2/LNO electrode has a higher electrolyte/solid surface area compared with the RuO2/SA electrode. When immersed in H2SO4 acid, voltammograms of both electrodes exhibit chemisorption and pseudocapacitive characteristics of the RuO2 single crystal. The chemisorption features decrease after repeated cyclic voltammetry (CV) sweeps, and the voltammograms become more mirror-like. The specific capacitance of the RuO2/LNO electrode measured in CV is 569 F g(-1), that of RuO2/SA 357 F g(-1). These values are reconfirmed in charging-discharging measurements. The measured capacitance decreases with the sweep rate, and the decreasing trend of RuO2/LNO is higher than that of RuO2/SA. Reduction of accessible charge at high sweep rates results from higher internal resistance of the RuO2/LNO electrode which is distributed because of its porous nature. The impedance spectrum of the RuO2/LNO electrode confirms its higher internal resistance. It also indicates the electrode is a nearly ideal capacitor below a knee frequency 200 Hz. Since the knee frequency is less than 1 Hz for most electrochemical capacitors, both RuO2/LNO and RuO2/SA are electrodes for fast charging-discharging applications.