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

Abstract

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.