Ti-V-W-O/Ti oxide electrodes prepared by a dip coating method provided a fairly large pseudocapacitance both in H 2 SO 4 and KOH solutions. The vanadium penetrates easily into the titanium oxide to form rutile Ti x V y O 2 aided by the tungsten species. These electrodes seem to have a potential for use as electrochemical capacitors. © 1999 The Electrochemical Society. S1099-0062(98)08-080-8. All rights reserved.Manuscript received August 20, 1998. Available electronically October 26, 1998 The RuO 2 -and IrO 2 -based oxide-coated titanium electrodes have been used for various electrolytic processes. They have also been examined as electrodes for electrochemical capacitors due to their large pseudocapacitance. [1][2][3][4][5][6][7][8] Since both ruthenium and iridium are expensive, less expensive electroconductive materials must be found for the development of electrochemical capacitors using the pseudocapacitive property of metal compounds. NiO 9,10 and the nitrides 11,12 of V, Nb, Mo, and W have also been proposed as electrode candidates for electrochemical capacitors. In the present investigation, the authors have found that Ti-V-W-O/Ti oxide electrodes show a fairly large pseudocapacitance both in H 2 SO 4 and KOH solutions.Experimental Oxide-coated electrodes in the present investigation were prepared by a dip coating method. For the dip coating procedure, 99.5% titanium rods etched in 10% oxalic acid solution at 80°C for 1 h were dipped into various solutions consisting of three different solutions of NH 4 VO 3 (50 mg [V] mL -1 ) and 5(NH 4 ) 2 O•12WO 3 •5H 2 O (50 mg [W] mL -1 ) in ethylene glycol + 10% nitric acid, and (C 4 H 9 O) 4 Ti (50 mg [Ti] mL -1 ) in ethylene glycol. The dipped titanium rods were dried at 60°C for 10 min and calcined at temperatures between 450 and 750°C in a preheated furnace for 10 min. The oxide loading estimated by the weight increase was about 0.05-0.07 mg cm -2 for one oxide coating cycle in this experiment.A beaker-type electrochemical cell equipped with a working electrode, a platinum plate counter electrode, and a Ag/AgCl reference electrode was used. The geometric surface area of the working electrode was 1 cm 2 . Cyclic voltammograms were recorded at 50 mV s -1 in 0.5 M (1 M = 1 mol dm -3 ) H 2 SO 4 or in 1 M KOH at 25°C. Electrode potentials were referred to the reversible hydrogen electrode (RHE) scale. A Luggin capillary faced the working electrode at a distance of 2 mm. A voltammetric charge density, corresponding to the electrochemically active surface area, was determined from integration of the enclosed area of the anodic curves between 0.30 and 1.10 V in the cyclic voltammogram. X-ray diffraction (XRD) analysis patterns of the samples were obtained using a Cu Kα radiation system (40 kV, 80 mA, Rigaku CN-2028). Elemental analyses were performed by X-ray emission spectroscopy (Philipps, EDAX-9100).Results and Discussion Figure 1 shows the steady-state cyclic voltammograms in 0.5 M H 2 SO 4 for the various compositions of the Ti-V-W-O/Ti oxide electrodes prepared by...