Mixtures of IrO 2 '/MnO 2 (30:70 mol%) have been electrochemically studied by cyclic voltammetry (CV) in acid solution. The crystalline structure, morphology and the electrochemical properties of the electrodes have been studied as a function of the annealing temperature. X-ray diffraction analysis (XRD), show absence of Mn 2 O 3 phase formation and suggest the possible of formation of a solid solution of IrO 2 and MnO 2 mainly between 400 and 450 8C. The voltammetric behavior depends on the potential cycle number and annealing temperature employed in the preparation of the oxide layer. A good potential window in aqueous H 2 SO 4 and high electroactive area are obtained due to the contribution of Ir redox transitions. Energy-dispersive X-ray (EDX) and scanning electron microscopy (SEM) analysis suggest an enrichment of the Ir content on the surface at the cost of the dissolution of the manganese present in the film when the electrode is submitted to the continuous potential scan. The electrodes have been found to perform well in electrochemical capacitor applications with a specific capacitance close to 550 F g (1. The large capacitance exhibited by this system arises from a combination of the double-layer capacitance and pseudocapacitance associated with surface redox-type reactions.

A new electrode based on IrO 2 ϩ Co 3 O 4 ͑30:70 mol %͒ composition has been prepared by thermal decomposition ͑400°C͒ from mixtures of chloride precursors and characterized by energy dispersive X-ray, scanning electron microscopy, X-ray diffraction analysis, cyclic voltammetry, and charging/discharging curves. The electrochemical behavior shows dependence on the cathodic potential limit employed, and a good potential window ͑1.4 V͒ in aqueous NaOH and high electrocatalytic area due to the contribution of different redox transitions of Ir and Co surface sites. The electrode has been found to perform as superior electrodes in electrochemical capacitor applications with a specific capacitance of 500-600 F g Ϫ1 . The large capacitance exhibited by this system arises from a combination of the double layer capacitance and pseudocapacitance associated with surface redoxtype reactions.