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The microstructure and electrochemical properties of IrO 2 -Ta 2 O 5 coated titanium anodes have been studied using scanning electron microscopy, energy dispersive X-ray analysis, and electrochemical impedance spectroscopy ͑EIS͒ polarization and accelerated life test. The morphologies of IrO 2 -Ta 2 O 5 anodes consist of dried mud-cracks surrounded by compact areas with superficial agglomerates except for 10% Ir (Ir:Ta ϭ 10:90 in mole ratio͒ anode. The composition of oxide coating is inhomogeneous with IrO 2 segregation in the agglomerates. EIS study indicates that 30% Ir is a critical concentration for IrO 2 -Ta 2 O 5 coating to achieve metallic conductivity. The anode with 50-70% Ir is found to have not only the largest electrochemically active surface area but also the highest electrochemical activity, with 70% Ir anode also presenting the highest stability.

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