The morphol. examn. and the structural anal. of DSA-O2 electrodes [IrO2-Ta2O5 (70:30 mol%) coating] show that at moderate firing temp. (about 550 Deg), sepn. of phases occurs with the formation of agglomerates of IrO2 crystals and amorphous Ta2O5. At higher temp. (.apprx.750 Deg) both cryst. IrO2 and Ta2O5 are present. The electrochem. active surface area, as measured by cyclic voltammetry, is found to decrease with increasing prepn. temps. The shapes of voltammograms are strongly influenced by the nature of the base metal, showing its contribution to the electrochem. measurements, due to the porous nature of the coating. [on SciFinder (R)]