The morphol. examn. and the structural anal. of the title DSA-O2 electrodes (IrO2-Ta2O5 coating) shows that at moderate firing temp. (.simeq.550 Deg) sepn. of phases occurs with the formation of agglomerates of IrO2 crystals and amorphous Ta2O5. At higher temp. (.simeq.750 Deg) both cryst. IrO2 and Ta2O5 are present. The electrochem. active surface area and the service life show a max. for a coating compn. of 70% IrO2-30% Ta2O5 (optimum compn.). Surface anal. of the coating during service life test has shown that the optimum anode coating proceeds by a uniform coating dissoln. while that for the nonoptimum coating is due to a preferential dissoln. of IrO2. The optimized coating acts like a pseudo-solid soln. (x-ray shows the absence of a true solid soln.). Anal. of coating by fluorescent x-ray shows that only 10-15% of the total coating initially present was dissolved during the accelerated service life test. On the basis of information obtained, it was presumed that the most serious cause of activity loss of DSA-O2 electrodes is the formation of a TiO2 nonconductive layer at the Ti-coating interface. The influence of base metal (Ti, Zr, Ta) on the accelerated service life test has shown that Ta gives the max. service life. [on SciFinder (R)]