Trimetallic Ru-, Ir-, and Ce-oxide materials were synthesized by using a hydrolysis method in ethanol medium and characterized to obtain information on their crystallographic structure, morphology, and chemical composition. Voltammetric measurements allowed us to evaluate the properties of these catalysts through the determination of their capacitance, active site number, and accessibility. The effect of cerium on the oxygen evolution reaction (OER) was also evaluated electrochemically and the catalytic layer stability was measured by using a repetitive cyclic voltammetry procedure. The catalysts stability in an acidic medium is not significantly affected by cerium addition. Moreover, the oxygen mobility in the ceria crystallographic structure may contribute to an enhanced electrocatalytic activity per active site. Tafel slope values were determined from electrochemical impedance spectroscopy fitting parameters and indicate the same OER rate-determining step for mono-, bi-, and trimetallic catalysts.