Surface characterization by UHV techniques and cyclic voltammetry of thermal IrO2-based electrocatalysts containing TiO2 and CeO2

Electrodes of nominal composition Ir0.3Ti0.7-xCexO2 (0 less than or equal to x less than or equal to 0.7) have been prepared by thermal decomposition of mixtures of the chloride precursors (450 degrees C). A systematic study of the morphology, chemical composition and surface properties of these electrodes was performed using both ex situ (SEM, EDX, XPS) and in situ (cyclic voltammetry) techniques. A spectrophotometric study of the precursor salt mixtures was done. SEM analysis showed the introduction of CeO2 into the binary system to provoke a significant increase in the active surface area of these electrode materials, which is corroborated by the CV data (anodic voltammetric charge, q(a)*, double layer capacitance, C-dl, and roughness factor). Apparent Ti-enrichment of the more external region of the coatings, as evidenced by EDX, is related to the fact this technique analyses a thicker part of the oxide bulk (estimated as ca. 1/3 of the layer thickness). No real surface Ti-enrichment occurs as supported by close to nominal Ir/Ti ratios obtained by XPS (a real surface technique). XPS measurements also support Ir, Ti and Ce are present in freshly prepared oxide layers in two oxidation states, which is in agreement with the spectrophotometric results.