On the faradaic selectivity and the role of surface inhomogeneity during the chlorine evolution reaction on ternary Ti–Ru–Ir mixed metal oxide electrocatalysts

The faradaic selectivity of the chlorine evolution reaction (CER) and oxygen evolution reaction (OER) on the industrially important Ti–Ru–Ir mixed metal oxide is discussed. Absolute evolution rates as well as volume fractions of Cl2 and O2 were quantified using differential electrochemical mass spectrometry (DEMS), while the catalyst surface redox behavior was analyzed using cyclic voltammetry. The spatial inhomogeneity of the surface catalytic reaction rate was probed using Scanning Electrochemical Microscopy (SECM). Although the nature of the competition between electrochemical discharging of chloride ions and water molecules remains elusive on a molecular scale, new insights into the spatial reactivity distribution of the CER and OER were obtained. Oxidation of water is the initial step in corrosion and concomitant deactivation of the oxide electrodes; however, at the same time the nature of interaction between the oxide surface and water is used as a rational indicator of selectivity and catalytic activity. An experimental procedure was established that would allow the study of selectivity of a variety of different catalyst materials using polycrystalline electrode surfaces.