Electronic structure vs. electrocatalytic activity of iridium oxide

The electrochemical oxidation and reduction of hexacyanoferrate redox couples at anodically formed iridium oxide (AIROF) and nanostructured iridium oxide produced by hydrolysis, hIrO2, are compared. Whereas AIROF displays the characteristics of a semiconducting electrode in its reduced state, hIrO2 is similar to a metal electrode. In view of also significant differences between the two oxides’ optical and intercalation properties, this strongly indicates that hIrO2 has a different bulk electronic structure. Yet, the charge-normalised electrocatalytic activity for the oxygen-evolution reaction at AIROF and hIrO2 is the same. This indicates that the electrocatalytic properties of iridium oxide are a function of the local structure at the oxide surface and not uniquely related to the bulk electronic structure.