Electrochemical comparison between IrO2 prepared by anodic oxidation of pure iridium and IrO2 prepared by thermal decomposition of H2IrC16 precursor solution

Surface redox activities, oxygen evolution reaction (OER), oxidation of formic acid (FA), and anodic stability were investigated and compared for IrO2 electrodes prepared by two techniques: the thermal decomposition of H2IrCl6 precursor (TDIROF) and the anodic oxidation of metallic iridium (AIROF). Surface redox activities involved on the AIROF were found to be much faster than those involved on the TDIROF. Concerning the oxygen evolution reaction, both films show a similar mechanism and specific electrocatalytic activities. The situation seems to be different for FA oxidation. In fact, on TDIROF, the oxidation of FA and the OER compete involving the same surface redox couple Ir(VI)/Ir(IV) contrary to FA oxidation on AIROF, where the Ir(V)/Ir(IV) surface redox couple is involved. Finally, electrode stability measurements have shown that contrary to TDIROF, which are very stable under anodic polarization, the AIROF are rapidly corroded under anodic treatment. This corrosion is enhanced even further in the presence of formic acid.