Iridium nanoparticles for the oxygen evolution reaction: Correlation of structure and activity of benchmark catalyst systems

The rotating disk electrode (RDE) is a well-known and established electrochemical tool for evaluating typical powdery electrocatalyst platforms such as platinum supported on carbon black. Unfortunately, the same cannot be said of the iridium-based catalysts typically used in polymer electrolyte membrane (PEM) water electrolyzers. The challenge essentially relies on three aspects: a) high anodic overpotentials which fatally destroy any electrode substrate; b) low loading RDE-inks for catalyst screenings may show strong sedimentation c) iridium does not show defined peaks during cyclic voltammetry. With this work, a newly developed method is presented which allows the characterization of the electrocatalytic properties of iridium based electrocatalysts in a true RDE configuration. Here we aimed to access the electrochemistry of various commercial iridium-based catalysts with different structures. We show that the stability of glassy carbon RDE and of carbon black, added to the ink in order to stabilize the dispersion is sufficient during the electrochemical testing protocol used. Reproducibility of activity results obtained on various samples is increased by stabilizing the dispersions with carbon black, resulting in reproducible and homogeneous catalyst thin films.