Electrochemical and Spectroelectrochemical Characterization of an Iridium-Based Molecular Catalyst for Water Splitting: Turnover Frequencies, Stability, and Electrolyte Effects

We present a systematic electrochemical and spectroelectrochemical study of the catalytic activity for water oxidation of an iridium-N-dimethylimidazolin-2-ylidene (Ir-NHC-Me-2) complex adsorbed on a polycrystalline gold electrode. The work aims to understand the effect of the electrolyte properties (anions and acidity) on the activity of the molecular catalyst and check its stability toward decomposition. Our results show that the iridium complex displays a very strong dependence on the electrolyte properties such that large enhancements in catalytic activity may be obtained by adequately choosing pH and anions in the electrolyte. The stability of the adsorbed compound was investigated in situ by Surface Enhanced Raman Spectroscopy and Online Electrochemical Mass Spectrometry showing that the catalyst exhibits good stability under anodic conditions, with no observable evidence for the decomposition to iridium oxide.