Investigating the Adsorption–Desorption Kinetics of a Molecular Water Oxidation Catalyst at an Electrode Interface

Probing the dynamics of molecular catalysts at electrode-electrolyte interfaces is essential for understanding catalytic mechanisms. Structure-specific spectroscopic methods are particularly powerful for examining electrocatalytic interfaces but are mostly used under steady-state conditions. Herein, we combined surface-enhanced infrared absorption spectroscopy (SEIRAS) with phase-sensitive detection (PSD) to investigate the dynamics of a molecular Ir-based water oxidation catalyst at the Au-electrolyte interface. We found that the amplitude of the absorbance of the catalyst is anticorrelated to that of interfacial water. This anticorrelation can be understood by the adsorption of the electrooxidized catalyst on the electrode and concurrent displacement of interfacial water. The infrared signals from the interface exhibit an increasing phase lag with respect to the electrode potential with an increasing scan rate of the potential. Kinetic modeling suggests that the potential-dependent adsorption-desorption kinetics of the molecular catalyst on the electrode gives rise to this phase lag. This study shows that PSD-SEIRAS is a powerful tool for investigating the interfacial dynamics of electrocatalytic systems.