Probing Electrocatalysis at Individual Au Nanorods via Correlated Optical and Electrochemical Measurements.

A novel analytical methodology based on correlated optical and electroanalytical measurements was developed to probe electrocatalytic reactions at individual nanoparticles (NPs) with well-defined geometries. The developed methodology, Optically Targeted ElectroChemical Cell Microscopy (OTECCM), relies on a combination of optical hyperspectral imaging, to locate individual NPs and provide structural information, and Scanning ElectroChemical Cell Microscopy (SECCM), to provide direct information on the electrochemical behavior of the same NPs. This complementary strategy allows for SECCM measurements to be carried out in a "targeted" fashion, offering significant throughput advantages over conventional, scanning-based approaches. The developed methodology was applied to study the electrocatalytic oxidation of hydrazine at individual Au nanorods (NRs). Correlated electron microscopy investigations were carried out to conclusively demonstrate the ability of the proposed methodology to probe electrochemical reactions at individual NRs. A wide variety in behavior of the individual NRs was observed, with surface reactions at Au playing a prominent role in the observed response. In situ spectroscopic investigations at individual NRs suggest surface restructuring and/or residual ligand desorption leads to significant changes in catalytic activity over time. Results from the correlated electron microscopy investigations as well as the statistical analyses of data obtained for hundreds of individual nanostructures suggest that the gross geometry of a NR is a poor predictor of its electrocatalytic performance.