An Imaging Ammeter for High Throughput Electrochemical Research

Rapid testing of electrocatalysts and corrosion resistant alloys accelerates discovery of promising new materials. Imaging amperometry, based on the deployment of colloidal particles as probes of the local current density, allows simultaneous electrochemical characterization of the entire composition space represented in a thin-film alloy "library" electrode. Previous work has shown that nanometer scale variations in particle-electrode distance for single particles in electric fields can be measured optically and translated into local current density, independent of electrical measurements. Implementation of this method to enable simultaneous measurements across non-uniform samples involves using a sparse, uniform layer of particles, which requires modification of previously existing theory and methods. Imaging individual particles for this application is infeasible at the low magnification levels needed to image an entire macroscopic (~1 square cm) sample. Mapping of electrochemical activity across the surface can be achieved nevertheless by imaging the entire electrode surface and gridding the resulting images into a mosaic of square “patch” areas 100 μm to a side, each containing 15-30 particles. The work presented in this dissertation shows that the integrated light intensity in each patch is the sum of the light scattering from all of the particles present in that patch, and that this total measured intensity can be used to infer the current density in the patch during electrochemical experiments. In addition to scaling the imaging ammeter up to ensembles of particles, the theory for translating measured particle motion to current density has been substantially improved. These improvements involve proper modeling of the