(415a) Imaging Amperometry: Single Particle Experiments and Theory

The ability to measure local electrochemical current density is important to a number of applications including the high throughput evaluation of electrocatalysts and corrosion studies. We have developed a method called Imaging Amperometry^1,2 that measures current density via an optical signal arising from a colloidal particle near a working electrode. The particle's height is a function of the intensity and direction of local current density, so by precisely measuring height to nanometer resolution, we infer local current density on the scale of the particle's diameter (~5 μm). Measurements are conducted using a new instrument, called the Electrochemical Total Internal Reflection Microscope (ETIRM), that combines techniques traditionally found in colloid science (TIRM) and electrochemistry (cyclic voltammetry). TIRM is used to monitor scattered light from a particle, as light intensity is exponentially related to the particle's height. A 3-electrode electrochemical measurement is conducted along with TIRM. We demonstrate this technique using a continuous Indium Tin-Oxide (ITO) thin film electrode, a discontinuous ITO thin film electrode, and a continuous (but electrochemically patchwork) ITO/gold thin film electrode. In all cases, we are able to measure local electrochemical activity by monitoring the scattered light intensity from the particle. In addition to these experimental studies, theory is presented to predict current density from the optical measurement.

1. Patent pending 2. P.J. Sides, C.L. Wirth, D.C. Prieve, An imaging ammeter for electrochemical measurements. Electrochemical and Solid State Letters, Accepted April 2010