Ensemble average TIRM for imaging ampero

Colloidal particles can function as probes of local electrochemical current density if a functional relationship between the response of the particles and the electric field in the vicinity of the particles can be established. The nanometer scale movement of a single colloidal particle during cyclic voltammetry can be observed with the aid of total internal reflection microscopy. The intensity of scattered light can be related back to the current density local to that particle, and hence the method is called imaging amperometry. Data acquisition and optical constraints, however, make a single-particle method impractical for analysis of macro-scale (C24 1c m2) surfaces covered by several hundred thousand particles. Subdivision of the electrode into small patches, each containing an ensemble of particles, solves this problem if the scattering from the ensembles can be related to the local electric field. For example, a 100 /C2 100 array of square 100 lm patches each containing approximately two dozen particles would form a mosaic of electrochemical activity with 0.01% area resolution on a 1 cm2 electrode having location-dependent electrocatalytic properties. The focus of this contribution, therefore, is adaptation of the method from single particles to particle ensembles.