Charge Diffusion on the Surface of Particles with Simple Geometries

The diffusion of charge transfer between electroactive sites on a modified surface of insulating particles is modeled assuming charge injection from an electrode supporting the particle. The current–time responses are studied for particles with shapes of a cylinder, sphere, and cube and can be used directly to determine the coverage of sites on the particle surface in a chronoamperometry measurement whereby the particles impacting an electrode hold at a suitable potential. It is shown that the current response has a characteristic behavior reflecting the particle shape and aspect ratio which allows the transient to distinguish between the various shapes and their orientations on the electrode. It is clearly shown that spherical particles have a non-Cottrellian behavior while cylinders and cubes have a characteristic Cottrellian current at sufficiently short times. Additionally, various aspect ratios of cylinders, such as flakelike, tube, or bamboolike particles, change the current response, and the shape can be assumed by comparing the current values at short and long times.