AbstractThe mass transport dynamics of ferrocene in polyelectrolyte polyethylene glycol lithium perchlorate (PEG · LiClO4) was studied by using chronoamperometry at a microdisk electrode. Chronoamperometry is a powerful method for the study of mass transport in polyelectrolyte, it has many advantages over the conventional methods at a microelectrode and the steady‐state method at an ultramicroelectrode. By using this method the apparent diffusion coefficientDappand concentrationCaof the electroactive species, can be estimated from a single experiment without previous knowledge of either one. We have estimatedDappandCaof ferrocene in PEG · LiClO4polyelectrolyte from 25°C to 75°C. The dependence on the concentration of electroactive species was observed. The diffusion coefficients decrease with increasing ferrocene concentration and decreasing temperature. The mass transport mechanism is explained by using a free volume