A new technique is described for direct measurement of mass changes of a conducting polymer electrode during electrochemical cycling. A quartz microbalance is used, with one of its contacts serving as the working electrode. Its high sensitivity permits resolution of mass changes less than 100 ng/${\mathrm{cm}}^2$. The results demonstrate that on reduction of poly(pyrrole perchlorate), charge compensation is achieved by diffusion of the lithium cation into the polymer and not the perchlorate anion into solution.

• Received 16 August 1984

DOI:https://doi.org/10.1103/PhysRevLett.53.2461