Poly[3-(3,4-difluorophenyl)thiophene], MPFPT, electrochemically deposited onto carbon paper, was studied in electrochemical capacitors utilizing several tetraalkylammonium/acetonitrile electrolyte systems. Although the surface morphology of the polymer varied with the anion used for polymerization, an open and porous structure on cross section was obtained with all the electrolytes. The cycle stability of model Tee cell devices incorporating 1 cm(2) polymer electrodes was affected by both polymerization and cycling electrolytes. In general, electrolytes employing the tetraethylammonium cation yielded better cycle stability than those with tetramethylammonium cations. Devices with electrodes prepared and cycled in tetraethylammonium bis(trifluoromethanesulfonyl)imide showed the best overall performance. Symmetric and asymmetric MPFPT devices were cycled up to 10,000 times retaining 50 and 70%, respectively, of their initial charge. In the case of the asymmetric device, little or no change in the capacity was observed after the first few hundred cycles.