Charge Storage Properties of Nanostructured Poly (3,4-ethylenedioxythiophene) Electrodes Revealed by Advanced...

PEDOT nanowires (NWs) directly grown on the conducting electrode of quartz resonators enable an advanced electrogravimetric analysis of their charge storage behavior. Electrochemical quartz crystal microbalance (EQCM) and its coupling with electrochemical impedance spectroscopy (ac-electrogravimetry or AC-EG) were used complementarily and reveal that TBA⁺, BF₄^- and ACN participate in the charge compensation process with different kinetics and quantity. BF₄^- anions were dominant in terms of concentration over TBA⁺ cations and the anion transfer results in the exclusion of the solvent molecules. TBA⁺ concentration variation in the electrode was small compared to that of the BF₄^- counterpart. However, M_w of TBA⁺ is much higher than BF₄^- (242.3 vs. 86.6 g·mol^-1). Thus, TBA⁺ cations' gravimetric contribution to the EQCM response was more significant than that of BF₄^-. Additional contribution of ACN with an opposite flux direction compared with BF₄^-, led to a net mass gain/lost during a negative/positive potential scan, masking partially the anion response. Such subtleties of the interfacial ion transfer processes were disentangled due to the complementarity of the EQCM and AC-EG methodologies, which were applied here for the characterization of electrochemical processes at the PEDOT NW electrode/organic electrolyte interface.