Abstract
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, Mw 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.
Highlights
Among the vast possibilities of electrode materials for pseudo-capacitors, electroactive conducting polymers (ECPs) are a very attractive solution due to their low price, non-toxicity and tunable chemical, electrical and physical properties [1]
Electrochemical quartz crystal microbalance (EQCM) and its coupling with electrochemical impedance spectroscopy were used complementarily and reveal that TBA+, BF4− and ACN participate in the charge compensation process with different kinetics and quantity
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Summary
Among the vast possibilities of electrode materials for pseudo-capacitors, electroactive conducting polymers (ECPs) are a very attractive solution due to their low price, non-toxicity and tunable chemical, electrical and physical properties [1]. These polymers can be electrochemically generated/doped in the presence of an electrolyte to obtain very good electrical conductivity (10 to 100 S·cm−1) and a wide electrochemical window. As the conducting polymer electrode is charged and discharged, the ionic exchanges with the electrolyte should happen very reversibly without damaging the polymer structure and should persist during a long cycling period, leading to suitable material for pseudo-capacitors. Even though the specific capacitance values achieved with these materials (300–800 F·g−1) are lower than those obtained with certain transition metal oxides [5,6], extensive works have been made and reported in the past decades to investigate their potential for capacitor applications [1,2,3]
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