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Electrolyte composition is a crucial factor determining the capacitive properties of a supercapacitor device. However, its complex influence on the energy storage mechanisms has not yet been fully elucidated. For this purpose, in this study, the role of three different types of electrolytes based on a propylene carbonate (PC) solution containing tetrabutylammonium perchlorate (TBAClO4), lithium perchlorate (LiClO4) and butyltrimethylammonium bis(trifluoromethylsulfonyl)imide (N1114TFSI) ionic liquid on vertically-oriented graphene nanosheet electrodes has been investigated. Herein, in situ electrochemical quartz crystal microbalance (EQCM) and its coupling with electrochemical impedance spectroscopy (EIS), known as ac-electrogravimetry, have allowed the dynamic aspects of the (co)electroadsorption processes at the electrode-electrolyte interface to be examined. A major contribution of ClO4− anions (TBAClO4) was evidenced, whereas in the PC/N1114TFSI mixture (50:50 wt%) both anions (TFSI−) and cations (N1114+) were symmetrically exchanged during cycling. In the particular case of LiClO4, solvation of Li+ cations in PC was involved, affecting the kinetics of electroadsorption. These results demonstrate the suitability of dynamic electrogravimetric methods to unveil the interfacial exchange properties of mobile species for the conception of new high performance energy storage devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

An integrated electrogravimetric study based on electrochemical quartz crystal microbalance (EQCM) unravels the interfacial ion transfer phenomena of the poly(ortho -phenylenediamine) (PoPD) thin film electrodes. Through a methodology coupling QCM with electrochemical impedance spectroscopy (ac -electrogravimetry), our work indicates that charge compensation process of PoPD in aqueous electrolytes (in acidified NaCl) occurs with the participation of multiple species, each playing a role at different temporal scales. The PoPD films are tested in a 2 electrode Swagelok cell in which Zn is used as both reference and counter electrodes and exhibit excellent stability over 8000 cycles with a relatively high specific capacitance of about 110 F g−1 at 30 C (0.63 mA cm−2) current density. The high rate capability and the excellent cycling stability of the PoPD electrodes are correlated to the electrolyte composition and the significant role of H+ to the charge compensation process is unravelled, which is made possible with coupled electrogravimetric methods of our study. By determining the interfacial flux dynamics and as well as the relative proportions of species transferred at the electrode/electrolyte interface, our results contribute to the understanding of the charge-discharge process of PoPD polymer, yet underexplored but emerging as a pseudo-capacitive electrode material. Image 1 • Poly(ortho-phenylenediamine) (PoPD) exhibits excellent stability over 8000 cycles. • Charge compensation of PoPD occurs with the participation of multiple species. • Each species' interfacial transfer takes place at a different temporal scale. • Significant role of H+ to the charge compensation is unravelled. [ABSTRACT FROM AUTHOR]

• Capacity fading of composite electrodes over cycling in Aqu-LIBs is investigated. • Water-assisted Li+ intercalation persists during cycling. • No mechanical degradation of LiCoO 2 composite electrode is observed. • Surficial evolution from LiCoO 2 to CoO results in the capacity fading. • Structural evolution of interface significantly slows down Li+ insertion kinetics. Unravelling the underlying reasons for degradation mechanism of battery materials is of great fundamental and practical importance. For a classical electrode consisting of an active material, a conductive additive, and a polymeric binder, its capacity fading is commonly related with (i) mechanical degradation of polymeric binder and/or (ii) structural and compositional degradation of active materials. The former is more relevant for electrodes showing volume expansion and represented by the progressive breakage of polymeric binder network during battery operation, leading to the dissolution of the other two components into electrolytes. The latter is generally reflected by an irreversible phase transition in active materials, which may affect the species exchanged at the electrode/electrolyte interface and their interfacial transfer dynamics. By employing a coupled methodology pairing electrochemical techniques with piezoelectric probes derived from quartz crystal microbalance (QCM), this work reports on the evolution of the interfacial processes during electrochemical cycling and correlates to the performance degradation of the electrodes. Shown on a LiCoO 2 (LCO) composite electrode as a model system, it was revealed that bare Li+ without a hydration sheath plays a dominant role in charge balance irrespective of the aging degree of the electrode under the experimental conditions of this work. However, Li+ transfer is closely accompanied with free H 2 O molecules with a Li+:H 2 O ratio around 10:1 at a polarization state close to LCO redox potential (0.65 V vs. Ag/AgCl). This ratio persists in all cycled electrodes with gradually faded interfacial transfer kinetics of Li+ and H 2 O along cycling. Such fading in species interfacial transfer kinetics driven by the surficial evolution from LiCoO 2 to CoO plays a major role in the electrode performance degradation during cycling. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The performances of all solid state potassium selective electrodes with polypyrrole film as solid internal contact were evaluated. Potentiometric measurements revealed near Nernstian responses close to values already given in the literature for classic ISEs. In addition, ac-electrogravimetry was used in order to study the ions and solvent motions at the membrane/electrolyte interface. We have found that potassium ions enter the selective membrane firstly but solvent molecules and anions are also participating in the phenomenon. [Copyright &y& Elsevier]

Models of an ion selective electrode involving an ionophore and mobile sites in a membrane are proposed. The first model, called the phase boundary potential model, supposed thermodynamic equilibrium; it allows the concentrations of the various species to be calculated. Then, a kinetic model, which takes into account the ionic transfer at the membrane|solution interfaces, was derived. The impedance of the membrane was calculated. It shows that a membrane with nernstian behavior shows only one capacitive loop in the impedance diagram, which is related to the conductivity and dielectric properties of the material of the membrane. Non-nernstian behavior is related to slow ionic transfer at the membrane|solution interfaces or/and transport limitation of the species in the membrane. Finite rate constants of the ionic transfer lead to a capacitive loop in the middle frequency range, whereas finite rate transport leads to a diffusional impedance in the low frequency range. [Copyright &y& Elsevier]

The impedance of an ion-selective electrode (ISE) to potassium with valinomycin as the ionophore and KBΦ4 as the ionic sites was measured. The membrane was made of PVC with DNP as a plasticizer. The influence of the content of the plasticizer and the membrane thickness was investigated. The concentrations of the ionophore and the ionic sites were changed to modify the response on the ISE. Finally, the selectivity was tested in terms of impedance. All impedance experiments were correlated to the potentiometric curves plotted under the same experimental conditions. The measured impedances were compared to the model proposed in the previous paper (paper I). A good agreement was found. [Copyright &y& Elsevier]

A model of ionic surfactant-selective electrodes with mobile ionic sites is proposed. The steady-state concentrations of the active species are calculated. The electrochemical impedance of the membrane immersed between electrolytic solutions is given. This model is in good agreement with the experimental results obtained on PVC membranes with various amounts of plasticizer sensitive to various ionic surfactants. The conclusion shows that to obtain a good sensitive membrane the dissociation of the species in the membrane is quite important and ionic transfer has to be fast. [Copyright &y& Elsevier]

Examines the polyphenol oxidase-alkaline phosphatase electrode in enzymes with complementary activities. Characterization of avidin coupling using quartz crystal microbalance; Derivation of biotinylated polypyrrole by electrooxidation of biotin pyrrole; Application of bienzyme electrodes.