Micromorphological Dynamics of Polypyrrole Films in Propylene Carbonate Solutions Studied by in Situ AFM and EQCM

Abstract

Polypyrrole (PPy) films obtained by low-current galvanostatic polymerization of pyrrole in propylene carbonate solutions exhibit excellent reversibility, high anodic stability, and, at the same time, a characteristic change in the shape of the voltammetric response and an increase in the film's doping level during longterm potentiodynamic cycling. To understand the behavior of PPy films, we performed their characterization by in situ atomic force microscopy, which shows drastic changes in the micromorphology (and its dynamics) of freshly prepared and long-term cycled PPy films. In addition, a parallel study of the same PPy film was performed by electrochemical quartz crystal microbalance (EQCM), to correlate micromorphological changes in the films occurring as a result of continuous cycling with their ion-exchange mechanism. The morphological and mass changes are discussed in light of the fact that there are chemically different structures of PPy and in terms of a conformational relaxation model.

Electrochemistry of Electronically Conducting Polymers

“…The potential first increases, and then decreases, due to the development of an internal surface of the deposited oligomeric nuclei. During the deposition process, the mass of the coating increases almost linearly with the charge involved, thereby demonstrating mass per electron (mpe) values of 52-56 g mol À1 [43]. The stoichiometry of the electropolymerization of pyrrole is the same as that for thiophene (see Figure 11.4), and estimated as 2.3e À per mol monomer units.…”

“…The growth of the polymeric film can be studied using chronoamperometry. An example [43] is shown in Figure 11.4, where a characteristic rising current transient is due to a gradual increase of the internal surface of the film through which the current passes (similar to the classical mechanism of electrodeposition of metals [44]). The higher is the potential, the faster is the nucleation step and the following films growth.…”

“…The complicated mechanism of doping is best studied by the combined application of CVand EQCM. A typical example is the galvanostatic polymerization of PPy films [43] (see Figure 11.5a). The potential first increases, and then decreases, due to the development of an internal surface of the deposited oligomeric nuclei.…”

The Art of SPM: Scanning Probe Microscopy in Materials Science

“…[28] Others have characterized phospholipid layers formed by solution spreading, which are models for biological membranes; [29] analyzed the reversible switching between ordered and disordered structures of molecular layers of hexadecane on Au(111) surfaces; [30] tracked the reorganization of polycrystalline monolayers at the solid/liquid interface; [31] and correlated morphological changes of polypyrrole films as a potential cathode material for Li-ion batteries with their ion-exchange characteristics during continuous cycling. [32] Moreover, studies of the enzymatic degradation of biodegradable polymers have been performed. [33] The authors were able to follow the degradation process of melt-crystallized poly[(R)-3-hydroxybutyric acid] (P3HB) in a phosphate buffer solution containing PHB depolymerase from a specific microorganism by in-situ AFM (Fig.…”

Review—Recent Research Progress in Surface Modification of LiFePO4Cathode Materials

“…82,83 Besides, PPy has a theoretical capacity of 72 mAh•g −1 . 84 However, PPy suffer from its worse structure stability. 85,86 To address these drawbacks, PEG polymers with a superior solubility have successfully developed to improve mechanical and structural properties of PPy as a coating layer for LiFePO 4 .…”