Polymer/electrolyte interface

The early literature (until 1982) is summarized in Refs. [1] and [2], Hundreds of papers have been published since then (most of them in since 1994) and it is impossible to summarize all of them here. The Proceedings of the conferences mentioned above are good, sources of recent developments though sometimes incomplete. Since the early 1980s new systems have been introduced. The most important of these are lithium-ion batteries (which have lithiated carbonaceous anodes) and polymer-electrolyte batteries. Until 1991 very little was published on the Li/polymer-electrolyte interface [3, 4], The application of the SEI model to Li-PE batteries is ad-... 

Paulus UA, Veziridis V, Schnyder B, Kuhnke M, Scherer GG, Wokaun A. 2003. Fundamental investigation of catalyst utilization at the electrode/solid polymer electrolyte interface. Part I. Development of a model system. J Electroanal Chem 541 77-91. 

At the polymer-electrolyte interface (y = mediation reaction Q + Red <= P-t-Ox into two half-reactions Q+e P and Ox+e Red, where electrons appears explicitly, in order to use the formalism of electrochemical kinetics. For the P/Q couple ... 

Polymer electrolyte fuel cell (PEFC) is considered as one of the most promising power sources for futurist s hydrogen economy. As shown in Fig. 1, operation of a Nation-based PEFC is dictated by transport processes and electrochemical reactions at cat-alyst/polymer electrolyte interfaces and transport processes in the polymer electrolyte membrane (PEM), in the catalyst layers consisting of precious metal (Pt or Ru) catalysts on porous carbon support and polymer electrolyte clusters, in gas diffusion layers (GDLs), and in flow channels. Specifically, oxidants, fuel, and reaction products flow in channels of millimeter scale and diffuse in GDL with a structure of micrometer scale. Nation, a sulfonic acid tetrafluorethy-lene copolymer and the most commonly used polymer electrolyte, consists of nanoscale hydrophobic domains and proton conducting hydrophilic domains with a scale of 2-5 nm. The diffusivities of the reactants (02, H2, and methanol) and reaction products (water and C02) in Nation and proton conductivity of Nation strongly depend on the nanostructures and their responses to the presence of water. Polymer electrolyte clusters in the catalyst layers also play a critical... 

When R2 R, the polymer is more conducting than the pores. The Randles circuit, which is located at the polymer/electrolyte interface (case b), shunts the resistive ionic rail through the polymer. At high frequencies, the equation can be simplified to... 

In an electrochemical experiment the polymer is a film sandwiched between a metal electrode, the working electrode, and a liquid electrolyte (Fig. 1). Electrons can be exchanged between the polymer (2P) and the metal (it). The exchange proceeds across the polymer-metal interface (0V it). In addition, to maintain electroneutrality in the polymer bulk, ions are exchanged between and the electrolyte (%), across the polymer-electrolyte interface ( >/%). In the case of p doping, which corresponds to oxidation of the polymer, electrons are transferred from 0 to it (and the reverse for n doping, which corresponds to a reduction). The cell includes a reference electrode, which is immersed in the electrolyte and connected to a high-impedence voltmeter. It measures the potential of the electrolyte with respect to that of a reference redox couple. Note that no current... 

Figure 18.2 depicts the electrode-polymer-electrolyte configuration that is used in the SmartSense system. Admittance in this type of electrode system is due to contributions from the interface and bulk film regions. For the electrodes under consideration, the polymer film thickness is of the order of 100 nm and the electrode separation is 0.05 cm for these dimensions, the impedance through the film itself should be in excess of 10 The measured impedance at 10 Hz, however, is of the order of 10 Q, implying that the predominant current path is across the polymer-electrolyte interface and through the electrolyte. 

As shown in figure 18.2, the electrode-polymer system is symmetric, which allows a half-cell analysis. To simplify the analysis, three assumptions are made at the outset (i) the electrolyte is highly conducting so that solution resistance is negligible (ii) oxidation occurs primarily at the polymer-electrolyte interface and (iii) the Pt-polymer interface admittance does not change substantially during an assay. Pt is the electrode material of choice because of its inertness in the system and its ability to form an ohmic contact with conducting polymers... 

Admittance spectra have been used to characterize conducting polymer-electrolyte interfaces for poly aniline [32], polypyrrole [33], and poly thiophene... 

Greszczuk et al. [252] employed the a.c. impedance measurements to study the ionic transport during PAn oxidation. Equivalent circuits of the conducting polymer-electrolyte interfaces are made of resistance R, capacitance C, and various distributed circuit elements. The latter consist of a constant phase element Q, a finite transmission line T, and a Warburg element W. The general expression for the admittance response of the CPE, Tcpr, is [253]... 

Figure 1. A photoelectrochemlcal cell with a polymer/electrolyte interface containing a light absorbing sensitizer (S) embedded in the polymer. Light absorption may enable a redox reaction of (R) dissolved in the electrolyte. When a semiconductor is the substrate, it is also often the sensitizer. (WE and CE denote working and counter electrodes).

This experiment may presage the growth of PEC systems where the light absorption, charge separation and resultant electrochemistry occur entirely within the polymeric substrate, or at the polymer/electrolyte interface. 

To improve the performance of low temperature fuel cell systems, effort has been devoted to improving the kinetics of oxygen reduction on platinum at solid polymer electrolyte interfaces. Polymer electrolyte materials, including polyperfluorosulfonic acid polymers such as Nafion -H, have been Incorporated... 

The development of an adequate equivalent circuit has been controversially discussed in the literature. Gabrielli et al. considered the polymer primarily as a non-porous layer. Transport processes in the polymer matrix dominated the impedance. Vorotyntsev et al. developed a model that took into account the electron transfer at the metal—polymer interface, transport of charge carriers in the film, and ion transfer at the polymer-electrolyte interface (Figure 11.16). 

Two charge-transfer semicircles are expected, which correspond to two RC parallel combinations of the doublelayer capacitance and charge-transfer resistance at the electrode-polymer interface and the double-layer capacitance and charge-transfer resistance at the polymer-electrolyte interface. At the metal-polymer interface, electron transfer would occur while at the polymer-electrolyte interface anion transfer is expected. 

The actuation model obtained in Section 5.3.1 is an infinite-dimensional transfer function. All parameters in the model are already fundamental material parameters and actuator dimensions except the double-layer capacitance C and the resistance R. Scaling laws for C and R can be further derived to obtain a fully scalable model. In particular, G is proportional to the area A of polymer/electrolyte interface. The resistance R can be obtained as a function of material resistivity and dimensions using a transmission line model [Fang et al. (2008d)]. Fig. 5.5 shows the experimental verification of the scaling laws for C and R, respectively. 

Kong R, McLarnon R. Spectroscopic ellipsometry of Uthium/polymer electrolyte interfaces, J. Power Sources 2000, 89, 180-189. 

It was initially assumed that polymer films in their insulating state should inhibit the reaction at the polymer electrolyte interface, such that kinetic measurements... 

The establishment of the location (reaction zone) of the electrocatalytic redox reaction is a rather complex issue. In principle, the reaction can take place at the polymer electrolyte interface, within the polymer matrix at the interfaces of the... 

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