The Fundamentals of a Polymer Electrolyte

PEO is found to be an ideal solvent for alkali-metal, alkaline-earth metal, transition-metal, lanthanide, and rare-earth metal cations. Its solvating properties parallel those of water, since water and ethers have very similar donicites and polarizabilities. Unlike water, ethers are unable to solvate the anion, which consequently plays an important role in polyether polymer-electrolyte formation. 

Noncoordination anions with extensive charge delocalization have been very suc-cesful in enhancing the performance of dry polymer electrolytes. Examples of these are given in Table 1. 

---

In this chapter, we have presented a molecular, statistical mechanical model for the computation of the spatially dependent water permittivity in the pores of hydrated polymer electrolyte membranes. We summarize as follows some of the fundamental features of the calculation ... 

In PEMFC systems, water is transported in both transversal and lateral direction in the cells. A polymer electrolyte membrane (PEM) separates the anode and the cathode compartments, however water is inherently transported between these two electrodes by absorption, desorption and diffusion of water in the membrane.5,6 In operational fuel cells, water is also transported by an electro-osmotic effect and thus transversal water content distribution in the membrane is determined as a result of coupled water transport processes including diffusion, electro-osmosis, pressure-driven convection and interfacial mass transfer. To establish water management method in PEMFCs, it is strongly needed to obtain fundamental understandings on water transport in the cells. 

Fletcher S 1993 Contribution to the theory of conducting-polymer electrode in electrolyte solutions J. Chem. Soc. Faraday Trans. 89 311-20 Kanatzidis M G 1990 Conductive Polymers Chem. Eng. News 68(49) 36-54 Bard A J and Faulkner L R 1980 Electrochemical Methods Fundamentals and Applications (New York Wiley)... 

Although the appearance of a working PT.EC is similar to a PLED based on the same electroluminescent polymer, the working mechanism of PLECs is fundamentally different from that of PLEDs. The emissive material in PLECs consists of electroluminescent polymer and electrolyte. The electrolyte is a solid-state ionic conductor consisting of lithium salt and ion-solvation polymer. Before the application of a voltage bias, the dissolved ions... 

The fundamentals of electrolytic expansion in polyaniline films have been discussed. Ion insertion and exclusion by electrolytic oxidation and reduction are the primary mechanisms. However, it is also evident that the changes in molecular conformations, arising due to the delocalisation of 7t-electrons and the electrostatic repulsion between the polycations, are other mechanisms operating in a conducting polymer microactuator. By investigating the molecular structure and the higher order structure to optimise the electrolytic expansion, it should be possible to improve the expansion ratio and the force for practical usage. 

It is well known today that perhaps the most dramatic application of the fuel cell—an electrochemical device that may be based in the future upon the oxidation of aliphatic hydrocarbons— was in the Gemini Space Mission. In this application, the cell was based upon the use of a solid polymer electrolyte —a cation-exchange membrane in its acid form—but with hydrogen and oxygen as the fuels rather than an aliphatic hydrocarbon. Considerable research and development preceded and supported these successful missions and the units demonstrated that indeed the H2/O2 fuel cell was capable of extended performance at relatively high current densities—2l capability of fundamental importance in commercial applications. 

The process of deposition of particles at interfaces which occurs in many industrial processes, such as surface coating, is described at a fundamental level. Particle deposition can be conveniently split into three major steps (i) transfer of particles from the bulk dispersion over macroscopic distances to the surface (ii) transfer of the particles through the boundary layer adjacent to the interface (hi) formation of a permement adhesive contact with the surface or previously deposited particles leading to particle immobilization (attachment). The role of interparticle interactions on deposition is described in terms of double layer repulsion and van der Waals attraction. Particular attention is given to the effect of addition of electrolytes on particle deposition. The measurement of particle deposition using rotating disc and cyhnder techniques is described. The effect of nonionic polymers and polyelectrolytes (both anionic and cationic) on particle deposition at interlaces is described. The most universal and convenient methods for measuring particle deposition are the indirect methods. 

Measurement of Ionic Conductivity. The synthesis of solvent-free metal salt complexes of polyethylene oxides prompted detailed electrical measurements with the thought that these materials might prove to be useful electrolytes, in a hydrous environment, for high energy density batteries (13-15). Many fundamental properties of these polymer electrolytes have been examined and a large literature on the subject is available (16-17). We prepared a disk of one of our polyether complexes and measured its conductivity by impedance methods. 

Alkaline solutions are generally known to lead to better catal5Tic activities than acidic solutions for many relevant electrode reactions. However, owing to the paucity in the development of suitable electrolyte materials, such as alkaline membranes, there has been much less fundamental work in the area of fuel cell catalysis in alkaline media. Nevertheless, there are a few hopeful developments in new alkaline polymer membranes [Varcoe and Slade, 2005] that are currently stirring up interest in smdying fuel cell catalytic reactions in alkalme solution. 

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. 

A fundamental fuel cell model consists of five principles of conservation mass, momentum, species, charge, and thermal energy. These transport equations are then coupled with electrochemical processes through source terms to describe reaction kinetics and electro-osmotic drag in the polymer electrolyte. Such convection—diffusion—source equations can be summarized in the following general form... 

---