Ideal electrolyte polymer electrolytes

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. 

Therefore, an ideal polymer electrolyte must be flexible (associated with a low Tg), completely amorphous, and must have a high number of cation-coordination sites to assist in the process of salt solvatation and ion pair separation (see Table 11). A review on this subject has been recently published by Inoue [594]. 

Although examining an ideal electrolyte is helpful in developing our understanding of dc polarisation, polymer electrolytes are not ideal systems since interactions between the ions of the salt are always likely to be significant in a medium of such low permittivity. It is therefore necessary to take into account two effects ... 

For a fully dissociated but non-ideal polymer electrolyte (i.e. long range ion interactions are present but not ion association) the following expressions for the steady state potential AV, and current may be derived, again assuming reversible electrode behaviour ... 

Consider a cell consisting of a polymer electrolyte, in which the salt, MX, dissociates fully into M and X " ions, the two electrodes, M, are reversible to M. The cell constant is unity, and the electrolyte is ideal. 

In the ideal situation of 100% utilization x = 1.0), the capacity corresponding to the above anode half reaction is 372 mA h g However, due to the low ion conductivity of the polymer electrolyte and the high interfacial impedance between it and the graphite electrode, this elegant example of electrochemical preparation of lithiated graphite is of limited practical significance. 

Equation (3) and (4) mean that the supply of the energetic e is needed to split water. This is the basic principle of water-electrolysis. The PEMFC is just the reverse operation of the SPE. Hydrogen fuel is decomposed into 2e and 2H+ by the catalytic cathode. The protons pass through the solid polymer (electrolyte) and arrive at the anode (A) to react with the electrons and the supplied oxygen. Then, water is produced. The electrons come to A via the external resistance. This fuel cell generates, ideally, about 1 V-direct current power. A stack of the cells is constructed to give the output power with, for example, 25 kW, which is set together to drive the vehicles. 

Supporting electrolyte-free electrolysis is an ideal way to realize perfed green synthesis assisted by electricity. Solid polymer electrolyte (SPE) technology, devel-... 

Dissociation pressures for elemental hydrides. The ideal pressure and temperature window for a practical hydride store for a transport application using a polymer electrolyte membrane (PEM) fuel cell is indicated by the grey box. 

A brief discussion on applying IS to investigate the electrical properties of polymer electrolytes has been dealt with in Chapter 7. This chapter, on the other hand, aims to introduce and provide the necessary background for beginners to use IS as a method of analysis. Thus, we begin the chapter with the definition of impedance, and then discuss the basic principles of IS followed by impedance data presentation and interpretation. Ideal and real impedance data will be presented, compared and discnssed in order to enable the readers to grasp a clearer picture on the electrical properties and electrochemical processes in a polymer electrolyte system. 

An overview on the topic of IS, with emphasis on its application for electrical evaluation of polymer electrolytes is presented. This chapter begins with the definition of impedance and followed by presenting the impedance data in the Bode and Nyquist plots. Impedance data is commonly analyzed by fitting it to an equivalent circuit model. An equivalent circuit model consists of elements such as resistors and capacitors. The circuit elements together with their corresponding Nyquist plots are discussed. The Nyquist plots of many real systems deviate from the ideal Debye response. The deviations are explained in terms of Warburg and CPEs. The ionic conductivity is a function of bulk resistance, sample... 

Therefore, the ideal solution in this field would he the use of solid plasticisers , namely of solid additives which would promote amorphicity at ambient temperature without affecting the mechanical and the interfacial properties of the electrolyte. A result that approaches this ideal condition has been obtained by dispersing selected ceramic powders, such as Ti02, AI2O3 and Si02, at the nanoscale particle size, in the PEO-LiX matrix [35-41]. The conductivity behaviour of a selected example of these nanocomposite polymer electrolytes is shown in Figure 7.5. 

For the first time, a totally solid-state electric double layer capacitor (EDLC) was fabricated using PEO-KOH-H2O as the SPE and the polymer electrolyte could replace large amount of liquid KOH electrolyte [17,18]. The ideal rectangular shape of cyclic voltammety result for this solid-state EDLC was obtained, and the real value of specific capacitance was 90 F g". It was only slightly lower than that of liquid electrolyte supercapacitor, and it might be related to the electrode material and structure. 

The absence of solvents in such solid-polymer-electrolyte photovoltaic cells presents the possibility of fabricating corrosion-free systems. The thin-film solid-state cells also allow fabrication of multispectral cells composed of more than one semiconductor in optical and electrical series. A solid-state photovoltaic cell, n-Si/Pt/PP/PEO(K.I/ l2)/Pt/ITO, was studied. The surface modifications of n-Si with PP can dramatically reduce the large activation energy barrier against efficient charge transfer between semiconductor and polymer-solid electrolyte. The efficiency of this cell is limited by a high surface recombination velocity associated with surface states of the n-Si. The cell had V = 225 mV and 11 niA cm at 100 mW cm illumination with junction ideality factor of 1.5. This implies the existence of deleterious surface states acting as recombination centres. 

Polymer Electrolyte Fuel Cells, Membrane-Electrode Assemblies, Fig. 4 Schematic depiction of the ORR on the Pt/C with ideal PFSA film in the CL... 

Fig. 4.2 (a) Ideal thermodynamic efficitaicy of polymer electrolyte membrane fuel cells (PEMFCs) compared to that obtained in the Camot process, (b) Comparison of processes in a cogenerated heat engine with fuel cell performance (From [2])... 

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