Redox-Active Solid-State Electrolytes

Zhong, J., Fan, L.-Q., Wu, X., Wu, J.-H., Liu, G.-J., Lin, J.-M., Huang, M.-L., Wei,Y.-L., 2015b. Improved energy density of quasi-solid-state supercapacitors using sandwich-type redox-active gel polymer electrolytes. Electrochim. Acta 166,150-156. 

Another opportunity to realize constant activity of the potential determining ion at the reference interface appears when one chooses the solid electrolyte in such a way that the ion of the redox couple is the same as one ion of the major component of the electrolyte. In that case, the change of the activity due to the electrode reaction with the gas can be neglected against the overall constant activity of that ion in the salt. This is the solid-state reference arrangement. An example is the chlorine sensor (Fig. 6.40), in which the reference potential is set up by the constant activity of CP in the solid AgCl electrolyte. This arrangement is equivalent to a reference electrode of the second kind, discussed in Section 6.2.2.1. 

Figure 5 shows an example from a new class of solid-state microelectrochemical transistors, which are based on redox-active molecules dissolved in the polymer. The redox-active material is N,N,N, N -tetramethyl-p-phenylenediamine (TMPD) which is sublimed into the MEEP/LiCF3S03 film. Here, the MEEP/LiCF3S03 acts as both polymer host and electrolyte. The transistor characteristic of this device is also shown in Figure 5. Below 0.0 V vs. Ag, the device is off, Iq = 0, since all the TMPD is neutral. As TMPD is oxidized, the device turns on, with a maximum Iq near /2 TMPD" /. We have...

Optical memory (open-circuit memory). Optical memory is defined as the time that an electrochromic material maintains its absorption state once the applied voltage is removed. Solution-based electrochromic systems will bleach (lose their absorptive state) more quickly than their solid-state counterparts [24]. In the solution case, the mobile redox-active species, which are dissolved in an electrolyte, can diffuse to both electrodes when the circuit is open. Therefore, there is no open-circuit memory in these devices and power must be supplied continuously to maintain coloration. 

Fig. 14.9 Schematic representation of the dominant processes assumed to influence the voltammetric response when a chemically modified electrode consisting of a redox-active microparticle adhered to an electrode and coated with a layer of ionic liquid is placed in contact with aqueous electrolyte, dj and 2 are the thicknesses of solid-state phase and ionic liquid phase respectively. Adapted with permission from Zhang et al.. Anal. Chem. 2003, 75, 6938-6948 [23]. Copyright 2013, American Chemical Society...

It should be noted also that the redox couple may be solution-soluble or may be immobilized within an electrode coating and that, in the former case, the chemical step may be carried out (1) with the organic substrate dissolved within the electrolyte (2) at the interface between the electrolyte and the substrate present as a separate phase or dissolved in a solvent immiscible with the electrolyte (3) within a solvent immiscible with the electrolyte, the redox reagent in its active oxidation state being extracted into the other solvent (maybe by phase-transfer catalysis) and (4) at the interface between the electrolyte and the organic substrate present as a solid. 

The superior mechanical properties of elastomeric electrolytes, combined with the simplicity of fabrication of thin separator films from these materials, has led to very active pursuit of solid state cells based on solid polymeric materials. However, the development of a novel class of solid state or nic positive electrodes which not only operate on an entirely new principle for energy storage, but have demonstrated performances in a number of instances exceeding those for intercalation electrodes in solid state hthium and sodium batteries. These new electrodes have been called solid redox polymerization electrodes (SRPE) and arc based on polysulfide polymers [-S(R) 0 (R) S-] where R is an organic radical such as CH3, QH, CF3, etc. The redox mechanism for the positive electrode is in essence a redox dimeriza-tion/scission reaction which occurs in two steps as... 

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