Ionic devices

A cumulative success of artificial ion-channel functions by simple molecules may disclose a wide gate for the design of ion channels and possible applications to ionics devices. Incorporation of these channels into bilayer lipid membrane systems may trigger the developments towards ionics devices. The conventional BLM system, however, is not very stable, one major drawback for the practical applications, and some stabilization methods, such as impregnating the material in micro-porous polycarbonate or polyester filters, are required. On the other hand,... 

The development of solid state conducting solids that are on a par with liquid electrolytes has revolutionized the design of batteries and other solid state ionic devices (SSIs) in recent years, and this section explains the operating principles behind some of these devices. Figure 5.15 is a simple schematic diagram which we can use to explain the operation of several different types of electrochemical device. 

Several types of studies directed towards the development of artificial ion channels and the understanding of ion motion in channels are being carried out. These effectors will be considered in Section 8.4 they deserve and will receive increased attention, in view also of their potential role as molecular ionic devices. 

As regulation systems involving effectors, coupled transfers of charges and of mass, gates and pumps, transport processes extend towards the chemistry of information storage and retrieval at the molecular level, and are a major component in the design of molecular ionic devices (see Section 8.4). They thus open wide perspectives for the basic and applied developments of the functional features of supra-molecular chemistry. 

Molecular devices have been defined as structurally organized and functionally integrated chemical systems they are based on specific components arranged in a suitable manner, and may be built into supramolecular architectures [1.7,1.9]. The function performed by a device results from the integration of the elementary operations executed by the components. One may speak of photonic, electronic or ionic devices depending on whether the components are respectively photoactive electroactive or ionoactive, i.e., whether they operate with (accept or donate) photons, electrons, or ions. This defines fields of molecular and supramolecular photonics, electronics and ionics. 

In particular, the formation of ordered arrays of photoactive units like porphyrins or of ion binding sites (e.g. macrocyclic polyethers see also [8.202]) may induce directional electron and energy transfer or ion channel features [9.171a, 9.172], Such effects are of interest for optoelectronic information storage and for ionic devices. 

The polymerized ionic liquid (IL) shows great promise for diverse applications. Some polymerization methods have already been oriented toward specific applications. Polymerized ILs are useful in polar environments or where there are ion species for transport in the matrix. Amphoteric polymers that contain no carrier ions are being considered for several porposes in polymer electrolytes. Zwitterionic liquids (ZBLs) were introduced in Chapter 20 as ILs in which component ions cannot move with the potential gradient. ZILs can provide ion conductive paths upon addition of salt to the matrix. It is therefore possible to realize selective ion transport in an IL matrix. If the resulting matrix can form solid film over a wide temperature range, many useful ionic devices can be realized. This chapter focuses on the preparation and characteristics of amphoteric IL polymers. 

PEVD has been applied to deposit auxiliary phases (Na COj, NaNOj and Na SO ) for solid potenfiometric gaseous oxide (CO, NO, and SO ) sensors, as well as a yttria stabilized zirconia (YSZ) ceramic phase to form composite anodes for solid oxide fuel cells. In both cases, the theoretically ideal interfacial microstructures were realized. The performances of these solid state ionic devices improved significantly. Eurthermore, in order to set the foundation for future PEVD applications, a well-defined PEVD system has been studied both thermodynamically and kinetically, indicating that PEVD shows promise for a wide range of technological applications. 

In spite of the great promise solid state ionic devices offer, few commercial successes have been reported to date. The major problems faced today in the field of solid state ionic devices are still material related. At present, the key technical challenge is development of reliable and cost-efficient techniques to synthesize solid state ionic materials to serve as solid electrodes and electrolytes. On the other hand, these materials are not used in isolation, but in an electrochemical system and must be in contact with each other. The response of solid state ionic materials in solid state ionic devices is highly... 

The present availabihty of numerous types of solid electrolytes permits transport control of various kinds of mobile ionic species through those solid electrolytes in solid electrochemical cells, and permits electrochemical reactions to be carried out with the surrounding vapor phase to form products of interest. This interfacing of modem vapor deposition technology and solid state ionic technology has led to the recent development of polarized electrochemical vapor deposition (PEVD). PEVD has been applied to fabricate two types of solid state ionic devices, i.e., solid state potenfiometric sensors and solid oxide fuel cells. Investigations show that PEVD is the most suitable technique to improve the solid electrolyte/electrode contact and subsequently, the performance of these solid state ionic devices. 

It has been more than 60 years since Wagner s electrochemical tarnishing theory was developed. Finally, the two parallel suggestions of material transport and energy transformation in the theory are interconnected, and newly developed PEVD will make solid state ionic devices better to serve today s ever-growing energy and environmental demands. 

Chu, W.F., Thin- and thick-film solid ionic devices, Solid State Ionics, 52, 243-248 (1992). 

Garzon, R., Mukundan, R. and Brosha, E.L. (2001) Modeling the response of mixed potential electrochemical sensors. Proceedings of the Electrochemical Society, 2000-32 Solid-State Ionic Devices II Ceramic Sensors, The Electrochemical Society, Pennington, New Jersey, pp. 305-13. 

Rutman, J. and Riess, 1. (2008) Reference electrodes for thin-film solid-state ionic devices. Solid State Ionics, 179 (1-6), 108-12. 

---