Solid electrolyte chemical sensors electrode materials

More types of oxides used for electrodes of the zirconia-based sensors both enable and encourage more possible combinations. Greater diversity in zirconia structures and types of oxide electrodes leads, in turn, to more incompatibilities in chemical, physical, electrochemical, and mechanical properties. The irony is that the more diversity achieved with advanced solid electrolyte and electrode materials, the bigger the challenges that arise for their joining. Beyond sheer diversity, modem... 

In practice, sensors with oxoanionic solid electrolytes are less successful till now, especially in tests of long-term stability. There are many reasons for this, a fundamental reason is given by the electrode processes taking place during unevitable current flows. Every direct current causes on one side a loss of solid electrolyte material in consequence of alkali ion migration and gas delivery. On the other side the discharge of alkali ions causes chemical reactions with gas components forming compounds like oxides, hydroxides, basic salts or hydrates which do not correspond to the solid electrolyte material. Every flow of direct current produces an asymmetry in the body of the oxoanionic solid electrolyte. At the cathode, besides the reactions (25-66) and (25-67), simultaneously electrode reactions are possible, for example. 

Not long ago,this group first described microelectrochemical devices, which are based on microfabricated arrays of electrodes, connected by electroactive materials. Because the active components of these devices are chemical in nature, many of these devices are chemically sensitive,and comprise a potentially useful class of chemical sensors. Devices showing sensitivity to pH, 02r 2 f and Na" have been demonstrated. These devices are, typically, operated in fluid solution electrolytes. If this class of devices is to be useful as gas sensors, systems which are not dependent on liquid electrolytes need to be developed. We have recently reported solid state microelectrochemical transistors, which replace conventional liquid electrolytes with polymer electrolytes based on polyethyleneoxide (PEG) and polyvinylalcohol (PVA). In this report, we discuss additional progress toward solid-state devices by employing a new polymer ion conductor based on the polyphosphazene comb-polymer, MEEP (shown below). By taking advantage of polymer ion conductors we have developed microelectrochemical devices, where all of the components of the device are confined to a chip. 

FICs are useful as electrochemical sensors, electrolytes and electrodes in batteries and in solid state displays (Farrington Briant, 1979 Ingram Vincent, 1984). If a FIC material containing mobile M ions separates two compositions with different activities of M, a potential is set up across the FIC that can be related to the difference in the chemical activities of M. By fixing the activity on one side, the unknown activity on the other can be determined. This principle forms the basis of a number of ion-selective electrodes LaFj doped with 5% SrF2 is used for monitoring fluoride ion concentration in drinking water. Similarly, calcia-stabilized-zirconia is used in cells of the type... 

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