Electrochemical Sensors with Liquid Electrolyte

It is clear that composites in electrochemical gas sensors with liquid electrolytes can be applied only in electrodes and membranes. It was established that the preparation of hybrid composite materials has led to the achievement of modified electrode surfaces that exhibit special properties due to the synergic effect from the individual components. 

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Electrochemical sensors with a liquid electrolyte are widely used for the detection of corrosive or toxic gases in the workplace. Portable monitors are used in short time measurements of exhaust gases as well. These sensors work amperometri-cally - an external voltage supply is connected with the electrode on both sides of the measuring cell. 

Electrochemical gas detection instruments have been developed which use a hydrated solid polymer electrolyte sensor cell to measure the concentration of specific gases, such as CO, in ambient air. These instruments are a spin-off of GE aerospace fuel cell technology. Since no liquid electrolyte is used, time-related problems associated with liquid electrolytes such as corrosion or containment are avoided. This paper describes the technical characteristics of the hydrated SPE cell as well as recent developments made to further improve the performance and extend the scope of applications. These recent advances include development of NO and NO2 sensor cells, and cells in which the air sample is transported by diffusion rather than a pump mechanism. 

Cai Q, Xian YZ, Li H, Zhang YM, Tang J, Jin LT (2001) Studies on a sulfur dioxide electrochemical sensor with ionic liquid as electrolyte. Huadong Sfaifan Dtixue Xuebao, Ziran Kexueban 2(X)l(3) 57-60 Demus D, Goodby J, Gray GW, Spiess H-W, Vill V (eds) (1998) Handbook of liquid crystals. Wiley, Weinheim, Vol. 1, Chap. 2, pp. 18-19... 

Materials for Electrochemical Gas Sensors with Liquid and Polymer Electrolytes... 

Solid-state electrochemistry — is traditionally seen as that branch of electrochemistry which concerns (a) the -> charge transport processes in -> solid electrolytes, and (b) the electrode processes in - insertion electrodes (see also -> insertion electrochemistry). More recently, also any other electrochemical reactions of solid compounds and materials are considered as part of solid state electrochemistry. Solid-state electrochemical systems are of great importance in many fields of science and technology including -> batteries, - fuel cells, - electrocatalysis, -> photoelectrochemistry, - sensors, and - corrosion. There are many different experimental approaches and types of applicable compounds. In general, solid-state electrochemical studies can be performed on thin solid films (- surface-modified electrodes), microparticles (-> voltammetry of immobilized microparticles), and even with millimeter-size bulk materials immobilized on electrode surfaces or investigated with use of ultramicroelectrodes. The actual measurements can be performed with liquid or solid electrolytes. 

Amperometric gas sensors are the second most important group of electrochemical gas sensors. The development of these sensors can be traced back to the introduction of the Clark-electrode in the mid-1950s, which is well known for the determination of dissolved oxygen. Amperometric gas sensors consist of a working electrode mostly covered by a membrane, a counter and a reference electrode which are in connection with a liquid electrolyte solution. These sensors have been designed in different forms and are significant also in commercial terms. The schematic setup is shown in Fig. 19.5. ... 

Although IL electrolytes provide partial selectivity, the primary selectivity of an IL-electrochemical sensor comes from the redox properties of the analyte observed using amperometric methods, wherein the electrical current generated by reaction of an analyte at an electrode at a fixed or variable potential is measured [22]. We have shown redox chemistry that occurs only in ILs and can be exploited to enhance sensor performance [202], As shown in Fig. 2.16, we discovered that at platinum electrode in [NTf2]-based ionic liquids (ILs), facile methane electro-oxidation is observed suggesting a unique catalytic Pt-INTfj] interface for electron-transfer reaction of methane at room temperature. Little methane electro-oxidation signals are observed in ILs with other anions. In this experiment, an oxygen reduction process... 

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