Heterogeneous membrane electrode

The glass membrane of the electrodes discussed above may be replaced by other materials such as a single crystal or a disc pressed from finely divided crystalline material it may be advantageous to incorporate the crystalline material into an inert carrier such as a suitable polymer thus producing a heterogeneous-membrane electrode. 

A. K. Covington, Heterogeneous membrane electrodes. Chapter 3 of Ion-Selective... 

A calcium-sensitive heterogeneous membrane electrode has been made by evaporating an alcohol-ether solution of collodion and calcium dioctylphosphate. ... 

Oscillometric or high-frequency titration was invented simultaneously and independently by Foreman and Crisp and also by Jensen and Parrak in 1946. Inorganic ion-selective heterogeneous membrane electrodes were introduced for electrometric titrations by Pungor in 1961 and those with neutral organic complexing or ion-exchange compounds by Simon in 1966. 

The real move towards ISEs based on non glass membranes came in 1961 when Pungor and Hollos-Rokosinyi (1 6) produced a membrane by incorporating silver iodide into paraffin. This led on to the development of heterogeneous membrane electrodes, especially those based on silicone rubber matrices (17 -20). 

Mascini M, Liberti A (1971) Preparation, analytical evaluation and applications of a new heterogeneous membrane electrode for coppeifll). Anal Chim Acta 53 202... 

Mascini M, Liberti A (1972) PreparatitHi and analytical evaluation of a new lead(ll) heterogeneous membrane electrode. Anal Chim Acta 60 405... 

Heterogeneous membrane electrodes, in which the active material is dispersed in an inert binder to give suitable mechanical properties (figure 1.2). Polyvinyl chloride and polystyrene, originally used as inert... 

It can be concluded that in principle the heterogeneous precipitate membrane electrodes act in the same way as the corresponding homogeneous electrodes, but often they are slower in response in practice however, they still offer manufacturing possibilities where suitable pellets of the pure crystalline material cannot be obtained. 

Heterogeneous liquid membrane electrodes. This type, which has become of considerable practical importance, consists of a liquid ion-exchange layer or a complex-forming layer within a hydrophobic porous membrane of plastic (PTFE, PVC, etc.), sintered glass or filtering textile (glass-fibre, etc.). The construction of such an electrode is depicted in Fig. 2.12. 

Fig. 2.12. Heterogeneous liquid membrane electrode (Courtesy of Orion).

Ion-selective electrodes are membrane systems used as potentiometric sensors for various ions. In contrast to ion-exchanger membranes, they contain a compact (homogeneous or heterogeneous) membrane with either fixed (solid or glassy) or mobile (liquid) ion-exchanger sites. 

The thiocyanate ion-selective electrode [21,247] This has a heterogeneous membrane containing AgCNS. It is used for the determination of the activity of SCN in suspensions of submitochondrial particles and chromatophores from Rhodospirillum rubrum in order to measure the membrane potential of these particles [200], as well as for other applications. 

Fig. 1.6 Illustration of a planar-stack, solid-oxide fuel cell (SOFC), where an membrane-electrode assembly (MEA) is sandwiched between an interconnect structure that forms fuel and air channels. There is homogeneous chemical reaction within the flow channels, as well as heterogeneous cehmistry at the channel walls. There are also electrochemical reactions at the electrode interfaces of the channels. A counter-flow situation is illustrated here, but co-flow and cross-flow configurations are also common. Channel cross section dimensions are typically on the order of a millimeter.

C3. Cattrall, R. W., Heterogeneous membrane, carbon support, and coated wire ion-selective electrodes. In Ion-Selective Electrode Methodology (A. K. Covington, ed.), Vol. 1, pp. 131-173. CRC Press, Boca Raton, Florida, 1979. 

Figure 2 Basic types of ISE (A) glass electrode (B) electrode with a solid homogeneous or heterogeneous membrane (C) classical liquid membrane electrode (D) electrode without internal solution (all-solid-state electrode) (E) coated-wire electrode. 1, Internal standard solution 2, internal reference electrode (Ag/AgCI) 3, membrane 4, glass or plastic body of the electrode 5, reservoir of the electroactive substance solution 6, solid-state contact and 7, metal wire.

Fig. 3. Ion-selective electrodes. (A) solid-membrane electrode, (B) glass electrode, (C) tip of glass microelectrode, (D) through-flow tubular electrode, (E) liquid ion-exchanger electrode, (F) electrode with restorable heterogeneous membrane layer...

Potentiometry, Fig. 4 Measuring ranges for two different potentiometric chloride electrodes with heterogeneous membrane... 

The membrane electrode assembly (MEA) in a proton exchange membrane (PEM) fuel cell has been identified as the key component that is probably most affected by the contamination process [1]. An MEA consists of anode and cathode catalyst layers (CLs), gas diffusion layers (GDLs), as well as a proton exchange membrane, among which the CLs present the most important challenges due to their complexity and heterogeneity. The CL is several micrometers thick and either covers the surface of the carbon base layer of the GDL or is coated on the surface of the membrane. The CL consists of (1) an ionic conductor (ionomer) to provide a passage for proton transport ... 

Membranes in contact with electrolyte solutions are heterogeneous systems (electrode/solution (c)/membrane/solution (c)/electrode) and generally two subsystems with different dielectric properties can be considered (the membrane and the electrolyte solution between the electrodes and the membrane surfaces). 

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