Sensor-electrode interface

Yoon el al. [112] reported an all-solid-state sensor for blood analysis. The sensor consists of a set of ion-selective membranes for the measurement of H+, K+, Na+, Ca2+, and Cl. The metal electrodes were patterned on a ceramic substrate and covered with a layer of solvent-processible polyurethane (PU) membrane. However, the pH measurement was reported to suffer severe unstable drift due to the permeation of water vapor and carbon dioxide through the membrane to the membrane-electrode interface. For conducting polymer-modified electrodes, the adhesion of conducting polymer to the membrane has been improved by introducing an adhesion layer. For example, polypyrrole (PPy) to membrane adhesion is improved by using an adhesion layer, such as Nafion [60] or a composite of PPy and Nafion [117],... 

Although the basic principles of type III potentiometric sensors are apphcable for gaseous oxide detection, this should not obscure the fact that these sensors still require further development. This is especially true in view of the kinetics of equilibria and charged species transport across the solid electrolyte/electrode interfaces where auxiliary phases exist. Real life situations have shown that, in practice, gas sensors rarely work under ideal equilibrium conditions. The transient response of a sensor, after a change in the measured gas partial pressure, is in essence a non-equilibrium process at the working electrode. Consequently, although this kind of sensor has been studied for almost 20 years, practical problems still exist and prevent its commercialization. These problems include slow response, lack of sensitivity at low concentrations, and lack of long-term stability. " It has been reported " that the auxiliary phases were the main cause for sensor drift, and that preparation techniques for electrodes with auxiliary phases were very important to sensor performance. ... 

Zhuiykoy S. (2005) Sensors measuring oxygen activity in melts Development of impedance method for in-situ" diagnostics and control electrolyte/liquid-metal electrode interface. Ionics, 11, 352-61. 

Consequently, the proposed model allows the necessary information regarding the electrolyte-metal electrode interface and about the character of the electronic conductivity in solid electrolytes to be obtained. To an extent, this is additionally reflected by the broad range of theoretical studies currently published in the scientific media and is inconsistent with some of the research outcomes relative to both physical chemistry of phenomena on the electrolyte-electrode interfaces and their structures. Partially, this is due to relative simplifications of the models, which do not take into account multidimensional effects, convective transport within interfaces, and thermal diffusion owing to the temperature gradients. An opportunity may exist in the further development of a number of the specific mathematical and numerical models of solid electrolyte gas sensors matched to their specific applications however, this must be balanced with the resistance of sensor manufacturers to carry out numerous numbers of tests for verification and validation of these models in addition to the technological improvements. 

FIGURE 4.17 Equivalent electrical circuit for electrochemical oxygen sensor a at the absence of polarization and b polarization of the solid electrolyte-electrode interface. (From Zhuiykov, S., In-situ" diagnostics of solid electrolyte sensors measuring oxygen activity in melts by developed impedance method, Meas. Sci. Technol. 17 (2006) 1570-1578. With permission.)... 

FIGURE 4.19 Calculated (solid line) and measured (dots) hodographs of impedance for the zrrconia-based oxygen sensor at a temperature of 480°C (a) at the absence of polarization and (b, c, and d) at the blocking reaction layer appearance on the sohd electrolyte/liquid-metal electrode interface at the following magnitudes R, - 1.6 x 10 c - 8 x 10 and d... 

The results of the present work may be applicable for diagnostics of oxygen sensors at more complicated applications, such as measurement of oxygen activity in liquid sodium, lithium, or lead-bismuth heat carriers for atomic power plants. Corrosion and mass transfer in nonisothermal lead-bismuth circuits with temperatures of a heat carrier of 300-500°C do usually occur at a concentration of dissolved O2 of 10 - 10 mass %. The proposed impedance method is developed for determining the level and the character of polarization at the electrolyte-electrode interface, which ensures a continuous oxide protection of materials against corrosion by means of zirconia sensors in all tanperature regimes of exploitation of liquid-metal circuits. 

For low-frequency application (mHz to MHz), the classical approach using two or four electrodes interfaces are commonly used. The three electrodes interface is usually employed in conjunction with active electrical properties at surfaces, such as sensor surfaces. Because the behavior within the immediate vicinity of the working electrode overwhelms the measurement, the results are basically monopolar measurements. 

Amperometry in chemistry and biochemistry is the detection of ions in a solution based on electric current or changes in electric current. Electrochemistry-based amperometric sensor is a detection technique wherein a known voltage difference is applied to the working electrodes which responds with an initial transient current [1]. The current is dependent on the activity of redox species at the electrodes interface. At the beginning, the current will leap from the base current Ii, followed by falling to a steady-state value I2, which is determined by the bulk... 

A conventional solid-state potentiometric gas sensor cmisists of two electrodes (usually comprised of porous metal layers) attached to both sides of a solid electrolyte (Fig. 3a). One electrode is exposed to the gas to be detected, while the other electrode (reference) is facing a reference gas with a constant concentration. The measured gas is converted to the predominant mobile ion of the solid electrolyte, i.e., the electrolyte should have a common species with the electrode or gas phase (gas electrode). The electrode (interface) potential of such type of electrodes, referred to as electrodes of the first... 

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