Fuel Cell Amperometric Sensors

The working and auxiliary electrodes in this sensor are placed in the same compartment. In what type of reactions could such an arrangement cause real 

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Fig. 7.17 Fuel cell amperometric sensor (adapted from Stetter and Li, 2008)...

Introduction of room-temperature ionic liquids (RTIL) as electrochemical media promises to enhance the utility of fuel-cell-type sensors (Buzzeo et al., 2004). These highly versatile solvents have nearly ideal properties for the realization of fuelcell-type amperometric sensors. Their electrochemical window extends up to 5 V and they have near-zero vapor pressure. There are typically two cations used in RTIL V-dialkyl immidazolium and A-alkyl pyridinium cations. Their properties are controlled mostly by the anion (Table 7.4). The lower diffusion coefficient and lower solubility for some species is offset by the possibility of operation at higher temperatures. 

Figure 4 shows how the short circuit current depends on the concentration of H2 which is diluted with air or N2- It is noteworthy that for H2 in air the short circuit current is approximately in direct proportion to the H2 concentration. As mentioned before, this fact suggests that for practical purpose the amperometric sensor is more accurate than a potentiometric sensor. When H2 was diluted with N2, the sensor exhibited a very different behavior with far greater current values and a nonlinear dependence on H2 concentration. In this case, the cell is actually an H2 02 fuel cell which accounts for the greater current values. 

Different electrochemical sensors have been developed for cell concentration measurement. The most promising of these sensors are based on impedimetric measurements. A commercial version of a sensor that measures the frequency-dependent i)ermittivity is available from Aber Instruments Ltd [137-139]. Another type of electrochemical probe measures the potential changes in the cell suspension caused by the production of electroactive substances during cell growth [140-143]. To date, no on-line applications of these potentiometric sensors under real cultivation conditions have been reported. Other types of probes, such as amperometric and fuel-cell sensors, measure the current produced during the oxidation of certain compounds in the cell membrane. Mediators are often used to increase the sensitivity of the technique [143-145]. 

Electrochemical sensors include amperometric cells, especially galvanic fuel cells, and polarographic cells. Both types are available from several manufacturers world-wide in large numbers for clinical use. Higher stability with fewer technical problems makes the galvanic cell currently the most popular oxygen sensor in the operating room environment [12]. 

V and therefore the cell reaction occurs spontaneously. These cells are sometimes referred to as Mackereth sensors . Such galvanic sensors are also often termed fuel cell sensors and it is possible to measure either the resulting current or the cell voltage. In the former case, the term amperometric sensor in its widest definition is still correct, although the cell is fundamentally different from the usual Faradaic amperometric systems. Note that for the determination of atmospheric oxygen an alternative has become available in recent years in the form of optical sensors based on fluorescence. These sensors are very robust as they do not contain electrodes or a liquid phase and show very fast response times. 

Lu X, Wu S, Wang L, Su Z (2005) Solid-state amperometric hydrogen sensor based on polymer electrolyte membrane fuel cell. Sens Actuators B 107 812-817... 

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