Electrochemical sensor with porous polymer

In addition to the modified electrodes described in the previous sections, which usually involve a conductive substrate and a single film of modifying material, more complicated structures have been described. Typical examples (Figure 14.2.4) include multiple films of different polymers (e.g., bilayer structures), metal films formed on the polymer layer (sandwich structures), multiple conductive substrates under the polymer film (electrode arrays), intermixed films of ionic and electronic conductor (biconductive layers), and polymer layers with porous metal or minigrid supports (solid polymer electrolyte or ion-gate structures) (6,7). These often show different electrochemical properties than the simpler modified electrodes and may be useful in applications such as switches, amplifiers, and sensors. 

One typical example of an electrochemical gas sensor is a NO2 sensor developed by Do and Chang. " PANI was coated on Au/Nafion to form a conjugated polymer/metal/Nafion working electrode. The porous stmcture of coated PANI on the Au/Nafion electrode increases the electroactive area and activity of the sensor. Consequently, an increase in the sensitivity of the NO2 gas sensor was expected when Au/Nafion was replaced with PANI/Au/Nafion as the working electrode. An increase in the concentration of NO2 (in the range 0-100 ppm) resulted in a linear inaease in the current flow of the sensor. The sensitivity of the sensor, which is the slope of the current versus NO2 concentration curve, increased upon exposure to higher gas flow rates as shown in Figure 9. 

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