Heterogeneous solid-state membrane electrodes

Since they operate in the same fashion, the electric and electrochemical properties of the heterogeneous solid-state membrane electrodes on the market today resemble those of the homogeneous precipitate membrane electrodes in many ways. The most important data are summarized in Table 3. By the same principles outlined in the previous chapter, the heterogeneous iodide electrode can also detect cyanide. In contrast to the homogeneous membranes, those which include silicone rubber as a support ma-... 

Table 3. Heterogeneous solid-state membrane electrodes... 

The commercially available heterogeneous solid-state membrane electrodes should be conditioned in a 0.1 M solution of the ion to be measured for about 2 hours before the first measurement. With self-made electrodes having materials which are not ion-conductors, a conditioning in a 1 M measured ion solution at 90°C is recommended. Drying out of the active phase is to be avoided, since the accompanying shrinkage can cause fine cracks in the membrane. Such electrodes are best handled like glass membrane electrodes, and stored in a 0.01 to 0.1 M solution of the indicated ion between measurements. 

Several quite different types of membranes have been used in the construction of ion-selective electrodes, namely (1) glasses (2) solid-state membranes (3) heterogeneous membranes and (4) liquid membranes. 

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.

Proton-conducting membranes can be applied to reduce NO emission by combining heterogeneous catalysis and solid-state electrochemistry. The solid electrolytes in membrane reactors serve to control chemisorp-tive bonds electrochemically and enhance catalytic activity. Figure 6.8 shows a schematic diagram of a steam electrolysis cell constructed with a proton conductor for reducing NO. Steam is electrolyzed at the anode. The electrode reactions are... 

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