Ring-Shaped Electrochemical Cell

As a first step in the development of new cell designs, ring-shaped electrochemical cells were prepared in our laboratory. This configuration, also termed bipolar configuration of the first generation, allows for experimental determination of the current bypass. Nearly bypass-free configurations have been realized. The feasibility of electrochemical promotion in such bipolar cells has been successfully demonstrated. 

Indirect bipolar (IB) polarization of the catalyst film in a ring-shaped electrochemical cell is realized by using the two gold electrodes as feeder electrodes. For advanced characterization of the cell, a third electric connection may be added. This latter, connected to the catalyst film itself, permits measurements also in the direct (monopolar) polarization mode, which is useful for the determination of the current bypass. 

The ring-shaped bipolar electrochemical cells were applied successfully to achieve electrochemical promotion in several systems. Efficient promotion of the combustion of ethylene using RUO2/YSZ cell of this type of configuration was reported first. Here the feasibility of electrochemical promotion with ring-shaped cells is illustrated with the example of the reduction of NO by propylene using a Rh/YSZ cell, of the same type presented in detail in the previous section.  

The results clearly demonstrate the feasibility of electrochemical promotion with bipolar configurations of the first generation. 

---

Figure 29. Schematic of various modes of polarization using a ring-shaped electrochemical cell.

Kinetic measurements with bipolar electrochemical cells were made using the same experimental setup as with single-pellet cells described in Section III.2.H and seen in Figure 7. Two types of bipolar electrochemical cells have been developed in our laboratory, a ring-shaped and a multi-channel configuration. As shown in Figure 28,... 

Figure 28. Left tubular reactor assembly and furnace used with bipolar cell configurations. 1 Pyrex tube (0=25/18 mm, length 400 mm, volume 150 mL) 2 electrochemical cell. Right bipolar electrochemical cells. A ring-shaped cell configuration B multiple-channel cell configuration.

ECO cell — Electrochemical cell which is applied in wastewater treatment. A rotating cylinder employed as cathode and fixed anodes at the periphery are separated by a diaphragm. Small disks reaching from the separator up to close to the rotating cathode split the catholyte section into small ring-shaped compartments. Movement of the solution from one compartment to the next is possible only through the small gap. 

Fig. 1.9 For in situ IR vibrational characterization of an electrochemical interface the silicon electrode in the double O-ring cell has to be shaped as an ATR prism.

A special O-ring cell design is needed for in situ infrared (IR) vibrational characterization of an electrochemical interface. The absorption of one monolayer (i.e. <1015 cm 2 vibrators) can be measured if the silicon electrode is shaped as an attenuated total reflection (ATR) prism, which allows for working in a multiple-in-ternal-reflection geometry. A set-up as shown in Fig. 1.9 enhances the vibrational signal proportional to the number of reflections and restricts the equivalent path in the electrolyte to a value close to the product of the number of reflections by the penetration depth of the IR radiation in the electrolyte, which is typically a tenth of the wavelength. The best compromise in terms of sensitivity often leads to about ten reflections [Oz2]. 

---