Electrolyzer assembly

The dimensionally slahle characteristic of the metal anode made the development of the membrane chlorine cell possible. These cells arc typically arranged in ail electrolyzer assembly which docs not allow for anodc-ro-cathode gap adjustment alter assembly. Also, very close tolerances are required. The latitude that titanium affords the cell designer has made a wide variety of monopolar and bipolar membrane cell designs possible. 

Smaller electrolyzers assembled in the workshop may be lifted into prepared cell room berths and installed. Piping connections can be made up (after completion of pipework testing) with slip plates inserted at the connecting flanges to prevent drying of membranes and accidental ingress of fluids. 

With the SPE configuration, electrodes are pressed against the membrane so that the thickness of the latter fixes the interelectrode gap. A membrane can be thiimer than a physical separator, thus reducing such a kind of contribution to IR. The ensemble of electrode and membrane is usually referred to as a membrane-electrode assembly (MEA). This term is used irrespective of the operation of the cell, that is, for both electrolyzers and fuel cells. 

Preparation of Potassium Hydroxide by the Electrolysis of a Potassium Chloride Solution. Assemble an electrolyzer (see Fig. 130, p. 231). Place small cylinder 2 (8 cm in height and 4 cm in diameter) made from uncalcined clay into 0.5-litre thick-walled beaker 1. Pour a saturated potassium chloride solution into both vessels so that the level of the liquid in them will be the same. Add a few drops of phenolphthalein to the electrolyte. Use carbon rod 4 as the anode and thick iron wire 3 as the cathode. Secure both electrodes with corks in the electrolyzer lid. A d-c source at 10 V is needed for the experiment. After assembling the electrolyzer, switch on the current. What happens in the anode and cathode compartments Write the equations of the reactions. What substances can form in the absence of a diaphragm ... 

Preparation of Potassium Permanganate by the Anode Oxidation of Manganese. Assemble an electrolyzer (see Fig. 130). Use an iron wire as the cathode and immerse it into the porous clay vessel. Take a piece of manganese produced by the aluminothermic process as the anode and fasten it in place with a thin platinum wire. Only the manganese should be submerged in the electrolyte in the anode compartment ... 

In the free space between the inner vessel and the outer box, resistance wires are placed to heat the electrolyzer at the start of the process. After the electrolyte has reached a sufficient temperature the electrical heating is disconnected and air, heated to some 230—250 °C, is blown into the space to keep a constant temperature in the bath during the electrolysis. 6 graphite anodes and 7 cathodes made of perforated silver sheet are alternately suspended in the inner vessel. Both cathodes and anodes are inserted into special diaphragms made of electron and perforated at the bottom. They enclose in the form of bells each electrode. The gases liberated during electrolysis are taken off at the top of the bells. The whole assembly of anodes and cathodes is covered by an electron cover. 

Into a freshly charged cell, as previously prepared, place 300 milliliters (10.1 fluid oz.) of ice-cold tap water into the anode compartment (clay pot), and then add and dissolve 50 grams (1.8 oz.) of sodium chlorate into this water. Thereafter, place 500 milliliters (17 fluid oz.) of ice-cold tap water into the cathode compartment, and then add and dissolve 50 grams (1.8 oz.) of sodium chlorate there into. Thereafter assemble the cell as illustrated below, and then place the cell into an ice bath, and then begin the electrolysis process. The desired dimensions of the titanium electrodes may vary, but it is recommended to use rectangular bars of 10 to 15 millimeters in width of surface area (0.39 inches by 0.59 inches), and the electrodes should be placed about 127 millimeters apart (5 inches). The current should be 1.5 to 2.7 volts DC current at about 50 amps. Over voltage should be minimum, and the cell temperature should be kept below 5 Celsius at all times. Electrolyze the solution for about 18 to 24 hours. 

A monopolar electrolyzer is assembled so that the anodes and cathodes are in parallel. As a result of tliis setup, the electrical potential of all cells in the electrolyzer is the same. Monopolar electrolyzers operate at a relatively low voltage, 3 to 4 V, and high amperage, allowing circuit construction of up to 200 electrolyzers. 

Fig. 25. OxyTech MGC electrolyzer a, membrane b, anode assembly c, manifold spacer d, anolyte outlet e, catholyte outlet f, bulkhead g, brine inlet h, NaOH inlet i, insulating channel j, bulkhead insulator k, interface material 1, cathode assembly m, intercell bus n, tie rod o, current distributor p,...

The unit thus far assembled has to be turned right side up (with the negative electrode connection on the bottom) to attach the other gasket and the top blind flange. This requires a structure that supports the unit, but does not interfere with or put weight on the external part of the negative electrode on the bottom flange. The electrolyzer unit cannot be put on a flat surface. Some iron or wood supports will suffice for this purpose. 

This assembly is one of several connecting assemblies in the system. It connects the pressure tank, electrolyzer and bubbler and includes a check valve, a pressure gauge, and an on/off valve. Stainless steel Yor-Lok tube fittings are used throughout with %" stainless steel tubing. 

The PEM cell design chosen for tlie current work employs a significantly different geometry than the Westinghouse cell. The PEM electrolyzer consists of a membrane electrode assembly (MEA) inserted between two flow fields. Behind each flow field is a back plate, copper current collector and stainless steel end plates. The MEA consists of a Nafion proton-exchange-membrane with catalyst-coated gas diffusion electrodes bonded on either side. 

The second electrolyser was a research unit assembled for SRNL by the University of South Carolina (USC). It was constructed with platinised carbon cloth electrodes, a Nafion 115 PEM electrolyte, carbon paper flow fields, solid graphite back plates, copper current collectors and stainless steel end plates. The USC electrolyser had an active cell area of 40 cm and a Pt catalyst loading of 0.5 mg/ cm (only one-eighth that of the commercial cell). The carbon-based configuration proved to be much more corrosive resistant than the commercial-type electrolyzer. A photograph of the two electrolyzer units is shown in Figure 3. 

In a bipolar electrolyzer, each electrode has both a positive and a negative face, with the positive face in one cell and the negative face in the adjacent cell. Proponents say that bipolar electrolyzers take up less floor space than unipolar ones and that they are better suited to high-pressure and high-temperature operation (which is more efficient). Their drawbacks are that they require much more precise tolerances in construction and that they are more difficult to maintain. (If one cell fails, the entire assembly has to be shut down.)... 

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