Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1998-06-04
2000-08-29
Gorgos, Kathryn
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204268, 204283, 204290R, C25B 900
Patent
active
061103349
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an electrolyte cell with an end anode and an end cathode and cell elements disposed between outer cell elements comprising these and electrically connected to them and connected in series with one another, wherein each cell element comprises one or two gas diffusion electrode(s), of which one forms simultaneously the ceiling of the subjacent electrolyte chamber and the floor of the superjacent electrolyte chamber as well as the end cathode and the anodes of the bipolar cell elements comprise a perforated, electrically well-conducting electrode structure, for example of nickel, wherein each electrolyte chamber is charged with electrolyte and reaction gas, such as oxygen, for example in the form of air, and a particular mixture of electrolyte and the resulting product as well as residual reaction gas is drawn off from each electrolyte chamber. Such an electrolyte cell has for example been suggested for the generation of ammonium polysulfide (APS) to which as the electrolyte is supplied an aqueous ammonium sulfide solution and from which is drawn off a solution comprising ammonium polysulfide. The electrolyte cell comprises an anode, a gas diffusion cathode and an electrolyte chamber disposed between the anode and the cathode. The cathode comprises an electrically conducting, gas-permeable carbon layer against which flows the gas comprising free oxygen and which is in contact with the electrolyte. Gas containing free oxygen is conducted into the electrolyte chamber and hyperoxide anions (OOHO--) are formed in it. From the electrolyte chamber are drawn off a solution containing ammonium polysulfide and a residual gas. Associated with the cathode is an areal, permeable metal element, for example a metal mesh or expanded metal, to which is connected a carbon layer. The carbon layer can be a carbon cloth coated with a mixture of graphite and PTF particles.
The use of a carbon cloth in gas diffusion electrodes is problematic in all application cases for the following reasons: into the gas diffusion electrode gas must diffuse, i.e. it must be porous. On the other hand, it is necessary to prevent gas from penetrating through the gas diffusion electrode since the desired reactions take place only on the surface of the electrolyte within the gas diffusion electrode. This means that fluid must also diffuse into the electrode. In the case of fuel cells this problem has been attempted to be solved thereby that the electrolyte was immobilized, i.e. a cloth or a felt was impregnated with the electrolyte. Thus, in each instance two porous cloths, namely for example the felt impregnated with the electrolyte and the gas diffusion electrode, are opposing one another in pressing contact with each moistening the other one, but not permitting penetration of the fluid.
In electrolyte processes in which substances dissolved in the electrolyte are to be converted and in which the solubility of the substances is limited, immobilizing the electrolyte is not possible. In the electrolytic generation of H.sub.2 O.sub.2 in an alkaline electrolyte, for example, the throughput of sodium hydroxide is determined by the solubility of Na.sub.2 O.sub.2 in the sodium hydroxide. If the carbon cloth on the side facing the fluid is made hydrophilic, and, on the side facing the gas, is made hydrophobic by impregnating the side facing the gas with PTFE, the electrolyte can penetrate up to the hydrophobic layer in the gas diffusion electrode. The gas can penetrate into the hydrophobic portion up to the hydrophilic portion filled with electrolyte. The reaction takes place at the boundary layer in the pores of the, overall, porous cloth. Due to differing capillary forces of the two different layers, however, the separating force is not unlimited. It is in general approximately 0.025 bar. However this also means that at a density of the electrolyte of 1 g/cm.sup.3 the height of one electrode is limited to 25 cm. This means further that the pressure difference in the reaction volumes can also not be gre
REFERENCES:
patent: 4728409 (1988-03-01), Oloman
patent: 5358609 (1994-10-01), Drackett
Gorgos Kathryn
Parsons Thomas H
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