Electrolyzers high temperature

There are many types of electrolyzers high temperature, high pressure, low temperature and low pressure, and liquid electrolyte and solid electrolyte forms. For solar hydrogen production, low to medium pressure, low temperature liquid electrolyte electrolyzers are preferred. When compared to the cost of high temperature, high pressure systems and/or solid electrolyte systems, they are inexpensive to make, purchase and maintain. 

Many electrochemical devices and plants (chemical power sources, electrolyzers, and others) contain electrolytes which are melts of various metal halides (particularly chlorides), also nitrates, carbonates, and certain other salts with melting points between 150 and 1500°C. The salt melts can be single- (neat) or multicomponent (i.e., consist of mixtures of several salts, for their lower melting points in the eutectic region). Melts are highly valuable as electrolytes, since processes can be realized in them at high temperatures that would be too slow at ordinary temperatures or which yield products that are unstable in aqueous solutions (e.g., electrolytic production of the alkali metals). 

Murray J.N., Yaffe M.R., Testing aqueous caustic electrolyzers at high temperatures, Int. ]. Hydrogen Energ., 4,193-204,1979. 

Figure 7.17 shows a summary of the available conditions of water electrolysis [72]. For each configuration there exists a range of performance. Conventional electrolyzers, which nevertheless are still the most common in the current production of H 2 on the intermediate and small scale, show high overpotential and a relatively small production rate. Membrane (SPE) and advanced alkaline electrolyzers show very similar performance, with somewhat lower overpotential but a much higher production rate. Definite improvements in energy consumption would come from high temperature (steam) electrolysis, which is, however, still far from optimization because of a low production rate and problems of material stability. 

Dutta S, Morehouse JH, Khan JA (1977) Numerical analysis of laminar flow and heat transfer in a high temperature electrolyzer. Int J Hydrogen Energy 22 883-895... 

Manganese also is produced by electrolysis of fused salt. In one such process, the reduced MnO is blended to molten calcium fluoride and lime. The latter is used to neutralize silica in the ore. The fused composition of these salts is electrolyzed at 1,300°C in an electrolytic cell made up of high temperature ceramic material, using a carbon anode and a cathode consisting of iron bars internally cooled by water. 

Metallic uranium can be prepared from its oxides or hahdes by reduction at high temperature. Uranium dioxide, UO2, or other oxides such as UO3 or UsOs may be reduced to uranium metal by heating with carbon, calcium or aluminum at high temperatures. Similarly, uranium tetrafluoride or other halides can be reduced to metal by heating with sodium, potassium, calcium, or magnesium at high temperatures. Alternatively, uranium tetrafluoride mixed with fused alkali chlorides is electrolyzed to generate uranium metal. 

Vanadium metal is prepared from pentoxide, V2O5, by reduction with calcium at elevated temperatures. Presence of iodine lowers calcium reduction temperature to 425°C because of heat of formation of calcium iodide. Pentoxide also may be converted to the trichloride, VCI3, and the trichloride reduced with magnesium metal or magnesium-sodium mixture at high temperatures to form high purity ductile metal. Alternatively, a fused mixture of vanadium chloride, sodium chloride, and hthium chloride may be electrolyzed to produce the metal in high purity. 

PCEC Protonic Ceramic Electrolyzer Cell (High Temperature, H+ conduction)... 

Should this prove insufficient, or in cases where Joule s heat cannot be used for some reasons, special heating devices must be employed. Heating devices installed outside the electrolyzer are suitable for open containers and not too high temperatures. Such heaters are installed before the first cell in an arrangement of cascades with a circulation of the electrolyte. The electrolytic cell can also be provided with a steam heating jacket. 

Summary Iron-II-oxide can be readily prepared by first, electrolyzing a solution of pickling salt using iron electrodes. During the electrolysis process, a messy precipitate of mixed hydrated iron oxides is formed. Thereafter, this precipitate is collected by filtration, and then dried. The dried messy mass is then dried in a desiccator under mild heat for 12 to 24 hours to facilitate formation of the iron-II-oxide. For the preparation of iron-III-oxide, the same electrolysis process is used to form the initial messy mass, and this mass is then collected by filtration and dried in the usual manner. However, instead of drying this mass in a desiccator, it is roasted at high temperature for several hours to facilitate formation of iron-III-oxide, which is formed by the oxidization of the iron-II-oxides. 

The reflected infrared radiation is gathered by a fiber-optics light pipe and conducted to the high-temperature solid-oxide electrolysis cell. The electrical output of the solar cells also powers the electrolysis cells. About 120 megajoules are needed—whether in electrical or thermal form, or both—to electrolyze water and generate 1 kg of hydrogen. The result is that more of the solar energy is used for... 

The production of the light actinide metals is usually accomplished through the reduction of tri- or tetrafluorides with an electropositive metal, for example, Ca, Zn, or Mg. The heavy actinides are typically made through the direct reduction of oxide phases. An alternative method to access the actinide metals is through pyrochemical methods. In this technique, actinides in high-temperature molten salts, for example, NaCl-KCl or LiCl-KCl eutectics, are electrolyzed... 

---