Steam electrolyzers,

Solid Oxide Electrolysers (SOE) are in development for steam electrolysis. As electrolysis is an endothermic process, a supply of waste heat can be used beneficially to reduce the electrolyzer voltage, and thus increase its electrical efficiency. Combination with nuclear power generation and geothermal heat sources is often encountered in development programs for SOE. 

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. 

At the Institution Sainte-Barbe he learned of Sainte-Claire Deville s researches on aluminum, and at the age of fifteen years he read the latter s famous treatise. Using the steam engine and dynamo of a small tannery which he had inherited in 1885, Heroult attempted to electrolyze various aluminum compounds. In the following year, when he was attempting to electrolyze cryolite, his iron cathode melted. Since the temperature was not high enough to account for this, Heroult realized that... 

In C. E. Acker s process (1898), now abandoned,47 sodium chloride was electrolyzed in a cell in which molten lead was used as cathode, and a carbon rod as anode. During the electrolysis, the molten lead dissolved the sodium forming an alloy the chlorine was drawn off from the anodes. The alloy of lead and sodium was decomposed by steam to form hydrogen and sodium hydroxide. 

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. 

When the operation started, the iron tank and the individual boxes were filled with saturated solution of sodium (or potassium) chloride while solid salt was put into the stoneware cylinders. The level of electrolyte in tho anode boxes was always somewhat higher than in the tank. During electrolysis the temperature was kept at 85 °C by steam heating steam entered the heating element of the tank through piping H. The voltage across the electrolyzer was 3.5 to 4.0 V. The total current load was about 2500 A which corresponded to a current density of some 2 A/sq. dm. 

A more important conclusion is reached from Figure 10, which indicates that there would be severe penalties in operating the coal and oil plants intermittently. It also indicates that even electrolysis, which has been promoted as an off-peak power user, would be very expensive if operated below the 20% to 30% plant factor that is associated with "cheap off-peak power. The huge reduction in capital cost promised by the SPE electrolyzer offsets this somewhat, but operation of even an advanced electrolyzer at less than 20% of the time (5 hours/day) is unattractive compared with a dedicated, full-time reformer or gasifier. The low capital cost of steam reforming is again shown to advantage. 

CF from Figure 6), so that a combination Steam-Iron/electrolyzer plant appears to have merit. 

The committee analyzed several implications relative to domestic resource use. For biomass production, it examined the amount of land that would be required to grow the crops used as feedstocks. For coal-based hydrogen production, it examined the amount of coal that would be used over time. For technologies involving sequestration, it examined the amount of C02 that would be sequestered on a year-by-year basis and the cumulative quantity sequestered. The committee did not try to quantify several other resource use impacts it did not examine the amount of land that would be required for wind farms, production facilities, or distribution infrastructure it did not examine the impacts on water use for steam reforming processes or for biomass production it did not attempt to examine any labor force issues nor did it examine the needs for metals or other materials for fuel cells, electrolyzers, or production facilities, or the number of pipelines, or other infrastructure. 

Pham, A.Q. 2000. High Efficiency Steam Electrolyzer. In Proceedings of 2000 Hydrogen Program Review. NREL/CP-570-28890. Golden, Colo. National Renewable Energy Laboratory. 

Using proton-conducting ceramics as an electrolyte for a steam electrolyzer involves the same reactions as for a low-temperature proton-conducting polymer membrane ... 

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