Water alkaline electrolysers

With the current status of water alkaline electrolysers, about 55 kWh of electrical energy is needed per kg H2. The lower heating value of H2 is 33 kWhkg . Hence,... 

Alkaline electrolysers are at an industrial stage, especially commercialized for on-site production of ultrapure hydrogen for industrial applications. In general, this hydrogen is needed at low to moderate pressure, and the cost demand is set in comparison to the alternative, which is in general the supply by tube trailers. High purity water is fed to the electrolyzer. State-of-the-art commercial alkaline electrolysers typically operate at HHV systems efficiency of 60-75% [44], Current... 

The alkaline electrolysers described here are one t5q)e of fuel cells (described as such in section 3.4). Although a detailed discussion of the quantum chemical processes involved in such devices is the subject of Chapter 3, some explanation will be given here of the mechanisms responsible for gas dissociation and the electrode losses appearing in (2.20). How do the water molecules and ions of the electrolyte behave near the electrode surfaces, or... 

FIGURE 13.37 Schematic representation of the alkaline electrolyser using a Pd-Ag thin-walled tube as cathode. (Reprinted from Int. J Hydrogen Energy, 36, A. Pozio et al., Pd-Ag hydrogen diffusion cathode for alkaline water electrolysers, 5211-5217, Copyright 2011, with permission from Elsevier.)... 

Pressurised alkaline water electrolysis technology has been state-of-the-art for many years. The system efficiency of real electrolysers ranges from 62% to 70%, including all auxiliaries (AC/DC converter, pumps, blowers, controls, etc.) based on the lower heating value of hydrogen. 

Electrolysers can be classified into three basic kinds, based on the type of electrolyte used alkaline water electrolysers, membrane electrolysers (PEM electrolysers) and high-temperature electrolysers. Alkaline water electrolysis, the oldest and, therefore, most widely used technology, is described in more detail below. Figure 10.6 shows a diagram of an alkaline water electrolyser. 

Figure 10.6. Block diagram of alkaline water electrolyser.

A concern for alkaline as well as solid polymer electrolysers should be the sensitivity of the electrolysers to contaminants in the feed water. The minimum required water quality of an industrial solid polymer electrolyzer is ASTM type II water [48], which contains at maximum 5 pg L 1 of sodium and chlorine, and 3 pg L 1 Si02 [52], It should have a maximum conductivity of 0.25 pS cm 1. Clean drinking water meeting Dutch standards contains around 60 mg L 1 of... 

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At the beginning of the past century, a few hundred electrolysers were in operation. Up to now, many electrolysis cells have been sold to produce a small amount of hydrogen from water electrolysis, but most commercial water electrolysers use an alkaline electrolyte even if other techniques are still being studied. 

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