ELECTROLYSER

A Technical Appraisal of Electrolyser Characteristics.

3. TYPES OF ELECTROLYSERS

1. ELECTROLYSERS WITH LIQUID ELECTROLYTE
 

Liquid electrolytes have to be circulated within the equipment. This requirement of pre-and-post circulate liquid electrolytes is one of the main constraints for working under fluctuating loads conditions since the electrolyte has to be kept continuously circulating through the electrolyser and increases significantly the energy overhead cost of the system.

2. ELECTROLYSERS WITH SOLID ELECTROLYTE

These are known either as proton-exchange membrane (PEM) or solid-polymer electrolyte (SPE). PEM technologies have resulted in electrolysers with low volume solid electrolytes and which operate at near ambient temperature that offer very rapid and safe start up, shut down and respond to fluctuating loads much easier than the liquid electrolyte type.

Other advantage of this type of electrolysers are that efficiency is independent of size of the system whilst cost increases nearly linear to size.

PEM materials presently in use are perfluorosulphonic-acid polymers, these are plastics with physical properties very similar to TEFLON, long-chain polymers that are capable of achieveing considerable higher power densities and since they are macroscopically homogeneous polymers they are physically and chemically stable.

At the moment there are two types of membrane available  - du Pont’s Nafion and Dow Chemical’s XUS-132040.10. Both are very similar in structure.

The main different types of commercially available electrolysers are listed in the table below, together with a short description of their characteristics:

The following graphs show different characteristics for the electrolysers listened above. These graphs have been extracted from the study “Hydrogen gas production and utilisation as electricity using renewable energy source” by Prof. Ass. Faten H. Famhy & Dr Zeinab S. Abdel-Rehim, 1998.

Figure 2. Current, voltage and power characteristics of the electrolyser cell

Figure 3. Energy consumption of the electrolyser

Figure 4. PV hydrogen production figures

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