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Project Description and Objectives: |
For advanced alkaline water electrolysis the following criteria are important:
The plant should reach high efficiency and reliability
Therefore the cell design should aim at zero-gap or micro-gap arrangement of the electrodes and the diaphragm.
The asbestos diaphragm has to be substituted for by another harmless and more stable material allowing higher operation temperatures and gas purity at partial load (20%).
The plant should be operated pressurized up to 30 bar to allow for higher temperatures. Low water vapor content in the product gases without the need of a gas compressor is a clear benefit of pressurized electrolysis for gas storage and pipeline transportation.
The plant should have the same life time than conventional alkaline electrolysis systems.
Recycling of the materials for the plant should be possible or at least the materials should be easily desintegratable to form products that do not pollute the environment.
The GHW concept (Gesellschaft für Hochleistungwasserelektrolyse) concept of an advanced alkaline water electrolyzer achieves these aims to very high degree.
The electrolyzer is a bipolar type for an operation temperature of 150°C and 30 bars pressure. The cell stack ist encapsulated in a pressure bearing container, the cell frames therefore can be manufactured the same way as for a pressureless electrolyzer and can be made from a polymer material. An inert medium connects the interspace between cell stack and container to the electrolyte loop and.thus avoides pressure differences.
The cell design is essentially determined by the newly developed EDE-element.
The EDE-element integrates the most important three parts of an electrolyzer - the anode, the cathode and the diaphragma - in form of a thin metal - oxide ceramic compound sheet.
The EDE-sheet is 0,8 mm thick and highly porous.
It is produced in an online powder technological process. First step, after preparing of the raw materials, is foil casting of the diaphragm layer.
The electrodes are screen printed in a second step onto both sides of the diaphragm foil. The green EDE - foil ist sintered in a third step in a combined reaction sintering process in which the oxide ceramic of the diaphragm layer ist first sintered under oxidizing athmospere thereafter the porous electrodes are formed and sintered under reductive athomosphere.
In a fourth step the EDE sheet together with the bipolar plate and special interlayers is integrated to form a sandwich. The sandwichs are frames and mounted to form cell stacks.
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