Enapter, a German cleantech company founded in 2017, develops and manufactures AEM (Anion Exchange Membrane) Electrolyzers to produce green hydrogen as a replacement for fossil fuels. Enapter's AEM Electrolyzers are modular and can be deployed for any amount of on-site hydrogen for any application.
Challenges: hydrogen fuel
Hydrogen can be produced from multiple sources such as fossil fuels (via reforming reactions) or water (via electrolysis).
The electrolysis of water produces gasses of the highest purity. If the energy source for the electrolysis is derived from renewable sources, the electrolysis of water has a minimal environmental impact and produces green hydrogen.
Industrial scale electrolysers, alkaline electrolyzers, have two half-cells having electrodes (made by steel disks, for the simplest configuration) separated by a porous septum within circulates the electrolyte, which typically contains 30% potassium hydroxide (KOH) or sodium hydroxide (NaOH).
Due to the highly corrosive nature of the concentrated hydroxide electrolyte, the electrodes for the electrolysis reaction are typically composed of costly anti-corrosive metals and alloys arranged in the form of nets or plates, as well as electrocatalysts composed of noble metals such as platinum.
The porous septum does not allow a defined physical separation of the hydrogen and the oxygen produced. The gasses are only polarized by the current at the electrodes. In order to prevent the formation of an explosive mixture, a perfect balance between the pressures of the two gasses is required for the production of hydrogen, which is directly compressed in the electrolyzer. A perfectly constant current flow must also be maintained.
As a result, this type of electrolyzer is typically employed to produce hydrogen at pressures not exceeding 7 bar. The produced hydrogen must be compressed to the required pressure for storage, which requires additional energy.
The power supply of this type of electrolysers is connected to the grid and cannot be coupled directly to intermittent renewable energy sources such as solar and wind.
Small-scale electrolyzers, such as proton exchange membrane (PEM) electrolyzers, typically use a polymeric PEM (usually Nafion®), instead of the porous septum.
The PEM forms a physical barrier between the two gasses, making it possible to produce both gasses at high differential pressures (up to 100 bar). Oxygen is typically produced at atmospheric pressure while hydrogen is pressurized to 50 bar. This is necessary to prevent the formation of explosive mixtures both in the event of power fluctuations and in the event that the membrane is accidentally perforated.
Industrialization of PEM electrolyzers is hindered by the high cost of the materials used for the membrane-electrode assembly. Indeed, the protonic membrane, working at a very acidic condition (pH between 0.5 and 1), requires anti-corrosive platinum cathodes, platinum-Iridium anodes, and electrodes plated by platinum or ruthenium. The devices require that the anode and the cathode are immersed in solutions containing electrolytes.
In addition, for each water molecule that splits into the gasses, three molecules are transported from the anodic half-cell to the cathode, due to electro-osmosis. It generates a dual circuit for the water, one at low and one at high pressure, and the need to separate the hydrogen produced from water by a dehumidification/drying step.
Enapter Technology
The Enapter electrolyzer produces hydrogen electrolytically from an aqueous alkaline solution using a safe electrolytic device. The electrolyzer’s power supply can be coupled directly to renewable energy sources, which are inherently intermittent. The production of hydrogen can be on an industrial scale.
Enapter electrolyzer
The AEM electrolyzer comprises two half-cells, anodic and cathodic, separated by an anion exchange membrane (AEM). The surface of AEM in contact with the cathodic half-cell is a membrane-electrode assembly (MEA), and the diluted alkaline solution is present only in the anodic half-cell. The cathode is dry. The electrodes can use platinum free catalysts and steel bipolar plates.
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