Our modular hydrogen production systems are based on the Enapter electrolysers. These hydrogen electrolysers use AEM technology to separate water into hydrogen and oxygen.
AEM Electrolysis.
Green hydrogen produced from water using renewable energy is recognized in many sectors as the most promising energy carrier we have for completely replacing fossil fuels. A handful of different technologies used to produce green hydrogen have been developed over the past century, but a very important piece of the puzzle has been missing for a long time. Enapter has completed this puzzle with its anion exchange membrane (AEM) technology for hydrogen production through electrolysis.
The AEM stack.
Before diving into the mechanisms of AEM electrolysis, let’s understand the most essential part in an AEM electrolyser: the AEM stack, where the water splitting reaction takes place. As shown in the figure below, the single cell is separated into two half cells by the ion exchange membrane. Each half cell consists of an electrode, a gas diffusion layer (GDL) and a bipolar plate (BPP).
Multiple single cells are connected by the bipolar plate to form the AEM stack.
The half-cell setup in an AEM electrolyser, unlike a traditional alkaline (TA) electrolyser, makes it possible to produce hydrogen and oxygen at a pressure of 35 bar and 1 bar, respectively. The pressure difference between the half-cells can prevent the produced oxygen from transferring to the high-pressure half-cell, so that the hydrogen has a very high purity (99.9%).
Split the H from the H2O.
The water electrolyte, containing only 1% potassium hydroxide (KOH), circulates only in the half-cell of the anode and wets the membrane, while the cathode side remains dry. Therefore, the hydrogen produced from the cathode half-cell has a low moisture content and it is important to note that no KOH can be found in the cathode half-cell. The water molecules pass through the membrane and are reduced at the cathode to produce hydrogen. The power supply from the external circuit is used to create an electrical potential difference at the interface of the electrolyte and the electrode. The potential difference then controls the hydrogen evolution reaction (HER) by means of electron (e–) transfer: 4H2O + 4e– → 4OH– + 2H2.
The hydrogen produced is then released to the discharge line via the GDL. Appropriate HER catalysts at the cathode facilitate the process by lowering the energy barrier of the reaction.
pH and oxygen evolution.
In the mild alkaline environment of the AEM electrolyser, the residual hydroxide ion (OH–) from the HER will return through the membrane to the half-cell of the anode. The exchanged OH– is an anion, from which the AEM takes its name. In a proton exchange membrane (PEM) electrolyser, the proton (H+) is transported through the PEM in a highly acidic environment.
Therefore, the PEM electrolyser requires platinum group metals (PGM) as catalysts and expensive bipolar titanium plates to survive the highly corrosive acidic environment, while non-PGM catalysts and steel bipolar plates are sufficient for effective hydrogen production in the AEM electrolyser. the diluted KOH solution in an AEM electrolyser is much safer to handle than the pH 14 electrolyte in a TA electrolyser.
After the OH– is transported back to the anode side of an AEM electrolyser, it is consumed by the oxygen evolution reaction (OER): 4OH– → 2H2O + O2 + 4e–. For every two units of hydrogen, one unit of oxygen is generated by transferring four units of electrons. Thus, the OH concentration in the electrolyte can remain constant by constantly feeding water without adding more KOH. The OER is driven by the potential difference at the catalytic sites on the anode and the oxygen produced is removed from the anode half-cell via GDL along with the electrolyte circulation.
Using AEM water electrolysis, Enapter’s modular electrolysers can produce 500 NL of green hydrogen per hour, with a purity of 99.9% (99.999% after drying) at 35 bar pressure from 0.4 L water and 2.4 kWh renewable energy. We think these results speak for themselves, but we cordially invite you to contact our team if you have any questions about how making green hydrogen through AEM electrolysis can work
Source: Jingwen Wang
