Enapter ($132M for producing AEM electrolyzers to produce green hydrogen as a replacement for fossil fuels)

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.

Enapter AEM electrolyzer (ref. US9340882).

The Enapter electrolyzer is capable of intermittent operation; its power supply can be coupled directly to renewable energy sources, and it can provide dry, highly pure hydrogen on an industrial scale.

In the Enapter electrolyzer, the diluted alkaline solution (containing just 1% KOH) is fed exclusively to the anodic half-cell, only circulating in the anode half-cell and wetting the hydrophilicity membrane up to the surface layer in contact with the cathodic half-cell. There is no KOH in the cathode half-cell. Therefore, the cathode remains dry.

In the AEM electrolyser, the diluted KOH solution is much safer to handle than the corrosive electrolyte in a conventional alkaline electrolyser. Thus, electrocatalysts for both electrodes can be selected from non-platinum metals. The electrocatalysts of anode based on Cu, Co, Ni, Mn or mixtures, the electrocatalysts of cathode based on Ni, Co, Fe or mixtures, and steel bipolar plates are sufficient for effective hydrogen production in the AEM electrolyser.

The polymeric AEM with a thickness between 30 and 150 microns acts as a physical barrier between the two gasses, which do not mix even after prolonged periods of inactivity of the device. This results in multiple advantages: (1) high purity of the produced hydrogen, free from oxygen, water and salts of the electrolyte; (2) the ability to store hydrogen directly pressurized up to a differential pressure between the cathodic and the anodic compartment of 100 bar; (3) the ability to operate the device intermittently or with strong power fluctuations, and thus the chance to work in combination with renewable energy.

The water molecules are reduced at the cathode after passing through the AEM. With appropriate platinum-free electrocatalysts at the cathode, the hydrogen evolution reaction is efficient. The high purity hydrogen gas produced contains little moisture. The hydrogen gas is then released to the output pipeline via the gas diffusion layer.

The remaining hydroxide ions produced by the cathodic half-reaction migrate through the membrane towards the other half-cell. The exchanged hydroxide ion is an anion, which gives the AEM its name. After the hydroxide ion is transported back to the anode, it is consumed by the oxygen evolution reaction, ensuring the conditions for electrolytic equilibrium.

For every two units of hydrogen, four units of electrons are transferred to produce one unit of oxygen. Therefore, the hydroxide ion concentration in the electrolyte remains constant as long as water is continuously supplied without adding more KOH. This quantity of water is sufficient for the formation of hydrogen at a rate that prevents water evaporation during the electrolysis reaction.

In contrast to conventional alkaline electrolysers, the half-cell configuration in an AEM electrolyser allows the production of hydrogen and oxygen at pressures of 35 bar and 1 bar, respectively. The pressure difference between the two half-cells can prevent the produced oxygen from entering the high-pressure half-cell, thus ensuring that the hydrogen gas is of extremely high purity (99.9%).

Enapter Patent

US9340882 Device for the production on-demand of hydrogen by electrolysis of aqueous solutions from dry cathode

Enapter Technology Applications

Enapter’s AEM electrolyzers are used in a variety of applications, including power-to-heat and power-to-gas solutions, electricity storage industry, mobility, and research sectors.

Enapter Products

Enapter AEM electrolyzers are flexible green hydrogen building blocks: Take one modular electrolyzer, stack multiple modules or scale up production to megawatts with the ready-made AEM Multicore electrolyzer system.

Enapter electrolyzers are hardware/software hybrids that can be remotely controlled and include an intelligent EMS Toolkit for automated energy generation, storage, and transmission.

Enapter EL 2.1

Enapter offers an AEM electrolyser, the EL 2.1. The cost to produce hydrogen with the EL 2.1 electrolyser is estimated at €6.67/kg.

Enapter electrolyzer price

The EL 2.1 unit currently retails at €9,000, but Enapter is looking to achieve a short-term cost reduction of 70% to €2,500.

Enapter EL 4.0

Enapter offers an AEM electrolyser, the EL 4.0, which is a compact solution for low-cost, high-quality hydrogen.

Enapter is also developing a MW-sized AEM electrolyzer.

Enapter Funding

Enapter has raised a total of $132.2M in funding over 9 rounds, including a Seed round, two Grant rounds, a Series A round, a Series B round, three Post-IPO Equity rounds and a Post-IPO Debt round. Their latest funding was raised on Mar 1, 2023 from a Post-IPO Debt round.