# AEM Technology

# What is the AEM technology?

Enapter’s core product is the standardized and stackable anion exchange membrane (AEM) Electrolyzer. Electrolyzers use electricity to split water (H2O) into hydrogen (H2) and oxygen (O2) through an electrochemical reaction. At the heart of the Electrolyzer sits the electrolytic stack. The stack is made up of multiple cells connected in series in a bipolar design. Enapter's unique technology relates to the special design and operation of these cells, each comprising a membrane electrode assemble (MEA) made from a polymeric AEM and specially designed low-cost electrodes. The anodic half-cell is filled with dilute KOH (alkaline) electrolyte solution; the cathodic half-cell has no liquid and produces hydrogen from water permeating the membrane from the anodic half-cell. oxygen is evolved from the anodic side and transported out from the stack through the circulating electrolyte. The hydrogen is produced under pressure (typically 35 bar) and already extremely dry and pure (about 99.9%). Using Enapter’s auxiliary Dryer module, hydrogen is delivered at 99.999% purity. As hydrogen is generated, the anodic half-cell side is topped up with distilled water or purified tap/rainwater.

# What is the difference between Proton exchange membrane (PEM) and anion exchange membrane (AEM)?

Proton exchange membrane Electrolyzers (PEM) use a semipermeable membrane made from a solid polymer and designed to conduct protons. While PEM Electrolyzers provide flexibility, fast response time, and high current density, the widespread commercialization remains a challenge largely due to the cost of the materials required to achieve good lifetimes and performance. Specifically, the highly acidic and corrosive operating environment of the PEM Electrolyzer cells calls for expensive noble metal catalyst materials (iridium, platinum) and large amounts of costly titanium. This poses an insurmountable challenge to the scalability of PEM Electrolyzers.

The anion exchange membrane Electrolyzers use a semipermeable membrane designed to conduct anions. They are a viable alternative to PEM with all the same strengths and several key advantages that lead to lower cost:

  1. AEM electrolysis works in an alkaline environment, where less expensive non-PGM1 catalysts have high stability. Therefore, PGM catalysts are not required.

  2. Due to the less corrosive nature of the environment, stainless steel can be used instead of titanium for the bipolar plates.

  3. AEM Electrolyzers can tolerate a lower degree of water purity, which reduces the complexity of the input water system and allows for the use of filtered rain and tap water. De-ionized water is not required.

# What is the difference between the traditional alkaline and AEM Electrolyzers?

Traditional liquid alkaline Electrolyzers have been on the market for quite a while and are relatively cheap. However, they are comparatively poor at responding to fluctuating power supply, and so it is difficult and costly to efficiently pair them with renewable energy sources. Traditional liquid alkaline Electrolyzers operate with highly concentrated electrolyte solutions and at low pressure. They require additional purification and compression steps to produce high quality gas at a higher output pressure. This is only cost-effective for centralized and monolithic multi-MW projects.

The AEM Electrolyzer builds on advantages from traditional alkaline Electrolyzers, but avoids its weaknesses:

  1. AEM electrolysis works in a highly diluted alkaline environment and is therefore much safer to handle.

  2. The AEM Electrolyzer can use similarly cost-efficient materials while making much purer hydrogen at higher efficiency.

  3. The AEM Electrolyzer can fully ramp and is ideal to link up with variable renewable energy sources.

# What are the advantages of AEM over PEM and alkaline?

AEM electrolysis combines the benefits of PEM and traditional alkaline.

  1. Flexible operation, safe due to the separation of H2 and O2

  2. Low stack material cost

  3. Low Balance of Plant (BOP) complexity and cost

  4. High purity hydrogen production (highest efficiency compared to PEM and traditional alkaline)

# Where are the Electrolyzers made?

At the moment, all production takes place in Italy.

# Is an oxygen concentration sensor in the hydrogen needed on the tank/vessel/cylinder? Could there be a case where oxygen from the Electrolyzer comes in, resulting in an explosive atmosphere?

No, due to the differential pressure operation of the stack (H2 at 30 bar, O2 at atmosphere), it is not possible for meaningful concentrations of O2 to get out from the H2 outlet into the tank.

# What is the operative power consumption of the AEM Electrolyzer?

The operative power consumption at standard conditions of the EL2.1 is 2.4 kW. The peak power consumption (max power draw at any time) is 3 kW and should be considered for sizing of electrical safety devices and wiring. You can find the standard specifications in the data-sheet.

# What is the hydrogen yield for the AEM Electrolyzer?

Enapter has standardized the AEM Electrolyzer into a fully stackable and flexible product: The EL2.1. Each module yields 500 NL/hr or 0.5 Nm3/hr of hydrogen gas output at 35 bar and with a purity of ~99.9% (optional >99.999% with a Dryer module). Multiple units of the EL2.1 Electrolyzers can be easily combined into one larger system.

# What is the efficiency of the Electrolyzer?

With the EL2.1, we need 4.8 kWh to produce 1 Nm³ of hydrogen. That means it takes 53,4 kWh to produce 1kg of hydrogen (compressed at 35 bar and with a purity of ~99.9%). 1 kg of hydrogen contains 33.33 kWh (using the lower heating value), i.e. our Electrolyzer already has an efficiency of 62,4%. System efficiencies (not stack efficiencies) need to be compared.

# What is the Electrolyzer cell DC voltage range?

Please understand that we don’t normally provide such information outside of an NDA, as it is part of Enapter’s intellectual property. The internal specifications of the cells, stack and other components within the Electrolyzer are not relevant to the purpose of the product, which is to produce hydrogen gas from electricity and water.

# What is the Electrolyzer cell minimum voltage?

Please understand that we don’t normally provide such information outside of an NDA, as it is part of Enapter’s intellectual property. The internal specifications of the cells, stack and other components within the Electrolyzer are not relevant to the purpose of the product, which is to produce hydrogen gas from electricity and water.

# What is the single Electrolyzer chamber voltage range?

We don’t provide such information.

# What is the electrolytic cell DC current range?

We don’t provide such information.

# How the hydrogen is pressurized inside the Electrolyzer?

Our cell allows for differential pressure when hydrogen is produced, it accumulates on the cathode side and fills the space before the back-pressure valve. Once the pressure reaches a set point (30 bar), hydrogen will start to flow from the hydrogen outlet of the Electrolyzer. The Electrolyzer will then continue to operate until the external pressure on the outlet reaches 35 bar, which is the point at which the Electrolyzer shuts down in “max pressure” mode.

# What is the pressure on the hydrogen side?

Hydrogen gas is produced at 35 bar (3.5 MPa).

# How is the pressure controlled for H2? Is it using a pressure switch and valve?

We utilize a proportional relief valve to pressurise our system before operation, and use a system of pressure transmitters to control and monitor stack and outlet pressures at all times. We use a (NO) solenoid valve to keep the process gas contained which opens and returns the system to a safe state if an error is detected.

# What is the pressure of the oxygen produced?

The pressure on the oxygen side is at atmosphere (0.1 MPa).

# What is the water content at hydrogen side outlet?

The water content in the hydrogen gas produced is ~1,000 ppm. Adding the optional Dryer removes trace amounts to >10 ppm (at -60˙C dewpoint) up to about 3 ppm (at -70˙C dewpoint) on average.

# What is the maximum differential pressure between hydrogen and oxygen side?

The differential pressure in normal operation is up to 35 bar (3.5 MPa), the maximum allowed before safety devices are triggered is 40 bar (4 MPa).

# What is the connection type and size at oxygen outlet?

The EL2.1 uses 10 mm Push Fit Quick Connectors made by John Guest for the oxygen vent outlet.

# What is the connection type and size of the water inlet?

The EL2.1 uses 8 mm Push Fit Quick Connectors made by John Guest for the refiling inlet.

# What are the connection type and size at hydrogen outlet?

The EL2.1 has the following water and gas connections: Water in, Hydrogen out, Hydrogen purge, oxygen vent, maintenance drain

# What is the water input quality requirement for the Electrolyzer?

The AEM Electrolyzer is highly resilient to water input and can be fed with purified rainwater or tap water. Simple and cheap reverse osmosis processes with resin filters can provide the required water quality. The water input to the Electrolyzer needs to be desalinated and have a conductivity of <20 microS/cm. It is not possible to use saltwater in the Electrolyzer.

# What is the required water input pressure?

Water input pressure: 0.5-4 bar.

# Can the unit be easily automatically started/stopped while in standby mode?

Yes, the unit can be controlled automatically to start/stop based on some logic rules or manual inputs via the Enapter monitoring and control system. It can also be controlled via a Modbus interface. you can also press the button on the front of the machine.

# What is the weight of the Electrolyzer (kg)?

The EL2.1 weighs 55 kg, so you must take care to handle it in a safe manner. The EL 2.1 is rack-mountable in a standard 19” cabinet. You can find all the standard specifications of the EL 2.1 on the data-sheet.

# What is the oxygen content (%) of untreated hydrogen at electrolytic cell outlet?

It is <1 ppm.

# What happens to the oxygen? Is it released back into the atmosphere? As it is also explosive are there any safety measures needed such as a dispersal unit?

There are two vent lines from the Electrolyzer which needs to be released to the atmosphere in a safe area without any ignition sources:

  1. The oxygen vent, where oxygen streams out at atmospheric pressure continuously during hydrogen generation.

  2. The hydrogen purge, where some hydrogen is vented out to release the pressure after a system shutdown.

# Are power electronics with a DC-DC conversion available?

We hope to have a feasible and cost-effective solution in the future. For now, unfortunately it is not available, and we only have the standard AC power supply option.

# What is the DC power consumption value per cubic meter of hydrogen (kwh/m3H2)?

It is 4.4-4.95 kWh/Nm3 H2. However, we do not have a DC-powered version of the EL2.1 yet. The standard power connection is 200 – 240 Vac, 50 – 60 Hz.

# What is the current density?

We don’t provide such information.

# What is the electrolytic cell rated operating temperature in degree Celsius and degree Fahrenheit?

The rated operating temperature is 55 °C and 131 °F.

# What is the ambient temperature for the operation of the EL2.1?

Our system operates at an ambient temperature of 5-45°C. The cabinet that we offer is passive and has no cooling or filters integrated. The airflow for the cooling of the systems is blown for each module individually from front to back, the cabinet allows accordingly undisturbed air flow through the front and rear door. An additional cooling cycle is not necessary. If our Electrolyzers are installed in locations with ambient temperatures outside of 5-45 ° C, or in locations with condensing humidity, the system integrator must take this into account when selecting the cabinet and, accordingly, use heating, cooling, filters, etc.

# What is the calorific value from electrolytic cell (Joule/h)?

We do not have exact measurements, the estimated value is 1840-3750 kJ/h.

# What is the partial load range of the device and how does the overall efficiency (LHV/P absorbed) behave in such range?

The system can operate from 60-100% of the nominal production rate. The power required at different production rates can be estimated with the following graph:


# What is H2 output at different production rates?

Production Rate 60% 70% 80% 90% 100%
Actual/Tested (Nl/h) 305.67 356.76 408.03 458.96 509.02
Setpoint (Nl/h) 300 350 400 450 500

Production Rate

# What is the waste heat of the Electrolyzer?

The EL2.1 is air-cooled, which means there is waste heat, which is around 400 watts. We are currently working on a water-cooled variant so that we can make better use of the waste heat.

# What maintenance is required on the AEM Electrolyzer?

The only regular maintenance needed is draining and refilling electrolyte once a year. The Electrolyzer operates with a slightly alkaline solution (1% KOH) which makes it safe and easy to handle. The electrolyte is filled into the Electrolyzer during the initial installation and is not consumed. Only water needs to be supplied to the Electrolyzer during operation, no KOH needs to be refilled. As part of the yearly maintenance of the Electrolyzer, we recommend replacing the electrolyte solution, which can be done by a technician in about 15 minutes.

# What is the lifetime of an Enapter Electrolyzer?

Based on the degradation data we have for our systems we expect a lifetime of the stacks of >30,000 hours.

# Can CO2 contamination negatively affect the lifetime of the Electrolyzer?

CO2 contamination is not a problem in our Electrolyzer, as our system design avoids potential interaction with the surrounding air. But, even if there would be CO2, they would only reduce the pH of the AEM, but this is reversible and would not contribute to explicit degradation of the membrane.

# Is Nitrogen used during the process?

No, our Electrolyzers do not use Nitrogen.

# How many connections does the Electrolyzer has?

Our Electrolyzers only have the following connections:

  1. Electrical power input.

  2. Clean water input.

  3. Hydrogen output.

  4. Oxygen vent.

  5. Hydrogen purge to safe area (for releasing the internal pressure).

# What effect do frequent start/stop cycles and ramping have on the longevity or system performance of the Electrolyzer?

The Electrolyzer is intended to be operated intermittently, as it can happen from renewable energy sources. However, like with most electrochemical systems, it is better to avoid cycling the system on and off very frequently, as this can accelerate the degradation of system performance. Meanwhile, normal use with several on-off cycles per day does not affect the system negatively.

In industrial or in-process use cases with frequent changes in the hydrogen consumption rate, we recommend installing a buffer tank (at least 50L) to hold some hydrogen and to avoid switching the Electrolyzers on and off every few minutes.

To help with the control of the devices for these constant consumption use cases, it is also possible to regulate hydrogen production to keep the outlet pressure stable at a given set point with the use of the Enapter gateway running rule-based controls; this also minimizes system cycling.

There are no specific prescriptions for the shutdown procedure, the system does this automatically. One thing to note is that after every shutdown, the system will release the internal working pressure (hydrogen at 30-35 bar) and purge a small amount of hydrogen gas from the purge line.

# What is the duration of starting the Electrolyzer until it is fully functional, in other words, what’s the warm up time?

The ramp up time of the AEM Electrolyzer depends on the electrolyte temperature (the ramp up is slower at cooler temperatures and quicker in warm temperatures). Typically, the system will start with a hydration period of 60 seconds, and then ramp up to the nominal production rate with the following values:

  • Warm-up time (time taken for the EL to heat up): The electrolyte working temperature in the AEM Electrolyzer is 55°C. The Electrolyzer can usually reach a heating ratio of 1 °C/min, at 55°C reaches maximum efficiency. For example, if we start the machine with an electrolyte temperature of 25°C it will take about 30 min to be fully operational and perform at its maximum efficiency.

  • Ramp up time (time to reach nominal production rate): Usually, the 500 NL/hr production rate is reached in about 2/3 of the total warm-up time (the warm up time is 30 min, so if you start at 25, you will need 20 min to reach max production rate)

  • Build pressure time: When the system starts and the Electrolyzer starts to heat up, the hydrogen production starts immediately, and the maximum production rate is reached later. With standard set-points, the pressure is completely built in 1/6 of the total warm up time (if you start at 25 °C, then the warm-up time is 30, so you need 5 min to build pressure)

# How constant is the output current or how sensitive does the Electrolyzer reacts to the fluctuations in the input power?

The PSU (Power Supply Unit) in the Electrolyzer needs an input voltage of 200-240 Vac. The Electrolyzer works in this range and the production rate can be varied flexibly. If the input voltage falls below the minimum voltage, the Electrolyzer switches off. If the available input current fluctuates, this information can be processed via the intelligent EMS and the production rate of the Electrolyzer can be adjusted accordingly.

# What is the surface area of the membrane?

We don’t provide such information.

# What happens after 30,000 hours, is the unit still operable with degraded performance?

Yes, the unit should still be operable with degraded performance. Towards the end of life, assuming there aren’t any other mechanical failures, the stack potential will have increased towards the maximum that can be supplied by the power supplies. The stack would still work, but it may take a longer time to ramp up, and eventually the maximum achievable production rate would decrease. Of course, this means that the efficiency would be reduced, and quite possibly at this point a module replacement will be very economical and advantageous.

1: Platinum Group Metals

2: ATmospheres EXplosible