# AEM Technology

# Hydrogen in General

# What is the energy content of hydrogen?

The energy content of hydrogen is described in the (lower and higher) heating value. The lower heating value of hydrogen can be expressed as 33.33 kWh/kg or 2.78 kWh/Nm3. The higher heating value of hydrogen is 39.41 kWh/kg or 3.28 kWh/Nm3. That means roughly 3 kWh/Nm3.

1 kg hydrogen is equivalent to 2.75 kg gasoline (based on the lower heating value).

# How much does hydrogen weight?

The weight of hydrogen is 0.08988 g/L. Enapter’s electrolysers produce 0.5 Nm3/h (500 NL/h) or 0.04494 kg/h. One EL2.1 module produces 12 Nm3 of hydrogen gas in 24 hours, weighing > 1kg (1.0785 kg). At the normal output pressure of the EL2.1 with 35 bar, 1 kg of hydrogen occupies a volume of 0.343 m3 (343 L).

A full tank of hydrogen for a passenger vehicle contains about 5 kg of hydrogen gas (stored at 700 bar) and can drive for over 500 km.

Filling up a 500 L tank with one EL running at 100% and at 35 bar takes about 35 hours until it is full.

# When stored in a tank, what are the losses over time through leakage? Does hydrogen, like for example diesel, have an "expiry date"?

When properly stored, there are no losses. While diesel and all other Hydrocarbon based fuels have an expiry date of around a year, hydrogen can be stored for years.

# Enapter's AEM Technology

# What is Enapter's AEM technology, and how does it work?

Enapter's core product is the standardised and stackable anion exchange membrane (AEM) electrolyser. Electrolysers use electricity to split water (H2O) into hydrogen (H2) and oxygen (O2) through an electrochemical reaction. The stack is the electrolyser's heart and comprises multiple cells connected in series in a bipolar design. Enapter's unique technology is the design and operation of these cells, consisting of a membrane electrode assemble (MEA), made from a polymeric AEM and specially designed low-cost electrodes. Oxygen is evolved from the anodic side and transported out from the stack through the circulating electrolyte. The hydrogen is produced under pressure (up to 35 bar) and already extremely dry and pure (about 99.9%). Using Enapter's auxiliary dryer module, hydrogen is delivered at 99.999% purity.

# What is the difference between the Proton Exchange Membrane (PEM) technology and the Anion Exchange Membrane (AEM) technology, and what are the advantages of AEM?

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

The anion exchange membrane electrolysers 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- Platinum Group Metals (PGM) 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 electrolysers can tolerate a lower degree of water purity, which reduces the input water system's complexity and allows filtered rain and tap water. A de-ionisation of the water is required.
  4. A flexible, safe operation due to the separation of H2 and O2
  5. High purity hydrogen production

# What is the difference between the traditional alkaline and AEM technology, and what are the advantages of AEM?

Traditional liquid alkaline electrolysers have been on the market for quite a while and are relatively cheap. However, they are comparatively slow at responding to a fluctuating power supply, so it is difficult and costly to pair them with renewable energy sources efficiently. Traditional liquid alkaline electrolysers 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 electrolyser builds on advantages from traditional alkaline electrolysers, but avoids its weaknesses:

  1. AEM electrolysis works in a highly diluted alkaline environment and is therefore much safer to handle.
  2. The AEM electrolyser can use similarly cost-efficient materials while making much purer hydrogen at higher efficiency.
  3. The AEM electrolyser is fully scalable and is ideal for linking up with variable renewable energy sources.

# What is the Enapter dryer? What is the technology behind it, and how can it be installed?

The Enapter dryer raises the output purity of hydrogen gas from the AEM electrolyser to >99.999% in molar fraction. It is a hybrid temperature/pressure swing adsorption system that comprises two cartridges filled with a highly adsorbent material. The system is fully integrated into the Enapter Energy Management System (EMS) (opens new window) to monitor the state, temperatures and pressures.

The dryer will be installed at the H2 outlet of the electrolyser. One dryer can dry the outlet of up to five electrolysers at 35 bar or two electrolysers at 8 bar.

# The electrolyser in general

# Where are the electrolysers manufactured? Where is Enapter producing its electrolysers?

Currently, all production takes place in Crespina, Italy, close to Pisa. Enapter is presently preparing a mass production site in Saerbeck, Germany.

# What is the lowest production rate? What is the hydrogen percentage while producing on the lowest production rate?

The lowest production rate is 60% of the 500 NL/h, meaning 300 NL/h. The lowest production limit was set to 60% to increase devices' safety. The amount of hydrogen in the vent line is then still less than 2%. The energy consumption is roughly linear to the production rate (60% of the total power consumption at 60% production rate). Ramping up the production rate by 10% takes about 21 sec. Ramping down by 10% takes less than 1 sec.


# What is the duration of starting the electrolyser until it is fully functional? How long is the warm-up/ramp-up time?

The ramp up time of the AEM electrolyser depends on the electrolyte temperature (the ramp-up is slower at cooler temperatures and quicker at warm temperatures). In most cases, 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 electrolyser is 55°C. The electrolyser reaches a heating ratio of about 1 °C/min and reaches maximum efficiency at 55°C. That means, if the machine is started 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/h production rate is reached after about 2/3 of the total warm-up time (the warm-up time is 30 min, so if starting at 25°C, it will need 20 min to reach the maximum production rate).
  • Build pressure time: When the system starts, and the electrolyser starts to heat up, the hydrogen production begins immediately, and the maximum production rate is reached later. With standard setpoints, the pressure is built up completely in 1/6 of the total warm-up time (if you start at 25 °C, then the warm-up time is 30, so 5 min to build up pressure are needed)

# Does frequent start/stop cycles and ramping affect the electrolyser's longevity or performance?

The electrolyser 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, regular use with several on-off cycles per day does not affect the system negatively.

In use cases with frequent changes in the hydrogen consumption rate, Enapter recommends installing a buffer tank (50 L recommended) to hold some hydrogen and avoid switching the electrolysers on and off every few minutes.

To help control the devices for constant consumption use cases, it is also possible to regulate hydrogen production. Using the Enapter gateway running rule-based controls keeps the outlet pressure stable at a given set-point minimizing 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.

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

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

# Is Nitrogen used during the process?

Enapter's electrolysers do not use Nitrogen.

# Stack specifications

# What is the surface area of the membrane?

This information is part of Enapter's intellectual property.

# What is the electrolyser cell DC voltage range?

This information is part of Enapter's intellectual property.

# What is the electrolyser cell minimum voltage?

This information is part of Enapter's intellectual property.

# What is the single electrolyser chamber voltage range?

This information is part of Enapter's intellectual property.

# What is the electrolytic cell DC current range?

This information is part of Enapter's intellectual property.

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

Enapter utilizes a proportional relief valve to pressurize the system before the operation and several pressure transmitters to control and monitor stack and outlet pressures. A solenoid valve keeps the process gas contained which opens and returns the system to a safe state if an error is detected.

# What is the current density?

This information is part of Enapter's intellectual property.

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

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