# Piping and Hydrogen

# Which piping and tubes should I use for connecting modules?

For the water piping we use John Guest components as they are easy to source and cheap, but it is no requirement to stick with this brand. The hydrogen piping must be stainless steel, we use Swagelok tube fittings, as they are easier to tighten than thread fittings. From the water trap (on floor of container) a vent line with an inner diameter of 10 mm or more must go up into a safety area, different from the safety area the purge line goes into (could be at two opposite sides of the container for example).

# 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 your system CE certified?

The EL2.1 is CE certified.

# Is the Electrolyzer ATEX2 certified and, if so, for which zone - 0, 1 or 2?

No, our system is not designed to be installed in an ATEX area. During normal operation, there is no leakage of any hydrogen or oxygen gases from the system. The product gases are only released from the designated interfaces (H2 outlet, O2 vent, and H2 purge) that have to be correctly managed during the on-site installation. It is the project developers/installers responsibility to ensure that the area where the electrolyzers are installed must never contain any explosive atmospheres during any time of regular operation. An appropriate safety concept must be in place to mitigate the risks of any failures that could result in leakage of flammable gases. Such a safety concept could involve, for example, hydrogen sensors, forced ventilation, or natural ventilation.

# Is the pipeline in accordance with any certification?

We make all our hydrogen piping in accordance with ASME B31.12 for hydrogen piping and pipelines. All the European guidelines refer to the ASME, which is something like a “gold standard” for anyone working with hydrogen.

# 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.

# Can the system itself introduce in the lab an ATEX area surrounding the Electrolyzer (implying specific requisites for other equipment installed)? Is it necessary to have the H2 outlet with a weldable connection, as to avoid the formation of a potentially dangerous (ATEX) zone in the area surrounding the system?

The Electrolyzer normally has a standard ¼” Swagelok bite-type Stainless Steel connector for the hydrogen outlet piping. The outlet pipe is protected internally by relief and check valves from any gas flow backwards into the machine from the external tank/H2 distribution lines. We don’t believe it is necessary to weld the connection to avoid ATEX – it is quite typical to have these Swagelok connections in gas piping in laboratories. However, this may change with local rules and regulations.

The only thing to note in terms of safety areas is that the Electrolyzer system has two outlets that need to be connected to a safe area without any ignition sources. The first is the oxygen vent, which consists of 250NL/hr of oxygen gas at atmospheric pressure and may also contain some water and a very small percentage of hydrogen. The other is the hydrogen purge pipe, from which the Electrolyzer releases the pressurized hydrogen gas after a system shutdown – here, it releases about 10NL of hydrogen gas at 35 bar into the atmosphere within about 2 seconds.

1: Platinum Group Metals

2: ATmospheres EXplosible