Technologies
Exion Hydrogen develops and manufactures advanced electrolyzer systems, built on two proven and complementary technologies: pressurized alkaline water electrolysis (AWE) and pressurized proton exchange membrane (PEM) water electrolysis.
Both approaches split water (H₂O) into hydrogen (H₂) and oxygen (O₂) using electricity. Each has its own characteristics and advantages, making them suitable for different applications in the energy, industrial, and mobility sectors.
How Electrolysis Works
Water is a very stable molecule and requires significant energy input to split into hydrogen and oxygen. This can be achieved electrically by applying current across two electrodes: a cathode (-) where hydrogen forms, and an anode (+) where oxygen forms. A separator is required to separate the gases safely.
Alkaline electrolysis
In alkaline electrolysis, a strong base (typically potassium hydroxide, KOH) is added to water, creating a conductive solution (“lye”). This approach is well established, robust, and reliable, but imposes material constraints due to the chemically aggressive environment and risks of stray currents.
PEM electrolysis
In PEM electrolysis, pure water is used, and a Proton Exchange Membrane replaces the liquid electrolyte. This technology allows higher current densities through the membrane, which means that the stacks will be significantly smaller compared to AWE to produce the same amount of hydrogen per cm² electrode surface. On top, the balance of plant only handles water instead of the highly alkaline solution in the AWE.
However: as internally the environment is highly acidic, precious metal group (PMG) materials are required as catalysts inside the stacks.
Both technologies benefit from the ability to operate under pressure, which reduces the need for mechanical compressors, improves hydrogen purity, and allows compact containerized systems.
Side-by-Side comparison
Pressurized (*)
Alkaline Water Electrolysis
(AWE)
Pressurized (*)
PEM Water Electrolysis
(PEM)
How AWE works
AWE uses a liquid alkaline electrolyte—typically potassium hydroxide (KOH)—and porous diaphragm separators. Water is fed into the electrolyzer cell, where an electric current drives the splitting of water molecules. Hydrogen and oxygen are generated under pressure, reducing or even eliminating the need for downstream compression. The electrical current through the electrolyte is carried by hydroxide ions (OH⁻), which migrate from the cathode to the anode.
How PEM works
PEM electrolysis uses a solid proton-exchange membrane as the electrolyte. Water is fed to the anode, where it is split into oxygen, protons, and electrons. The protons (H⁺) migrate through the membrane to the cathode, where they recombine with electrons to form hydrogen gas. The electrical current through the membrane is driven by this migration of the protons from the anode to the cathode.
Key Characteristics of AWE
- The most proven and well-established technology with decades of industrial use.
- Operates with lower current densities, providing robust performance and long system lifetimes.
- Typically uses widely available and lower-cost materials (e.g., nickel-based electrodes).
- Well-suited for hydrogen production across a wide range of industrial applications—from specialized uses to large-scale operations—particularly where high-purity electrolytic hydrogen is required.
Key Characteristics of PEM
- A newer but commercially proven technology.
- Operates at higher current densities, allowing for compact system footprints.
- Utilizes noble metal catalysts (e.g., platinum, iridium) and advanced membranes.
- Especially well-suited for dynamic operation with fluctuating renewable power inputs.
AWE benefits
- Proven reliability and durability in industrial operation.
- High efficiency at steady loads.
- Ability to operate at elevated pressures, reducing compression costs.
- More forgiving of feedwater quality and generally lower in overall system cost for large installations.
PEM benefits
- Fast response to load changes, ideal for grid balancing and renewable integration.
- High purity hydrogen output with minimal gas crossover.
- Compact and modular design for flexible installation.
- Effective at smaller to medium scales, including mobility and decentralized applications.
(*) Atmospheric alkaline water electrolysis is a proven legacy technology that operates at lower current densities and has traditionally been used for high-capacity, large-scale industrial applications. However, because it does not produce hydrogen at pressure, most installations require additional compression, adding substantial capital costs. Moreover, atmospheric systems demand considerably more footprint than pressurized alkaline units for the same output, and they require extra equipment and higher operating expenditures—particularly in energy consumption—to manage and compress the hydrogen downstream.
Producing hydrogen directly under pressure offers key benefits: it removes or reduces the need for extra compression, allows quick startup and shutdown for flexible operation, and enables compact, factory-tested skid systems. This leads to faster on-site installation and ensures high-purity hydrogen with simpler downstream handling.
Typical – common – standard specifications
| Alkaline Water Electrolysis (AWE) | Feature | PEM Water Electrolysis (PEM) |
|---|---|---|
| Temp: 60–100 °C; Pressure: up to ≈30 bar |
Operating Conditions | Temp: 50–80 °C; Pressure: up to ≈30 bar |
| 0.2–1.0 A/cm²; ≈1.0 W/cm² max | Current Density / Power Density | 0.6–5.0 A/cm²; up to ≈4.4 W/cm² |
| 62–82 % | Stack Efficiency (HHV) | 67–82 % |
| Conductivity tolerance: ~1–5 µS/cm | Water Quality Needs | Much stricter—<0.1 µS/cm |
| Nickel-plated stainless steel or nickel-based electrodes; diaphragm separators; liquid KOH electrolyte; stainless steel | Material & Design | Solid polymer membrane; PGM (Platinum Group Metals) catalysts like Platina or Iridium; titanium components |
| 60-90k hours; system life: 20–30 years |
Stack Lifetime | 20-80k hours; system life: 10 – 20 years |
| Robust, efficient at steady large-scale operation; lower capital cost; long lifetime; very high H₂ purity | Strengths | Compact, fast dynamic response; very high H₂ purity; modular design |
When evaluating electrolyzer technologies, buyers should consider the overall system offering rather than focusing on a single metric. Both PEM and alkaline systems are evolving, and supplier offers vary significantly in scope and value. Deployment costs, cell stack and system lifetime, water treatment needs, and application requirements are all critical factors.
It is important to note that nearly all PEM and alkaline systems operate within a similar efficiency range when compared on a consistent basis. Efficiency figures for these electrolyzers are only meaningful when evaluated at the same current density. Since OEMs report values at different operating points, datasheet numbers can be misleading; however, normalizing to a consistent current density shows that both technologies usually fall within a similar efficiency range.
Meaning, current density is the hidden axis behind these claims, explaining why systems may look different on paper yet align under equivalent conditions. This has direct implications for OPEX, TCO, and ultimately LCOH: efficiency affects electricity consumption, which is the dominant operating cost driver; misinterpreting datasheet values can therefore distort total cost assessments. A consistent basis for efficiency comparison is essential to accurately estimate operating expenses, project total cost of ownership, and derive a realistic levelized cost of hydrogen.
Key considerations
