Water Electrolyzers

Water Electrolyzers

Alkaline, PEM and AEM Electrolyzers

Pure Hydrogen generation
AEM Electrolyzers Alkaline Electrolyzers PEM Electrolyzers Porous Transport Layers for Water Electrolyzers

PEM Electrolyzers

 


In a stark contrast to alkaline water electrolyzers (ALK WEs) proton exchange membrane water electrolyzers (PEMWEs) use a solid polymer electrolyte membrane (also known as ion exchange membrane) instead of a liquid electrolyte to split ultra-pure water into hydrogen and oxygen.

The limitations of ALK WEs have driven significant innovation in electrolyzer stack designs; most notably, the development of solid polymer electrolyte membranes, also known as ion exchange membranes. These proton-conducting membranes were originally developed in the 1960s for fuel cell applications (see: proton exchange membranes for fuel cells) and played a key role in early space exploration missions. Over the decades, their design and performance have been refined, making them suitable for electrolysis applications as well.

 

Water Electrolyzer Technology Advancement Timeline

Advancements in Water Electrolyzer Technology: From Alkaline to PEM Systems

 

Innovations in water electrolyzer technology have emerged to address the limitations of the first-generation alkaline water electrolyzers. A major turning point came in the 1960s with the invention of proton exchange membranes (PEMs), which paved the way for PEM electrolyzers. These newer systems offered improved performance, higher current densities, and more compact designs.


How do PEM Water Electrolyzers Work?

Hydrogen and oxygen gases are produced on either sides of the membrane and are  removed from the back of the electrodes through suitable cathode gas diffusion layers and anode porous transport layers. PEMWEs operate under highly acidic conditions (pH <2), where water splitting occurs through the following half-reactions:

  • At the anode, water molecules are oxidized, producing oxygen gas, protons (H⁺), and electrons: H2O (l) → 2 H+ (aq) + ½ O2 (g) + 2 e–
  • At the cathode, protons (H⁺) are reduced, producing hydrogen gas: 2 H+ (aq) + 2 e– → H2 (g)
A diagram illustrating the anode and cathode reactions in a PEM water electrolyzer

Cathode Reactions in Proton Exchange Membrane Water Electrolyzers

Anode Reactions in Proton Exchange Membrane Water Electrolyzers

 

PEM Water Electrolyzer Components

Labeled diagram of a PEM water electrolyzer showing key components including the proton exchange membrane, anode and cathode catalyst layers, porous transport layers, bipolar plates

PEM water electrolyzers consist of several key components that work together to enable efficient hydrogen production: a proton exchange membrane, catalysts, cathode gas diffusion layer (GDL), and anode porous transport layer (PTL). Each layer is engineered to support water management, gas diffusion, and electrochemical performance under highly acidic and pressurized operating conditions.

In addition to the membrane-electrode assembly (MEA), balance of stack components such as flat gaskets, bipolar plates, and cell frames ensure proper sealing, electrical conductivity, and structural support across the stack.

Proton Exchange Membrane

An ion exchange membrane (IEM) is a thin barrier that allows the selective passage of ions from one electrode to another of electrochemical devices. In PEM water electrolyzers, a proton exchange membrane (also called a proton-conducting membrane) enables the transport of H⁺ ions from the anode—where they are generated—to the cathode, where they are consumed.

More importantly, proton exchange membranes keep the anode and cathode physically separated, preventing the mixing of H₂ and O₂ product gases. This is a crucial safety feature—just 4.6% oxygen in a hydrogen stream or 3.8% hydrogen in an oxygen stream is enough to form an explosive mixture at 80 °C, which is close to the typical operating temperature of water electrolyzers.

Diagram showing the functions of a proton exchange membrane in a water electrolyzer



Read more about proton exchange membranes for PEM water electrolyzers.


Anode and Cathode Catalyst Layers (Catalyst + Ionomer)

Catalysts speed up reactions without being consumed in the process. In water electrolyzers, catalysts enable reactions that generate H2 and O2 gases to happen efficiently at practical input voltage.

In PEM water electrolyzers, the cathode catalyst speeds up the hydrogen evolution reaction (HER). On the other side, the anode catalyst drives the oxygen evolution reaction (OER). These catalysts are typically noble-metal-based due to the harsh, acidic environment of PEM systems. Platinum is the most commonly used catalyst at the cathode because of its excellent HER activity and durability. At the anode, iridium oxide or ruthenium oxide is used for OER.

Illustration showing anode and cathode catalyst layers in a PEM water electrolyzer


Catalysts are usually in powder form.  How do we actually use them in electrochemical devices like PEM water electrolyzer stacks? It all starts with an ink.

This catalyst ink is a mixture of the powdered catalyst, a solvent (like water or alcohol), and an ionomer or a polymer that conducts protons and helps bind the catalyst particles to the membrane or gas diffusion layer. The ink is applied as a thin coating, typically through spraying, printing, or brushing, to create what’s called a catalyst layer. Once dried and properly processed, this layer becomes an integral part of the membrane electrode assembly (MEA), where the electrochemical reactions take place.

Catalyst ink components: solid catalyst particles and ionomer in a solvent
Catalyst ink components: solid catalyst particles and ionomer in solvent
Coating catalyst ink onto a membrane or gas diffusion layer
Coating catalyst ink onto membrane or gas diffusion layer
Gas Diffusion Electrode (GDE) vs Catalyst-Coated Membrane (CCM)
GDE vs CCM: Catalyst layer on backing vs directly on membrane

 

 

Pemion PP1-HNN8-00 Ionomer for PEMWE Catalyst Inks


PEMION® PP1-HNN8-00 Ionomer is a high-performance proton exchange ionomer designed for use in PEM water electrolyzers and fuel cells. It offers excellent proton conductivity, chemical stability in acidic environments, and superior film-forming properties, making it ideal for catalyst ink formulations and membrane electrode assemblies (MEAs).
Ionomer Type IEC (meq/g) EW (g/eq.) Density (g/cm³) Solubility
PP1-HNN8-00 2.8 - 3.1 320 – 360 1.2 Alcohols and alcohol/water mixtures
Ionomer Type (reference)
Long side-chain PFSA
(for reference only)		 0.9 - 1.0 1000 – 1,100 2.0 Alcohols and alcohol/water mixtures
Short side-chain PFSA
(for reference only)		 1.1 - 1.3 770 – 910 2.0 Alcohols and alcohol/water mixtures

⚡ Applications

  • Catalyst ink formulations for PEM water electrolyzers

  • Membrane Electrode Assemblies (MEAs) in fuel cells

✅ Advantages

✔ High proton conductivity for efficient ion transport

✔ Excellent chemical stability under acidic and oxidative conditions

✔ Superior film-forming capability for uniform catalyst layers


📥 Downloads

⬇ Technical Data Sheet - PEMION® PP1-HNN8-00

 

How can you reduce the cost of PEM electrolyzers?

  1. The first thing you can do is increase the active area. A large active area decreases the cost per kg of H2 produced. Linqcell carbon panels are typically 40 x 40cm but larger sheets can be produced if there is a significant business case.
  2. High-pressure PEMS. If the GDLs are compressible than we eliminate a compression step that allows customers to buy less expensive compressors and reduce their overall costs. Linqcell papers withstand a significant amount of pressure and can be compressed up to 15-20% of their initial thickness, depending on the grade.
  3. Using Carbon panels instead of Sintered titanium reduces the material cost.
  4. Carbon panels have a very long useful life, usually outcompeting the ion exchange membranes themselves. so this is an extra cost saving step that graphitized carbon panels can help us with.

When we are looking specifically on how we can reduce the cost of the panels themselves, there are three areas that we're focusing on.

One area is to optimize the furnace runs. Furnace runs up to 2000°C are very expensive. With the rising cost of energy this is one the most important aspects of carbon panel production since this is almost one third of the cost. If we can optimize those and make sure that ovens are always full and we are taking full advantage of the space and consumed energy, we will be able to reduce the cost of the panels. This means that low volume run are very expensive since we are consuming the same energy either with 1 sheet or with 10000 sheets. Optimization is key. That's why there is a linear relationship between cost and the number of units produced.

Another one is machining costs. If we can work together to be able to accept a greater tolerance, then the machining cost which represents almost a third of the final cost can be reduced.

Finally, it comes down to materials and size. If you are asking for die-cut circles there is going to be a long of materials waste and machining cost. Custom molds can be made but the volumes and commitment needs to be there, in order to justify such an investment.

 

Applications of Carbon Panels

GDLs can be used in a variety of Technical Engineering Applications such as

  • PEM Electrolyzers
  • Fuel Cells
  • Heat Management
  • Redox Flow Batteries
  • Gas Diffusion Layers
  • Gas Diffusion Media
  • Porous Graphitized Carbon Sheets
  • Fuel Cell Powered City Buses

Benefits:

  • Lower Cost compared to Titanium Mesh / Sintered Ti for Cathode (H2 Side) Electrode Thicker Plates (Up to 5mm)
  • Higher Density (up to 1 g/cc)
  • Higher Bending Stiffness vs Stacking of Thin Papers
  • High Elastic Spring Compression Constant (up to 30% compression with full recovery)
  • Good Machinability
  • Hybrid Constructions Possible
  • Long Term Performance / Corrosion Resistance
  • Demonstrated: Commercial / Military Applications
  • Laboratory/ Prototype and Commercial Scale
Figure 7. Clockwise from left: PEM Electrolyzers, PEM Electrolyzer stack, Electrolyzers for military and self-containing applications (in this case, the O2 is produced to provide breathable air), China Bus program used Spectracarb carbon paper for fuel cells.
 

Using Carbon Paper & Panels as Cathode-side Current Collectors

LINQCELL GDL1500  are optimum for use as Cathode (Hydrogen Side) Current Collectors in PEM Electrolyzers. Unlike the standard thin/low density Gas Diffusion Layers (GDL) that are intended mainly for PEM and PAFC fuel cells, the Spectracarb Porous Graphite Engineered Panel Family has been specifically engineered for the special requirements of PEM electrolyzers. Features include thicker structures from 1.5 to over 4 millimeters, and densities up to 0.95 g/cm3. These panels also have controlled compressibility to support the external forces from the assembly. In addition to several standard grades, these engineered panels can be made on a laboratory, prototype or production scale to meet specific customer requirements.

Watch our presentation on PEM electrolyzers as current collectors, in Hannover Messe 2016.



Please note that Spectracarb has since been discontinued and replaced by the much more efficient LINQCELL product series below:

 

i
Thick Carbon plates for PEM electrolyzers
Product Thickness Thickness (mm) Density (g/cm3) Basis weight (g/m2) Through-Plane Resistance (mΩcm2) Through-Plane Resistivity (mΩcm) Voltage Loss (mV)
LINQCELL GDL 1500 0.059" 1.5 0.60 858 13.32 90.6 24.3
LINQCELL GDL 1500B 0.059" 1.5 0.60 670 21 140 39
LINQCELL GDL 1850 0.072" 1.85 0.85 1562 13.18 70.5 25.5
LINQCELL GDL 2200 0.086" 2.2 0.6 1550 17 110 35
LINQCELL GDL 2900 0.011" 2.9 0.60 1734 24.57 87.7 27.6

All values are indicative and subject to tolerance