Water Electrolyzers
Alkaline, PEM and AEM Electrolyzers
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Alkaline Electrolyzers
Formally, water electrolysis is the process of splitting water into its constituent gases, H2 and O2, through the application of a direct current. Water splitting can be performed under different reaction conditions. It can occur either in alkaline or acidic conditions and at low (<100 °C) and very high temperatures (>500 °C). Water electrolysis cells can be broadly classified into four categories: alkaline, proton exchange membrane (PEM), alkaline anion exchange membrane (AEM), and solid oxide electrolysis cells (SOEC). Each type involves different electrode reactions, depending on the type of charge transported through the electrolyte.
Alkaline water electrolyzers (AWEs) are the most mature and commercially developed hydrogen production technology. In AWEs, water splitting occurs through the following half-reactions:
- At the cathode, water molecules are reduced, producing hydrogen gas and hydroxide ions: 2 H2O(l) + 2 e– → H2(g) + 2 OH–(aq)
- At the anode, hydroxide ions are oxidized, producing oxygen gas and water, and releasing electrons: 2 OH–(aq) → ½ O2(g) + H2O(l) + 2e–
As in other electrolysis technologies, the overall reaction is H2O(l) → H2(g) + ½ O2(g).
The reactions in alkaline water electrolyzers (AWEs) take place on electrode surfaces, which are separated by a porous diaphragm that allows ions to pass while preventing the mixing of the product gases. In AWEs, the electrolyte is a liquid caustic solution, typically NaOH or KOH, pumped through the system. This creates highly alkaline operating conditions, hence the name.
Because the electrolyte is highly concentrated, typically 5 to 7 M KOH or a 30% KOH solution, the materials used in the AWE stack must be able to withstand these harsh conditions to ensure long-term durability and performance.
Separators for Alkaline Water Electrolyzers
Porous separators are widely used in commercial alkaline water electrolyzers to physically separate the anode and cathode, preventing the crossover and mixing of the product gases, H₂ and O₂, while still allowing ionic contact between the electrodes.
Porous separators are composite membranes made of inorganic (ceramic) nanoparticles dispersed in a polymer. The polymer binder creates a highly interconnected inorganic–organic porous structure, while the ceramic nanoparticles provide hydrophilicity, improving ion conduction within the separator.
When used for electrolysis, porous separators need to meet these two performance requirements:
LOW OHMIC RESISTANCE
They must have low ohmic resistance to facilitate ion transport across the electrodes and maintain electroneutrality between the cathode and anode.
HIGH BUBBLE POINT PRESSURE
They must have high bubble point pressure or the minimum pressure of gas to penetrate the separator to avoid the crossing over and mixing of product gases.
Of course, these two requirements only touch the surface. In reality, a lot of property interplays are at work.
Questions to ask when Choosing Separators for Alkaline Water Electrolyzers
✅ What is the ion conductivity of the separator?
✅What is the separator's bubble point pressure?
✅Is the separator chemically stable in concentrated KOH solutions?
✅How does the separator perform at temperatures around 80 °C?
✅What is the separator’s pore size distribution?
✅Is the separator hydrophilic enough?
✅Is the separator mechanically strong enough to withstand operating pressures?
✅How long is the expected lifespan of the separator under typical operating conditions?
LINQCELL ALK-PCS Porous Composite Separator for Alkaline Water Electrolyzers
LINQCELL ALK-PCS is a composite separator made of a polyphenylene sulfide (PPS) mesh matrix reinforced with a ceramic nano coating. The PPS structure provides high mechanical strength and pressure resistance, making it ideal for high-pressure alkaline water electrolyzers. The ceramic nano coating enhances hydrophilicity, improving water management during electrolysis. Additionally, the polymeric binder with nanopores in the dense coating acts as a gas barrier, reducing gas crossover and enhancing operational safety.
| Property | Value | Unit |
|---|---|---|
| Thickness | 500±50 | µm |
| Porosity | 55±10 | % |
| Average Pore Diameter | <150 | nm |
| Maximum Pore Diameter | 200 | nm |
| Bubble Point | 3–5 | bar |
| Area Specific Resistance (80 °C, 30% KOH) | ≤0.15 | Ω·cm² |
| Maximum Operating Temperature | 110 | °C |
⚡ Applications
▪ Renewable energy
▪ Large-scale (1000 Nm3/h) and high-pressure hydrogen production
✅ Advantages
✔ Making electrolysis more efficient with superior gas barrier capabilities
✔ Making production highly scalable
✔ Withstands mechanical stress and pressure variations, ensuring long-term durability
📥 Downloads
⬇ Technical Data Sheet - LINQCELL ALK-PCS
Electrodes for Alkaline Water Electrolyzers
Electrodes are critical components in electrochemical devices, particularly in alkaline water electrolyzers, where they facilitate the electrochemical reactions at both the anode and cathode. At the cathode, they serve as the sites for the hydrogen evolution reaction (HER), while at the anode, they enable the oxygen evolution reaction (OER). The efficiency of these reactions directly impacts the overall performance of the alkaline water electrolyzer.
The first alkaline water electrolyzers used nickel-based electrodes, and these materials continue to be widely used today. Since AWEs operate in alkaline conditions, nickel and other transition metals are ideal electrode materials due to their excellent corrosion resistance and good electrocatalytic activity for hydrogen and oxygen reactions in alkaline environments. Nickel-based materials, such as Ni foams, Ni wire meshes, sintered Ni powders, and sintered Ni fibers, offer not only strong performance but also cost-effectiveness, as they are more affordable and abundant than precious metals. This makes AWEs an attractive option for large-scale hydrogen production, both in early applications and in modern systems.
Benefits of Using Nickel-based Electrodes in Alkaline Water Electrolyzers
HIGH CORROSION RESISTANCE IN ALKALINE CONDITIONS
Nickel has strong resistance to corrosion in the highly alkaline environment of water electrolyzers. This corrosion resistance results in reduced maintenance and longer-lasting electrodes.
HIGH ELECTROCATALYTIC ACTIVITY
FOR OER AND HER
Nickel has high catalytic activity towards HER and OER, reducing energy losses and increasing reaction rates.
ABUNDANCE AND LOW COST
Compared to precious metals, nickel is abundant and more affordable, making it a cost-effective choice for large-scale hydrogen production without compromising performance.
LINQCELL NICKEL Wire Mesh & Sintered Fibers for Alkaline Water Electrolyzers
Since electrodes are the key sites for electrochemical reactions in alkaline water electrolyzers, they are typically made from porous materials that provide a large surface area for efficient reaction kinetics. LINQCELL Nickel Wire Mesh and Sintered Fiber Felts are designed specifically to meet these needs, offering excellent corrosion resistance and high electrocatalytic activity.
LINQCELL Nickel Wire Mesh is a high-purity, finely woven mesh available in two wire diameters: 0.25 mm (LINQCELL NWM250) and 0.30 mm (LINQCELL NWM300), offering superior electrical conductivity, corrosion resistance, and mechanical durability. With at least 99% nickel content and compliance with GB/T 17492, it ensures long-lasting reliability in demanding electrochemical applications. Available in mesh counts of 30, 40, 46, and 60, and two nickel grades (N4 and N6), LINQCELL Nickel Wire Mesh is ideal for precise tuning in alkaline water electrolyzers and other electrochemical devices.
LINQCELL Sintered Nickel Fibers feature a unique three-dimensional porous structure, offering high porosity and specific surface area for efficient permeation and diffusion. These sintered fibers ensure consistent performance with their uniform pore size distribution. Made from high-purity Ni200 and Ni201, LINQCELL Sintered Nickel Fibers offer high corrosion resistance, water permeability, and efficient heat dissipation, making them ideal electrodes for alkaline water electrolyzers. They are available in two thicknesses: 250 µm (LINQCELL NFP250) and 500 µm (LINQCELL NFP500), and can be custom-made according to specifications.
Torn between LINQCELL Nickel Wire Mesh and Sintered Nickel Fiber?
Both materials are made from high-purity nickel, but their structures are different. Nickel wire mesh consists of woven metal wires, creating a flat, rigid grid with consistent openings, making it ideal for structural support and durability. In contrast, sintered nickel fiber is made up of small nickel fibers fused together into a spongy, three-dimensional network with higher surface area and porosity. The choice ultimately depends on your application.
⚡ Applications
▪ Alkaline water electrolysis
▪ Anion exchange membrane water electrolysis
▪ Nickel–metal hydride (NiMH) and nickel–cadmium (NiCd) batteries
✅ Advantages
✔ High electrical conductivity that minimizes overpotential
✔ High corrosion resistance that makes electrolysis cells durable
✔ Low cost that reduces capital expenditures
Frequently Asked Questions about Alkaline Water Electrolyzers
Alkaline electrolyzers use a liquid alkaline electrolyte and non-precious metal catalysts, whereas PEM electrolyzers use a solid polymer membrane and typically require precious metal catalysts like platinum or iridium. Alkaline systems are more established and cost-effective, while PEM electrolyzers offer higher efficiency and faster response times.
What are the advantages of alkaline water electrolysis for hydrogen production?Alkaline water electrolysis offers several advantages, including a lower capital cost due to its use of non-precious metal electrodes and mature technology. The system is built with durable materials that ensure a long operational lifespan, providing extended service life even under demanding conditions. Additionally, alkaline electrolyzers are highly scalable, making them suitable for both small-scale and industrial hydrogen production, meeting various production needs effectively.
While alkaline electrolyzers are traditionally designed for steady operation, newer designs with advanced electrodes and separators can handle intermittent power input, making them compatible with renewable energy sources like solar and wind.
What are the limitations of alkaline water electrolysis?Alkaline water electrolyzers have a few limitations, including slower response times, making them less suited for rapid power fluctuations. They also exhibit lower current density compared to PEM electrolyzers, which means that larger stacks are needed to achieve the same hydrogen output. Additionally, there are risks of gas crossover, necessitating the use of efficient separator materials to minimize losses and ensure safe operation.
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