What Is AEM Water Electrolysis?
Anion Exchange Membrane Water Electrolysis (AEMWE) is an emerging electrochemical technology for producing hydrogen from water using electricity. It combines some of the advantages of traditional alkaline water electrolysis and Proton Exchange Membrane (PEM) water electrolysis.
AEM water electrolysis uses an anion exchange membrane (AEM) as the electrolyte separator. Unlike PEM electrolyzers, which conduct protons (H⁺), AEM electrolyzers transport hydroxide ions (OH⁻) through the membrane.
One of the most attractive features of AEMWE is using non-precious metal catalysts and less expensive cell components, thus reducing the material cost of electrolyzers while maintaining relatively high current density and compact system designs.
As renewable electricity continues to expand, AEMWE is receiving increasing attention as a potential technology for cost-effective green hydrogen production.
How Does AEM Water Electrolysis Work?
At its most basic level, an AEM electrolyzer splits water into hydrogen and oxygen using electricity.
A typical AEM electrolyzer consists of:
- Anode
- Anion exchange membrane
- Cathode
- Porous transport layers (PTLs)
- Bipolar plates or flow fields
- Sealing and compression components
During operation, water is supplied to the electrolyzer and an electrical potential is applied between the anode and cathode.
At the cathode, water is reduced to produce hydrogen:
Cathode reaction:
2H₂O + 2e⁻ → H₂ + 2OH⁻
The hydroxide ions then migrate through the anion exchange membrane toward the anode.
At the anode, hydroxide ions are oxidized to produce oxygen and water:
Anode reaction:
4OH⁻ → O₂ + 2H₂O + 4e⁻
The overall reaction is:
2H₂O → 2H₂ + O₂
The chemical feedstock required is water, while electricity provides the energy needed to drive the reaction.
What Is the Role of the Anion Exchange Membrane?
The anion exchange membrane is one of the most important components in an AEM electrolyzer, as in other electrolysis technologies.
The membrane performs several functions simultaneously:
- Conducts hydroxide ions (OH⁻).
- Separates hydrogen and oxygen gases.
- Provides electrical insulation between the anode and cathode.
AEMs typically contain fixed positively charged functional groups within a polymer matrix. These fixed charges facilitate the transport of negatively charged ions such as OH⁻.
The performance of an AEM depends on several properties, including:
- Ionic conductivity
- Chemical stability
- Mechanical strength
- Dimensional stability
- Gas crossover resistance
- Thickness
The development of durable, highly conductive AEM materials is therefore a major area of research in AEM water electrolysis.
AEMWE vs. PEM and Alkaline Electrolysis
AEMWE is often described as a technology positioned between conventional alkaline electrolysis and PEM electrolysis.
Alkaline Water Electrolysis
Traditional alkaline electrolyzers generally use a liquid alkaline electrolyte, typically 5M potassium hydroxide (KOH), together with relatively inexpensive catalysts such as nickel-based materials.
The technology is mature and has been commercially deployed for decades. In the last few years, AWE technology has advanced significantly in scales, performance. For instance, nowadays, 5MW single-stack AWE electrolyzer is a standard size for large scale applications, and 10MW single stack is coming soon. The benefit of scaling up is reducing the cost further. The limitation of the AWE is often related to inflexible dynamic operation, lower current density, strong base-related maintenance etc.
PEM Water Electrolysis
PEM electrolyzers use a proton exchange membrane and typically operate at high current density and relatively compact cell dimensions. It has a much better dynamic operation and high pressure H2 output, such as 3MPa or higher.
The limitation of PEM technology is related to the use of platinum-group-metal catalysts, particularly iridium-based catalysts for the oxygen evolution reaction (OER) and precious metal-coated anode components. The availability and cost of these materials are important considerations for large-scale deployment. PEM technology has also improved significantly over the last few years. For instance, iridium loading has been reduced from 2-4mg/cm2 to 0.4mg/cm2 and membrane thickness has been reduced from 125-180µm to 80-50µm, which improves electrolysis efficiency greatly.
AEM Water Electrolysis
AEMWE attempts to combine some of the advantages of both technologies.
| Feature | Alkaline | AEMWE | PEM |
|---|---|---|---|
| Main ion transported | OH⁻ | OH⁻ | H⁺ |
| Precious metal catalyst requirement | Low or none | Potentially low | Generally higher |
| Current density | Low | Moderate–high | High |
| System compactness | Moderate | Potentially high | High |
| Dynamic operation | Moderate | Potentially high | High |
| Technology maturity | High | Developing | High |
The exact performance of each technology depends strongly on cell design, operating conditions, catalyst loading, membrane properties, and system architecture.
Key Components of an AEM Electrolyzer
Understanding AEMWE requires understanding how the individual components work together.
1. Anion Exchange Membrane
The AEM transports OH⁻ ions while separating the hydrogen and oxygen compartments.
Important membrane specifications include:
- Thickness
- Ionic conductivity
- Water uptake
- Reinforcement
- Mechanical strength
- Chemical stability
- Gas permeability
- Dimensional stability
A thinner membrane can reduce ionic resistance and thus improve the efficiency of electrolysis, but membrane thickness must be balanced against mechanical properties and gas crossover. Reinforcement is commonly used to improve the mechanical properties of the membrane.
2. Catalyst Layer
The catalyst layer contains electrochemically active materials that accelerate the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER).
Typical AEMWE catalyst families include:
Cathode HER catalysts
- Platinum-based catalysts, such as Pt/C or PtRu/C
- Non-precious metal-based catalysts, such as NiMo-based materials (to be validated)
Anode OER catalysts
- Nickel-iron oxyhydroxides NiFeOx
- Cobalt-based materials
- Other transition-metal oxides and hydroxides
The nanopowder catalyst is often combined with an ionomer to improve ionic connectivity within the catalyst layer. For anode electrode, a widely used catalyst layer is catalysts coated substrate (CCS), also called gas diffusion electrode (GDE), where catalyst is grown on a substrate, typically Ni-based substrate.
3. Ionomer
The ionomer plays an important role in AEM electrode architecture. It acts as a binder to keep nanopowder catalyst together, provides hydroxide-ion conduction inside the catalyst layer, and helps connect catalyst particles to the membrane.
Consequently, catalyst loading, ionomer content, catalyst particle size, porosity, and electrode structure must be considered together.
4. Porous Transport Layer
The porous transport layer, or PTL, provides several important functions.
It can:
- Transport water to the catalyst layer
- Remove generated gases
- Provide electrical conductivity
- Support the catalyst layer
- Provide mechanical support
Common PTL materials for AEMWE include nickel-based porous structures such as:
- Nickel foam
- Nickel felt
- Nickel microporous layer
Surface structures and microporous layers can be engineered to improve contact, transport, and electrode performance.
5. Membrane Electrode Assembly
The membrane electrode assembly (MEA) is the heart of an AEM electrolyzer.
A simplified AEMWE MEA consists of:
Anode catalyst layer | AEM | Cathode catalyst layer
The MEA is integrated with porous transport layers and plates to form the electrochemical cell.
MEA performance depends on the interaction among:
- Membrane
- Catalyst
- Ionomer
- Electrode structure
- PTL
- Compression
Therefore, optimizing one component independently does not necessarily produce the best overall cell performance.
6. What Determines AEMWE Performance?
Several parameters are commonly used to evaluate AEM electrolyzers.
Cell Voltage
The lower the cell voltage at a given current density, the higher the electrical efficiency, assuming other operating conditions are comparable.
Cell voltage consists of several contributions, including:
- Thermodynamic voltage
- Activation losses
- Ohmic losses
- Mass-transfer losses
Reducing membrane resistance, improving catalyst activity, optimizing interfaces, and improving transport can therefore help reduce cell voltage.
Current Density
Current density is usually expressed in A/cm²
It indicates how much electrical current is generated per unit electrode area. Higher current density generally means greater hydrogen production from a given electrode area.
However, increasing current density can also increase:
- Cell voltage
- Heat generation
- Mass-transfer limitations
- Gas crossover
- Component degradation
Therefore, high current density alone should not be used as the sole measure of electrolyzer performance.
Hydrogen Production Rate
The theoretical hydrogen production rate is directly related to current.
According to Faraday's law, approximately:
1 A of current corresponds to about 7 mL/min of H₂ at standard temperature and pressure, assuming 100% Faradaic efficiency.
In practical systems, hydrogen production also depends on Faradaic efficiency, operating pressure, temperature, and water management.
7. The Importance of MEA and Interface Engineering
One of the key lessons in AEMWE development is that overall performance is determined by the interaction between components.
For example, a highly conductive membrane may not produce a high-performing cell if the catalyst layer has poor ionic connectivity.
Similarly, a highly active catalyst may not deliver its theoretical performance if:
- The catalyst layer is poorly designed
- Water transport is insufficient
- Gas removal is inefficient
- Contact resistance is high
- The membrane-electrode interface is poor
This is why modern AEMWE research increasingly focuses on integrated MEA and interface engineering rather than optimizing individual materials in isolation.
8. AEMWE and the Future of Green Hydrogen
The cost of renewable electricity is an important factor in the economics of green hydrogen, often cited as 70% of the total cost of green hydrogen.
Electrolyzer technologies must continue improving:
- Electrical efficiency
- Durability
- Current density
- Manufacturing cost
- Dynamic operating capability
AEMWE has the potential to contribute to the green hydrogen economy by using cheaper materials, such as those used in AWE, and producing hydrogen at a high current density, like PEM technology with a modest dynamic operation capability.
The AEMWE technology is still developing, and long-term durability and reliable large-scale operation remain critical areas of research and engineering.
The future competitiveness of AEMWE will ultimately depend not only on technical advancement of individual components, but also on the successful integration of membranes, catalysts, ionomers, electrodes, PTLs, MEAs, stacks, and balance-of-plant systems.
9. Conclusion
Anion Exchange Membrane Water Electrolysis is an emerging approach to hydrogen production that combines the earth abundant materials of AWE with high current density and flexible dynamic operation of PEM electrolysis.
At the same time, challenges remain in membrane durability, catalyst stability, gas crossover, MEA optimization, and stack scale-up. Continued progress in AEM materials, catalyst development, ionomers, porous transport layers, membrane-electrode interfaces, and stack engineering will be essential for translating AEMWE from laboratory research into reliable commercial hydrogen production.
For researchers, engineers, and companies working on the hydrogen economy, AEMWE represents an important technology platform with significant opportunities for innovation across the entire electrochemical value chain.
ElectroHy provides AEM water electrolysis materials and components, including anion exchange membranes, ionomer, catalysts, cathode, anode, porous transport layers, MEAs, and AEM electrolyzer systems for research, development, and industrial applications.
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