Water Electrolyzers

Electrolyzers

Alkaline, PEM and AEM Electrolyzers

Pure Hydrogen generation

AEM Electrolyzers

An AEM (Anion Exchange Membrane) electrolyzer is an electrochemical device that uses an anion exchange membrane to split water into hydrogen and oxygen. The AEM electrolyzer works by passing an electric current through water, which causes the water molecules to dissociate into positively charged hydrogen ions (protons) and negatively charged hydroxide ions. The hydrogen ions are attracted to the cathode, while the hydroxide ions are attracted to the anode.

In an AEM electrolyzer, the anion exchange membrane serves as a barrier between the cathode and the anode, allowing only the positively charged hydrogen ions to pass through while blocking the negatively charged hydroxide ions. The membrane is made of a polymer material that contains positively charged functional groups that can attract and transport the hydrogen ions. The hydrogen ions combine with electrons at the cathode to form hydrogen gas, while the hydroxide ions combine with water molecules at the anode to form oxygen gas and additional hydroxide ions.

One of the advantages of AEM electrolyzers is that they operate at higher pH than PEM electrolyzers, which can reduce the corrosion of the electrodes and increase the overall efficiency of the electrolysis process. The AEM electrolyzers can also use non-precious metal catalysts, which can lower the cost of the electrolyzer.

However, there are some challenges associated with AEM electrolyzers, including membrane stability, limited membrane conductivity, and potential formation of chlorine gas at the anode. These issues can affect the durability and performance of the electrolyzer and require further research and development to optimize the technology.

ionomr - AEM electrolyzer structure

How does a typical AEM Electrolyzer assembly looks?

Anode compartment: This is the compartment on the left side of the electrolyzer, where the anode electrode is located. It is typically separated from the cathode compartment by the anion exchange membrane.

  • Anode flow field: This is the space in the anode compartment where the reactant gas (typically oxygen or air) is introduced. The anode flow field is designed to evenly distribute the gas across the surface of the anode.

  • Anode gas diffusion layer: This is a thin, porous layer that is placed between the anode electrode and the anode flow field. Its primary function is to transport the reactant gas to the surface of the electrode while also removing excess water produced during the electrochemical reaction.

  • Anode porous transport layer: This is a thin, porous layer that is placed between the anode gas diffusion layer and the anode electrode. Its primary function is to facilitate mass transport of reactant gases and water to the electrode surface, and to help manage the water content in the electrolyzer.

  • Anode electrode: This is the electrode where the oxidation reaction takes place, and where negatively charged ions (such as chloride ions) are attracted and release electrons to become neutral atoms or molecules. In a water electrolyzer, the anode is typically made of an inert material like titanium or platinum, and the reaction occurring is the oxidation of water molecules to produce oxygen gas and positively charged hydrogen ions (H+).

Anion exchange membrane (AEM): This is a selectively permeable membrane that separates the anode and cathode compartments in the electrolyzer, and only allows positively charged ions (such as H+) to pass through while blocking negatively charged ions (such as hydroxide ions, OH-). The AEM is an important component for maintaining the pH balance and preventing unwanted reactions from occurring.

Cathode compartment: This is the compartment on the right side of the electrolyzer, where the cathode electrode is located. It is typically separated from the anode compartment by the anion exchange membrane.

  • Cathode electrode: This is the electrode where the reduction reaction takes place, and where positively charged hydrogen ions are attracted and receive electrons to become neutral hydrogen molecules. In a water electrolyzer, the cathode is typically made of an inert material like nickel or stainless steel, and the reaction occurring is the reduction of H+ ions to produce hydrogen gas.

  • Cathode porous transport layer: This is a thin, porous layer that is placed between the cathode gas diffusion layer and the cathode electrode. Its primary function is to facilitate mass transport of reactant gases and water to the electrode surface, and to help manage the water content in the electrolyzer.

  • Cathode gas diffusion layer: This is a thin, porous layer that is placed between the cathode electrode and the cathode flow field. Its primary function is to transport the reactant gas (typically hydrogen) to the surface of the electrode while also removing excess water produced during the electrochemical reaction.

  • Cathode flow field: This is the space in the cathode compartment where the reactant gas (typically hydrogen) is introduced. The cathode flow field is designed to evenly distribute the gas across the surface of the cathode electrode.

Electrolyte: This is the solution that carries ions between the anode and cathode compartments, allowing the electrochemical reactions to occur. In a water electrolyzer, the electrolyte is typically a dilute solution of an alkali metal hydroxide, such as sodium or potassium hydroxide.

 

How do you make an AEM Electrolyzer?

To make an AEM (Anion Exchange Membrane) electrolyzer, you will need the following materials:

  1. Anion exchange membrane: The anion exchange membrane is a critical component of the AEM electrolyzer, as it allows the transport of positively charged hydrogen ions while blocking the negatively charged hydroxide ions. The membrane is typically made of a polymer material that contains positively charged functional groups, such as quaternary ammonium or imidazolium groups.

  2. Electrodes: The AEM electrolyzer requires two electrodes, an anode and a cathode, to facilitate the electrochemical reaction. The electrodes are typically made of a conductive material, such as carbon or metal, and coated with a catalyst, such as platinum or nickel, to increase the rate of the reaction.

  3. Electrolyte: The AEM electrolyzer requires an electrolyte to conduct the electric current between the electrodes. The electrolyte is typically a concentrated solution of an alkaline material, such as potassium hydroxide (KOH) or sodium hydroxide (NaOH).

  4. Frame and casing: The AEM electrolyzer requires a frame and casing to hold the membrane, electrodes, and electrolyte in place. The frame and casing are typically made of a non-conductive material, such as plastic or metal.

  5. Power source: The AEM electrolyzer requires a power source, such as a DC power supply, to drive the electrochemical reaction and split the water into hydrogen and oxygen gas.

  6. Gas collection system: The AEM electrolyzer requires a gas collection system to collect the hydrogen and oxygen gas produced during the electrolysis process. The gas collection system typically includes gas lines, valves, and storage tanks to collect and store the gases.

Overall, the materials required to make an AEM electrolyzer are similar to those required for other types of electrolyzers, such as PEM and alkaline electrolyzers, but the specific materials and design may vary depending on the application and performance requirements.

 

Can you use carbon papers for an AEM electrolyzer?

Carbon papers can be used as porous transport layers and electrode materials in an AEM (Anion Exchange Membrane) electrolyzer, but they are not typically used as Gas Diffusion Layers (GDLs) in AEM electrolysis.

In AEM electrolysis, the anion exchange membrane serves as the barrier between the anode and cathode, allowing only the positively charged hydrogen ions to pass through while blocking the negatively charged hydroxide ions. The membrane is typically made of a polymer material that contains positively charged functional groups, such as quaternary ammonium or imidazolium groups.

For the electrodes, metal catalysts, such as platinum or nickel, are typically used to increase the rate of the electrochemical reaction. However, there is ongoing research and development to explore alternative, non-precious metal catalysts that can reduce the cost and increase the scalability of AEM electrolyzers. Carbon papers, alebit atypical, are slowly finding their way into electrodes and gas diffusion layer in the stacks. 

Anion Exchange Membranes
Product Type Thickness (um) Tensile strength (MPa) Young's Modulus (MPa) Elongation (%) Water uptake (%) Max process temp (°C) Reinforced
AF3- CLF9-25 Anion 25 > 85 > 480 > 80 <15 150 NW PTFE
AF3- CLF9-50 Anion 50 > 80 > 450 80 - 120 <15 150 NW PTFE
AF3-HWK9-75 Anion 75 > 57 > 630 27 <15 150 Woven PEEK