Proton exchange membrane (PEM) water electrolysis for green hydrogen production

Proton exchange membrane electrolysis (PEM electrolysis) is an electrochemical process for producing hydrogen by means of water electrolysis. The process uses an electrolyzer that contains an anode and a cathode. The anode and cathode are separated electrically by a proton exchange membrane, which is also called a polymer electrolyte membrane. When the electrolysis process runs on electricity from renewable energy sources such as solar power, hydropower, or wind power, the hydrogen produced is known as green hydrogen.

In PEM electrolysis, ultrapure water flows around a proton exchange membrane (PEM). Located between the anode and the cathode, this membrane is ionically conductive. When an electric voltage is applied to both electrodes, the water on the anode side oxidizes to oxygen, free electrons, and hydrogen ions (Oxygen Evolution Reaction, OER). The ions pass through the membrane by diffusion. They then combine with the electrons at the cathode side to form hydrogen gas (Hydrogen Evolution Reaction, HER). The reaction products of PEM electrolysis are hydrogen and oxygen.

A PEM electrolyzer is a system that splits water into its component parts of hydrogen and oxygen by means of an electrochemical reaction. The hydrogen produced in this way is used as an efficient energy source.

We manufacture the most important component of a PEM electrolyzer – the stack, which is, in a sense, the beating heart of water electrolysis.

Compared to other electrolysis methods, such as alkaline electrolysis (AEL), PEM water electrolysis boasts a number of key benefits:

• high power density,
• high energy efficiency,
• high hydrogen output pressure.

In addition, PEM electrolyzers offer a range of further advantages:

• They offer maximum flexibility and require very little space: The compact design of the PEM electrolysis stack allows for space-saving and flexible integration into various environments, from decentralized production to large industrial plants. Its ability to handle a wide operating range makes it highly adaptable to different production needs.

• They can be scaled with ease: The system is designed for scalability; by combining multiple stacks, hydrogen production can be increased to meet the demands of large-scale, energy-intensive industries.

• The process is very safe and reliable: The PEM electrolysis process is a mature and reliable technology suitable for long-term, dependable operation.

Proton Exchange Membrane (PEM) electrolysis has emerged as a key technology for electrolytic hydrogen production. Its high efficiency and fast dynamic response allow it to rapidly adapt to variable renewable energy sources like wind and solar power.^1,2 This makes PEM systems, in contrast to conventional alkaline electrolysis, particularly suitable for Power-to-X applications and decentralized energy systems.²

Furthermore, PEM electrolyzers produce high-purity hydrogen¹ and can operate at high current densities and elevated pressures, reducing downstream compression requirements.^1,2 These characteristics make PEM electrolysis highly attractive for mobility applications such as hydrogen refueling stations and fuel cell vehicles, where compact system design and high hydrogen quality are essential.

In addition, the technology is applied in industrial sectors including chemical production, energy storage, and grid stabilization, where flexible and reliable hydrogen generation is required for the transition toward a low-carbon energy infrastructure.²

^{1 Koponen, J., Kosonen, A., Ruuskanen, V., Huoman, K., Niemelä, M., & Ahola, J. (2017). Control and energy efficiency of PEM water electrolyzers in renewable energy systems. International Journal of Hydrogen Energy, 42(45), 29648-29660.
2 Hancke, R., Holm, T., & Ulleberg, Ø. (2022). The case for high-pressure PEM water electrolysis. Energy Conversion and Management, 261, 115642.}

A PEM electrolisisyzer stack is the core assembly inside a Proton Exchange Membrane (PEM) water electrolyzer, a component that splits water into hydrogen (H₂) and oxygen (O₂) using electricity. It is a collection of many individual cells connected electrically in series and hydraulically in parallel. Each cell performs water electrolysis and stacking them increases total hydrogen production.

At the heart of each cell is the Catalyst Coated Membrane (CCM), an electrically insulating polymer that allows protons to pass through. Water is supplied to the anode side of this membrane via a metallic, Porous Transport Layer (PTL). At the anode, a catalyst splits the water into oxygen, protons, and electrons. While the electrons are conducted away, the protons migrate directly through the membrane to the cathode. There, they react to form hydrogen gas, which is then removed through a porous carbon Gas Diffusion Layer (GDL).

We manufacture PEM stacks in industrialized series production.

In PEM electrolysis, ultrapure water flows around a proton exchange membrane (PEM). Located between the anode and the cathode, this membrane is ionically conductive. When an electric voltage is applied to both electrodes, the water on the anode side oxidizes to oxygen, free electrons, and hydrogen ions (Oxygen Evolution Reaction, OER). The ions pass through the membrane by diffusion. They then combine with the electrons at the cathode side to form hydrogen gas (Hydrogen Evolution Reaction, HER). The reaction products of PEM electrolysis are hydrogen and oxygen.