Hydrogen is increasingly gaining recognition as a cornerstone of the energy transition. It will play a vital role in storing renewable energy, decarbonizing hard-to-abate sectors like steel, ammonia, chemical production and electricity generation.

Today, the majority of hydrogen is produced through steam methane reforming (SMR), a process that relies on fossil-based methane and emits CO₂ as a byproduct. Several alternative methods are in development for clean hydrogen production. Among them, water electrolysis, powered by renewable energy, offers a clean pathway. Yet, electrolysis still accounts for less than 1% of global hydrogen production. That share must rapidly grow if the world is to meet its decarbonization goals.

What's in a PTL?

Renewable energy is the gateway to decarbonizing hard-to-abate sectors like steel. It smooths out the works, fuels green systems, and pushes us toward a more sustainable future. As the energy landscape continues to evolve, it’s bold innovations that keep momentum moving forward. We are in an age of endless debates on membranes and catalysts. But what about the components that rarely make the news? The ones quietly shaping performance from within. At the center of an electrolyzer, the porous transport layer (PTL) is hard at work. It may often go unnoticed, but this small part is laying the groundwork for the global energy transition.

Exploring Porous Transport Layers

A PTL is an engineered, porous material designed to support several key processes inside an electrolyzer. You’ll find it in both PEM (proton exchange membrane) and AEM (anion exchange membrane) electrolyzer systems. Far from being a passive spacer, the PTL is central to the electrochemical reaction zone. It serves as a physical and functional bridge between the catalyst coated membrane (CCM) and bipolar plate. And its performance directly impacts how well the stack operates, and durability over time.

Advantages and Features of Stainless steel

Small fiber diameter provides high surface area
Corrosion resistance
Electrical conductivity
A variety of felt thicknesses
Customizable shapes and sizes

Proton exchange membrane water electrolysis (PEMWE) is a leading technology for producing hydrogen and oxygen from water using electricity. While still in development, PEMWE systems have already been deployed at the megawatt scale. A PEMWE stack is made up of several single cells. Each cell contains key components platinum group metal (PGM) catalysts (at the anode and cathode), titanium-based porous transport layers, and bipolar plates.

Together, the membrane and catalyst layers form the membrane electrode assembly (MEA) - also known as the catalyst-coated membrane (CCM). Despite its potential, PEMWE faces two main challenges: the high cost of components (CAPEX), and the need for long-term durability and performance (OPEX).

One major cost driver is the use of PGMs—specifically iridium (at the anode) and platinum (at the cathode). These materials are expensive, limited in supply, and associated with a high CO₂ footprint. Iridium, in particular, is scarce, with only 7–8 tons produced globally each year, primarily as a byproduct of platinum mining.

Explore the science behind Bekaert's metal fiber PTLs and see how we develop cutting-edge PTL solutions at our Hydrogen Innovation Hub.

Among the various PTL materials begin developed, metal fibers stand as the frontrunner. They offer high performance and long-term stability that operating stacks require. Unlike flat sheet metals, or other types of PTLs, metal fiber PTLs feature a wide range of porosity without sacrificing strength. This means that they are able to provide optimal mass transfer at a wide range of current densities and withstand high pressures and repeated thermal cycling.

Material-wise, titanium PTL (plain or Pt coated titanium PTL) remains the gold standard for PEM electrolyzers. Although it comes at a higher cost, titanium's inherent corrosion resistance is ideal in acidic conditions. And, for AEM systems, nickel is the most common to offer a reliable solution in the strong alkaline media, while stainless steel provides a cost-effective solution in a milder environment.

The function of AEM

Anion Exchange Membranes (AEM) offer an alternative method of hydrogen electrolysis. AEM electrolysis uses a water splitting reaction to separate hydrogen and oxygen gases. The membrane is permeable to hydroxide ions.

Reduces electrolyzer operational costs
Improves scalability and accessibility
Mechanical stability
Corrosion resistance
Electrical conductivity

The function of PEM

Proton Exchange Membranes (PEM) are a thin polymer electrolyte membrane. It's used in fuel cells and electrolyzers to conduct positively charged hydrogen ions or protons, producing water and hydrogen as byproducts. The PEM separates the anode from the cathode.

High durability and standard lifetime
Improved electrical potential
Resistant to corrosion and oxidation

The future of hydrogen runs through metal fibers

As the hydrogen economy evolves, the industry is learning that success is in the details. PTLs may not be the most visible component of an electrolyzer stack, but they're foundational to overall performance. In fact, a PTL's ability to balance mass and heat transport, electrical performance, and long-term durability makes them an indispensable component of next-gen green hydrogen systems. With metal fiber PTLs and Bekaert's advanced PTL solutions, stack designers don't have to compromise. They simply select a solution engineered to keep up the pace, and push performance forward. Because, in the grand scheme of things, microns matter.

Explore the science behind Bekaert's metal fiber PTLs and see how we develop cutting-edge PTL solutions at our Hydrogen Innovation Hub.

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The story of PEM

08 January 2026

Discover the story of PEM, from early fuel cell research and spaceflight missions to modern PEM water electrolysis that produces green hydrogen supported by corrosion-resistant metal fiber PTLs.