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 (or 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.

The function of PTLs
Despite its thin profile, the PTL manages a surprising number of complex tasks. To operate reliably in corrosive environments, PTLs must strike a balance between physical and electrical properties. A well-designed PTL performs a myriad of functions, including:

Mass transport
It delivers water to the catalyst layer while allowing oxygen gas (produced at the anode) to exit efficiently.
Electrical conductivity
It creates a low-resistance pathway for electrons to travel between the catalyst layer and bipolar plate, to support the flow of current through the stack.
Thermal conductivity
It helps evenly dissipate heat generated by an electrolyzer. This prevents hotspot formation, local degradation, and system inefficiencies.
Mechanical support
It acts as a structural component. The PTL supports the membrane and catalyst layer, preserving stack compression, and protecting against deformation and physical wear.
Corrosion resistance
Material integrity isn’t optional. A PTL must endure tens of thousands of hours operating in highly oxidative and acidic/alkaline conditions.

Not all PTLs are created equal
With so many performance demands, selecting the right PTL material isn’t as simple as selecting something that “works”. Each electrolyzer environment comes with unique challenges. Material decisions have a direct influence on durability, efficiency, and overall cost. A poorly chosen PTL can accelerate degradation of adjacent components, increase system resistance, or introduce reliability issues. For OEMs and system developers aiming to commercialize green hydrogen at scale, PTLs are no place to cut corners. That’s why material innovation is at the heart of the conversation. It’s also where metal fiber PTLs are making their mark.

The case for metal fiber PTLs
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 (plain or Pt coated) 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 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.

Are you designing th enext big thing in hydrogen generation? Explore the science behind Bekaert's metal fiber PTLs and see how we develop cutting-edge PTL solutions at our Hydrogen Innovation Hub. Or, fill out our contact form to get in touch with a team member.