The PTL sits behind the MPL. It is thicker, more mechanically robust, and engineered for macro-scale transport and structural durability. At its core, PTL:
- Provides mechanical stability for the active area (under differential pressure and compressive load)
- Ensures consistent contact across the cell (to minimize resistance and hotspots)
- Enable through-plan transport pathways (so water can reach the catalyst efficiently)
- Contribute to stack-level thermal and pressure management (especially under high-current conditions)
How do MPLs and PTLs work together?
Rather than viewing MPLs and PTLs as separate items on a checklist, it’s more accurate to think of them as a single, integrated system: PTL → MPL → catalyst. Their performance is inherently interdependent, particularly under the demanding conditions of PEM electrolysis. When they’re poorly matched, performance losses emerge that neither component can resolve alone.
When they’re designed to work together, however, the interface behaves like a cohesive system. At high current densities, both layers are pushed to support rapid water delivery to the catalyst and efficient removal of generated oxygen. The aggressive oxygen evolution reaction (OER) environment introduces continuous bubble formation and localized stresses that must be managed across the interface. Not by one layer alone, but by how the layers function together. Over time, thermal cycling and compressive loads further challenge the stability, contact quality, and transport pathways of the combined system.
Reframing the question
Viewed through a stack-level lens, the roles of each layer become clear. While the MPL shapes the micro-environment and interfacial behavior directly at the catalyst, the PTL provides the structural, electrical, and transport backbone that supports stable operation. Performance doesn’t stem from one layer outperforming the other. It emerges when these elements are engineered as a cohesive interface system, aligned with real operating conditions.
With that perspective in mind, the “MPL vs PTL” question shifts to “How effectively do the transport and interfacial layers work together under the conditions my stack actually faces?” That shift from comparison to interaction is what enables meaningful progress toward higher performance, improved reliability, and long-term operation.
As hydrogen systems push toward higher efficiency and industrial-scale deployment, progress will favor an approach that treats MPLs and PTLs as co-designed, evolving components. Rather than alternatives to be weighed against each other. If you’re interested in exploring how advancement in MPL technology supports this kind of system-level thinking, download our MPL white paper.
