MPL lessons for PEM electrolyzers

Microporous layers (MPLs) did not emerge with PEM electrolyzers. Their foundation was established in PEM fuel cells, where decades of development refined how microstructure, porosity, and surface properties influence performance. And, because of that history, electrolyzer developers are not starting from scratch. Instead, they are building upon a mature understanding of how to manage fluid transport, electrical contact, and catalyst utilization at the micro-scale. While this legacy provides a strong starting point, it does not transfer directly. Considering the operating realities of PEM electrolysis, including higher current densities, different transport directions, and harsher oxidative environments, proven MPL principles must be reinterpreted rather than reused.

 
Microstructure defines performance 
One of the clearest lessons carried forward is the importance of microstructure control. In fuel cells, engineered pore size distribution and the combination of micro- and mesoporous networks enabled a careful balance between gas diffusion and water management. That same principle remains central in electrolyzers, but its application shifts. Instead of facilitating reactant gas access and water removal, MPLs must now support consistent water delivery to the catalyst while enabling efficient oxygen evacuation. The balance is still there, but the dominant transport mechanisms and constraints are different. Designs that work under fuel cell conditions can fall short if the transport behavior differences aren’t accounted for.

What must evolve for electrolyzers? 
Durability considerations further highlight where adaptation is required. Fuel cell-era MPLs provide valuable lessons around cracking, compression, and long-term mechanical stability. Electrolyzers build on this, but operate under added stressors: strong oxidative conditions, higher pressure gradients, and extended operation at elevated loads. Materials and structures must therefore be more robust, and integration with components, such as titanium PTLs, must be carefully managed. At the same time, experience has shown that MPLs cannot be optimized in isolation. Improvements made at the component level do not always translate to system-level gains—and can even introduce new limitations if interactions with the CL or PTL are not considered.

In conclusion
Taken together, decades of MPL development have established a clear foundation. Microstructure matters, uniformity matters, and interfaces matter. In PEM electrolyzers, the challenge is not to rediscover these principles, but to apply them with greater precision under more demanding operating conditions. To explore how these principles are being applied in practice, and what they mean for next-gen design, read our MPL white paper.