Project HollowEL started: Advancing next-gen bubble-free PEM electrolysis towards industrial application

Published on: June 30, 2026

1 Min. Reading time

Green hydrogen production relies on electrolysis technologies that combine high efficiency, durability, scalability, and cost-effective manufacturing. However, conventional electrolyzer cells still suffer from performance losses caused by gas bubble formation at the electrode surfaces, which impairs mass transport and increases cell overpotentials.
The recently launched HollowEL research project (Joint Project: 01286840/1) addresses this challenge by advancing an innovative bubble-free proton exchange membrane (PEM) electrolysis concept based on hollow-fiber-enabled direct water supply. Within the project, FEV leads the industrialization and scale-up activities.

Project kickoff meeting participants at Fraunhofer IMWS Weitere Zeilen anzeigen — © Fraunhofer IMWS, used with permission

What is the HollowEL approach?

At the core of HollowEL is a cell concept in which water is supplied directly to the polymer membrane via hollow-fibers. By avoiding gas bubble formation, the approach aims to reduce energy losses and improve the efficiency of hydrogen production. The underlying concept has already been demonstrated at laboratory scale. HollowEL will now focus on maturing the technology and its development for industrially relevant cell formats and scale-up approaches.

What is the role of FEV?

FEV plays a key role in the HollowEL project by leading the simulation-driven design and optimization of PEM electrolyzer cells based on hollow-fiber enabled direct water supply. FEV is responsible for cell design, stack design, and system design activities, ensuring an efficient transfer from component-level innovation to scalable electrolyzer systems.
In addition, FEV develops and applies advanced testing and validation methodologies to evaluate electrochemical performance, mechanical integrity, and structural durability of cell prototypes and stacks. Through the combination of modeling, experimental validation, and system engineering, FEV supports the development of a commercially viable technology with improved efficiency, reduced hydrogen production costs, and a clear roadmap towards industrial implementation.

Why does this matter for industrial hydrogen production?

For bubble-free electrolysis to progress beyond laboratory scale, the technology must demonstrate robust performance, durability, and scalability under industrially relevant conditions. HollowEL brings together expertise from research and industry to address these challenges and accelerate the transfer of bubble-free PEM electrolysis towards practical application.
The consortium includes Fraunhofer IMWS, Fraunhofer IKTS, Fraunhofer IGB, Fraunhofer IWES, RWTH Aachen University, Heraeus Precious Metals, Fumatech, Das Keramik-Institut and FEV. The project runs from March 2026 to February 2029 and is funded by the German Federal Ministry for Economic Affairs and Energy.
By connecting materials development, cell design, prototype manufacturing, validation, and system integration, HollowEL aims to establish the technological foundation for the future industrial deployment of highly efficient bubble-free PEM electrolysis.

Learn more about the HollowEL project