Multilayer TPC achieves electrically conductive, gas-impermeable fuel cells at 100 microns

CW has written extensively about the growing use of hydrogen storage and fuel cells for a range of transport applications as countries committed to mitigate climate change. But with Trump’s emphasis on war and fossil fuels, the imperative for zero emissions has suffered some setback, and the drive for hydrogen has now pivoted to aviation.

However, fuel cells present aerospace engineers with a materials paradox. Bipolar plates must simultaneously conduct electricity with metallic efficiency while preventing hydrogen gas permeation at the molecular level. Conventional metallic plates address conductivity effectively but succumb to corrosion in the harsh electrochemical environments of fuel cells, requiring expensive protective coatings that ultimately fail. Composite materials offer corrosion immunity, weight savings and optimal specific strength, yet polymer matrices are inherently electrically insulating and gas-permeable.

Carbon ID (Lyon, France), a composite materials startup, questioned whether this contradiction stemmed from material selection or architectural design. In search of an answer, founder Pascal Poulleau and his team developed a multilayer thermoplastic composite (TPC) system where discrete layers contribute specific functional characteristics. The resulting bipolar plate material achieves electrical conductivity comparable to metallic alternatives while maintaining complete gas impermeability at a thickness of 50-200 microns, with 100 microns as the standard production specification.

Several OEMs are now validating the material for regional aircraft applications targeting 2030-2035 commercial deployment, at which point Carbon ID aims to be producing 1 million square meters (m²) of its product annually to meet the projected fuel cell production demand.

Electrochemical environment

Bipolar plates serve as structural separators between individual cells within fuel cell stacks, simultaneously distributing hydrogen and oxygen gases to reaction sites, conducting electrons between cells and removing reaction byproducts. Electrical conductivity must approach metallic levels, typically requiring through-thickness resistivity below 10 milliohm-cm² (mΩ·cm²) to minimize parasitic losses across hundreds of stacked plates. Gas impermeability must prevent hydrogen crossover, which, if it does happen, reduces efficiency and creates safety hazards.

The aerospace operating environment imposes additional constraints: pH levels fluctuate between highly acidic and neutral conditions, temperatures reach 200°C in high-temperature proton exchange membrane (PEM) systems and thermal cycling between ambient and operating temperatures occurs throughout every flight cycle. Metallic bipolar plates address conductivity requirements but fail durability criteria, with corrosion often initiating within months despite protective coatings. Gold coating prevents corrosion but proves prohibitively expensive and heavy. Additionally, a complete metallic bipolar plate stack for a regional aircraft fuel cell system can exceed 200 kilograms.

Many previous composite bipolar plate attempts focused on incorporating conductive fillers into thermoset matrices at 40-60% loading fractions. These formulations achieve marginal conductivity but remain orders of magnitude less conductive than metals. Thermoset processing limits manufacturing scalability, with the most widely used compression molding restricting production rates incompatible with aerospace requirements.

Functional layer architecture

Carbon ID’s approach originated in 2021 when researchers from a French energy institute presented Poulleau with corroding metallic bipolar plates. The initial assessment focused on geometric feasibility and, more specifically, whether composite tooling could reproduce intricate flow channel geometries. This proved straightforward given the founders’ aerospace background.

The fundamental challenge emerged during requirements analysis. “We are composites people, and composites people don’t know much about electrochemical things,” explains Poulleau. “Step by step, we found out we need to be gas-tight with hydrogen and other fluids, chemically resistant and electrically conductive as much as a metallic part. And, well, polymers and composites made from them are quite insulating , so this was the challenge.”

Rather than forcing a single material to satisfy all requirements, the team reconceptualized bipolar plates as functional layer assemblies. Each laminate layer provides specific properties, with the complete assembly meeting all criteria through architectural design rather than material compromise. This methodology extended aerospace composite design principles, where tailored fiber orientations optimize structural performance to functional rather than mechanical properties.

“We had to read a lot about hydrogen test standards and made our own test bench to measure electrical properties,” Poulleau notes. “We leveraged our workshop capabilities to design and fabricate custom measurement fixtures, enabling rapid iteration. We built up homemade resistivity measurement devices, so we were able to analyze step by step.”

The experimental methodology resembled recipe development. Carbon ID’s laboratory became a formulation testing environment where thermoplastic matrices, conductive charges and reinforcement fibers were combined in varying ratios, processed into coupons approximately half A4 format, and characterized for electrical, mechanical and barrier properties. Weekend work sessions became routine as the team balanced revenue-generating contracts with fuel cell material development.

To maintain legitimacy as a fully composite solution, all conductive additives required nonmetallic carbon-based formulations. Graphite and carbon black provided conductivity enhancement, while carbon and glass fiber reinforcements contributed mechanical properties. The thermoplastic matrix selection balanced processing temperature, chemical resistance and mechanical performance across target operating ranges.

Multilayer construction

Carbon ID’s final material architecture comprises multiple discrete TPC layers, each contributing specific performance attributes. While Carbon ID maintains formulation details under French patents and international patent applications, the functional design principles are evident from validation testing.

The base system uses thermoplastic matrices for three operational temperature ranges: 100°C for automotive and stationary applications, and 150°C and 200°C for high-temperature aerospace systems. Carbon and glass fiber reinforcements provide mechanical integrity and dimensional stability. “Carbon fiber offers high specific stiffness but creates anisotropic electrical properties,” highlights Poulleau. “Glass fiber provides electrical isolation where required at lower cost but contributes lower mechanical performance.”

Conductive charges dispersed throughout the thermoplastic matrix provide through-thickness electrical conductivity. Graphite and carbon black particles create percolating networks that transport electrons between layers. Achieving metallic-equivalent conductivity requires optimized particle size distributions, loading fractions approaching rheological limits and specialized mixing processes that uniformly disperse particles without agglomeration.

The most innovative element addresses gas impermeability. “At the beginning, gas tightness was not good at all,” Poulleau acknowledges. “On paper, composite materials seem the wrong material to provide gas tightness.” Carbon ID’s solution applies a specialized surface layer functioning as a molecular barrier, preventing hydrogen permeation while maintaining electrical conductivity. “We successfully achieved that down to 50 microns,” Poulleau notes. “Though 100 microns represents the standard specification balancing handleability and performance.”

Manufacturing employs continuous processing adapted from thermoplastic film production. Raw materials feed into a production line that combines layers, applies heat and pressure for consolidation and outputs finished material in rolls up to 600 millimeters wide. In-line quality control monitors thickness variation and electrical conductivity continuously, ensuring specification compliance. Finished material rolls proceed to bipolar plate fabrication through thermoplastic forming. Cut blanks are heated above the glass transition temperature and then formed using matched tooling that impresses flow channel geometries, after which they are cooled. The complete cycle requires seconds rather than hours typical for thermoset processing, enabling high-volume production rates. Robotic automation and hydraulic press systems provide aerospace-grade precision and repeatability.

Validation testing, proven performance

Performance validation focused on aerospace certification requirements, where 30-year operational lifespans represent minimum acceptable durability. Carbon ID collaborates with several aerospace OEMs to define testing protocols across four critical areas: electrical conductivity, gas impermeability, chemical resistance and thermal cycling durability.

“Through-thickness contact resistance measured below 10 mΩ·cm² across the standard 100-micron thickness, meeting or exceeding metallic performance,” Poulleau highlights. “Conductivity remains stable across the full operating temperature range from ambient to 200°C, with no degradation during thermal cycling tests simulating thousands of flight cycles.”

Gas permeability testing measured hydrogen transmission rates under differential pressure conditions. “The surface barrier layer prevented molecular hydrogen transport, with measured permeability rates falling below detection limits,” Poulleau explains.

Chemical resistance validation employed an accelerated aging standard in aerospace qualification; test coupons underwent immersion in high-acidity solutions at elevated temperatures for extended durations, simulating years of electrochemical exposure. “The method is to put the material into a very high acidity environment and very high temperatures for days versus months and years,” Poulleau describes. The material sustained no measurable degradation throughout aging cycles simulating 30 years of operational exposure.

Carbon ID is still conducting advanced characterization beyond conventional testing. Microscopic cross-sectioning and spectroscopy techniques will examine whether acid penetration occurred at the molecular level. “We will go through specific testing inside the material to see if we’ve had some acid going into the thermoplastic,” Poulleau notes. “These investigations, scheduled for late 2025, will provide detailed materials science data necessary for formal aerospace certification.”

The performance validated to date includes thermal expansion characteristics that provide additional advantages over metallic alternatives. Aerospace fuel cell stacks contain hundreds of bipolar plates with elastomeric seals preventing gas leakage. Because the Carbon ID composite plates exhibit thermal expansion coefficients significantly lower than metallic alternatives they are better matched to seal materials, reducing thermomechanical stress and improving long-term sealing reliability. They also achieve up to 50% reduction in weight compared to metallic bipolar plates, with savings exceeding 100 kilograms for complete regional aircraft fuel cell stacks, directly contributing to payload capacity and range performance.

Production scaling trajectory, significant demand

Carbon ID’s commercialization strategy pivots on aerospace applications despite initial automotive interest. “At the beginning, we thought maybe the automotive industry would be interested, and they were, but they were more interested in quickly developing a working fuel cell today, rather than spending time to develop carbon bipolar plates,” Poulleau explains. “Automotive timelines seem to prioritize rapid deployment using available metallic technology, accepting corrosion limitations.”

Aerospace presents contrasting requirements. Regional aircraft targeting 30-50 passenger capacity require fuel cell systems significantly larger than automotive applications, with hundreds of kilowatts to megawatt-scale power output. “They probably don’t believe it would take off with large, metallic, heavy fuel cells made of steel or titanium,” Poulleau observes. “Aerospace customers also require 30-year component lifespans with minimal maintenance, making corrosion-free composite plates essential.”

Multiple aerospace and eVTOL manufacturers are developing hydrogen fuel cell propulsion with target entry-into-service dates between 2030 and 2035. Carbon ID currently engages with customers across North America and Europe, with the fastest development pace occurring in the U.S. market.

Furthermore, Carbon ID’s production capacity planning reflects aerospace demand projections. The company currently operates a pilot line producing approximately 10,000 m² annually, supporting development programs and qualification testing. A new facility under construction will house a 600-millimeter-wide continuous production line commissioned in 2026, supporting material qualification and initial customer deliveries in 2027.

Scaling to 1 million m² annual capacity by 2030 requires multiple production lines operating continuously. Each regional aircraft fuel cell stack contains 300-800 bipolar plates, totaling 50-100 m² of material per aircraft. Production rates of 10 aircraft per month consume approximately 12,000 m² monthly from a single customer. Carbon ID’s 1 million m² target serves only two confirmed aerospace customers, indicating substantial market potential.

Carbon ID’s current business model positions it solely as a raw material manufacturer. Finished material ships in roll format to fuel cell manufacturers or specialized forming subcontractors who perform final plate fabrication. “We will probably find a partner to form the bipolar plate. We will focus on being a material manufacturer rather than a part manufacturer,” Poulleau clarifies.

Beyond bipolar plates, Carbon ID has developed composite terminal plates — structural end plates that contain fuel cell stacks. These components achieve 40% weight reduction compared to aluminum while integrating functional features including sealing surfaces and fluid supply passages, extending Carbon ID’s addressable market.

The convergence of aerospace hydrogen propulsion developmentand Carbon ID’s composite material validation and production capacity scaling positions its technology as a potential enabler for zero-emissions aviation — an outcome for the whole industry that will hopefully become evident as aircraft development programs progress toward certification over the next 5 years.