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Decarbonizing heavy mobility is a challenge that presents significant opportunities for hydrogen fuel cell powertrains. These systems offer the necessary power, range and durability essential for commercial applications, while reducing mass compared to battery electric options.

A critical component of the hydrogen fuel cell is the bipolar plate, which facilitates the electrochemical processes that produce electricity. Bipolar plates distribute reactant gases — hydrogen at the anode and oxygen or air at the cathode — across the active area of what’s known as the membrane electrode assembly (MEA). Their primary role is to ensure consistent reaction rates and prevent localized reactant starvation, which can hinder the cell’s performance.

In addition to gas distribution, bipolar plates are vital for current collection. They conduct electrons generated at the anode — where hydrogen is oxidized to protons and electrons — through an external circuit to the cathode. At the cathode, these electrons combine with oxygen and protons that have migrated through the proton exchange membrane (PEM) to form water. As a result, bipolar plates must have high electrical conductivity to minimize ohmic losses, which negatively affect fuel cell efficiency. Moreover, these plates account for approximately 75% of a fuel cell stack’s weight and about 30% of its cost.

A typical fuel cell designed for a 250-kilowatt (kW) heavy-duty vehicle uses approximately 600 individual bipolar plates. The size and design of these plates are thus critical for enhancing overall gravimetric efficiency. Various materials are employed for bipolar plates, each with distinct types, costs and performance characteristics.

Graphite plates, for example, are known for their high conductivity and chemical stability, but they must be about 2 millimeters thick to maintain sufficient mechanical strength, which results in hydrogen fuel cell stack power densities of around 1.2 kilowatts per kilogram (kW/kg). Alternatively, metal plates, commonly made from stainless steel with specialized coatings, deliver higher power densities of up to 4.0 kW/kg. However, these face durability issues; even with the best coatings they have a maximum lifespan of roughly 10,000 hours. Expanded graphite serves as a compromise, reaching a power density of 3.8 kW/kg. But its natural brittleness presents challenges during assembly and introduces potential failure points.

These composite plates also exhibit significant advancements in electrical conductivity and structural integrity compared to traditional materials like graphite or metal. Key performance metrics include a surface resistivity of less than 5 mΩ·cm², hydrogen impermeability below 1.5e-⁶mol/s/m²/MPa and durability exceeding 30,000 hours. Additionally, the plates feature a Young’s modulus of 11.7GPa and a tensile strength of 67MPa, conducive to handling high-volume manufacturing processes.

Hycco’s material and manufacturing technique combination contributes to a substantial enhancement in gravimetric efficiency at the fuel cell level, owing to the improved specific density of the composite. As a result, the company’s nonwoven composite bipolar plates can attain power densities of up to 7.5 kW/kg, representing an 81% improvement over current solutions in the market.

“We saw bipolar plate technology as a tremendous opportunity for innovative composites,” says Romain Di Costanzo, CEO of Hycco. “Hycco’s goal was to create a step-change in what is possible with hydrogen fuel cell design, enabling more compact, efficient and commercially viable fuel cell systems.”

Nonwoven material development

According to Hycco, the alignment of fibers is essential for determining the conductive properties of nonwoven composite bipolar plates. This process begins with laying down continuous fiber sheets in a cross-laid pattern to achieve the desired thickness and control the lateral orientation of the fibers. Next, the needle-punch process — in which barbed needles puncture the layered fiber sheets repeatedly — is used to mechanically bond the sheets together.  As the needles penetrate the layers, they pull fibers from the outer layers through the thickness of the material. This leads to a carefully tailored alignment of fibers in three dimensions.

Hycco’s bipolar plates exhibit low ohmic resistivity due to 10-60% reinforcing fibers oriented along the plate axis. This alignment creates conductive pathways that enhance electrical performance while also bolstering the structural integrity of the plate in that direction. The precise formulation of these plates can be tailored to meet the specific requirements of the final fuel cell’s application.

The thermoplastic matrix plays an equally crucial role in the bipolar plate’s performance. Hycco says it is specifically tailored for compatibility with both low-temperature proton exchange membrane fuel cells, which typically operate between 60-90°C, and high-temperature fuel cell environments, where operating temperatures can reach 180°C. The fiber volume fraction (FVF) is typically between 20-60%, depending on the specific demands of the bipolar plate application.

Hydrogen permeability is addressed through precise control of the fiber-matrix interface. An undisclosed technique is used without requiring additional barrier layers or coatings. This is accomplished while maintaining a relatively low density of 1.8 g/cm³, contributing to the plate’s optimal specific performance capabilities.

Thermocompression, quality assurance

After needle-punching, the next step is thermocompression manufacturing. This technique begins with the meticulous layering of the needle-punched nonwoven reinforcement and thermoplastic matrix materials, while strategically adding release films to the stack to ensure high surface quality.

Compression molding takes place at moderate pressures between 6-12 MPa. During the thermocompression stage, the materials are subjected to temperatures ranging from 140-400°C, tailored to the specific matrix system and performance requirements of the final product.

“This approach reduces the necessity for high FVF and allows for better control of matrix viscosity,” highlights Di Costanzo. “The combination of low pressure and high temperature enables improved fiber wet-out and consolidation, minimizing fiber deformation and the likelihood of porous cavities, which could compromise permeability.”

The core processing steps are efficiently completed in under 2 minutes. Following this, a cooling and consolidation phase regulates cooling rates between 40-90°C/minute, enhancing the development of crystallinity in the semi-crystalline structure. This process ensures that the final product achieves a void content of less than 1%, contributing to its semi-isotropic mechanical properties.

“Quality assurance is seamlessly woven into every stage of our production process,” notes Di Costanzo. “It starts with the meticulous verification of raw materials and extends through to post-molding dimensional analysis, assembly verification and final performance validation.

“Each plate we produce is rigorously assessed using laser profilometry for dimensional control, and we use statistical sampling to ensure the Young’s modulus and tensile strength as well as the desired electrical conductivity,” he continues. “A cornerstone of our quality assurance protocol is 100% leak testing of all plates, with every component receiving a unique 5 × 5-millimeter data-matrix marking to ensure complete traceability.”

Bipolar plate performance validation

Full-scale application testing of Hycco’s composite bipolar plates has been successfully demonstrated in the MangabHy project, a collaboration involving Delair (Toulouse, France), IAE Supaero (Toulouse, France), Pragma Industrie (Biarritz, France) and Hycco, which focused on the development of long-distance drones powered by hydrogen fuel cells.

Delair supplied its DT 46 vertical takeoff and landing (VTOL) drone, developed in partnership with ISAE Supaero and powered by a Pragma hydrogen fuel cell stack which features Hycco’s composite bipolar plate technology. The application demanded high power density and reliable performance from a 1-kW fuel cell stack that could carry out 8-12 hours of flight autonomy with a 4-kilogram payload capacity. Performance testing revealed compelling results in direct comparison with traditional materials.

The Hycco-equipped fuel cell stack prototype achieved identical polarization curves to the graphite plate equipped baseline while reducing the bipolar plate mass by more than 69% from 2.6 kilograms to 0.8 kilogram. This translated to a 40% decrease in total stack mass from 4.0 kilograms to 2.4 kilograms, enabling a 19% increase in payload capacity (1.7 kilograms). Di Constanzo highlights, “Much lower weight could be achieved if we work on the other components of the stack as well.”

Durability testing also proved the plates demonstrate lifespans exceeding 30,000 hours, matching the durability of graphite plates while significantly outperforming metallic alternatives that typically achieve only 10,000 hours. This longevity has been validated through accelerated aging stress tests simulating real-world operating conditions. “Principally, the only degradation observed is MEA degradation,” says Di Constanzo. “This proves that our components are fully inert in H2 fuel cells.”

Hycco is already developing its next-generation composite bipolar plates for applications like the DT46 drone. Reducing the plate thickness to 150 microns, it aims to lower the plate mass to 0.3 kilogram, which could enhance the payload capacity by a further 26% to 2.3 kilograms. The company has also formulated specific material configurations designed for various electrochemical fuel cell environments, catering to low- and high-temperature PEM fuel cells, as well as redox flow batteries, demonstrating the versatility and robustness of the company’s core technology.

Market impact and future outlook

As the hydrogen mobility sector advances toward wider adoption, Hycco is positioning its bipolar plate technology to capture a significant share of this emerging market. The company is focusing on decarbonization of heavy mobility applications, which corresponds with the increasing demand for high-performance and durable alternative powertrains.

Currently, the company produces 10,000 bipolar plates each year, but there are plans to ramp up production to 350,000 plates annually by 2026 through the establishment of a new pilot production line. This expansion strategy aims to secure 10-12% of the global bipolar plate market by 2030, with a projected turnover of €330 million.

The company’s growth strategy takes a dual approach: develop its own manufacturing capabilities while also exploring technology licensing opportunities for partners interested in producing plates in different regions. These partnerships are expected to target continuous production lines that can achieve outputs of 2-3 million bipolar plates annually by 2030.

Recent collaborations highlight the significant market potential of Hycco’s technology. A noteworthy partnership with Hynology, said to be the sole producer of membrane electrode assemblies (MEA) in France, has led to the creation of a 100-kW fuel cell demonstrator stack. This stack is specifically tailored for heavy-duty mobility applications and has received support through a €3.34 million award from the French eco-transition agency ADEME. The project focuses on qualifying essential fuel cell components such as MEAs and bipolar plates, with the goal of establishing a comprehensive French supply chain for these critical components.

In addition to partnerships, Hycco has enhanced its testing capabilities by developing a 60-kW fuel cell stack testing platform that enables potential industrial clients to evaluate their technology with representative systems. This capability is crucial for developers transitioning from prototype development to production, enabling customers to validate performance advantages for their specific applications.

Looking ahead, Hycco is seeking to raise €5 million in equity funding to support the next phase of its development and the launch of its pilot factory in Occitanie region of France. This strategic expansion is aligned with the expected increase in market demand for high-performance fuel cell components, particularly in the heavy mobility sector.