Optimal Bipolar Plate Materials for PEM Fuel Cells

Bipolar plates are a crucial component of proton exchange membrane fuel cells (PEMFCs). They play multiple roles, including transporting reactant gases, carrying current, providing heat and water management, and separating individual cells. However, these plates also contribute to a significant portion of the fuel cell’s weight, volume, and cost. Therefore, it is essential to find optimal bipolar plate materials that enhance efficiency and durability while minimizing these factors.

In this article, we will explore the importance of bipolar plates in PEMFCs, the challenges associated with metal bipolar plates, and the benefits of using carbon bipolar plates. We will also delve into a cost comparison between carbon and metal plates, discuss the durability and power density of carbon plates, and highlight their overall superiority for PEM fuel cells.

Importance of Bipolar Plates in PEMFCs

Bipolar plates are critical components of proton exchange membrane fuel cells (PEMFCs) due to their multifunctional roles that are essential for the efficient operation of the fuel cell system.

Firstly, these plates facilitate the transport of reactant gases within the fuel cell, ensuring a smooth flow and efficient distribution. This transportation process is crucial for enabling the electrochemical reactions that produce the electrical energy.

Secondly, bipolar plates provide electrical conductivity, allowing the generated electrons to flow from the anode to the cathode, ultimately producing the desired electrical power output.

Furthermore, these plates play a significant role in managing heat and water within the fuel cell system. They aid in distributing the heat generated during the electrochemical reactions and help regulate the temperature to optimal levels for the fuel cell’s performance. Additionally, bipolar plates facilitate the management of water by enabling its transport and removal, preventing the flooding of the cells.

In addition to their functional contributions, bipolar plates also act as separators, keeping the individual cells isolated from each other. This separation ensures that the reactant gases, ions, and electrons flow only in the desired paths, preventing any cross-contamination or short-circuiting.

Lastly, bipolar plates provide crucial mechanical support to the entire fuel cell stack, ensuring its structural integrity and stability.

The significance of bipolar plates in PEMFCs is unquestionable. Their design, material selection, and performance impact the overall efficiency, durability, and cost-effectiveness of the fuel cell system. By optimizing the functionality of these plates, researchers and engineers can advance the development and commercialization of proton exchange membrane fuel cells, opening up possibilities for cleaner and more sustainable energy options.

Challenges with Metal Bipolar Plates

Metal bipolar plates have long been a common choice for fuel cells due to their electrical conductivity and mechanical strength. However, the use of metal plates in fuel cell systems presents significant challenges that limit their effectiveness and cost-efficiency.

Corrosion in the Acidic Environment

One notable challenge associated with metal bipolar plates is their susceptibility to corrosion in the highly acidic environment of fuel cells. The corrosive nature of the fuel cell’s electrolyte gradually degrades the metal surface, leading to compromised performance and potential system failure. To address this issue, additional protective coatings are required to shield the metal plates from corrosion, thus adding extra costs and complexity to the system.

Higher Costs

Another drawback of metal bipolar plates is their inherently higher cost compared to other plate options. The materials used for metal plates, such as stainless steel or titanium alloys, incur higher manufacturing expenses, contributing to the overall cost of the fuel cell system. These higher costs pose challenges for widespread adoption, especially in cost-sensitive applications.

Shorter Lifetimes

Metal plates also have shorter lifetimes, limiting their suitability for applications that require extended operation and reliability. Over time, the corrosive environment and the mechanical stresses experienced by metal plates can lead to degradation, performance loss, and ultimately, the need for replacement. The shorter lifetimes of metal bipolar plates result in increased maintenance and replacement costs over the lifetime of the fuel cell system.

Considering the challenges posed by corrosion, higher costs, and short lifetimes, it becomes essential to explore alternative materials with improved durability, cost-effectiveness, and performance. Carbon bipolar plates provide a promising solution to overcome these limitations, as discussed in the subsequent sections.

Benefits of Carbon Bipolar Plates

Carbon bipolar plates offer several advantages over metal plates in proton exchange membrane fuel cells (PEMFCs). These plates provide lower upfront and long-term costs, higher durability, flexible design, and high power density, making them a superior choice for fuel cell applications.

Lower Costs

One of the key benefits of carbon bipolar plates is their lower cost compared to metal plates. Carbon materials and manufacturing processes are more cost-effective, resulting in reduced upfront expenses. Additionally, the long-term cost savings are significant as carbon plates have proven durability, allowing for extended lifetimes and minimal maintenance requirements.

Higher Durability

Carbon bipolar plates demonstrate superior durability in PEMFCs. They have been extensively tested and proven to have lifetimes exceeding 30,000 hours in fuel cell transit buses. This exceptional durability ensures reliable and long-lasting performance, reducing the need for frequent replacements and associated costs.

Flexible Design

The flexible design of carbon bipolar plates offers several advantages. Carbon materials can be easily formed into various shapes and sizes, enabling the creation of intricate designs tailored to specific fuel cell requirements. This flexibility allows for improved performance and better flow management within the fuel cell stack, ultimately leading to enhanced efficiency.

High Power Density

Carbon bipolar plates contribute to achieving high power density in PEMFCs. Their lightweight and compact design, coupled with excellent electrical conductivity, enable the creation of fuel cell stacks with higher power output. The optimized power density not only increases the overall efficiency of the fuel cell but also enables the development of smaller and more compact fuel cell systems.

Cost Comparison between Carbon and Metal Bipolar Plates

A comprehensive cost study conducted by Ballard in collaboration with Strategic Analysis, Inc., sheds light on the cost comparison between carbon and metal bipolar plates, two commonly used materials in proton exchange membrane fuel cells (PEMFCs).

The study conclusively demonstrates that carbon bipolar plates offer a significant cost advantage over their metal counterparts across all manufacturing volumes. By using carbon plates instead of metal plates, manufacturers can achieve substantial cost savings, making fuel cell technology more economically viable.

In the medium-duty vehicle fuel cell segment, the study reveals that the adoption of carbon plates can result in potential cost savings of up to $5 per kilowatt (kW). For passenger car fuel cell stacks, the savings can reach up to $3 per kW.

One of the key factors contributing to the lower cost of carbon plates is the ability to refurbish and reuse them in new fuel cell stacks. Recycling and repurposing carbon plates significantly reduce the overall cost compared to metal plates, offering a sustainable and cost-effective solution in the long term.

Cost Comparison between Carbon and Metal Bipolar Plates:

• Carbon plates are the lower-cost option across all manufacturing volumes.
• Potential cost savings of up to $5/kW for medium-duty vehicle fuel cells.
• Potential cost savings of up to $3/kW for passenger car fuel cell stacks.
• The ability to refurbish and reuse carbon plates reduces the overall cost compared to metal plates.

Durability of Carbon Bipolar Plates

Carbon bipolar plates have consistently demonstrated high durability in various applications. They have undergone rigorous testing and proven to have lifetimes exceeding 30,000 hours in fuel cell transit buses. Notably, these plates have operated issue-free for over 10,000 hours in material handling vehicles as well.

The impressive durability of carbon plates makes them a reliable and cost-effective choice for fuel cell systems, particularly in medium and heavy-duty applications. Their extended lifetimes ensure long-lasting performance and reliability, reducing the need for frequent replacements and maintenance, thereby minimizing operational costs.

With their exceptional durability, carbon bipolar plates offer a sustainable and efficient solution for achieving reliable and long-term operation in proton exchange membrane fuel cells (PEMFCs).

Power Density and Design Flexibility of Carbon Bipolar Plates

Carbon bipolar plates offer superior power density and design flexibility compared to metal plates. The formability of carbon allows for the creation of 3D designs, leading to higher performance, lower weight, and improved freeze start capability.

The higher power density achieved with carbon plates results from their ability to optimize the flow of reactant gases and the distribution of current. The 3D designs made possible by the formability of carbon maximize the active surface area, promoting efficient electrochemical reactions and reducing ohmic losses within the fuel cell stack.

Design flexibility is a significant advantage of carbon bipolar plates. They can be easily customized to meet specific fuel cell geometries and performance requirements. Carbon plates can accommodate complex shapes, intricate flow channels, and unique stack configurations, enabling fuel cell designers to optimize stack performance for various applications.

The weight reduction achieved with carbon plates not only enhances power density but also improves overall fuel cell system efficiency. Lighter plates minimize the weight burden on vehicles, contributing to increased energy efficiency and extended driving range.

Carbon plates also offer improved freeze start capability, reducing the need for external heating systems in cold weather conditions. The formability of carbon allows for the creation of integrated internal flow channels that facilitate rapid heat transfer, preventing the accumulation of ice and ensuring reliable fuel cell operation even in low-temperature environments.

In conclusion, carbon bipolar plates provide superior power density and design flexibility compared to metal plates. Their formability enables the creation of 3D designs that optimize performance, reduce weight, and enhance freeze start capability. These advantages make carbon plates an attractive choice for achieving high power density in fuel cell stacks, leading to more efficient and compact fuel cell systems.

Overall Superiority of Carbon Bipolar Plates

When it comes to proton exchange membrane fuel cells (PEMFCs), carbon bipolar plates have established their overall superiority in terms of cost-effectiveness, durability, power density, and design flexibility. These plates offer a compelling solution that outperforms metal plates in various aspects, making them a preferred choice for fuel cell technology.

One key advantage of carbon bipolar plates is their lower cost compared to metal plates. The materials and manufacturing processes for carbon plates are more affordable, resulting in significant cost savings across all manufacturing volumes. A cost study conducted by Ballard in collaboration with Strategic Analysis, Inc. confirmed these findings, revealing potential savings of up to $5/kW for medium-duty vehicle fuel cells and $3/kW for passenger car fuel cell stacks.

In addition to their cost-effectiveness, carbon bipolar plates demonstrate higher durability and performance. With proven lifetimes exceeding 30,000 hours in fuel cell transit buses and issue-free operation for more than 10,000 hours in material handling vehicles, carbon plates offer long-lasting and reliable performance. This durability translates to reduced maintenance and replacement costs, further enhancing their appeal for diverse fuel cell applications.

Furthermore, carbon plates provide superior power density and design flexibility. The formability of carbon enables the creation of 3D designs, resulting in higher performance, lower weight, and improved freeze start capability. Additionally, the well-established high volume production of thin, high-quality carbon plates makes them a viable option for achieving high power density in fuel cell stacks.

In conclusion, the overall superiority of carbon bipolar plates in terms of cost-effectiveness, durability, power density, and design flexibility makes them the ideal choice for proton exchange membrane fuel cells. With their proven track record and the ability to refurbish and reuse them, carbon plates offer a sustainable and efficient option for the commercialization of fuel cell technology in various applications.