In a previous article, we explored the various materials commonly employed as gas diffusion layers (GDLs). Among these, two stand out as the most common choices for fuel cells and electrolyzers: graphitized carbon fiber paper or panel (also called molded graphite laminate) and sintered titanium.
GDLs play a crucial role in both the anode and cathode compartments of fuel cells and electrolyzers. They facilitate the efficient delivery of reactants to the catalyst layer, ensuring uniform distribution and optimal chemical interactions. In proton-exchange membrane (PEM) fuel cells, the anode GDL enables the diffusion of H2 gas to the catalyst layer, where it undergoes the hydrogen oxidation reaction (HOR), producing H+ ions and electrons. These electrons travel through the external circuit to the cathode, passing through the GDL. At the same time, the cathode GDL allows the diffusion of O2 gas, which reacts with the H+ ions that permeate through the membrane, forming liquid H2O. From this, GDLs not only facilitate gas diffusion but also aid electron transport and assist in water removal to prevent stack swelling.
Graphitized carbon paper is versatile and can effectively function as both the anode and cathode GDLs in PEM fuel cells. Meanwhile, sintered titanium has been used as an alternative oxidant diffusion medium, i.e., cathode GDL. For the sake of argument, in this article, we will focus on the cathode side because both sintered titanium and carbon-based GDLs work well there.
Assuming sintered titanium and graphitized carbon fiber paper have equally desirable properties (although they don’t, we’ll discuss this later), the cost of the gas diffusion layer (GDL) becomes a crucial factor in material selection. Let’s delve into the primary factors influencing GDL cost and compare how they differ for carbon panels and sintered titanium. To begin, let’s outline the main cost considerations:
- Raw material costs
- Manufacturing process
- Scalability
- Energy consumption
- Application-specific requirements
Raw Material Costs
Graphitized carbon panels are typically more cost-effective to produce compared to sintered titanium. While sintered titanium is produced from expensive titanium ore, which contains titanium in minerals like rutile, ilmenite, or titanite, graphitized carbon panels are manufactured using carbon-based raw materials that tend to be more economical. These organic precursors include polyacrylonitrile, pitch, cellulose, or lignin.
- Polyacrylonitrile (PAN) is a synthetic polymer produced from acrylonitrile monomers. It is widely produced on an industrial scale and accounts for over 90% of carbon fiber production. This keeps raw material costs relatively stable.
- Pitch is a dark-colored substance formed during the process of distilling coal tar, wood tar, or petroleum (bitumen). It is also known as the natural petroleum residue, asphalt. It contains a high proportion of carbon and other organic compounds. The cost can change based on crude oil prices and demand. High-quality pitch can cost more, but carbon fibers made from it are usually cheaper than PAN.
- Cellulose is a natural polymer found in plants like cotton, bamboo, or wood pulp. It’s renewable and widely available. Using it to make carbon fibers is often cheaper than synthetic materials like PAN, but costs can vary based on harvesting and processing.
- Lignin is a byproduct of the pulp and paper industry and is often considered a waste material. Raw material costs for lignin-based carbon fibers may be relatively low since lignin is readily available as a byproduct. However, additional processing steps may be required to convert lignin into a suitable precursor for carbon fiber production, which can affect overall production costs.
Let’s briefly compare these organic materials.
| Precursor | Advantages | Disadvantages |
|---|---|---|
| Polyacrylonitrile (PAN) | High carbon yield, good mechanical strength | Expensive, requires oxidation |
| Pitch | High carbon content, low cost | High processing temperatures |
| Cellulose | Renewable, low cost | Lower carbon yield, longer processing |
| Lignin | Renewable, abundant | Variable quality, complex processing |
Manufacturing Process
Manufacturing sintered titanium powder is more costly than producing graphitized carbon fiber papers or panels. To gain a deeper understanding of how graphitized carbon fiber papers are made, we encourage you to explore our in-depth blog post on the manufacturing process. On the other hand, the manufacturing process for sintered titanium powder involves several key steps. First, titanium ore is processed to extract titanium dioxide, which is then further processed into titanium powder. Next, the titanium powder is compacted into the desired shape and sintered at high temperatures under vacuum. This heating process causes the particles to bond together, increasing the strength and density of the material. After sintering, the surface of the titanium powder may undergo additional treatments to improve its properties. Throughout the process, quality control measures ensure that the sintered titanium powder meets required standards.
Overall, sintered titanium powder production is expensive due to the high cost of titanium ore and the complex processes involved. In contrast, manufacturing graphitized carbon fiber panels involves less energy and equipment, utilizing techniques like wet paper laying, compression molding, and graphitization.
Scalability
Scalability in manufacturing refers to how well a process can ramp up production without driving up costs per unit. For GDLs in fuel cells, scalability plays a crucial role in determining the product’s overall cost.
Graphitized carbon fiber paper GDLs offer several advantages over titanium in terms of production capacity, manufacturing techniques, cost efficiency, lead time, and customization. These materials can be produced in larger quantities from various sources and using versatile manufacturing techniques, which can be easily scaled up to industrial levels. This scalability leads to economies of scale, resulting in lower production costs per unit compared to titanium. Additionally, carbon materials typically have shorter lead times for production, allowing for more flexibility in meeting market demands and reducing inventory costs. Furthermore, the scalability of carbon-based materials enables easier customization and innovation in product design, allowing manufacturers to experiment with different formulations and configurations to optimize performance and cost for specific applications.
To address problems related to scalability and complexity of the manufacturing process, titanium fiber felt emerges as a promising alternative to sintered titanium powder. Unlike the intricate and energy-intensive production methods involved in sintering titanium powder, the manufacturing of titanium fiber felt involves comparatively simpler techniques.
This involves the creation of titanium fibers followed by sintering to form a cohesive structure. With its simpler manufacturing process and better scalability, titanium fiber felt presents itself as a viable option for various applications where titanium’s exceptional properties are desired, providing an accessible and versatile solution for industries seeking cost-efficient and scalable material solutions
| Criteria | Sintered Titanium Powder | Titanium Felt |
|---|---|---|
| Porosity and Permeability | High porosity and permeability | High porosity, slightly lower permeability compared to sintered powder due to fibrous structure |
| Surface Area | Large surface area due to fine particles | Relatively lower surface area compared to sintered powder due to fibrous structure |
| Mechanical Strength | Lower mechanical strength | Higher mechanical strength due to fibrous structure |
| Conductivity | Generally good electrical conductivity | Good electrical conductivity, depending on manufacturing process |
| Corrosion Resistance | Good corrosion resistance due to titanium composition | Good corrosion resistance due to titanium composition |
| Cost | Can be more expensive due to processing steps | Can be more cost-effective, depending on manufacturing process |
| Manufacturability | Requires specialized equipment and processes | Relatively easier to manufacture and shape |
In conclusion, the cost-effectiveness of graphitized carbon panels compared to sintered titanium for gas diffusion layers stems from various factors, including raw material costs, manufacturing processes, and scalability. Graphitized carbon panels offer a compelling alternative with their abundance of raw materials, simpler manufacturing techniques, and better scalability potential. As industries continue to seek cost-efficient and high-performance solutions for gas diffusion layers, the advantages offered by graphitized carbon panels make them an increasingly attractive choice. For those interested in exploring available gas diffusion layer options, CAPLINQ offers a range of solutions tailored to meet diverse application requirements, providing reliable and innovative materials to support the advancement of various industries.
