Selection and manufacturing schemes of materials for fuel cell power batteries

International pressure for energy diversification has led to a dynamic investment environment for alternative energy options. Fuel cells are almost the most efficient, and the global fuel cell market is expected to reach over 25 billion US dollars by 2025.

The demand for increasingly efficient and cost-effective fuel cells will influence the choice of materials and the manufacturing techniques selected.

Traditionally, bipolar fuel cell plates are machined by CNC. Graphite is a very expensive and highly permeable material, which is not suitable for large-scale production applications. It can be said that many materials have been evaluated as alternative materials, and due to the demand for competitive prices and relatively easy manufacturing, durable materials, metals (especially stainless steel and titanium) have become increasingly popular. Stainless steel has a series of properties that make it very suitable for bipolar fuel cell plates, such as its inherent strength, chemical stability, low cost and relative ease of mass production.

Fuel cells are made by stacking precisely complex plates, which are processed with intricate grooves or channels to allow the flow of liquids and gases. They can be manufactured using various techniques such as CNC machining and stamping, but the scalability and functionality of these processes are questionable.

Traditional metal processing techniques, such as stamping - and more recently, hydroforming - compromise flatness and introduce stress and burrs. Single-point machining processes and stamping tools can also be slow and uneconomical to produce, especially during the R&D phase.

The little-known photochemical etching process offers distinct advantages to manufacturers when producing complex components such as bipolar fuel cell plates.

First and foremost, photolithography does not require any hard tools. The use of digital tools is inexpensive for production and adaptation, so designs can be optimized at minimal cost.

This process also enables a rapid increase from prototype batch to mass production, offers almost unlimited part complexity, produces burr-free and stress-free components (especially important for fuel cell plates where imperfections could compromise the stack bonding force), does not affect metal tempering and properties, is suitable for all grades of steel, and achieves an accuracy of ±0.025mm - all delivery times are measured in days rather than months.

Photolithographic etching removes metal simultaneously, which means that complex channels or flow fields can be etched on both sides of the board. This versatility enables designers to change the size and shape of the channels and incorporate header, collector and port functions without incurring additional costs, which other technologies cannot achieve.

PrecisionMicro typically manufactures bipolar plates using 316 or 904 grade stainless steel, with plate dimensions of 1500mm x 600mm. However, plates can also be specified using special hard-to-machine metals such as titanium to reduce weight and enhance corrosion resistance at high temperatures for fuel cell applications.

The versatility of photochemical etching makes it an extremely attractive option for manufacturing complex sheet metal parts in a wide range of applications, and because it eliminates the design engineer's constraints inherent in traditional techniques, it inspires innovation.