A bipolar plate is a conductive separator between adjacent cells in a fuel cell stack. In a hydrogen–air fuel cell, one face guides hydrogen along the anode side of one cell. The opposite face guides air along the cathode side of the next cell. The plate connects the cells electrically and works with seals to keep the fluid paths separate.
Bipolar plates can be made from graphite, graphite–polymer composites or metals. The sections below explain what to look for on a plate and which material questions to ask.
Key takeaways
- A bipolar plate has two working faces that serve neighboring cells.
- The plate guides reactants, carries current, separates fluid paths and supports the stack.
- Compare materials in their finished condition, including any coating or impregnation.
What Is a Bipolar Plate?
Start with the layers of one proton exchange membrane fuel cell, or PEM fuel cell. The membrane electrode assembly, or MEA, contains the membrane, catalyst layers and gas diffusion layers. A gas diffusion layer, or GDL, is the porous layer between the catalyst and the plate face. It gives reactants a path from the channels to the catalyst.
Now look at the plate between two cells. Its hydrogen-side face borders the anode GDL of one MEA. Its air-side face borders the cathode GDL of the neighboring MEA. A flow field is the channel pattern on a plate face. The bipolar plate is the shared part that carries those patterns and connects the adjacent cells electrically.
What Are the Main Features of a Bipolar Plate?
When looking at a plate drawing or photograph, start at the openings and follow the path toward the center. Four features help you read the layout:
- Flow channels and ribs. Grooves guide gas across the active area, where the cell reacts. The raised material between grooves forms ribs, or lands. These ribs contact and compress the GDL.
- Ports and distribution areas. Ports connect to stack supply and return routes. The distribution areas lead fluid between the ports and the channel pattern.
- Sealing lands. These are surfaces where seals bear against the plate. Together with the plate, gaskets at the assembly edges help keep gases in their intended paths.
- Optional coolant passages. Some plate assemblies include dedicated passages for liquid coolant, separate from the reactant channels on the working faces.
For more detail on how these features meet the rest of the stack, see PEM fuel cell operating conditions and interfaces.
What Do Bipolar Plates Do in a Fuel Cell Stack?
A fuel cell bipolar plate brings gas routing, electrical connection and stack support together at the boundary between cells.
| Function | What the plate does |
|---|---|
| Reactant distribution | The flow fields direct hydrogen and air along their respective electrode sides. |
| Electrical conduction | The conductive plate connects adjacent cells in series. |
| Fluid separation | The plate and its seals keep the reactant paths separate from each other and from any coolant circuit. |
| Water and heat management | Cathode channels provide a path for product water to leave. Where the plate includes a liquid cooling circuit, coolant carries away heat. |
| Mechanical support | The plate supports the layered assembly and provides surfaces that bear against the GDL under compression. |
When reading a stack drawing, trace the gas paths along the plate faces and the electrical path through the plate body. For the effects on flow, resistance and water management, see how bipolar plates work in fuel cells.
Common Bipolar Plate Materials
The main bipolar plate materials are graphite, graphite–polymer composites and metals. Start by identifying the form of the plate, then check the properties it must deliver in the stack.
| Material family | Typical form | What to check |
|---|---|---|
| Graphite | Graphite plate stock, including impregnated graphite | Graphite provides an electrical path. Check the finished plate’s strength and gas permeability. |
| Graphite–polymer composites | Molded plates made with graphite particles and a polymer binder | The formulation and molding process matter to electrical and mechanical properties. Compare the specific compound and finished part. |
| Metals | Stainless steel or titanium sheet, with a coating where specified | Metal sheets can be used for thin plates. Check corrosion behavior and electrical contact in the specified surface condition. |
For a coated metal bipolar plate, specify both the base alloy and the coating. Bulk conductivity and resistance at the contact interface are different checks. A material name alone leaves the surface condition and test conditions unspecified.
For decisions about grade, finish and manufacturing route, see choosing a bipolar plate material for your application.
Where Are Bipolar Plates Used?
Fuel cell stacks power cars and buses, as well as warehouse forklifts and stationary backup power systems. In PEM stacks, the plates perform the same basic jobs at each cell boundary: route fluids, connect cells and support the assembly.
For a new application, start with the stack dimensions, operating conditions and cooling arrangement. For example, when reviewing a plate originally drawn for a vehicle stack for use in a backup power unit, confirm those requirements before carrying the drawing over.
How Are Metal Bipolar Plates Made?
Metal flow channels can be formed into sheet or created by removing material. In photochemical machining, a patterned protective layer called photoresist covers selected areas. The etchant removes exposed metal. Stopping the etch within the sheet leaves a recessed channel.
For an etching review, provide the alloy, starting thickness, required channel cross-section and minimum metal thickness beneath the channel. Specify whether you need a patterned sheet, a finished half-plate or a joined assembly. See bipolar plate manufacturing from drawing to delivery for the wider process.
TMNetch Case: Reviewing Channels and the Outline Separately
A TMNetch project for patterned flow plates combined chemical etching and laser cutting. The materials used most often in the project were 316 stainless steel and titanium.
Apply the same principle to a metal bipolar plate drawing: review the recessed channels, through-openings and outside profile separately, then discuss which process suits each. The case illustrates how the two processes can be combined; its published record does not include fuel cell stack testing.
Review Your Metal Bipolar Plate Drawing
Planning custom etched bipolar plates? Share your drawing, material, plate thickness, channel dimensions and delivery requirements with TMNetch for a chemical etching feasibility review.
FAQs About Bipolar Plates
Do All Bipolar Plates Have Coolant Channels?
No. Some stacks circulate coolant through dedicated passages in the plate assembly. Others use a different stack cooling arrangement. Check the stack drawing to see which passages carry coolant and which carry reactants.
Can Bipolar Plate Channels Be Chemically Etched?
Yes. Chemical etching can create recessed channels in suitable metal sheet. Review the alloy, sheet thickness, channel profile and remaining wall together before specifying the process.
Conclusion
Bipolar plates guide reactants, connect adjacent fuel cells electrically, and help keep fluid paths separate. When comparing graphite, graphite–polymer composites, and metals, evaluate the finished plate against the stack’s requirements for electrical contact, sealing, and mechanical support. Include the coating or impregnation in that assessment where applicable.
If you’re designing a metal bipolar plate, share your drawing and operating requirements with TMNetch to review whether chemical etching suits your channel geometry.
