Bipolar plate coatings can protect metal surfaces and control electrical contact in proton exchange membrane fuel cells, or PEMFCs. Their performance depends on the coating structure, substrate and operating conditions. Selection should therefore address corrosion, contact resistance and durability together.
A coating that improves one property may leave another unchanged or worse.
This guide focuses on fuel cell coatings applied to bipolar plates. It explains the main material systems, substrate requirements and evidence needed before approving a design.
Key Takeaways
- Bipolar plate coatings are used mainly to control corrosion and electrical contact resistance. No single coating is best for every PEM fuel cell design.
- Coating performance depends on the complete coating–substrate system. Carbon, metal nitride, gold, multilayer and conductive polymer systems can behave differently on stainless steel, titanium or other substrates.
- Low initial contact resistance is not enough. Interfacial contact resistance should also be evaluated after corrosion or durability exposure.
- Coating thickness cannot be specified with one universal value. It depends on the coating structure, substrate, deposition process, coverage requirement and acceptance criteria.
- Photochemical etching is not a coating process. Etching creates the bipolar plate geometry, while the functional coating is applied in a separate manufacturing step.
- Final coating selection should be based on comparable test conditions and representative manufactured parts, not coating names or isolated laboratory values.
How Do Bipolar Plate Coatings Affect Fuel Cell Performance?
Contact Resistance at the Plate–GDL Interface
Bipolar plates conduct current between neighboring cells. Interfacial contact resistance, or ICR, describes resistance at contacting surfaces, including the plate and gas diffusion layer, or GDL. It differs from resistance within the plate material.
For custom metal bipolar plates, define how contact performance will be measured before testing begins. The evaluation should specify the compression condition, contact materials, test pressure and whether measurements are taken before and after corrosion exposure.
When comparing test reports, use the same contact materials, pressure and measurement method. Otherwise, differences in test setup can make the results difficult to compare directly.
Ask whether the reported value represents one interface or the full measurement path. When resistance is normalized by area, retain the units and calculation basis. This avoids comparing values that share a label but describe different measurements.
Corrosion Protection and Surface Stability
Protective coatings can reduce substrate corrosion under defined conditions. However, the coating must also retain suitable electrical contact.
A coating can improve corrosion resistance while also increasing interfacial contact resistance. These properties should therefore be evaluated together rather than treating corrosion performance alone as proof of suitability.
For bipolar plate applications, coating qualification should consider both durability in the intended environment and the required electrical contact performance.
For the underlying failure mechanisms, see our guide to bipolar plate corrosion resistance.
Wettability and Water Management
Surface wettability affects how liquid water moves and accumulates. A water contact angle alone does not establish which treatment will work best in a cell.
In experiments on non-active outlet regions, hydrophilic treatments reduced water accumulation more effectively than the hydrophobic treatments tested. That result applies to the studied geometry and conditions.
Evaluate the treated region, drainage behavior and pressure drop together. Any claimed efficiency gain needs a defined cell comparison; lower ICR or improved drainage cannot establish a universal percentage.
Which Bipolar Plate Coating Materials Are Used?
The following systems have been investigated for PEMFC bipolar plates. Use the table to organize a shortlist, then compare evidence for the exact coating–substrate combination.
| Coating system | Evaluated substrate examples | Target properties | Main trade-off | Evidence to request |
|---|---|---|---|---|
| Carbon-based films | Stainless steel, titanium | Electrical contact and corrosion protection | Deposition-dependent structure | Composition and aged performance |
| Metal nitrides | Stainless steel | Corrosion and contact behavior | Electrical and corrosion results may differ | Both properties after exposure |
| Gold-based coatings | Stainless steel | Contact and surface protection | Coverage, thickness and cost | Thickness-specific qualification |
| Multilayer systems | Stainless steel | Combined interface and surface performance | More complex layer structure | Complete stack and manufacturing tests |
| Carbon–polymer systems | Stainless steel | Contact and protective behavior | Potential-dependent stability | Exposure range and resistance change |
Carbon-Based Coatings
Carbon coatings include amorphous and graphite-like structures. Their properties depend on how the layer is produced.
Research on carbon films deposited over chromium interlayers found that deposition bias changed carbon structure, contact resistance and corrosion behavior. A graphite plate, a graphite-like film and a diamond-like carbon coating should therefore have separate specifications.
Request the layer composition and deposition route, rather than accepting “carbon coating” as a complete description. Include any interlayer in the specification and ask how material identity is verified. A supplier change should trigger review of the qualified structure, even when the coating keeps the same general name.
Metal Nitride Coatings
Titanium nitride, or TiN, and chromium nitride, or CrN, are studied coating materials. Their performance depends on the substrate, deposition process and exposure.
Tests on formed 316L plates with nitride coatings found different ICR responses before and after corrosion. Initial conductivity is therefore insufficient for choosing a nitride system.
Noble-Metal Coatings
Gold has been evaluated on stainless steel for low contact resistance and corrosion protection. The necessary thickness depends on the function and deposition method.
Gold coating thickness should be defined according to the required corrosion protection and electrical contact performance. The thickness sufficient to reduce contact resistance may not be the same as that needed to provide adequate surface coverage and corrosion resistance.
For bipolar plate applications, specify coating thickness and coverage based on the substrate, environment and acceptance criteria rather than applying a universal gold-layer requirement.
Multilayer and Hybrid Coatings
Multilayer systems combine materials such as a nitride layer and a carbon top layer. Each layer contributes to the behavior of the complete structure.
Research on TiN+C and CrN+C coatings found lower ICR than the corresponding nitride-only systems. It also linked durability to coating type, thickness and position on stamped plates.
More layers alone do not prove better performance. Qualify the complete structure after the intended manufacturing steps.
Conductive Polymer and Carbon–Polymer Systems
A carbon-filled polymer coating differs from an unfilled water-repellent polymer layer. Specify the conductive filler, binder and processing route.
A coating’s electrical resistance can change after electrochemical polarization, and the extent of that change may depend on the applied potential and exposure conditions.
For bipolar plate applications, coating suitability should therefore be verified across the intended operating range. Results obtained under a limited set of test conditions should not be generalized to all potentials, environments or service conditions.
Which Bipolar Plate Coating Is Best?
There is no universally best coating for a fuel cell bipolar plate.
The appropriate choice depends on four main variables: plate substrate, required electrical contact resistance, corrosion environment and durability requirement.
Carbon-based coatings are commonly evaluated when both electrical contact and surface protection are important. Metal nitrides such as TiN and CrN are another option for metallic plates, but their electrical behavior can change after corrosion exposure. Noble-metal coatings can provide low contact resistance and corrosion protection, although coating coverage, thickness and cost become important design constraints. Multilayer systems combine different materials to balance these requirements but require qualification of the complete coating stack.
For engineering selection, compare the complete substrate + coating + manufacturing process + operating environment rather than selecting a material from the coating name alone.
How Should a Coating Be Matched to the Plate Substrate?
Stainless Steel Bipolar Plates
Specify the steel grade and surface condition before comparing coatings. Evidence from 410 stainless steel does not automatically qualify a coating on 316L.
Keep the substrate, preparation and contact test consistent when comparing suppliers. The studies above demonstrate why a coating name alone cannot predict the result.
Use our bipolar plate material selection guide for the broader substrate decision.
Titanium Bipolar Plates
Titanium still requires evaluation of its surface and electrical contact. Its corrosion resistance does not remove the need to qualify the coated interface.
Carbon coatings on titanium can provide low contact resistance and reduced corrosion current under defined test conditions. However, performance depends on factors such as coating structure, thickness, deposition quality and the electrochemical environment.
For bipolar plate applications, results from one coating system should not be generalized to all carbon-coated titanium plates. Each material and coating combination should be validated under the intended operating and acceptance conditions.
Request the titanium grade, coating structure, test pressure and exposure conditions before transferring a published result into a drawing requirement.
Aluminum, Graphite and Polymer-Composite Plates
Aluminum requires careful assessment of coating integrity. The DOE bipolar plate workshop report identifies the stronger protection demands associated with less corrosion-resistant substrates.
A coating may help enable a lightweight design, but plate mass also depends on substrate density, thickness and geometry. The coating itself does not guarantee weight reduction.
For graphite and polymer-composite plates, define the actual surface-treatment objective separately. Do not apply a metal-corrosion specification without checking its relevance. Plate strength, sealing and gas separation also need their own acceptance requirements.
Which Operating Conditions Change the Coating Requirements?
Define the service environment before selecting the coating. Bipolar plate corrosion test protocols can differ in applied potential, temperature, solution chemistry and gas conditions. These variables can significantly affect the measured corrosion behavior.
For meaningful comparison, results should be evaluated only when the test conditions and methods are sufficiently consistent. Data generated under different protocols should not be treated as directly interchangeable.
| Input | Information to define |
|---|---|
| Application | PEMFC type and intended service |
| Exposure location | Anode, cathode and other wetted surfaces |
| Operating range | Temperature, humidity and electrical potential |
| Transients | Startup, shutdown and relevant abnormal conditions |
| Contact conditions | GDL type, compression and surface condition |
| Durability | Exposure time, cycles and allowable property changes |
Specify the reference electrode whenever reporting potential. Include the test medium and temperature with corrosion data.
A steady exposure result does not establish startup and shutdown durability. Likewise, a low-temperature PEMFC coating should receive a separate assessment before use in a PEM electrolyzer or another electrochemical system.
How Are Bipolar Plate Coatings Applied—and Where Does Etching Fit?
Deposition and Coating Processes
Physical vapor deposition, or PVD, forms a deposited film. Other systems use wet application. The carbon–polymer example above used spraying followed by hot pressing during binder curing.
Choose a process that can produce the specified material and coverage on the actual plate. Confirm compatibility with subsequent forming, joining and handling.
Mark the required coated regions on the drawing. Identify contact lands, channel surfaces, edges, joining areas and sealing interfaces. State where coverage is mandatory and where masking is required. Agree on inspection locations so a result from an accessible flat area does not become the sole acceptance evidence for the whole part.
Photochemical Etching Is a Separate Manufacturing Step
Photochemical Etching uses a patterned photoresist to control where metal is etched. It removes metal to produce geometry; the temporary resist is not the plate’s service coating.
Functional coating deposition is a separate operation. Its sequence must suit the qualified manufacturing route.
For preparation and process-interface details, see how etching quality affects coating performance.
What Evidence Should Support a Coating Selection?
Build the approval package around measurable requirements. Separate flat-coupon screening from finished-plate and cell validation.
The national-laboratory guidance on metallic plate testing addresses corrosion, contact resistance and in-cell evaluation. Use these distinct evidence levels when reviewing a supplier’s claims.
| Decision | Minimum report context |
|---|---|
| Electrical contact | Contact materials, pressure, method and ICR before and after exposure |
| Corrosion | Substrate, layers, medium, temperature, potential, reference electrode and duration |
| Durability | Representative manufactured samples, exposure or cycles, and post-test condition |
| Water management | Treated region, drainage or pressure-drop results, and operating conditions |
| Cell performance | Comparable geometry, membrane electrode assembly, GDL, compression and operation |
| Cost | Coated area, material use, yield, throughput and inspection assumptions |
For performance comparisons, identify every changed variable. If the coating and flow-field geometry both change, report the result as a combined design comparison.
Also define the claimed outcome. Ask whether an improvement means higher voltage at a fixed current, greater peak power, slower degradation or improved conversion efficiency. For efficiency, specify the energy-input basis and system boundary, including whether auxiliary power is counted. Present each result under its actual measurement name rather than combining different gains into one percentage.
When a report references external performance targets or development benchmarks, retain the target year, intended application and relevant test-method notes. These details are necessary to interpret the values correctly.
Development targets should be treated as reference benchmarks rather than automatic acceptance criteria. Final requirements should be defined by the specific project, component design, operating conditions and agreed verification method.
For repeat orders, retain the approved coating revision, substrate lot and process record. Define when a material or process change requires requalification.
Agree on limits before sampling. A purchasing requirement should identify what must pass, how it will be tested and whether acceptance applies before or after aging. Our bipolar plate requirements and testing guide provides a broader framework.
FAQs About Bipolar Plate Coatings
What materials are used for bipolar plate coatings?
Investigated systems include carbon-based films, metal nitrides, gold, multilayers and conductive polymer composites. Select a specific composition and structure supported by evidence for the intended substrate and environment.
Do coated bipolar plates always improve fuel cell efficiency?
No fixed improvement applies to every system. Evaluate contact resistance, corrosion and water management separately, then use controlled cell tests to establish any performance gain.
How thick should a bipolar plate coating be?
There is no universal thickness. Specify the layer structure, coverage and required performance, then qualify thickness for the chosen process and substrate.
Can bipolar plate coatings delaminate or degrade?
Yes. Manufacturing and exposure can affect durability, so evaluate representative parts after the agreed process sequence and aging conditions. Initial adhesion alone cannot establish lifetime performance.
Is photochemical etching a coating method?
No. Photochemical etching selectively removes metal. A functional protective or conductive film requires a separate coating or surface-treatment operation.
Conclusion: Select the Coating–Substrate System, Then Validate It
Choose bipolar plate coatings by matching the complete material system to the substrate, contact requirements and operating environment. Compare electrical and corrosion results together, and verify performance after relevant manufacturing and exposure.
Planning an etched plate? Share your material grade, drawing, flow-channel requirements, coating specification and acceptance criteria with TMNetch. Start with our custom bipolar plates page to discuss the component and its manufacturing requirements.
