Bipolar plate corrosion resistance matters because surface degradation can affect electrical contact, release metal ions and damage functional surfaces. In proton exchange membrane fuel cells, or PEMFCs, a metal plate must maintain both corrosion protection and suitable electrical contact. A protective surface film can support one requirement while making the other harder to meet.
The central issue is the relationship between passivation and contact resistance. A plate may resist dissolution yet develop greater electrical resistance at its contact surface.
This guide explains the causes, failure paths and evidence needed to assess corrosion protection in low-temperature PEMFC bipolar plates.
Key Takeaways
Bipolar plate corrosion resistance matters because surface degradation can affect electrical contact, release metal ions and damage functional surfaces.
Corrosion resistance and contact resistance must be evaluated together. A passive film may reduce metal dissolution while increasing interfacial contact resistance, or ICR.
Low corrosion current alone does not prove long service life. Test potential, medium, temperature, exposure history and reference electrode all affect the result.
Stainless steel, titanium and graphite require separate interpretation. Results from one material grade or surface condition should not be transferred directly to another.
A useful validation plan combines electrochemical response, ICR, surface inspection and metal-release measurements where relevant.
Coupon tests are useful for screening, but representative manufactured bipolar plates should be included before final approval.
Why Does Corrosion Resistance Matter for Bipolar Plates?
Corrosion resistance matters because bipolar plate surface degradation can affect both electrochemical stability and electrical contact. Corrosion may release metal ions, alter surface films and increase plate–GDL contact resistance before the plate loses structural integrity.
Metal Dissolution and Contamination Risk
Metal ions released from components can enter the cell environment. If they reach the membrane or electrode ionomer, they can affect proton transport and cell performance. The effect depends on the ion and contamination level, as demonstrated by controlled metal-ion contamination experiments.
Keep three questions separate: Was metal released? Did it accumulate in a sensitive component? Did that accumulation cause a measurable change?
Finding metal in a sample does not answer all three. For an investigation, identify possible sources, use suitable controls and examine where the metal accumulates.
Surface Damage and Electrical Loss
Contact degradation can matter before a plate loses structural integrity. Increased resistance at the plate–gas diffusion layer interface has been linked to declining cell performance during operation with a 316L stainless steel plate.
Localized damage also needs attention. Simulated operating cycles can produce pits and disrupted surface films. Inspect their location and extent before deciding whether they threaten the part’s remaining functional margin. A visible pit alone does not establish that a plate leaks.
What Causes Bipolar Plate Corrosion in PEM Fuel Cells?
Local Water Chemistry and Wetted Interfaces
Corrosion depends on the environment at the surface. The relevant conditions include local liquid chemistry, temperature, gas exposure and electrical potential.
An operating plate can experience thin, discontinuous liquid layers, which differ from the fully immersed conditions used in many laboratory tests. This distinction affects how a screening result should be interpreted.
Specify the medium, pH and any added contaminants. For titanium, fluoride concentration and acidity influence electrochemical behavior. Those variables should accompany any result used to justify material suitability.
Treat chloride exposure or external salt contamination as project-specific questions. Establish the exposure route before using them to explain corrosion inside a flow channel.
Surface Potential and Operating Transients
Potential influences whether a surface dissolves, forms a protective film or undergoes further surface changes. Repeated potential changes can also produce different damage from a steady exposure. Under simulated load and startup–shutdown conditions, 316L surface films can undergo repeated breakdown and transformation.
However, cell voltage, electrode potential and local plate-surface potential are different quantities. At wetted interfaces, the plate potential can be only weakly coupled to the neighboring platinum electrode.
Therefore, retain the reference electrode and exposure history with every reported test potential. An accelerated test provides evidence for its stated conditions; interpreting it as an operating-life prediction requires additional justification.
How Are Corrosion, Passivation and Contact Resistance Connected?
Does Passivation Improve or Harm Bipolar Plate Performance?
Passivation can improve corrosion protection while making electrical contact more difficult.
A passive film can reduce further metal dissolution under suitable conditions, but the same surface layer may increase interfacial contact resistance between the bipolar plate and gas diffusion layer.
For this reason, passivation should not be judged as simply beneficial or harmful. The relevant question is whether the resulting surface provides sufficient corrosion protection while keeping ICR within the project’s acceptance limits.
The correct engineering target is therefore not maximum passivation, but a stable surface condition that balances electrochemical protection and electrical contact.
A Protective Film Can Change Electrical Contact
Passivation is the formation of a surface film that can limit further metal dissolution under suitable conditions. On stainless steel, passive-film formation can increase electrical contact resistance, even while the film provides protection.
Interfacial contact resistance, or ICR, concerns current crossing a contact boundary, such as the plate and gas diffusion layer, or GDL. It differs from resistance through the bulk metal.
For 316L, oxide-film thickness, applied potential and contact load are related to measured ICR. This explains why material conductivity alone cannot predict the electrical behavior of an exposed plate.
The practical objective is to limit damaging surface reactions while retaining acceptable electrical contact.
A corrosion-resistant bipolar plate is not automatically an electrically suitable bipolar plate. Passivation can reduce dissolution but increase ICR, so corrosion and contact performance should be assessed as a coupled design problem.
Use several observations together:
| Observation | Possible interpretation | Follow-up evidence |
|---|---|---|
| Exposure current falls while ICR rises | Film formation may protect the substrate while changing contact | Surface-film analysis and metal-release measurements |
| Average current is low but local damage appears | An overall reading may not fully describe local condition | Inspection of damage location, depth and exposed regions |
| ICR rises without visible rust | Surface-film or contact changes may be present | Repeat contact testing under controlled pressure and examine the surface |
These are investigation paths, not diagnoses from one reading. Confirm the explanation before changing a material or coating specification.
Why Stainless Steel and Titanium Need Separate Interpretation
For stainless steel, compare the exact grade and surface condition. In 316L exposure tests, metal release and contact resistance change with surface-film development. Transferring a result to another alloy or surface treatment needs supporting evidence.
Titanium also requires separate chemical and electrical assessment. Under specified simulated cathode conditions, a protective titanium film can have high contact resistance. Its resistance to corrosion does not establish acceptable plate–GDL contact.
For both materials, qualify the surface in the condition in which it will operate. Avoid treating a stronger protective barrier as proof of better overall plate performance.
What About Graphite Plate Corrosion Resistance?
Graphite plate corrosion resistance must be assessed for the actual material and electrochemical environment. Graphite sinters have shown resistance in specified simulated anode and cathode environments, but those results apply to the tested material and conditions.
Do not extend them to every graphite grade, resin composite, temperature or potential. Identify the material system and relevant aging conditions before making a durability claim.
Corrosion resistance also needs separate treatment from porosity, strength and sealing. Our bipolar plate requirements guide covers that wider qualification framework.
How Can Corrosion Risk Be Reduced?
Start with the failure path that needs control. Then choose a substrate and surface system supported by evidence for the intended environment.
A conductive protective layer must balance corrosion protection with electrical contact. Coated stainless steel experiments demonstrate that meeting one requirement does not automatically satisfy the other. Our bipolar plate coating materials and selection guide compares the main options.
Uncoated stainless steel also needs a condition-specific decision. Under particular controlled operating tests, uncoated plates have maintained stable contact resistance without significant added metal contamination. This supports qualification by evidence, rather than a universal rule that every plate must receive the same coating.
For etched parts, address manufacturing preparation through etching quality and coating performance. Keep those process controls connected to, but distinct from, the corrosion validation.
How Should Bipolar Plate Corrosion Protection Be Validated?
Separate Screening Curves from Exposure History
A polarization scan examines electrochemical response across a selected potential range. A potential hold examines behavior over time at a selected potential. Cycling adds a changing exposure history. These approaches address different questions within metallic bipolar plate testing.
Ask which question each reported result answers. Record whether a value is an estimated corrosion current, a passive current or a measured current during exposure.
A falling current can accompany film formation. For 316L, low steady metal release can remain after a barrier film develops. Interpret the current alongside surface and release measurements before describing the process as corrosion-free.
Pair Electrochemical Results with Contact and Surface Evidence
A useful assessment connects four evidence types:
- Electrochemical response under defined exposure.
- ICR before and after exposure.
- Metal-release measurements where relevant.
- Surface inspection and suitable chemical or cross-sectional analysis.
Keep contact materials, pressure and measurement setup consistent. The DOE contact-resistance method notes explicitly connect contact measurements with compression and pre- and post-exposure condition.
Electrochemical impedance spectroscopy, or EIS, provides information about electrochemical processes. Its charge-transfer resistance is a different quantity from electronic contact resistance at the plate–GDL interface. Separate electrochemical and contact measurements are needed to evaluate both.
For example, lower exposure current combined with higher ICR suggests a possible protection–contact trade-off. Use film analysis and metal-release evidence to test that explanation.
Check Whether the Test Represents the Intended Cell
A flat immersed coupon and an operating plate provide different evidence. Their wetting and local polarization conditions can differ, so document what each test reproduces.
Before accepting a report, confirm:
- Material grade, surface treatment and specimen condition.
- Medium, temperature and gas conditions.
- Applied potential, reference electrode and exposure history.
- Contact-test conditions and post-test inspection.
- Agreed acceptance criteria.
For internal PEMFC service, request relevant electrochemical evidence alongside any salt-spray report. Use our bipolar plate requirements and testing framework to connect corrosion findings with the complete project specification.
TMNetch Manufacturing Case: Thin Bipolar Plate Welding
A published TMNetch bipolar plate welding case involves 0.15 mm plates and reports a flatness result of 0.08 mm. The same page also presents a separate example of welding bridges to close flow channels.
These are reported manufacturing results. The published case does not provide corrosion-current, metal-release or post-exposure ICR results.
For a comparable project, include representative manufactured parts in the qualification plan. Define whether assessment applies before or after joining and surface treatment. Manufacturing-development work on coated bipolar plates likewise considers forming, joining and coating together.
The engineering lesson is to maintain separate evidence for geometry, joint integrity and electrochemical surface performance.
FAQs About Bipolar Plate Corrosion
Can a plate resist corrosion but still have high contact resistance?
Yes. A protective surface film can increase ICR. Evaluate both properties under the agreed conditions.
Does low corrosion current prove long service life?
A short test cannot establish service life by itself. Review the exposure protocol and supporting measurements, including changes after relevant aging.
Is salt-spray testing enough for a PEMFC bipolar plate?
For internal PEMFC approval, request tests addressing the intended electrochemical environment. A salt-spray report alone does not establish performance under the potential, medium and contact conditions used in PEMFC corrosion evaluation.
Conclusion: How Should Bipolar Plate Corrosion Resistance Be Evaluated?
Bipolar plate corrosion resistance should be evaluated as a surface-performance problem, not as a single corrosion-current number.
The plate must resist damaging electrochemical degradation while maintaining acceptable electrical contact. Passive films, coatings and surface treatments can reduce metal dissolution, but they may also change interfacial contact resistance.
A reliable qualification plan should therefore combine electrochemical response, ICR before and after exposure, surface inspection and metal-release measurements where relevant. Test conditions should retain the material grade, surface condition, medium, temperature, applied potential, reference electrode and exposure history.
Most importantly, validate the plate in a condition representative of the actual manufacturing route. Corrosion resistance, geometry, joining quality and contact stability are separate requirements and should be supported by separate evidence.
For etched metallic bipolar plates, share the material grade, channel geometry, planned surface treatment and corrosion/contact-resistance requirements with TMNetch so the manufacturing route and downstream validation needs can be reviewed together.
If you are considering chemical etching for custom metal bipolar plates, send TMNetch your drawing, material grade, channel dimensions and planned surface treatment.
