Bipolar plates are the workhorses of a PEMFC stack. They separate individual cells, distribute hydrogen and air across the electrode surfaces, carry current from cell to cell, and help manage water and heat. Traditionally, plates were machined from graphite, which is conductive and corrosion-resistant but brittle, thick, and costly to manufacture at volume. Metallic plates, by contrast, can be stamped into thin, intricate flow fields in seconds, making them far lighter and cheaper for automotive applications. The catch is that metals corrode in the acidic, humid environment inside a fuel cell, and the passive oxide films that form on their surfaces are poor conductors. That oxide layer is precisely what drives up interfacial contact resistance, or ICR, the area-specific resistance measured between the plate and the adjacent porous transport layer under the compressive load of stack assembly.

Researchers have explored a zoo of protective coatings to solve this, from physical vapour deposited nitrides to amorphous carbon films. But vapour-phase techniques require expensive vacuum equipment and struggle to coat complex, porous geometries uniformly. Sevinc and Hazar took a different route: a combined aqueous electrodeposition and electrophoretic deposition (EPD) process, carried out entirely in water-based baths. Electrodeposition builds the metallic matrix of the coating, while EPD uses an electric field to drive charged graphene particles toward the substrate, embedding the carbon sheets into the growing film. The approach is low-cost, scalable, and, crucially, compatible with porous structures that vacuum processes cannot easily penetrate.

The team applied their Ni–Cr–Ta–graphene coatings to an unusually broad set of substrates: dense aluminum, dense nickel, and AISI 316L stainless steel, the three most commonly discussed metallic bipolar plate materials, plus porous aluminum and porous nickel structures. Porous flow fields are an emerging design concept in which the conventional machined channels are replaced by an open-pore metal foam, giving vastly more contact area for gas distribution and water management. Coating such structures without clogging the pores is a major challenge, and demonstrating that an EPD-based coating preserves pore accessibility is one of the study’s most practically significant results.

The researchers systematically varied the deposition bath composition, designated S1 through S5, and the deposition time, then examined the resulting surfaces with scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). These techniques revealed how uniformly the coating covered each substrate and how the graphene and metallic elements were distributed. The morphology proved highly sensitive to processing conditions: too short a deposition time left the surface incompletely covered, while excessive deposition produced thicker, less uniform layers. An optimized deposition time of 120 seconds yielded comparatively uniform coatings across the series and delivered the best electrical contact behavior within the investigated set of formulations.

The headline numbers come from the ICR measurements, taken under compressive pressures relevant to real PEMFC stack assembly, up to 140 N/cm². Among all tested formulations, the coating designated S4 achieved the lowest interfacial contact resistance, approximately 78 mΩ cm² at 140 N/cm² on the aluminum substrate. To appreciate how substantial that improvement is, consider the benchmark the team used for comparison: an aluminum specimen pre-coated with nickel alone, representing a conventional baseline, exhibited roughly 269 mΩ cm² under the same conditions. The multi-component graphene-containing coating therefore cut the contact resistance to less than a third of the baseline value, a reduction of nearly 70 percent achieved purely through smarter surface chemistry and processing.

The authors are refreshingly candid about the remaining gap. The U.S. Department of Energy has set a target of 10 mΩ cm² for bipolar plate contact resistance, a figure that reflects what is needed for maximum stack efficiency in mass-market vehicles. Even the best S4 coating remains approximately 7.8 times higher than that target. The study’s results, in other words, represent a relative improvement within the investigated coating series rather than a solved problem. Further optimization of bath chemistry, particle loading, deposition parameters, and possibly post-treatment steps will be required before these coatings can meet the stringent demands of commercial fuel cell stacks. This honesty is valuable in a field where headline numbers sometimes obscure how far laboratory results still sit from deployment thresholds.

Why does adding graphene to a nickel–chromium–tantalum matrix help so much? The answer lies in the complementary roles of each constituent. Nickel provides the conductive metallic backbone and serves as the electroplating medium from the aqueous bath. Chromium contributes corrosion resistance, helping to shield the underlying metal from the acidic PEMFC environment and suppress the growth of insulating oxide films. Tantalum is prized in the bipolar plate literature for its exceptional passivity and stability in simulated fuel cell conditions, and prior studies have shown tantalum-modified stainless steel plates resisting corrosion effectively. Graphene, meanwhile, brings its legendary in-plane electrical conductivity and chemical inertness; sheets distributed through the coating create conductive pathways and can act as a barrier to corrosive species. Together, the four constituents aim to satisfy the two demands that usually trade off against each other: protecting the metal from corrosion while keeping the surface electrically accessible.

The combined electrodeposition–EPD strategy also matters from a manufacturing standpoint. Metal matrix composite coatings produced by co-depositing particles into an electroplated layer are an established and diversifying technology, but systematic studies on Ni–Cr–Ta–graphene systems, particularly on both dense and porous substrates, had remained limited. By showing that the same water-based process works across aluminum, nickel, and stainless steel, and that it coats porous foams while keeping their pores open, the Firat University team has expanded the design space available to fuel cell engineers. Aqueous processing avoids the capital cost and geometric limitations of PVD and CVD chambers, and it integrates naturally with existing electroplating infrastructure in the automotive supply chain.

The work, which draws on the first author’s doctoral dissertation on metal-based flow plates for PEM fuel cells in electric vehicles and was funded by Firat University’s Scientific Research Projects Coordination Unit, arrives at a moment when hydrogen technology is scaling up globally. Every reduction in ohmic loss inside the stack translates directly into more kilometers per kilogram of hydrogen, and bipolar plate coatings are among the most cost-effective levers for achieving that. Sevinc and Hazar’s results demonstrate that aqueous EPD-based Ni–Cr–Ta–graphene coatings provide an effective route to improving electrical contact performance while preserving the pore accessibility that next-generation porous flow fields demand. The DOE target remains the finish line, but this study maps out a credible, low-cost path toward it, one graphene-laden layer at a time.

Subject of Research: Ni–Cr–Ta–graphene composite coatings for reducing interfacial contact resistance of metallic bipolar plates in proton exchange membrane fuel cells

Article Title: Microstructural and contact resistance behavior of Ni–Cr–Ta–graphene coatings on metallic bipolar plate substrates

Article References: Sevinc, H., & Hazar, H. (2026). Microstructural and contact resistance behavior of Ni–Cr–Ta–graphene coatings on metallic bipolar plate substrates. Ionics. https://doi.org/10.1007/s11581-026-07541-9

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07541-9

Keywords: PEMFC, bipolar plate, graphene, electrophoretic deposition, contact resistance, coatings, nickel, chromium, tantalum, corrosion, fuel cells, porous metal