Bipolar plates are the workhorses of a proton exchange membrane fuel cell, or PEMFC. Stacked between membrane electrode assemblies, they distribute hydrogen and oxygen evenly across the cell surfaces, carry current from one cell to the next, manage the water and heat produced during operation, and act as gas barriers that prevent fuel and oxidant from leaking or crossing over. A single failure in any of these roles degrades the whole stack. The plates also account for a substantial share of a fuel cell’s cost and weight, which is why materials scientists have spent decades searching for something cheaper and lighter than machined graphite yet more corrosion-resistant than coated metals.

Composite plates made of conductive graphite particles embedded in an insulating polymer resin have long been viewed as the most promising compromise. They avoid the brittleness of pure graphite plates and the corrosion weaknesses of metal ones. But they suffer from a fundamental trade-off. The obvious way to raise electrical conductivity is to pack in more graphite, yet past that point the resin can no longer wet all the particles, pores form, and the plate’s flexural strength collapses. In the new study, published in the Journal of Saudi Chemical Society, the researchers quantified this dilemma precisely: with no additives, a composite containing 85 percent natural graphite achieved an in-plane conductivity of 246.4 S/cm, but its through-plane conductivity languished at 52.3 S/cm, far below the 2025 US Department of Energy target of 118.3 S/cm, while flexural strength fell away sharply as graphite content climbed above 70 percent.

The team’s way out of this bind was to stop thinking about filler quantity and start thinking about network architecture. Their chosen ingredient is a silver nanowire coated with a carbon shell, which they call a carbon-fenced silver nanowire, or C@AgNW. Silver is the most electrically conductive of all metals, and the wires synthesized by the group are extraordinary structures: 50 to 80 nanometres in diameter but roughly 100 to 120 micrometres long, giving them an aspect ratio in the thousands. Dispersed through a composite, such ultra-long wires behave like metallic nanofibres, bridging graphite flake to graphite flake and weaving a dense three-dimensional conductive web that electrons can traverse even when the graphite content is modest.

Bare silver nanowires, however, have a fatal flaw in the acidic, humid, electrochemically aggressive environment inside a fuel cell. They oxidize and corrode readily. The researchers therefore grew a protective carbon shell, 20 to 30 nanometres thick, around each wire using a solvothermal treatment with glucose as the carbon source. Electron microscopy and energy-dispersive X-ray analysis confirmed a silver core sheathed in carbon, with an atomic composition of roughly 75 percent carbon, 17 percent silver and 8 percent oxygen. Crucially, the shell does more than protect. It also improves the affinity between the metallic wires and the graphite particles, ensuring good electrical contact at every junction in the network.

The protective shell proved its worth in brutal tests. When films of bare nanowires were heated to 150 degrees Celsius in an oxygen-ozone mixture, they were completely oxidized into silver oxide nanoparticles and their conductivity plummeted. Films of the carbon-fenced wires, by contrast, showed only a 27 percent increase in sheet resistance under the same treatment, with their morphology intact. In aerated sulfuric acid at 80 degrees Celsius, a simulation of the PEMFC environment, bare nanowire films reacted to form silver sulfate, their resistance rising eighteenfold within five hours and becoming fully dielectric after ten. The carbon-fenced films lost far less performance, gaining just 1.8-fold in resistance after five hours and 2.7-fold after ten. The carbon fence, in short, turns a fragile metal into a durable electrode material.

Mixed into the graphite-phenolic composite at just a few percent by weight, the fenced wires transformed the material’s properties. With only 1 percent C@AgNWs, through-plane conductivity jumped enough to exceed the DOE criterion at 70 percent graphite content. The optimum recipe emerged at 2.5 percent nanowires and 60 percent graphite: a through-plane conductivity of 127.4 S/cm, comfortably above the DOE standard, paired with a flexural strength of 51.2 MPa. Scanning electron micrographs revealed why the dosage matters so much. At 2 percent, individual wires could be seen spanning multiple graphite flakes, knitting the composite into a continuous three-dimensional network. At 3 percent, the wires began to aggregate, damaging the network, raising porosity and degrading both conductivity and corrosion resistance.

The corrosion and gas-barrier results were equally striking. The composite plate with 2.5 percent nanowires showed a corrosion current density of just 0.972 microamperes per square centimetre in simulated PEMFC conditions, meeting the 2025 DOE criterion, and it exhibited the lowest gas permeability of any formulation tested. The researchers attribute the tight gas sealing to reduced porosity: with the nanowires doing the electrical heavy lifting, less graphite is needed, the resin wets the particles properly, and the internal structure stays dense. That combination of high conductivity, mechanical strength, corrosion resistance and gas tightness in a single material is exactly the multi-objective balance that has eluded composite plate designers for years.

The proof came in a real fuel cell. The team machined multi-serpentine flow channels into their composite plates, sandwiched a Nafion 115 membrane electrode assembly between them, and ran the cell on humidified hydrogen and oxygen at 50 degrees Celsius. At a current density of 1,250 milliamperes per square centimetre, the cell reached a maximum power density of 685 milliwatts per square centimetre, and its performance at 1,000 milliamperes per square centimetre matched that of a commercial graphite bipolar plate. Electrochemical impedance spectroscopy at high current showed no mass-transport limitations and better behaviour than the commercial plates, consistent with the composite’s excellent through-plane conductivity. The researchers also compared their material against plates reinforced with graphene, carbon nanotubes, carbon nanofibres, copper fibres and copper foams reported in the literature, and found their composite offered a relatively high flexural strength among plates meeting DOE requirements.

What makes the result potentially transformative is economics. Graphene and multi-walled carbon nanotubes, the fashionable conductive additives of the past decade, remain expensive to produce at scale, which has limited their practical use in bipolar plates. Silver nanowires, by contrast, can be manufactured in large quantities by well-established polyol synthesis, and the carbon coating is applied in a simple one-step solvothermal reaction with ordinary glucose. The wide workable window of 55 to 65 percent graphite content also gives manufacturers flexibility in formulation and scale-up. The researchers conclude that their graphite/C@AgNW/phenolic resin composite is a promising candidate for next-generation PEMFCs, and if the polyol route to silver nanowires translates to industrial production as smoothly as they suggest, the humble bipolar plate may finally stop being the fuel cell’s bottleneck.

Subject of Research: Carbon-coated silver nanowire reinforcement of graphite/phenolic resin composite bipolar plates for proton exchange membrane fuel cells

Article Title: Performance improvement of graphite/phenolic resin composite bipolar plates for PEMFCs using carbon-fenced AgNWs

Article References: Pak, H., Sin, G., Ri, S., Kim, K., & Jon, S. (2026). Performance improvement of graphite/phenolic resin composite bipolar plates for PEMFCs using carbon-fenced AgNWs. Journal of Saudi Chemical Society, 30(3), Article 32. https://doi.org/10.1007/s44442-026-00084-8

Image Credits: AI Generated

DOI: 10.1007/s44442-026-00084-8

Keywords: PEMFC, bipolar plates, silver nanowires, carbon shell, graphite composite, phenolic resin, fuel cells, electrical conductivity, corrosion resistance, flexural strength, nanomaterials, hydrogen energy

The stakes are considerable. The United States Department of Energy has set technical targets for bipolar plates ahead of anticipated fuel cell stack commercialization by 2030, demanding an in-plane electrical conductivity above 100 siemens per centimeter, a flexural strength above 40 megapascals, and robust chemical resistance, processability, and long-term reliability. Meeting all of those requirements simultaneously has proven difficult. Metallic plates offer strength and easy machining but corrode without expensive surface treatments. Pure graphite plates conduct beautifully and resist chemicals, yet they are brittle and hard to form into the thin, intricate shapes that modern stack designs demand. Resin-based carbon composites, which blend moldable polymer with conductive graphite fillers, have emerged as a compelling middle path, but their performance depends exquisitely on the microstructure that forms during fabrication.

Researchers led by Seon Ho Lee and Song Mi Lee of Chungnam National University and the Korea Institute of Energy Research attacked the problem from three directions at once: the loading of multi-walled carbon nanotubes, the particle size of the graphite filler, and the mixing method used to combine everything with epoxy resin. Carbon nanotubes are the stars of the conductive composite world. Roughly 20 nanometers in diameter and up to 50 micrometers long, they possess extraordinary intrinsic conductivity and tensile strength, and they readily form interconnected electron highways through a material. But they carry a notorious flaw. Strong van der Waals attractions between their nonpolar surfaces cause them to clump into agglomerates, and those clumps act as defects rather than reinforcements, degrading both the electrical and mechanical performance of the finished composite.

The team’s solution was elegantly practical. In the conventional dry mixing route, graphite and nanotubes are simply stirred into the resin, leaving stubborn clumps intact. In the wet mixing route, the epoxy resin, curing agent, and accelerator are first dissolved in acetone, and the graphite and nanotubes are then blended into this dilute solution before the solvent is removed by rotary evaporation and oven drying. The dilution gives each nanotube room to unbundle and allows the resin to coat the graphite particles uniformly. When the coated powders were hot-pressed into plates at 160 to 200 degrees Celsius, the difference was visible to the naked eye. Dry-mixed samples collapsed at low molding pressures of 20 megapascals, while wet-mixed counterparts held their shape, and at 60 megapascals both routes produced dense, mirror-smooth surfaces. Quantitatively, wet mixing delivered 15 to 25 percent higher flexural strength at every pressure tested, a benefit the authors attribute to fewer microvoids and better mechanical continuity.

Scanning electron microscopy revealed exactly why the solvent makes such a difference. In cross-sections of dry-mixed composites, nanotubes sit in obvious clumps on the graphite surfaces, blocking resin infiltration and weakening the bonds between particles. In wet-mixed samples, the nanotubes are spread evenly along the interfaces between graphite grains, where they can do their intended job: bridging gaps, transferring stress, and stitching together a continuous conductive network. The images also showed that adding 7 weight percent nanotubes fills the voids between graphite particles with conductive bridges, explaining the sharp gains in conductivity and strength relative to nanotube-free plates.

Graphite particle size turned out to be the other decisive variable. The researchers compared a fine synthetic graphite with particles around 6 to 7 micrometers against a coarser grade reaching 48 to 65 micrometers. Counterintuitively, the coarse graphite won on nearly every electrical metric. Larger particles provide broader contact areas with their neighbors, so electrons hop more easily from grain to grain, and the wider interparticle spaces give well-dispersed nanotubes room to span the gaps. Composites built on large graphite particles consistently showed higher density, higher conductivity, and lower interfacial contact resistance than their fine-particle counterparts, although the finer particles offered a slight hardness advantage at low nanotube loadings, where the sheer number of particle contact points matters more.

The optimum formulation, labeled W-LG-CNT7 for wet mixing, large graphite, and 7 weight percent nanotubes, proved to be a genuine sweet spot. Its electrical conductivity reached 151.6 siemens per centimeter, comfortably beating the Department of Energy target of 100. Its flexural strength hit 56.7 megapascals, well above the 40 megapascal requirement, and its interfacial contact resistance measured just 4.6 milliohm square centimeters, far below the 10 milliohm square centimeter benchmark and better than the 8 to 12 milliohm square centimeters typical of commercial SIGRACELL graphite plates. Push the nanotube content to 9 weight percent, however, and everything deteriorates. The excess nanotubes re-agglomerate, creating resistive dead zones and microvoids that undermine both electron transport and mechanical bonding. More is not better; well-dispersed and just enough is better.

Durability testing delivered perhaps the most commercially significant result. Bipolar plates in a working fuel cell are exposed to phosphoric acid that leaches from the membrane electrode assembly, so the team immersed their samples in 95 percent phosphoric acid for 1,000 hours to simulate years of operation. Every composite lost less than 15 percent of its flexural strength, but the optimized wet-mixed plate lost only 8.2 percent, its dense, well-coated microstructure effectively blocking acid and moisture penetration. That kind of chemical resilience, combined with the corrosion immunity that composites enjoy over metals, addresses one of the last major obstacles to long-life fuel cell stacks.

The ultimate proof came in a real single-cell fuel cell test. The researchers assembled a 25 square centimeter cell with a Nafion membrane, platinum catalysts, and carbon paper gas diffusion layers, operated it at 70 degrees Celsius on humidified hydrogen and oxygen, and swept the current to map its performance. The optimized bipolar plate delivered a stable open-circuit voltage of about 0.97 volts and a peak power density of 0.86 watts per square centimeter, more than 30 percent higher than an identical cell built with a nanotube-free plate. The gains were most pronounced at high current densities between 1.0 and 1.6 amperes per square centimeter, precisely the region where internal resistance losses normally throttle a stack, confirming that the nanotube network was genuinely improving electron transfer under load.

What makes this study resonate beyond the laboratory is its message about manufacturing. No exotic materials were invented; the breakthrough lies in a solvent, a particle size, and a dosage. As hydrogen economies scale up worldwide, such process-level refinements, cheap to implement in existing compression-molding lines, may matter as much as catalyst breakthroughs. A bipolar plate that is stronger, more conductive, more acid-resistant, and demonstrably capable in a working cell brings the 2030 commercialization horizon measurably closer, one well-stirred batch of acetone and nanotubes at a time.

Subject of Research: Optimization of carbon nanotube loading, graphite particle size, and wet mixing for carbon composite bipolar plates in proton exchange membrane fuel cells

Article Title: Enhanced mechanical and electrical properties of carbon composite bipolar plates in PEMFCs via wet mixing and CNT optimization

Article References: Lee, S. H., Lee, S. M., Park, S., Jung, D.-H., Song, W.-J., & Lee, Y.-S. (2025). Enhanced mechanical and electrical properties of carbon composite bipolar plates in PEMFCs via wet mixing and CNT optimization. Advances in Industrial and Engineering Chemistry, 1(1), Article 27. https://doi.org/10.1007/s44405-025-00020-1

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00020-1

Keywords: bipolar plates, PEMFC, carbon nanotubes, wet mixing, graphite composites, epoxy resin, electrical conductivity, flexural strength, interfacial contact resistance, fuel cell durability, hydrogen energy, compression molding

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