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