Folic Acid-Derived Carbon Sheets Supercharge ReS2 Electrodes for Supercapacitors

Supercapacitors promise to bridge the gap between batteries and conventional capacitors, delivering bursts of power in seconds and surviving hundreds of thousands of charge-discharge cycles. Yet the materials at their heart face a stubborn trade-off: carbon electrodes conduct electricity beautifully but store modest amounts of charge, while transition-metal compounds store far more charge but often crumble and fade with use. A research team at Lingnan Normal University in Zhanjiang, China, has now reported a clever way to get the best of both worlds, and their recipe begins with an unexpected ingredient: folic acid, the synthetic form of vitamin B9. Writing in the journal Ionics, Jing Wang, Yihao Yuan, Yanjie Xi and their colleagues describe a rhenium disulfide composite built on nitrogen-doped carbon nanosheets derived from the vitamin, achieving a specific capacitance of 758.78 farads per gram at a current density of 1 ampere per gram, along with an energy density of 15.32 watt-hours per kilogram in a full asymmetric device.

The star of the study is rhenium disulfide, or ReS2, a member of the transition metal dichalcogenide family that also includes the better-known molybdenum disulfide. What makes ReS2 special among two-dimensional materials is its unusually weak interlayer coupling: unlike MoS2, whose stacked layers interact strongly, the individual ReS2 sheets behave almost as if they were isolated, giving the material effectively two-dimensional electronic and optical properties even in thick crystals. For electrochemists, that decoupled structure is a gift. It means ions and electrons can access active sites throughout the material rather than only at the surfaces, and ReS2 has already earned a reputation as a high-rate pseudocapacitive energy storage material in earlier work. Pseudocapacitance, unlike the purely electrostatic charge storage of carbon double-layer capacitors, involves fast, reversible faradaic reactions at or near the electrode surface, allowing much higher charge storage per unit mass.

But ReS2 has two Achilles heels. First, like many layered sulfides, it suffers from structural deterioration during repeated cycling: as ions push in and out of the lattice, the material swells, cracks and eventually detaches from the current collector, killing the electrode. Second, its intrinsic electrical conductivity is poor, which throttles the very fast charge transport that pseudocapacitors need. The Lingnan Normal team set out to solve both problems at once with a single architectural move: anchoring ReS2 nanoparticles onto conductive, nitrogen-doped carbon nanosheets made by pyrolyzing folic acid. The carbon scaffold acts as a mechanical buffer that suppresses the aggregation of ReS2 particles and absorbs the mechanical strain of cycling, while the interconnected carbon network provides a highway for rapid electron transport and ion diffusion throughout the electrode.

The choice of folic acid as the carbon and nitrogen precursor is more than a laboratory curiosity. The vitamin molecule is rich in nitrogen atoms, carrying pteridine, amide and amine groups within a single compact structure, so when it is heated in the absence of oxygen it self-assembles into ultrathin carbon sheets with nitrogen already woven into the lattice. That built-in nitrogen doping matters electrochemically: nitrogen atoms in the carbon framework alter the local electronic structure, improve wettability with aqueous electrolytes and can contribute additional pseudocapacitance of their own. Previous studies have shown that folic acid pyrolysis yields nitrogen-doped graphitic carbon with well-defined structural evolution, and the approach has been used to host single-atom metal catalysts. Here, the researchers harnessed the same chemistry to create a conductive, nitrogen-rich mat on which ReS2 nanoparticles could be grown and anchored through a facile pyrolysis route.

The fabrication strategy follows a broader and rapidly growing trend in electrode engineering: hybridizing metal sulfides with biomass-derived or molecule-derived nitrogen-doped carbon. In recent years, teams have embedded tungsten disulfide in gelatin-derived honeycomb carbon networks, coupled tin sulfide with nitrogen-doped porous carbon, nanoconfined ReS2 in biomass-derived three-dimensional porous carbon architectures, and grown manganese sulfide on carbon sheets from coordination frameworks. The logic is always the same. The sulfide supplies high theoretical capacitance; the carbon supplies conductivity, structural confinement and extra surface area; and the nitrogen dopants boost both the electronic properties of the carbon and its chemical affinity for the sulfide phase. What distinguishes the new work is the molecular precision of the folic acid precursor, which delivers a high nitrogen content without the need for separate nitrogen sources or harsh post-treatments.

The electrochemical results are striking. The ReS2/nitrogen-doped carbon electrode delivered a specific capacitance of 758.78 farads per gram at 1 ampere per gram, a figure that places it among the better-performing transition metal dichalcogenide-carbon hybrids reported for pseudocapacitors. Equally important was the material’s superior rate capability, meaning it retained a large fraction of its capacitance as the charging current was increased. Rate capability is where many high-capacitance materials fail, because sluggish ion diffusion and poor conductivity cannot keep up with fast charge injection. The interconnected carbon network in the composite appears to have solved that bottleneck, allowing electrons to reach the ReS2 particles and ions to reach the active sites even at high current densities.

To test the material under realistic device conditions, the researchers constructed an asymmetric supercapacitor, pairing the ReS2/carbon composite as one electrode with a counter-electrode of complementary potential range. Asymmetric designs are the standard route to high-voltage aqueous supercapacitors: by using two electrodes with different operating windows, the total cell voltage, and with it the energy density, can be pushed well beyond what either electrode could achieve alone, since stored energy scales with the square of voltage. The resulting device achieved an energy density of 15.32 watt-hours per kilogram alongside a power density of 3.16 kilowatts per kilogram. For context, that energy density approaches the lower range of lead-acid batteries while retaining the rapid charge-discharge behavior and power delivery characteristic of supercapacitors, a combination that makes such devices attractive for regenerative braking, grid frequency regulation and portable electronics.

The work also speaks to a wider question in materials chemistry: how to design electrodes that survive the mechanical punishment of cycling. The nanosheet architecture of the composite is central here. Because the ReS2 nanoparticles are well anchored and spatially separated on the carbon sheets, they cannot coalesce into larger particles during cycling, and the flexible carbon matrix absorbs the volume changes that would otherwise fracture a bulk electrode. This confinement-and-buffering principle has proven its worth across the sulfide-carbon literature, from lithium and sodium battery anodes to supercapacitor electrodes, and the new study extends it to one of the least conventional dichalcogenides. The authors note that the composite demonstrates clear potential as an electrode for energy conversion and storage devices, positioning ReS2 hybrids alongside more established candidates.

Challenges remain before vitamin-derived rhenium electrodes power anything in your pocket. Rhenium is one of the rarest and most expensive elements on Earth, which likely confines ReS2 devices to niche, high-value applications unless loading can be minimized or the material recycled. The study reported here is an early-stage laboratory demonstration, and long-term cycling data, manufacturing scalability and full cost analysis will determine whether the architecture can make the leap from beaker to product. Still, the research adds an elegant entry to the catalog of molecule-derived carbon scaffolds, showing that a humble vitamin can be transformed into the conductive backbone of a high-performance energy storage material. As the demand for fast-charging, long-lived energy storage continues to grow, hybrid electrodes that marry reactive sulfides with nitrogen-doped carbon, whether derived from vitamins, biomass or metal-organic frameworks, are likely to remain at the forefront of the field, and this folic acid route offers a particularly clean and versatile way to build them.

Subject of Research: ReS2/nitrogen-doped carbon nanocomposites for pseudocapacitive supercapacitor electrodes

Article Title: ReS2 hybridized with folic acid-derived N-incorporated carbon sheets to enhance pseudocapacitive property

Article References: Wang, J., Yuan, Y., Liang, Q., Wang, X., Ma, L., Jiang, R., Cai, H., & Xi, Y. (2026). ReS2 hybridized with folic acid-derived N-incorporated carbon sheets to enhance pseudocapacitive property. Ionics. https://doi.org/10.1007/s11581-026-07560-6

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07560-6

Keywords: supercapacitors, rhenium disulfide, nitrogen-doped carbon, folic acid, pseudocapacitance, nanocomposites, transition metal dichalcogenides, energy storage, pyrolysis, asymmetric supercapacitor, electrode materials, biomass-derived carbon