The layered nature of WO3·H2O itself deserves emphasis. Unlike anhydrous tungsten oxide polymorphs, the hydrated phase incorporates water molecules between tungsten oxide planes, and these structural water molecules serve a dual purpose. First, they widen the interlayer gap, lowering the activation barrier for proton insertion and extraction during charge and discharge. Second, they can buffer the mechanical stress that accompanies repeated ion intercalation, which is one of the principal causes of capacity fade in intercalation-type electrode materials. This helps explain why hydrated tungsten oxides have attracted attention as pseudocapacitive candidates despite tungsten oxide’s intrinsically modest electronic conductivity compared with, for example, ruthenium oxide. The present work builds on this foundation by showing that the hydration framework survives the wet-chemical doping process intact, which is a nontrivial outcome because acidic precipitation routes can sometimes drive partial dehydration or phase transitions if the temperature and pH are not carefully controlled.

The synthesis route described, based on acidification of sodium tungstate with oxalic acid and hydrochloric acid at elevated temperature, is an example of a low-temperature solution-phase approach that favors the formation of well-defined nanoplates. Nanoplate morphologies are particularly favorable for pseudocapacitive charge storage because they expose large basal planes to the electrolyte, shortening the diffusion distance for protons and increasing the fraction of the material that participates in redox reactions within the timescale of a voltammetric sweep. The one-step nature of the synthesis is also practically significant. Doping strategies often require post-synthetic treatments such as high-temperature annealing in controlled atmospheres, which can sinter nanostructures, remove structural water, or complicate scale-up. Incorporating the dopant directly during precipitation avoids these complications and ensures atomic-level mixing of magnesium within the tungsten oxide host, which is generally more effective for modifying electronic properties than surface-only treatments.

The reported specific capacitance of 158 F per gram at 1 A per gram for the optimally doped composition should be interpreted in the context of aqueous acidic electrolytes and the intrinsic properties of tungsten oxide. While some literature values for hydrated tungsten oxide-based electrodes exceed this figure, direct comparisons across studies are complicated by differences in mass loading, electrode preparation, electrolyte choice, and the voltage window used in the capacitance calculation. What is more diagnostic in this study is the combination of capacitance with the kinetic analysis summarized by the b-value. In cyclic voltammetry, the peak current typically scales with scan rate according to a power law, and the exponent, known as the b-value, distinguishes between diffusion-limited battery-like behavior (b near 0.5) and surface-dominated capacitive behavior (b near 1.0). A b-value of 0.82 for the Mg-doped material indicates that a substantial majority of the charge storage occurs through fast, surface-near processes rather than slow solid-state diffusion. This is precisely the regime desired for supercapacitor electrodes, since it supports high-rate operation and reduced susceptibility to diffusion-induced structural degradation during cycling.

The improvement in ion diffusion kinetics attributed to Mg doping can be rationalized through several complementary mechanisms. Divalent cation substitution can widen transport pathways through lattice expansion and defect formation, lower the energy barrier for proton hopping between adjacent oxygen sites, and increase the density of electroactive sites where interfacial charge transfer occurs. Electrochemical impedance spectroscopy, which the authors employed, typically reveals such effects as reduced charge-transfer resistance and altered Warburg behavior corresponding to more facile ion diffusion in the electrode. The fact that the intermediate doping level, approximately three percent magnesium, outperformed both the pristine material and the higher-doped compositions reflects a common pattern in doped oxides: too little dopant leaves the electronic structure largely unmodified, while too much dopant can disrupt the crystal framework, create insulating secondary phases, or block diffusion channels, all of which degrade performance. The existence of an optimal doping concentration near the lower end of the tested range suggests that the beneficial effects of magnesium incorporation saturate quickly relative to the structural penalties of heavier doping.

The fabrication of an aqueous asymmetric supercapacitor represents an important step beyond half-cell characterization. Asymmetric devices pair a battery-like or pseudocapacitive positive electrode with a capacitive negative electrode, in this case activated carbon, allowing the operating voltage window of the full cell to exceed the thermodynamic stability limit of water at a single electrode. By balancing the charges stored on the two electrodes, the device exploits the full electrochemical stability window of the aqueous electrolyte, which can push cell voltages toward or beyond 1.6 volts in acidic media. Because energy density scales with the square of voltage, even modest extensions of the window translate into meaningful gains in deliverable energy. The use of a dilute sulfuric acid electrolyte also aligns with the proton-conduction mechanism of hydrated tungsten oxide, since protons are the working ions for intercalation in this material, and acidic media provide them at high concentration with minimal transport resistance.

Long-term cycling stability is arguably the most demanding metric for pseudocapacitive intercalation materials, because repeated insertion and extraction of protons induces volume changes that can pulverize nanostructures, delaminate electrodes, and dissolve active material. The demonstration of stable coulombic efficiency over 5,000 cycles in the asymmetric device suggests that the Mg-doped nanoplates resist these degradation pathways. Several features of the material plausibly contribute to this durability. The structural water in the hydrated phase cushions intercalation-induced strain, the nanoplate morphology accommodates volume change in two dimensions rather than three, and the dopant-stabilized defect structure may pin domain boundaries against coarsening. Additionally, the surface-dominated charge storage indicated by the high b-value reduces the depth of ion penetration per cycle, lessening the mechanical fatigue associated with bulk expansion and contraction.

From a practical standpoint, the choice of abundant, low-toxicity elements is worth noting. Tungsten and magnesium are both relatively inexpensive compared with the noble metals that defined early pseudocapacitor research, and magnesium in particular is benign and plentiful. The wet-chemical synthesis operates at modest temperatures with water and ethanol as solvents, avoiding energy-intensive calcination steps. These attributes matter for the economic viability of supercapacitor electrodes at scale, where the cost of active material and processing can dominate device cost. The aqueous electrolyte further enhances safety and environmental profile relative to organic electrolytes used in commercial double-layer capacitors, albeit at the cost of a narrower voltage window that asymmetric architectures partially compensate for.

Looking forward, the results suggest several avenues that follow naturally from this work. Systematic variation of dopant identity among alkaline-earth cations could clarify whether the observed benefits stem primarily from defect generation, lattice strain, or electronic structure modification, since these cations differ systematically in radius and charge density. Quantitative separation of capacitive and diffusion-limited contributions across scan rates, which the b-value analysis gestures toward, could be extended with methods such as Dunn analysis to map how doping shifts the balance of storage mechanisms. Coupling the electrodes with complementary pseudocapacitive or battery-type positive materials in full cells might further raise energy density while retaining the power capability that motivates supercapacitor use. Finally, evaluating performance under realistic operating conditions, including elevated temperature, partial states of charge, and mechanical flexing, would help bridge the gap between laboratory half-cell metrics and the durability requirements of portable electronics, electric vehicles, and industrial power buffering applications that motivate research in this field.

Subject of Research: Mg-doped hydrated tungsten oxide nanostructures as pseudocapacitive electrodes for high-performance aqueous asymmetric supercapacitors

Article Title: Mg-doped hydrated tungsten oxide nanostructures as pseudocapacitive electrodes for high-performance aqueous asymmetric supercapacitors

Article References: Nishad, H. S., Jaiswar, R. R., Shirodkar, M., Patil, B. M., Chaskar, A. C., & Walke, P. S. (2026). Mg-doped hydrated tungsten oxide nanostructures as pseudocapacitive electrodes for high-performance aqueous asymmetric supercapacitors. Frontiers in Batteries and Electrochemistry, 5, Article 1883507. https://doi.org/10.3389/fbael.2026.1883507

Image Credits: AI Generated

DOI: 10.3389/fbael.2026.1883507

Keywords: supercapacitors, pseudocapacitance, hydrated tungsten oxide, magnesium doping, nanoplates, asymmetric supercapacitor, energy storage, electrochemistry, oxygen vacancies, ion diffusion, Mg-doped, hydrated

The secret lies in pairing two materials with complementary personalities. Polypyrrole is a conducting polymer prized for its theoretical specific capacitance exceeding 600 farads per gram and its excellent electrical conductivity. It stores charge through fast, reversible redox reactions—a pseudocapacitive mechanism in which electrons are transferred as the polymer’s chemical state changes. But polypyrrole has a stubborn flaw: during repeated doping and dedoping, electrolyte ions repeatedly enter and leave the polymer matrix, causing volumetric swelling and shrinking that gradually destroys the electrode’s structural integrity. Its dense structure also impedes ion transport, capping the energy density it can deliver.

Reduced graphene oxide offers the perfect antidote. Its edges are decorated with oxygen-containing functional groups—carboxyl, aldehyde, and hydroxyl—that act as chemical anchors for polymer growth, while strong van der Waals interactions between the π-conjugated polypyrrole chains and the aromatic graphene basal planes bind the two materials together. The result is a composite in which rGO nanosheets serve as both a conductive scaffold and a mechanical buffer, absorbing the volumetric stresses that would otherwise tear a pure polypyrrole electrode apart. The large surface area of the graphene sheets also contributes its own electrical double-layer capacitance, adding to the pseudocapacitive storage of the polymer.

What sets this work apart is the fabrication method. Rather than grinding powders into pastes and gluing them to current collectors with polymer binders—the standard approach that adds dead weight and resistance—the researchers used chemical bath deposition (CBD) to grow the composite directly on stainless steel substrates. In the CBD process, pyrrole monomers are chemically oxidized by ammonium persulfate in a sulfuric acid solution, with the sulfuric acid doubling as a dopant. Positively charged pyrrole cations adsorb onto the negatively charged rGO surface through π-π stacking, hydrogen bonding, and electrostatic forces, nucleating polymerization across the vast rGO surface. Within hours, a smooth, adherent, black composite film forms spontaneously on the metal, with no binder, no pressing, and no complicated equipment.

Timing proved to be the critical variable. The team deposited films at one, two, and three hours, labeling them RP1, RP2, and RP3. Electron microscopy revealed a striking evolution: at short polymerization times, sparse polypyrrole particles dotted the rGO sheets; at two hours, spherical polypyrrole nanoparticles—roughly 100 nanometers across—acted as spacers that prevented the graphene sheets from restacking, creating a porous network with pores around one micrometer in diameter. At three hours, however, overgrowth caused the sheets to collapse into a denser, less accessible structure. The sweet spot, RP2, also exhibited the best wettability, with a contact angle of just 29 degrees, ensuring intimate contact between electrode and electrolyte.

A battery of characterization techniques confirmed the composite’s architecture. X-ray diffraction showed the films to be amorphous, as expected for room-temperature deposition. Raman spectroscopy revealed the characteristic D and G bands of rGO, with an increased disorder ratio indicating that polypyrrole particles were prying apart the multilayered graphene sheets. X-ray photoelectron spectroscopy mapped the chemical bonds—carbon, nitrogen, and oxygen in atomic percentages of 71.72, 13.39, and 14.89 percent—while nitrogen adsorption measurements showed the composite’s specific surface area more than doubling from 26 to 54 square meters per gram compared with pure polypyrrole.

The electrochemical results were equally compelling. In cyclic voltammetry at a slow scan rate of 5 millivolts per second, the RP2 electrode delivered 987 farads per gram—nearly triple the 356 farads per gram of pure polypyrrole deposited the same way. Galvanostatic charge-discharge tests at 1 ampere per gram confirmed a capacitance of 888 farads per gram. Impedance spectroscopy told the underlying story: the optimized composite had the lowest solution resistance (0.15 ohm square centimeters) and charge-transfer resistance (50 ohm square centimeters) of all the films, thanks to its porous structure and the lateral electron-transport channels provided by the sp²-hybridized graphene sheets.

Analysis of the charge-storage kinetics added further insight. By fitting the scan-rate dependence of peak currents to a power law, the team extracted a b-value of 0.84 for RP2—close to 1, indicating that surface-controlled capacitive processes dominate, though diffusion of ions into the bulk still contributes measurably. At slow scan rates, diffusion-controlled storage accounted for up to 53 percent of the total charge, exploiting the electrode’s open porous channels; at fast rates, surface adsorption took over. This dual mechanism explains why the composite performs well across a wide range of operating conditions.

To demonstrate real-world viability, the researchers assembled an aqueous asymmetric supercapacitor pairing the rGO/Ppy composite as the positive electrode with tungsten trioxide (WO₃) as the negative electrode in 1 molar sulfuric acid. WO₃ was chosen for its large theoretical capacitance of 1,112 farads per gram and its broad negative operating window of about 0.8 volts. With the electrode masses balanced for equal charge storage, the full cell operated at 1.3 volts and delivered a device-level capacitance of 61 farads per gram, a specific energy of 11 watt-hours per kilogram at a specific power of 0.474 kilowatts per kilogram—figures that outperform previously reported rGO/Ppy devices, which typically managed 4 to 8 watt-hours per kilogram.

The device also endured 3,000 cycles at 3.5 amperes per gram with 74 percent capacitance retention. Post-cycling microscopy showed only slight morphological changes, though the authors note that the repeated volume changes of polypyrrole during doping and dedoping remain the main source of gradual degradation—an effect the rGO framework mitigates but cannot eliminate. Even so, the study demonstrates that a low-cost, scalable bath-deposition process can transform a temperamental conducting polymer into a robust, high-capacitance electrode. As demand surges for fast-charging storage in wearables, electric vehicles, and grid buffering, such binder-free composite architectures may prove to be exactly the kind of practical innovation the supercapacitor field has been waiting for.

Subject of Research: Reduced graphene oxide/polypyrrole composite electrodes for supercapacitor energy storage

Article Title: Enhanced supercapacitor performance of reduced graphene oxide/polypyrrole composite for energy storage application

Article References: Pawar, D. C., Malavekar, D. B., Bagde, A. G., Kim, J. H., & Lokhande, C. D. (2026). Enhanced supercapacitor performance of reduced graphene oxide/polypyrrole composite for energy storage application. Frontiers in Batteries and Electrochemistry, 5, Article 1935857. https://doi.org/10.3389/fbael.2026.1935857

Image Credits: AI Generated

DOI: 10.3389/fbael.2026.1935857

Keywords: supercapacitor, reduced graphene oxide, polypyrrole, chemical bath deposition, pseudocapacitance, energy storage, composite electrode, asymmetric supercapacitor, tungsten trioxide, specific capacitance, cyclic stability, conducting polymer

The material at the heart of the work, labeled MZ-(1:1), is a nanocomposite of molybdenum disulfide (MoS₂) and zinc sulfide (ZnS) mixed in equal mass proportions. Both compounds belong to the family of transition-metal sulfides, a class of materials that has attracted intense attention in energy storage because their metal centers can shuttle between oxidation states during charging and discharging, storing charge through fast surface redox reactions rather than the sluggish diffusion processes that limit conventional batteries. Molybdenum disulfide, in particular, is a layered two-dimensional material whose sheets can host ions between them, while zinc sulfide brings its own electrochemical activity and structural stability to the partnership. The researchers synthesized the composite through a combination of hydrothermal processing, in which the precursors react in a sealed, pressurized water vessel at elevated temperature, and subsequent wet-processing steps that assemble the two sulfide phases together.

Before any electrochemistry took place, the team confirmed that both crystalline phases had indeed formed and coexisted in the final powder. X-ray diffraction, the workhorse technique for identifying crystal structures, revealed the characteristic diffraction signatures of both MoS₂ and ZnS, verifying that the synthesis had produced a genuine composite rather than a mixture of separate, unconnected phases. This structural verification matters because the entire premise of the composite approach rests on synergy: the two sulfides are supposed to complement each other electrochemically, with the redox activity of molybdenum ions in the +2 oxidation state and zinc ions in the +2 oxidation state contributing jointly to charge storage. If the phases had not integrated properly, the composite would simply behave like the average of its components rather than something better than either alone.

The electrochemical testing produced the study’s most striking finding. When the MZ-(1:1) electrode was cycled in a 6 molar potassium hydroxide electrolyte, it delivered a specific capacitance of 123 farads per gram at a current density of 1 ampere per gram. In the more dilute 3 molar electrolyte, the same electrode managed only 96 farads per gram under identical conditions. That difference of roughly 28 percent, achieved without changing anything about the electrode itself, underscores how much the electrolyte concentration shapes the charge storage behavior of sulfide-based pseudocapacitive materials. In alkaline electrolytes, hydroxide ions participate directly in the surface redox reactions that store charge, so a higher hydroxide concentration increases the availability of these charge-carrying species at the electrode interface, deepening the extent of the redox reactions and boosting the measured capacitance.

The authors attribute the enhanced performance to the synergistic redox activity of the molybdenum and zinc ions working in tandem. In such composites, the two metal centers can undergo overlapping but distinct faradaic reactions with hydroxide ions, effectively widening the window of potential over which the electrode stores charge and providing multiple parallel pathways for electron and ion transfer. The layered structure of MoS₂ offers abundant active sites and short diffusion distances for the electrolyte ions, while the ZnS phase contributes additional redox capacity and helps maintain the mechanical integrity of the electrode during repeated cycling. The systematic comparison between the two electrolyte concentrations elevates the work beyond a simple materials report: it offers a methodical explanation of how electrolyte engineering, a variable that is often treated as a fixed background condition, can be tuned deliberately to optimize sulfide electrodes.

Capacitance measured on a single electrode, however, is only half the story. Real devices need two electrodes working together, and asymmetric supercapacitors pair a battery-type or pseudocapacitive electrode with a capacitive counter-electrode to maximize the operating voltage window. The researchers assembled a full asymmetric device using activated carbon as the positive electrode and the MZ-(1:1) nanocomposite as the negative electrode. Activated carbon stores charge through the formation of an electrochemical double layer, a purely physical accumulation of ions at its vast internal surface, which complements the fast redox chemistry of the sulfide electrode. The pairing allowed the device to operate stably at a cell voltage of 1.1 volts, a respectable window for an aqueous alkaline system where water splitting normally constrains the upper voltage limit.

The device-level numbers tell a story of practical promise. In 6 molar potassium hydroxide, the MZ-(1:1)//activated carbon cell achieved an energy density of 9.3 watt-hours per kilogram at a power density of 2780 watts per kilogram. In the 3 molar electrolyte, the corresponding figures were 7.7 watt-hours per kilogram and 2680 watts per kilogram. While lithium-ion batteries store far more energy per kilogram, supercapacitors of this type can deliver their charge orders of magnitude faster and tolerate hundreds of thousands of cycles, making them attractive for applications that demand rapid bursts of power, such as regenerative braking, grid frequency regulation, and backup power for portable electronics. The fact that the denser electrolyte outperformed the dilute one at the device level, mirroring the half-cell results, reinforces the central claim that electrolyte concentration is a genuine optimization lever rather than an incidental detail.

Durability, the Achilles heel of many high-capacitance sulfide electrodes, proved surprisingly strong. After 6000 galvanostatic charge-discharge cycles at a current density of 2 amperes per gram, the device retained 94 percent of its initial capacitance in the 6 molar electrolyte and 85 percent in the 3 molar version. Cycle life of this order suggests that the composite structure withstands the mechanical stresses and dissolution processes that typically degrade metal sulfides in alkaline media. The zinc sulfide component may play a stabilizing role here, anchoring the structure and buffering the volume changes that accompany repeated redox reactions. For a device built entirely from abundant, inexpensive materials, this combination of rate capability and cycling endurance is a meaningful result.

The novelty of the study, as the authors frame it, lies less in the composite itself, which builds on a growing body of work on MoS₂-based and ZnS-based electrodes, and more in the formal, systematic treatment of how electrolyte concentration governs charge storage in this material system. Previous studies have explored MoS₂/ZnS composites and reported enhanced pseudocapacitive performance, but the explicit comparison of the same electrode in two electrolyte molarities, carried through from half-cell testing to full asymmetric device fabrication and long-term cycling, provides a template for how electrolyte engineering should be incorporated into electrode optimization workflows. It also demonstrates that the performance gains from a more concentrated electrolyte persist at the device level and do not come at the cost of stability.

The broader implications reach across the field of aqueous energy storage. Transition-metal sulfides are among the most heavily researched alternatives to noble-metal oxides for supercapacitor electrodes precisely because they are cheap, conductive, and electrochemically versatile, yet they have struggled to combine high specific capacitance with long-term cyclic stability in a single cost-effective system. By showing that a carefully formulated MoS₂/ZnS composite can deliver both, and that a simple change in electrolyte molarity unlocks an additional quarter of the available capacitance, the Ha’il-led team offers electrode designers a low-cost, easily implemented knob to turn. The MZ-(1:1) nanocomposite, they conclude, is a feasible and adaptable electrode material for advanced supercapacitor applications, and the electrolyte-concentration effect they documented may well prove transferable to the wider family of sulfide-based electrodes now under development worldwide.

Subject of Research: Electrolyte-concentration-dependent charge storage in MoS2/ZnS nanocomposite electrodes for asymmetric supercapacitors

Article Title: Electrolyte-dependent synergistic enhancement in MoS₂/ZnS nanocomposites electrode for asymmetric supercapacitors

Article References: Alshammari, M. F., Ali, N., Al-Hinaai, M. M., Hameed, R. A., Alshammari, F. K., Alanazi, K. D., Alhawsawi, M. A., Hegazy, A., Farghaly, O., Muhammad, D., & Shah, S. H. (2026). Electrolyte-dependent synergistic enhancement in MoS₂/ZnS nanocomposites electrode for asymmetric supercapacitors. Ionics. https://doi.org/10.1007/s11581-026-07580-2

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07580-2

Keywords: supercapacitors, MoS2, ZnS, nanocomposite, electrolyte concentration, pseudocapacitance, asymmetric supercapacitor, transition-metal sulfides, KOH electrolyte, energy storage, hydrothermal synthesis, electrode materials

The central problem the team set out to solve is a well-known quirk of transition metal dichalcogenides. MoS2 owes its catalytic and electrochemical behaviour largely to sulfur ions exposed at the edges of its sheets, where unsaturated bonds can grab onto reacting molecules and shuttle electrons. The vast flat faces of the sheets, known as basal planes, are largely catalytically inert; their sulfur atoms are fully coordinated and offer little purchase for reactions. For a material whose appeal lies in its enormous theoretical surface area, this is a frustrating paradox: most of the real estate is effectively switched off. Researchers have tried defect engineering, strain tuning and heterostructure design to wake up those basal planes, but many approaches are complex or expensive.

The Indian group, led by G. Rajasulochana of Arignar Anna Government Arts College in Namakkal with colleagues from Selvam College of Technology, Salem College of Engineering and Technology, and Government Arts and Science College in Komarapalayam, took a more direct route. They grew MoS2 in the presence of activated carbon under hydrothermal conditions, allowing the carbon to coat the growing two-dimensional crystals. According to the team, the activated carbon activates the basal plane surfaces of MoS2, increasing the density of catalytically and electrochemically active sites across the whole material rather than just along the sheet edges. In effect, the carbon turns the inert faces of the semiconductor into productive reaction surfaces while simultaneously contributing its own conductivity and porosity.

Structural characterisation confirmed that the strategy worked. X-ray diffraction showed carbon fully integrated into the MoS2 lattice assembly rather than sitting as a separate phase, a sign of intimate contact between the two components. Scanning electron microscopy then revealed how dramatically the carbon changes the material’s growth habit. Pure MoS2 synthesised under the same conditions forms sheet-like shapes, whereas the carbon-coated composite self-assembles into disc and flower-like structures. That morphological shift matters for practical devices: flower-like architectures expose abundant edges and interlayer spaces, shorten diffusion paths for ions and molecules, and help prevent the restacking of individual sheets that normally erodes the effective surface area of layered materials over time.

The photocatalytic results are the most eye-catching. The researchers dispersed the composite in a suspension of methylene blue, a common cationic dye used as a stand-in for the organic pollutants that textile and printing industries release into waterways, and illuminated it with visible light. The dye’s characteristic absorption peaks vanished within just ten minutes, corresponding to a degradation efficiency of 99.33 percent at an optimal carbon concentration of 0.005 molar. For context, many photocatalysts require hours of irradiation to achieve comparable removal, and many of the most active ones rely on ultraviolet light, which represents only a small fraction of sunlight. A material that works this fast under visible light is far better matched to real-world solar-driven water treatment.

The mechanism behind that speed, the team reports, involves hydroxyl radicals. When the photocatalyst absorbs visible photons, charge carriers are generated and migrate to the surface, where they react with water and dissolved oxygen to produce these highly reactive radical species. The hydroxyl radicals then attack the dye molecules, breaking their conjugated structures into smaller fragments until the colour and the pollutant itself are destroyed. The researchers found that visible-light irradiation broke down methylene blue greatly via this hydroxyl radical pathway, and the carbon coating plausibly assists by improving charge separation, giving photoexcited electrons a conductive escape route that reduces the recombination of electron-hole pairs, the process that ordinarily wastes most of a photocatalyst’s absorbed energy.

On the electrochemical side, the team built three-electrode cells in a 2 molar potassium hydroxide electrolyte to measure how well the composite stores charge as a supercapacitor electrode. The MoS2@C electrode achieved a specific capacitance of 1385 farads per gram at a current density of 1 ampere per gram, a remarkably high figure for a molybdenum disulfide-based material. Just as important for any device that must survive years of charge-discharge cycling, the electrode retained 89 percent of its capacitance after 10,000 cycles. That combination of high initial capacity and strong cycling stability suggests the carbon scaffold does more than boost raw performance; it also mechanically and electrically stabilises the MoS2 layers as they swell and contract during repeated ion insertion.

To demonstrate that the material could function in a realistic device rather than only in laboratory half-cells, the researchers assembled an asymmetric supercapacitor, pairing the MoS2@C electrode with a complementary counter electrode. The full cell delivered an energy density of 231 watt-hours per kilogram alongside a power density of 1137 watts per kilogram. Energy density describes how much charge a device can pack away; power density describes how quickly it can deliver it. Achieving both at high levels simultaneously is the central challenge of energy storage, since batteries typically offer high energy but modest power, while conventional capacitors offer power but little energy. An asymmetric device with these figures, built from inexpensive and abundant constituents, points toward supercapacitors that could buffer renewable electricity or power portable electronics with rapid charging.

The economic argument is a recurring theme in the paper. The authors frame the 2-dimensional layered carbon-coated MoS2 as a cost-effective material for both photocatalytic and electrochemical applications, and the ingredients support that claim. Molybdenum and sulfur are abundant and cheap compared with the noble metals often used in catalysis, activated carbon can be produced from a wide range of carbonaceous precursors, and the hydrothermal synthesis is a standard, scalable technique requiring no exotic equipment or vacuum processing. The work was carried out without dedicated funding, according to the authors’ declaration, underscoring that the advance rests on clever materials design rather than resource-intensive fabrication.

The study also fits into a broader research wave connecting layered dichalcogenides with carbon materials. Previous efforts have combined MoS2 with graphene, carbon nanotubes, carbon nanofibres and porous tubular carbons for supercapacitors, and with graphitic carbon nitride or graphene for photocatalysis. What distinguishes the new report is the dual functionality from a single synthesis and the specific claim that activated carbon wakes up the basal planes, converting the material’s largest but least useful surfaces into active ones. If that activation mechanism can be generalised to other dichalcogenides such as WS2 or MoSe2, the implications could extend to hydrogen evolution catalysis, sensing and battery electrodes. For now, the Tamil Nadu team’s hybrid stands as a striking demonstration that sometimes the cheapest modification, a coat of carbon, can switch on the hidden potential of a celebrated but underperforming material, simultaneously cleaning polluted water and storing renewable electricity with record-setting efficiency.

Subject of Research: Activated carbon-coated two-dimensional MoS2 hybrid for photocatalytic dye degradation and supercapacitor energy storage

Article Title: Highly efficient 2-dimensional layered MoS2@activated carbon hybrid for electrochemical and photocatalytic applications

Article References: Rajasulochana, G., Seenivasan, S., Vijayakumar, P., Jayanthi, K., & Sivakumar, P. (2026). Highly efficient 2-dimensional layered MoS2@activated carbon hybrid for electrochemical and photocatalytic applications. Ionics. https://doi.org/10.1007/s11581-026-07559-z

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07559-z

Keywords: MoS2, activated carbon, photocatalysis, supercapacitors, methylene blue degradation, transition metal dichalcogenides, hydrothermal synthesis, basal plane activation, energy storage, visible light photocatalyst, hydroxyl radicals, asymmetric supercapacitor

The material belongs to a class called layered double hydroxides, or LDHs, structures best imagined as positively charged metal hydroxide sheets stacked like a deck of cards, with water and mobile anions filling the spaces between them. That architecture gives LDHs an unusually high density of electroactive sites exposed to the electrolyte, which is exactly what a pseudocapacitive electrode needs, because charge storage in these materials relies on fast, reversible redox reactions occurring at or near the surface. Nickel and cobalt have dominated the field precisely because both metals shuttle readily between oxidation states, but LDHs made from them suffer from well-known weaknesses: sheets that tend to restack and block access to active sites, moderate electrical conductivity, and structural degradation under the mechanical stress of long-term cycling.

The Indian team’s strategy was to attack those weaknesses from two directions at once. First, they chose a hydrothermal synthesis route, sealing metal precursors in an aqueous reaction medium and letting them crystallize under elevated temperature and pressure. Hydrothermal growth is prized in electrode research because it encourages the formation of well-ordered nanosheet architectures rather than tangled or amorphous precipitates. In the resulting material, scanning electron microscopy and transmission electron microscopy revealed a hierarchical nanostructure—a network of sheets arranged across multiple length scales—which the authors attribute to the controlled crystallization that the hydrothermal environment makes possible. Such hierarchical textures matter enormously in practice, since they create channels for ions to penetrate deep into the electrode rather than stalling at its outermost surface.

The second lever was the lanthanum itself. Lanthanum ions, with their large ionic radius and stable trivalent state, act as a structural and electronic modifier when incorporated into the nickel-cobalt hydroxide layers. According to the study, the presence of La3+ produced a slight increase in the interlayer spacing—the gap between the stacked hydroxide sheets—effectively propping the deck of cards open. Wider galleries mean easier access for hydroxide ions from the electrolyte, more intercalation sites during charging and discharging, and reduced sheet-to-sheet restacking that would otherwise render much of the material electrochemically dead. Rare-earth elements have been steadily gaining attention in the electrode literature for exactly this kind of role, with earlier work reporting improved capacity and lifespan when lanthanum or other rare earths were coupled with nickel-cobalt systems, including recent studies on synergistic lanthanum and scandium doping in nickel-cobalt LDHs and on lanthanum-oxide and nickel-cobalt LDH nanocomposites.

Structural confirmation came from X-ray diffraction, which verified the formation of the LDH crystalline phase through its characteristic (003) and (006) reflections—the fingerprint of a well-ordered layered lattice. The doping-related expansion of the interlayer spacing showed up as a small shift in these peaks, tying the atomic-level chemistry directly to the nanostructure. That connection between synthesis, structure, and performance is the intellectual core of the work: the authors argue that the synergistic effects of multi-metal redox properties and the structural adjustments induced by lanthanum incorporation are jointly responsible for the electrode’s behavior, rather than any single ingredient acting alone.

The electrochemical evidence followed a standard but rigorous testing regime. Cyclic voltammetry traced the redox reactions as the applied potential was swept back and forth, mapping how much charge the material could store and how quickly. Galvanostatic charge-discharge cycling measured the practical capacity under constant current, while electrochemical impedance spectroscopy probed the internal resistance and the speed of ion and electron transport within the electrode. Together, the three techniques returned the headline numbers: 390.3 mAh per gram of specific capacity, roughly 85.5 percent capacity retention over extended cycling, and 98.56 percent coulombic efficiency, meaning that almost every electron injected into the electrode during charging is recovered during discharge—a critical figure for real devices, where side reactions silently bleed away stored energy.

Crucially, the researchers did not stop at the half-cell level, which can flatter a material before it meets the demands of a complete device. They assembled an asymmetric supercapacitor, pairing the NiCoLa LDH as the battery-like faradaic electrode with a capacitive counter-electrode, allowing the device to span a wider operating voltage window than either electrode could tolerate alone. The full cell delivered a specific capacity of 34.17 mAh per gram, a specific energy of 17.08 Wh per kilogram, and a specific power of 500 W per kilogram. Those figures sit in a genuinely interesting part of the energy landscape: conventional carbon-based supercapacitors typically offer high power but only a few watt-hours per kilogram, while batteries deliver far more energy but slower charging and shorter cycle lives. An asymmetric device in the double-digit energy range with strong power delivery and rapid charging ability is precisely the hybrid profile that applications from regenerative braking to grid frequency regulation demand.

The broader context makes the result more than a one-off material triumph. The field of nickel-cobalt LDH electrodes has produced a rich catalogue of enhancement strategies in recent years: doping with sulfur, pairing LDHs with MXenes or graphene, growing heterostructures with oxides and sulfides, anchoring nanosheets onto carbon cloth or nickel foam, and assembling trimetallic layered hydroxides with hierarchical micro-flower morphologies. Each approach targets the same set of bottlenecks—conductivity, surface area, structural stability, and rate capability. The new study’s contribution is to show that lanthanum incorporation, delivered through a relatively simple and scalable hydrothermal route, can address several of those bottlenecks simultaneously without the complexity of multi-step heterostructure engineering. The hydrothermal method also avoids the need for binders in some configurations and produces crystalline material in a single vessel, factors that matter when research results must eventually translate into manufacturable electrodes.

There are, of course, the familiar caveats that attend any laboratory-scale energy-storage advance. The reported capacity retention, while respectable at about 85.5 percent, still implies measurable fading over the tested cycling window, and the path from a coin-cell or beaker-scale device to the robust, kilowatt-scale modules that real infrastructure requires involves challenges of electrode loading, electrolyte management, and thermal behavior that laboratory papers rarely address in full. The authors themselves frame the work as establishing the material as an advanced candidate for next-generation supercapacitors—a claim about promise and mechanism rather than a finished commercial technology. Still, the specific numbers reported are competitive within the current literature on LDH-based asymmetric devices, and the mechanistic story—lanthanum widening the interlayer galleries while nickel and cobalt carry the redox load—offers a clear design rule for other researchers to test and refine.

What gives the work its wider significance is the growing recognition that rare-earth chemistry may be one of the more underexploited levers in pseudocapacitor design. Lanthanum’s large size, its reluctance to participate directly in the redox chemistry, and its oxophilic character make it less a charge-storage agent than an architect: it holds the layered house open, stabilizes the lattice against the swelling and shrinking of repeated cycling, and subtly redistributes electronic density across the nickel and cobalt centers that do the electrochemical work. The Madurai team’s demonstration that this architectural role can be delivered through straightforward hydrothermal synthesis—using equipment and processes already common in materials laboratories—suggests that NiCoLa LDH and its cousins could move quickly from journal pages to prototype devices. For a world urgently needing storage that bridges the gap between instantaneous power and long-duration energy, electrodes built from carefully tailored decks of metal hydroxide cards may prove to be one of the quiet, materials-level breakthroughs on which faster progress is built.

Subject of Research: Lanthanum-doped nickel-cobalt layered double hydroxide electrodes synthesized hydrothermally for high-performance supercapacitor energy storage

Article Title: Tailoring NiCoLa layered double hydroxide via hydrothermal synthesis for superior supercapacitor performance

Article References: Prabhu, B., Karthickprabhu, S., Mahendran, M., & Deepikaa, M. (2026). Tailoring NiCoLa layered double hydroxide via hydrothermal synthesis for superior supercapacitor performance. Ionics. https://doi.org/10.1007/s11581-026-07477-0

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07477-0

Keywords: layered double hydroxide, supercapacitor, hydrothermal synthesis, lanthanum doping, nickel-cobalt electrode, pseudocapacitance, energy storage, asymmetric supercapacitor, electrochemistry, rare earth elements, specific capacity, nanosheets

The choice of cobalt disulfide, or CoS2, is no accident. Transition metal sulfides have become darlings of the pseudocapacitance world because their sulfur atoms help shuttle electrons quickly through the crystal lattice while the metal centers host fast, reversible surface redox reactions. CoS2 in particular offers metallic-like conductivity compared with many oxide alternatives, which means charge can move in and out of the active material without the crippling internal resistance that plagues poorer conductors. The catch is that sulfide electrodes often degrade over thousands of cycles, so the team paired CoS2 with neodymium oxide, a rare earth sesquioxide known for chemical stability and a knack for improving charge-transfer kinetics when incorporated into composite electrodes.

The synthesis was tuned with care. The researchers settled on a confirmed cobalt-to-neodymium molar feed ratio of 2:1, a proportion that produced a composite dominated by mesopores, pores in the two-to-fifty-nanometer range that are large enough for electrolyte ions to penetrate rapidly yet numerous enough to expose enormous internal surface area. Gas adsorption measurements using the Brunauer-Emmett-Teller method put that surface area at 213.21 square meters per gram, a figure comparable to many dedicated activated carbons but achieved here in a redox-active composite. That combination of open pore architecture and electrochemically active components is what allows an electrode to deliver charge both quickly and in quantity.

When tested in a three-electrode configuration, the CoS2/Nd2O3 composite delivered a specific capacitance of 1961 farads per gram at a modest current density of 1 ampere per gram. More impressive still is what happened under stress: at a punishing 20 amperes per gram, twenty times the current, the electrode still managed 1401 farads per gram. That rate capability, retaining roughly 71 percent of its low-rate capacitance, is the signature of an electrode where ions do not get bottlenecked in tortuous pores and electrons do not get stranded in resistive regions. After 10,000 charge-discharge cycles, the material retained 87.6 percent of its capacitance, evidence that the neodymium oxide component and the composite structure helped stabilize the sulfide against the mechanical and chemical wear that typically erodes such electrodes.

On the other side of the cell, the team turned to carbon nanotubes, the cylindrical graphitic filaments prized for their continuous one-dimensional conductivity. Pristine nanotubes store charge mostly through the electric double-layer mechanism, physically separating ions at their surface, which is fast but modest in capacity. The researchers treated the nanotubes with sulfur, creating sulfur-related surface species while preserving the continuous conductive network. The result was an S-CNT negative electrode delivering 431 farads per gram at 1 ampere per gram, 28.7 percent higher than untreated nanotubes measured under identical conditions. Even at 20 amperes per gram the S-CNTs held onto 81.0 percent of their capacitance, confirming that the sulfur modification added pseudocapacitive character without sacrificing the speed that makes carbon electrodes attractive.

Putting the two together yielded an aqueous asymmetric supercapacitor, a device architecture that exploits the different operating voltage windows of the two electrodes to push the total cell voltage well beyond what either electrode could sustain alone. Water-based electrolytes are inherently safer and cheaper than the organic solvents used in many commercial supercapacitors, though they traditionally cap the voltage window near 1.6 volts before water begins to split. The asymmetric design squeezes maximum benefit from that constraint by balancing a high-capacity battery-like positive electrode against a fast, stable carbon negative electrode.

The full two-electrode device held 73.3 percent of its capacitance when the current density was raised from 1 to 15 amperes per gram, and it survived 10,000 cycles with approximately 95.0 percent retention, a durability figure that stands out even among laboratory-scale aqueous devices. The authors are candid about the engineering subtleties involved. A retrospective first-order charge-balance analysis, which examines whether the charges stored on the positive and negative electrodes are properly matched, indicated that further optimization of the electrode mass ratio would be beneficial. In asymmetric supercapacitors, mismatched electrode masses leave one electrode underutilized, wasting capacity and shortening cycle life, so this kind of self-critical analysis points directly at the next round of improvement.

The motivation behind the work is refreshingly concrete. Short-duration and repetitive power fluctuations from train acceleration, braking, and regenerative-energy recovery demand storage devices with rapid response, high-rate capability, and stable cycling, and the authors frame their material pair as a laboratory-scale platform for exactly that kind of short-duration power buffering in rail transit. Regenerative braking energy is notoriously difficult to capture because it arrives in sharp spikes rather than smooth flows; batteries absorb it slowly and degrade quickly, while conventional double-layer capacitors lack the energy density to make a dent in a metro line’s power budget. A pseudocapacitive composite that can swallow thousands of farads per gram and release them at 20 amperes per gram, cycle after cycle, fits the profile of what wayside and on-board storage systems need.

The team is equally clear about what remains to be done before such a device could ride the rails. They note that composition optimization, complete-device impedance characterization, and application-specific pulse validation would further strengthen the assessment for rail-transit use. Impedance characterization, in particular, matters because real transit duty cycles involve not just repeated pulses but temperature swings, vibration, and years of continuous service, all of which show up first as changes in a device’s internal resistance. The authors also report that no datasets were generated or analyzed beyond the study itself, and the work was supported by the Key Project of the 2025 Educational Science Program of Heilongjiang Province under the 14th Five-Year Plan.

Still, the numbers tell a compelling story. A positive electrode approaching 2000 farads per gram, a sulfur-doped carbon negative electrode beating its untreated counterpart by nearly 29 percent, a full cell that keeps 95 percent of its capacitance over ten thousand cycles, and an honest roadmap for refinement together sketch a credible path from bench chemistry to power electronics. If subsequent work tightens the mass balance and validates the device under realistic pulse profiles, the humble pairing of a cobalt sulfide, a rare earth oxide, and a dash of sulfur on carbon nanotubes could find itself quietly smoothing the electricity of the world’s metro systems, one braking train at a time.

Subject of Research: CoS2/Nd2O3 composite and sulfur-doped carbon nanotube electrodes for asymmetric supercapacitors aimed at rail-transit power buffering

Article Title: Preparation of CoS2/Nd2O3 composites and S-CNTs and their electrochemical performance in asymmetric supercapacitors

Article References: Zhang, W., Lan, Y., Zheng, X., Zhang, Y., & Shen, W. (2026). Preparation of CoS2/Nd2O3 composites and S-CNTs and their electrochemical performance in asymmetric supercapacitors. Ionics. https://doi.org/10.1007/s11581-026-07486-z

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07486-z

Keywords: asymmetric supercapacitor, CoS2/Nd2O3 composite, sulfur-doped carbon nanotubes, pseudocapacitance, electrode materials, regenerative braking, rail transit energy storage, mesoporous materials, aqueous electrolyte, cycle stability, rate capability, electrochemistry

The study, published in the journal Ionics by Shisen Bo, Ruifeng Liu, Fang Lei, Mei Wang, Tantan Liu, Yuting Liu and Ying Li, describes a nanoflower-like composite built from iron oxyhydroxide (FeOOH) and titanium carbide MXene, written chemically as Ti₃C₂Tₓ. The researchers grew the composite directly onto nickel foam using electrochemical deposition, a technique that is fast, scalable and operates at low temperatures. The resulting electrode delivered an areal specific capacitance of 745 millifarads per square centimetre at a current density of 1 milliampere per square centimetre, a figure that places it among the more capable pseudocapacitive electrodes reported for this class of materials.

The elegance of the work lies in how the two components compensate for each other’s weaknesses. MXenes, a family of two-dimensional carbides first discovered about a decade ago, are prized for their metallic conductivity and their surface chemistry, which can be tuned with terminations such as oxygen, fluorine and hydroxyl groups, collectively denoted Tₓ. But MXene nanosheets have a stubborn tendency to restack, collapsing into dense layers that block the electrolyte from reaching active sites. FeOOH, by contrast, is a rich source of pseudocapacitance, storing charge through fast surface redox reactions, yet it swells and deforms as ions shuttle in and out during cycling, which eventually grinds the electrode apart.

The Chinese team exploited a simple but clever physical principle to assemble the hybrid. Ti₃C₂Tₓ nanosheets carry a negative surface charge in suspension, while iron ions carry a positive charge. Under an applied electric field during electrodeposition, the electrostatic attraction between the two drives Fe³⁺ ions toward the MXene sheets, where they hydrolyse and precipitate as FeOOH. The result is a nanoflower morphology, with petal-like structures blooming across the nickel foam scaffold. This architecture is not merely decorative: the open, flower-like geometry maximises electrolyte access and keeps the MXene sheets propped apart, preventing the restacking that would otherwise strangle the electrode’s performance.

The partnership works in both directions. While FeOOH acts as a spacer that stops the MXene sheets from clumping, the flexible MXene layers in turn cushion the FeOOH against the mechanical stress of repeated charging and discharging. Volume expansion and structural deformation, the classic failure modes of iron oxyhydroxide electrodes, are mitigated by the compliant two-dimensional scaffold. The researchers report that this mutual reinforcement preserves the structural integrity of the electrode over long-term cycling, which is precisely the property that separates laboratory curiosities from practical devices.

To demonstrate real-world utility, the team went beyond testing the composite in isolation and assembled a full asymmetric supercapacitor. The nanoflower-like FeOOH/Ti₃C₂Tₓ electrode served as the anode, paired with a cathode made of manganese dioxide deposited on carbon paper. Asymmetric designs of this kind extend the operating voltage window beyond what a symmetric cell can achieve, because the two electrodes operate in complementary potential ranges. The device achieved an energy density of 270.3 microwatt-hours per square centimetre at a power density of 1003.5 microwatts per square centimetre, numbers that represent a meaningful step toward the energy densities typically associated with battery-type chemistry while retaining capacitor-like power delivery.

Perhaps even more impressive is the device’s endurance. After 15,000 charge-discharge cycles at a current density of 7 milliamperes per square centimetre, the asymmetric supercapacitor retained 86 percent of its initial capacitance. For a pseudocapacitive material that stores charge through redox reactions, which are inherently more structurally demanding than the pure ion adsorption that occurs in carbon-based double-layer capacitors, this level of cycling stability is a strong indicator that the MXene cushioning strategy works as intended. It suggests the electrode does not simply start strong and fade, but maintains its architecture through tens of thousands of ion insertion and extraction events.

The work sits within a broader and rapidly growing research effort to marry MXenes with transition metal compounds for electrochemical energy storage. Recent studies have explored FeOOH-MXene heterostructures for quasi-solid-state asymmetric supercapacitors, MXene composites with layered double hydroxides for potassium-ion supercapacitors, and electrodeposited iron oxyhydroxide on porous graphene for on-chip micro-supercapacitors. What distinguishes the new study is the one-step electrodeposition route, which grows the composite directly on the current collector without binders, high-temperature treatment or multi-stage synthesis. Electrodeposition has attracted increasing attention as a manufacturing strategy for functional energy storage electrodes precisely because it offers fine control over morphology while remaining compatible with roll-to-roll and substrate-based production.

The choice of nickel foam as the substrate also matters. The three-dimensional, highly conductive metallic foam provides an interconnected pathway for electrons and a porous framework that supports high mass loading of active material without sacrificing rate capability. Combined with the nanoflower architecture grown in place, the design minimises the dead volume and interfacial resistance that plague electrodes assembled from powders and slurries. For applications such as wearable electronics, regenerative braking systems, grid frequency regulation and hybrid electric vehicles, where devices must deliver high power in compact footprints and endure relentless cycling, these are the metrics that count.

Challenges remain before such electrodes reach commercial deployment, including scaling the electrodeposition process to large areas, optimising electrolyte systems, and demonstrating performance at the device level under realistic operating conditions. But the study offers a clear design principle: rather than searching for a single miracle material, engineers can pair a high-capacitance but fragile redox phase with a conductive and mechanically resilient two-dimensional scaffold, letting each material protect the other. With supercapacitors increasingly seen as essential complements to batteries in the electrified economy, nanoflower electrodes like this one suggest that the gap between capacitors and batteries is beginning to close, one carefully engineered petal at a time.

Subject of Research: Electrodeposition of a nanoflower-like FeOOH/Ti₃C₂Tₓ MXene composite electrode for high-performance asymmetric supercapacitors

Article Title: Nanoflower-like FeOOH/Ti₃C₂Tₓ composite fabricated by electrodeposition for superior supercapacitor performance

Article References: Bo, S., Liu, R., Lei, F., Wang, M., Liu, T., Liu, Y., & Li, Y. (2026). Nanoflower-like FeOOH/Ti₃C₂Tₓ composite fabricated by electrodeposition for superior supercapacitor performance. Ionics. https://doi.org/10.1007/s11581-026-07465-4

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07465-4

Keywords: supercapacitor, MXene, FeOOH, electrodeposition, nanoflower structure, energy density, pseudocapacitance, asymmetric supercapacitor, nickel foam, cycling stability, energy storage, two-dimensional materials

Writing in the journal Ionics, Changxu Qu, Jing Wang and their colleagues at Harbin University of Commerce, Harbin Institute of Technology and Ningxia University describe an asymmetric supercapacitor built around two carefully engineered electrodes. The positive electrode is made of iron molybdate, Fe2(MoO4)3, a bimetallic oxide that has attracted attention for its rich redox chemistry but has been held back by poor electrical conductivity and structural fragility. The negative electrode is a composite of tin oxide nanoparticles and carbon nanotubes, chosen for its conductivity and fast ion transport. Together, in a flexible gel electrolyte of polyvinyl alcohol and potassium hydroxide, the two electrodes deliver an energy density of roughly 45 watt-hours per kilogram at a current density of 3 amperes per gram, with a power density of about 800 watts per kilogram. When the current is pushed to 15 amperes per gram, the device still holds around 30 watt-hours per kilogram while its power density climbs to approximately 2400 watts per kilogram.

Those numbers matter because energy density has been the stubborn bottleneck of supercapacitor design. Commercial carbon-based devices typically manage only 5 to 10 watt-hours per kilogram, an order of magnitude below lithium-ion batteries. The new device approaches the lower range of battery territory while preserving the defining supercapacitor virtues: it operates stably across a 0 to 1.6 volt window and, after 10,000 charge-discharge cycles at 5 amperes per gram, retains about 93.3 percent of its capacitance. For a device that might be cycled hundreds of times a day in a regenerative braking system or a wearable gadget, that kind of durability is as important as the headline energy figure.

The secret to the cathode’s performance lies in two intertwined strategies: defect engineering and architectural design. The researchers synthesized lanthanum-doped iron molybdate through a hydrothermal method, followed by morphology regulation, and cast the resulting active material as a slurry onto carbon cloth. Lanthanum, a rare-earth element with an ionic radius much larger than iron’s, does not simply sit quietly in the crystal lattice. Its incorporation induces local lattice distortion, and X-ray diffraction and high-resolution transmission electron microscopy revealed the structural consequences. More significantly, deconvolution of the oxygen 1s signal in X-ray photoelectron spectroscopy showed an increased proportion of oxygen vacancies and defective-oxygen species in the doped material.

Those oxygen vacancies are far more than cosmetic flaws. In transition-metal oxides, missing oxygen atoms act as donors and create pathways that make it easier for electrons to hop through the crystal, while the surrounding distorted lattice can lower the energy barrier for charge transfer at the electrode-electrolyte interface. The result, as the team’s electrochemical measurements confirmed, is a material with enhanced electrical conductivity and faster charge-transfer kinetics, precisely the properties that pristine Fe2(MoO4)3 lacks. The doping also plays a structural role: the lanthanum ions help stabilize the framework during repeated insertion and extraction of hydroxide ions, which is what allows the electrode to survive thousands of cycles without crumbling.

The second strategy is geometric. Rather than compact particles, the optimized material forms three-dimensional flower-like architectures, with petals radiating from a central core. This morphology dramatically increases the accessible surface area, reaching up to 190.58 square meters per gram after lanthanum doping, a figure comparable to some porous carbons. In an electrode, surface area is currency: every square meter offers more sites where electrolyte ions can adsorb and react. The open, petal-like structure also creates abundant ion-transport pathways, so electrolyte can penetrate deep into the electrode rather than lingering at its surface, and the architecture buffers the volume changes that accompany cycling, improving structural stability over the long term.

When tested in a three-electrode configuration, the optimized cathode, containing 0.3 weight percent lanthanum, delivered a specific capacitance of 600 farads per gram at 1 ampere per gram, an impressively high value for a bimetallic oxide cathode. Equally telling is its rate and cycling behavior: at a demanding 5 amperes per gram, the electrode retained more than 98.2 percent of its capacitance after 5000 charge-discharge cycles. That combination of high capacitance and minimal fade suggests that the defect-engineered, flower-like structure is not a laboratory curiosity but a genuinely robust electrode design.

On the other side of the cell, the team paired the cathode with a composite anode of tin oxide grown on carbon nanotubes. Tin oxide contributes additional pseudocapacitance through its own redox reactions, while the carbon nanotube network provides a conductive scaffold that keeps electrons moving and ions diffusing quickly. Electrochemical impedance measurements showed that the composite has a much lower charge-transfer resistance than pristine carbon nanotubes alone, meaning that the reactions at its surface proceed with less energy wasted as heat. In an asymmetric supercapacitor, where the positive and negative electrodes must be carefully balanced in charge capacity, having a fast, stable negative electrode is essential to unlocking the full potential of the cathode.

The word asymmetric is key to understanding why the device reaches 1.6 volts. In a conventional symmetric supercapacitor, both electrodes are made of the same carbon material, and the cell voltage is limited by how far each electrode can be polarized. An asymmetric design uses two different materials with complementary operating windows: the iron molybdate cathode works over one potential range and the tin oxide composite anode over another, so their combined window is wider than either could achieve alone. Since the energy stored scales with the square of the voltage, stretching the window from roughly 1.0 to 1.6 volts more than doubles the available energy for a given capacitance. The PVA-KOH gel electrolyte, meanwhile, makes the device inherently flexible and safe, opening the door to wearable electronics and conformal energy storage.

The work, supported by the National Natural Science Foundation of China and partner institutions, points toward a broader lesson in electrode design: the most effective energy-storage materials are rarely those with the most exotic chemistry, but those whose defects and shapes have been deliberately tuned to work with, rather than against, the physics of ion and electron transport. By injecting a trace of rare-earth dopant into a humble iron molybdate and sculpting it into a flower, the researchers transformed a conductivity-limited compound into the backbone of a device that charges fast, stores substantially, and endures. If the strategy can be scaled from carbon-cloth laboratory electrodes to industrial formats, lanthanum-doped flower-like oxides and their bimetallic cousins could become serious contenders in the race to bridge the gap between batteries and supercapacitors, a gap that has narrowed considerably with this latest advance.

Subject of Research: Defect-engineered bimetallic oxide electrodes for high-performance asymmetric supercapacitors

Article Title: La-doped flower-like Fe2(MoO4)3 cathodes coupled with SnO2/CNT anodes for high-performance asymmetric supercapacitors

Article References: Qu, C., Xing, M., Hao, T., Hao, J., Cao, J., Zhi, H., & Wang, J. (2026). La-doped flower-like Fe2(MoO4)3 cathodes coupled with SnO2/CNT anodes for high-performance asymmetric supercapacitors. Ionics. https://doi.org/10.1007/s11581-026-07458-3

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07458-3

Keywords: supercapacitors, iron molybdate, lanthanum doping, oxygen vacancies, tin oxide, carbon nanotubes, asymmetric supercapacitor, energy density, defect engineering, hydrothermal synthesis, cycling stability, energy storage

The choice of material is deliberate. Bismuth sulfide is an earth-abundant, environmentally benign semiconductor that has attracted growing attention as an electrode material for energy storage. Its layered orthorhombic crystal structure, built from covalently bonded Bi2S3 ribbons held together by weaker van der Waals forces, offers open channels along which ions can migrate, making it naturally suited to intercalation-based charge storage. Previous studies have produced Bi2S3 in the form of nanorods, nanowires, nanoflowers and nanoflakes using solvothermal, chemical bath and spray methods, and several groups have reported respectable supercapacitor performance from composites that pair the sulfide with graphene, carbon nitride or nickel foam. What has been missing, the authors argue, is a systematic understanding of how the electrolyte itself, not just the material, controls the charge storage process.

To build their electrode material, the researchers turned to hydrothermal synthesis, a technique that grows crystals from aqueous precursors inside a sealed, heated vessel. Under the right combination of temperature, time and precursor chemistry, the reaction self-assembles Bi2S3 into petal-like nanopetals, which the team abbreviates BSNP. This flower-like architecture is more than aesthetic. The petals create a high surface-area scaffold with abundant exposed active sites, short diffusion pathways for ions and open voids that accommodate the volume changes that occur as charge is stored and released. Such morphological engineering is a central strategy in modern electrode design, because electrochemical reactions happen only at surfaces and interfaces; the more accessible surface a material presents to the electrolyte, the more charge it can store and the faster it can deliver it.

The heart of the experiment is a comparison across three alkaline electrolytes: 2 M solutions of lithium hydroxide (LiOH), sodium hydroxide (NaOH) and potassium hydroxide (KOH). All three contain the same charge-carrying hydroxide ion, but they differ in the size and hydration behavior of their cations, and those differences ripple through every aspect of electrode kinetics. When the team tested BSNP as the positive electrode in each solution, the results were striking. In 2 M KOH, the nanopetals delivered a gravimetric capacity of 797.9 coulombs per gram at a scan rate of 1 millivolt per second, outperforming the same material in LiOH and NaOH. In other words, simply swapping the electrolyte cation from lithium or sodium to potassium unlocked a substantially larger fraction of the material’s theoretical storage capability.

Why would potassium ions give bismuth sulfide an edge? The answer, the researchers show, lies in the electronic and ionic interplay at the material’s surface. Using DFT calculations, they probed how hydroxide species interact with the Bi2S3 lattice under each electrolyte condition. Orbital hybridization analysis revealed favorable overlap between the electronic states of the surface and the adsorbed species in the KOH case, while Bader charge analysis quantified the electron transfer between them. Charge density difference maps and electron localization function analysis visualized where electrons accumulate and deplete during adsorption, painting a consistent picture: the potassium-containing environment promotes stronger, more favorable electronic coupling at the Bi2S3 surface, which lowers the energetic barriers for the redox reactions that store charge. This computational evidence aligns neatly with the electrochemical data, giving the performance claims a mechanistic foundation rather than leaving them as empirical observations.

Kinetic analysis added another layer of insight. Applying Dunn’s method, a widely used technique that separates the capacitive (surface-controlled) and diffusion-controlled contributions to charge storage from cyclic voltammetry data measured at different scan rates, the team confirmed that diffusion-dominated processes govern the behavior of the BSNP electrode. That finding matters because it places the material firmly in the battery-type category rather than the purely capacitive one. Battery-type electrodes store charge through faradaic reactions, in which ions insert into the crystal lattice and electrons transfer to or from the metal centers, allowing much more charge to be packed per gram than in the electrostatic double-layer storage that characterizes carbon-based supercapacitor electrodes. It is precisely this battery-like positive electrode, paired with a capacitive negative electrode, that defines the supercapattery architecture.

To prove the concept at the device level, the researchers assembled an asymmetric supercapacitor (ASC) in which the BSNP nanopetals served as the positive electrode and activated carbon, a classic high-surface-area capacitive material, served as the negative electrode. The two electrodes were balanced in mass and charge so that each could operate within its stable voltage window, maximizing the overall cell voltage. The finished device achieved a gravimetric capacity of 209.76 coulombs per gram at a current density of 1 ampere per gram and, more importantly for real-world applications, an energy density of 46.61 watt-hours per kilogram. That figure sits well above what conventional symmetric supercapacitors typically deliver and approaches the lower range of lithium-ion batteries, while retaining the rapid charge-discharge capability and long cycle life that batteries struggle to match.

The significance of the electrolyte comparison extends beyond this particular material. Electrolyte engineering is often treated as an afterthought in electrode research, yet the ionic radius, mobility, hydration shell and desolvation energy of the charge carriers fundamentally shape how deeply ions can penetrate an electrode and how quickly redox reactions proceed. Potassium ions, being larger than lithium and sodium ions in their bare form but less strongly hydrated in aqueous solution, can shed their water shell more easily and interact more directly with electrode surfaces. The present study demonstrates that this seemingly subtle difference can translate into hundreds of coulombs per gram of additional capacity, a lesson that applies to the entire family of transition metal and post-transition metal sulfides under investigation for supercapatteries.

There are, of course, hurdles between a laboratory cell and a commercial device. Aqueous supercapatteries are inherently limited to modest cell voltages by water’s electrochemical stability window, and the long-term cycling stability, rate capability at high current densities and mechanical robustness of sulfide electrodes must be validated over thousands of cycles before such devices could power phones or grid buffers. The authors note that their data are available upon reasonable request, inviting the community to build on the results, and the combination of hydrothermal scalability, inexpensive raw materials and water-based processing gives the approach a credible path toward practical manufacturing. The work was supported by the Ongoing Research Funding Program at King Saud University, with additional support from the University of Kerala.

What makes this study a compelling piece of the energy storage puzzle is its methodological completeness. Rather than reporting a capacity number in isolation, the team connected morphology, electrolyte chemistry, electronic structure and device performance into a single coherent narrative, using DFT not as decoration but as a genuine explanatory tool. As the world races to decarbonize electricity grids and electrify transport, hybrid devices that blend the best of batteries and supercapacitors could fill critical niches, from regenerative braking and renewable energy smoothing to portable electronics that charge in minutes. Petal-like bismuth sulfide, coaxed into existence in a simple hydrothermal reactor and tuned by nothing more exotic than the right potassium hydroxide bath, may prove to be one of the quiet building blocks of that future.

Subject of Research: Electrolyte-dependent charge storage in hydrothermally synthesized petal-like Bi2S3 nanostructures for supercapattery electrodes

Article Title: Electrolyte-dependent charge storage in hydrothermally synthesized petal-like Bi2S3 nanostructure: experimental and DFT insights

Article References: Mottammal, D., Thomas, S. A., Cherusseri, J., Arumugam, D., Pallavolu, M. R., Fatehmulla, A., Ramasamy, S., Parasuk, V., & Rajendran, D. N. (2026). Electrolyte-dependent charge storage in hydrothermally synthesized petal-like Bi2S3 nanostructure: experimental and DFT insights. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13692-x

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13692-x

Keywords: bismuth sulfide, supercapattery, asymmetric supercapacitor, hydrothermal synthesis, DFT calculations, potassium hydroxide electrolyte, battery-type electrode, energy density, charge storage kinetics, nanopetals, aqueous electrolytes, energy storage materials

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