The trick behind the material lies in how it is made. Rather than precipitating nickel sulfide particles directly from solution, the researchers used a metal-organic framework, or MOF, as a sacrificial template. MOFs are crystalline lattices built from metal ions connected by organic linker molecules, and they are famous for being riddled with regularly spaced pores at the molecular scale. By converting this framework through a sulfurization strategy, the team preserved a memory of the original porous structure while transforming the chemistry from a hybrid organic-inorganic framework into a pure inorganic sulfide. The result is a sponge-like NiS2 architecture in which mesopores, pores in the range of roughly two to fifty nanometers, are abundant and interconnected, producing a high specific surface area that would be difficult to achieve by conventional synthesis routes.

That architecture matters because the performance of a battery or supercapacitor electrode is governed largely by how easily ions can reach the electroactive sites where charge storage happens. In a dense, poorly connected material, ions from the electrolyte must diffuse long distances through tortuous pathways, and much of the interior of the material is effectively wasted. In the sponge-like NiS2, the abundant mesopores act as highways for hydroxide ions and other electrolyte species, shortening diffusion lengths dramatically, while the large surface area exposes a vast number of electroactive sites for the surface redox reactions that store charge. The hierarchical porosity also helps accommodate the volume changes that accompany repeated charging and discharging, a key factor in the material’s observed cycling stability.

The electrochemical results are the heart of the study. When tested as a supercapacitor electrode in alkaline electrolyte, the NiS2 electrode delivered a specific capacitance of 1227.5 F g−1 at 0.5 A g−1, a value that reflects an exceptional density of accessible charge-storage sites. Specific capacitance measures how much electric charge a gram of electrode material can hold per volt of potential, and values above one thousand farads per gram are characteristic of high-performance pseudocapacitive materials, which store charge through fast, reversible surface reactions rather than purely electrostatic adsorption. Nickel sulfides are well suited to this role because nickel can shuttle between multiple oxidation states during charging and discharging, enabling rich redox chemistry at the electrode surface.

Perhaps the most commercially interesting finding is that the material is bifunctional. The same NiS2 electrode that excels in a supercapacitor configuration can also serve as the cathode in an aqueous nickel-zinc battery, where it delivers high specific capacity and stable long-term performance. Ni-Zn batteries are an attractive technology because they use water-based electrolytes, which are inherently safer and cheaper than the flammable organic solvents found in lithium-ion cells, and because zinc is abundant and easy to handle. The catch has historically been finding cathode materials that can withstand the demanding alkaline environment while storing enough charge to make the cells competitive. The demonstration that a single MOF-derived sulfide can serve both device types suggests a versatile platform rather than a one-off material.

The study situates itself within a broader surge of interest in aqueous energy storage. Water-based devices occupy a compelling middle ground between supercapacitors, which charge in seconds but store limited energy, and conventional batteries, which store more energy but charge more slowly and carry greater safety burdens. Recent literature highlighted in the paper’s reference list spans electrochemical activation tactics for aqueous devices, rechargeable zinc-based storage, molecularly crowding electrolytes for micro-supercapacitors, and flexible yarn-like Ni-Zn batteries for wearable electronics. Transition metal sulfides, including nickel sulfides such as Ni3S4 and NiS2, have emerged as leading candidates in this space because they combine high theoretical capacity, good electrical conductivity relative to oxides, and low cost.

The MOF-derived approach itself is part of a wider design philosophy in materials chemistry. By using a preassembled framework as a template, chemists can impose order on a material at the nanoscale that would be hard to achieve through direct synthesis. In this case, the sulfurization step converts the nickel-containing framework into NiS2 while retaining the sponge-like morphology, a process analogous to casting a sculpture in a mold. Earlier work by some of the same authors produced accordion-like iron-doped NiS2 and surface-amorphized nickel sulfides for aqueous storage, indicating that the group has been systematically exploring how morphology and surface chemistry tune the performance of nickel sulfide electrodes. The new sponge-like architecture extends that program by emphasizing interconnected mesoporosity as the central design feature.

There are, of course, caveats that temper any immediate industrial enthusiasm. The reported measurements were made on laboratory-scale electrodes in alkaline electrolyte, and translating a promising lab material into a commercial device requires solving problems that go beyond the cathode itself, including zinc anode durability, electrolyte optimization, and full-cell engineering. The paper’s own framing is careful: the authors describe the work as establishing NiS2 as a promising electrode material for aqueous energy storage devices and providing a feasible synthetic pathway for designing high-performance transition metal sulfide electrodes, rather than claiming a ready-made product. Still, the combination of high capacitance, cycling stability, and bifunctionality in a single low-cost material is exactly the kind of result that device engineers look for when deciding which candidates to pursue.

The broader significance of the work lies in its demonstration that structure, not just composition, is the lever that unlocks performance. Nickel disulfide has been recognized as a sustainable, low-cost electrode material before, but the sponge-like hierarchical architecture reported here shows how much headroom remains in a familiar compound when its porosity is engineered deliberately. As the demand for safe, inexpensive, grid-scale and wearable energy storage continues to grow, strategies that turn molecularly precise templates into functional inorganic electrodes are likely to play an increasing role. For now, a synthetic sponge made of nickel and sulfur, born from a crystalline framework and hardened into a charge-hungry electrode, offers a vivid example of how rational design at the nanoscale can translate directly into better electrochemical numbers.

Subject of Research: MOF-derived hierarchical porous NiS2 electrode materials for aqueous supercapacitors and Ni-Zn batteries

Article Title: MOF-derived sponge-like NiS2 with a hierarchical porous architecture for aqueous supercapacitors and Ni-Zn batteries

Article References: Gong, G., Liu, X., Ma, H., Lv, D., Luo, H., Liang, M., Zhou, Y., Wang, H., Zhao, Y., Lashari, N. U. R., & Miao, Z. (2026). MOF-derived sponge-like NiS2 with a hierarchical porous architecture for aqueous supercapacitors and Ni-Zn batteries. Ionics. https://doi.org/10.1007/s11581-026-07558-0

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07558-0

Keywords: NiS2, metal-organic framework, supercapacitor, Ni-Zn battery, aqueous energy storage, transition metal sulfide, mesoporous structure, electrode material, pseudocapacitance, sulfurization, energy storage, Ionics

Polypyrrole, often abbreviated PPy, is one of the most tractable conducting polymers in electrochemistry. It can be grown directly onto a conductive surface by simply applying a potential to a solution of pyrrole monomers, a process known as electropolymerization or electrodeposition. The resulting film is electrically conductive, chemically stable, and stores charge through a pseudocapacitive mechanism: as the polymer is oxidized and reduced, ions from the electrolyte move in and out of the film to balance the electronic charge on the polymer backbone. This ion exchange gives polypyrrole a respectable capacitance, but pure polymer films suffer from well-known weaknesses. Their charge storage is limited by the density of accessible redox sites, and the repeated swelling and shrinking that accompanies ion insertion and removal gradually degrades the film, causing capacitance to fade over repeated cycling.

The research team, led by Hanane Khentite of Ferhat Abbas University of Sétif 1 together with colleagues at Mohamed Boudiaf University of M’sila and Mohamed El Bachir El Ibrahimi University of Bordj Bou Arréridj, addressed both weaknesses at once by incorporating nickel oxide, a transition metal oxide with its own rich pseudocapacitive chemistry, into the polymer matrix. Nickel oxide stores charge through reversible surface redox reactions involving the Ni2+/Ni3+ couple, and it is inexpensive, abundant, and environmentally benign compared with many alternative metal oxides such as ruthenium dioxide. The idea of combining metal oxides with conducting polymers is not new, but the details of how the two components are integrated often determine whether the composite outperforms its constituents or merely averages their shortcomings.

The fabrication method was deliberately straightforward. The researchers used indium tin oxide coated glass, a transparent conducting substrate, as the working electrode in an electrochemical cell. By controlling the deposition conditions, they grew a polypyrrole film in which nickel oxide particles were successfully embedded, producing what they designate as the ITO/PPy-NiO electrode. For comparison, they also prepared a pure polypyrrole film on the same substrate under analogous conditions. Electrochemical deposition has a practical advantage over many alternative synthesis routes: the film forms directly on the current collector, eliminating the need for polymer binders and conductive additives that add dead weight and interfacial resistance in conventional slurry-cast electrodes.

Before any electrochemical testing, the team subjected both films to a battery of structural and morphological characterization techniques. Fourier-transform infrared spectroscopy confirmed the chemical signatures of the polymer and the incorporated oxide. X-ray diffraction provided evidence of the crystalline nickel oxide phase within the composite. Scanning electron microscopy and atomic force microscopy revealed how the presence of nickel oxide altered the surface morphology of the films, changes that matter enormously in pseudocapacitive materials because charge storage occurs at or near surfaces where the electrolyte can reach the active material. A rougher, more porous morphology generally means more electrochemically accessible area and therefore higher capacitance.

The electrochemical results were unambiguous. Using cyclic voltammetry at a scan rate of 5 millivolts per second, the composite electrode delivered a specific capacitance of 230.22 farads per gram, while the pure polypyrrole film managed only 150.79 farads per gram under identical conditions. Galvanostatic charge-discharge measurements, which provide a more application-relevant picture of how an electrode behaves under constant current, told a consistent story: the composite achieved 214.87 farads per gram at a current density of 0.3 amperes per gram, against 138 farads per gram for the pristine polymer. In other words, adding nickel oxide boosted capacitance by roughly half, a substantial gain for a relatively modest modification of the synthesis recipe.

Perhaps the most striking result concerns durability, the perennial Achilles heel of conducting polymer electrodes. After 1,000 charge-discharge cycles, the composite electrode retained 89 percent of its initial capacitance, with a Coulombic efficiency above 95 percent, meaning that nearly every unit of charge put into the electrode during each cycle came back out. The pure polypyrrole electrode, by contrast, retained only 50 percent of its capacitance over the same number of cycles. This near-doubling of cycling stability suggests that the nickel oxide particles do more than simply add their own charge storage capacity; they appear to reinforce the polymer mechanically and electrochemically, buffering the volume changes that normally tear polypyrrole films apart during repeated ion insertion and removal.

The galvanostatic measurements also yielded energy and power density figures for the composite: an energy density of 19.1 watt-hours per kilogram at a power density of 120 watts per kilogram. The authors are careful to note that these values were derived from three-electrode measurements and are included for comparative purposes only. This is an important caveat that honest electrochemists increasingly emphasize. Three-electrode data reflect the behavior of a single electrode material in isolation, whereas real devices pair two electrodes in a full cell, and the device-level energy density is inevitably lower than the single-electrode figure suggests. Reporting such numbers with this qualification is a welcome example of restraint in a field where inflated claims have sometimes muddied the literature.

Mechanistically, the improvement can be understood as a synergy between two complementary charge storage mechanisms. The polypyrrole contributes a conductive, ion-permeable network that stores charge through doping and dedoping of its conjugated backbone, while the nickel oxide contributes high-capacity surface redox reactions. The conductive polymer can also serve as an electron highway to oxide particles that would otherwise be poorly connected, and the oxide in turn provides structural anchoring that limits the polymer’s swelling. Similar hybrid strategies have been explored with manganese dioxide, graphene, and other additives, and the present work situates nickel oxide within that broader family of conducting polymer-metal oxide composites that the same research group and others have been developing for years.

The practical implications are modest but real. Electrodeposition is a scalable, low-temperature, solution-based technique compatible with a variety of substrates, and nickel oxide is among the cheapest pseudocapacitive oxides available. An electrode that combines a 50 percent capacitance gain with dramatically improved cycling stability, achieved through a one-step electrochemical route without binders, is exactly the kind of incremental engineering advance that accumulates into commercially meaningful progress. The work, published online on 29 September 2026 in Ionics, adds to a growing body of evidence that the future of supercapacitor electrodes lies not in any single miracle material but in carefully engineered composites where a conductive polymer and a redox-active oxide each compensate for the other’s weaknesses. For grid buffering, regenerative braking, and portable electronics, where devices must deliver power in a flash and survive decades of abuse, that kind of durability-first design philosophy may prove more valuable than any headline-grabbing record.

Subject of Research: Nickel oxide-incorporated polypyrrole composite electrodes for supercapacitor energy storage

Article Title: Increased polypyrrole sheet electrochemical performance for supercapacitor applications by incorporation nickel oxide

Article References: Khentite, H., Habelhames, F., Bahloul, A., Nessark, B., Sayah, A., & Boughezal, A. (2026). Increased polypyrrole sheet electrochemical performance for supercapacitor applications by incorporation nickel oxide. Ionics. https://doi.org/10.1007/s11581-026-07546-4

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07546-4

Keywords: polypyrrole, nickel oxide, supercapacitor, electrochemical deposition, pseudocapacitance, composite electrode, cycling stability, specific capacitance, energy storage, conducting polymer, electrochemistry, Ionics