The central idea is deceptively straightforward. Nickel sulfate hexahydrate, an inexpensive and widely available salt, is dissolved and spray-coated onto nickel foam, a porous metallic scaffold commonly used as a current collector in aqueous electrochemistry. Once the precursor layer is in place, a CO₂ laser operating at its familiar wavelength of 10.6 micrometers is scanned over the surface. The laser rapidly heats the coated foam, decomposing the sulfate salt and oxidizing the nickel locally, so that a crystalline NiO layer forms directly on the metallic substrate within seconds of exposure. Because the oxide grows in place, it is electrically wired to the underlying foam without any polymer binder, the insulating additive that conventional paste-based electrodes require and that adds dead weight, blocks pores, and degrades over repeated cycling.

Binder-free construction matters more than it might first appear. In a typical slurry-cast electrode, active material particles are glued to a metal foil with a polymer such as polyvinylidene fluoride, along with conductive carbon additives. Every interface introduced by these extra phases adds resistance and a potential failure point. Growing the active material directly on a conductive scaffold eliminates the binder entirely, ensuring that every bit of electrochemically active NiO is in intimate contact with the current collector. It also preserves the open pore structure of the foam, allowing electrolyte ions to flood the interior and reach active sites efficiently. The King Faisal team’s laser route achieves this architecture in a single rapid step, which is precisely what makes it attractive for scale-up.

To tune the electrode, the researchers varied the number of spray passes, which controls how much precursor, and therefore how much final NiO, is loaded onto each square centimeter of foam. Three versions were fabricated with 5, 10, and 20 spray passes. Structural and compositional analyses confirmed that the laser treatment produced crystalline NiO in all cases, but the electrochemical results revealed a clear optimum. The 10-pass electrode, with an intermediate mass loading, consistently outperformed both the lighter and heavier coatings, striking the best balance between having enough active material to store charge and keeping the layer thin enough for ions to access it all.

Tested in a concentrated 5 molar potassium hydroxide electrolyte, the optimized 10-pass electrode reached an areal capacitance of 5838 millifarads per square centimeter at a scan rate of 2 millivolts per second, and 6907 millifarads per square centimeter when driven at a current density of 10 milliamperes per square centimeter. Those figures translate into an areal capacity of 0.94 milliampere-hours per square centimeter, or a specific capacity of 249.9 milliampere-hours per gram. Areal metrics are the ones that matter for practical devices, because they measure how much charge a given footprint of electrode can store, and the reported values place this laser-written NiO among the competitive performers for nickel oxide-based supercapacitor electrodes.

Just as important as the headline numbers is how the electrode behaves under stress. The 10-pass coating maintained high capacitance even when the current density was pushed higher, a sign that ions and electrons can move through the structure without choking. In many electrode materials, capacitance collapses at high rates because the innermost active material becomes inaccessible on the timescale of the charge-discharge cycle. The laser-formed layer on nickel foam apparently avoids that pitfall, indicating efficient ion transport and fast charge transfer, likely a consequence of the direct electronic connection to the metal scaffold and the open porosity that the spray-and-laser process leaves intact.

The team then went a step further and assembled the optimized cathode into a full aqueous nickel–zinc battery, pairing it with a zinc anode in alkaline electrolyte. Nickel–zinc chemistry has attracted renewed attention as a safer, cheaper alternative to lithium-ion systems, using water-based electrolyte and abundant materials, but its performance depends heavily on the quality of the nickel-based positive electrode. The laser-fabricated NiO cathode retained its charge-storage functionality in the full-cell configuration, confirming that the material works beyond the idealized three-electrode setup used for single-electrode screening. The assembled battery delivered an areal capacity of 0.31 milliampere-hours per square centimeter, equivalent to 81.57 milliampere-hours per gram, at a current density of 0.44 milliamperes per square centimeter.

Cycling stability, the perennial challenge for oxide-based aqueous electrodes, was moderate rather than spectacular: the Ni–Zn cell retained roughly 70 percent of its capacitance after 1000 cycles. That figure leaves room for improvement, and the authors are candid that their work is a proof of concept. The demonstration was carried out on 9 square centimeter electrodes, with a preliminary extension to a 16 square centimeter full-cell electrode, showing that the laser process is not confined to tiny laboratory coupons. The researchers identify large-area coating uniformity as the key target for further optimization, since consistent precursor loading across a wide foam sheet will be essential if the technique is to move toward practical device fabrication.

According to the authors, this is the first reported case of direct CO₂ laser fabrication of NiO on nickel foam from a nickel sulfate hexahydrate precursor. That distinction matters because CO₂ lasers are among the most mature, affordable, and widely deployed industrial laser systems, already commonplace in cutting, engraving, and marking lines. Building an electrode fabrication step on top of such hardware means the barrier to adoption is low: no vacuum chambers, no electrodeposition baths, no multi-hour hydrothermal reactions in pressurized autoclaves. A spray gun and a laser scanner, in principle, could pattern active electrode material onto metal scaffolds at production speeds, and the precursor is a commodity chemical rather than a specialized organometallic reagent.

The broader significance lies in what the approach represents for energy storage manufacturing. Supercapacitors and aqueous batteries both depend on electrodes that pack a large amount of electrochemically active material into a small footprint while keeping ion and electron pathways short. Laser conversion of a sprayed precursor achieves both goals in one motion, and the identification of precursor loading as the single most important control parameter gives engineers a simple dial to tune performance. If the uniformity challenges on large areas can be solved, the same spray-and-laser recipe could plausibly be extended to other metal salts and substrates, opening a general route to binder-free oxide electrodes written directly onto current collectors. For now, the King Faisal team’s nickel oxide electrodes stand as a compelling demonstration that a tool as ordinary as a CO₂ laser can help build the next generation of energy storage hardware.

Subject of Research: CO₂ laser-assisted fabrication of binder-free NiO electrodes on nickel foam for supercapacitors and Ni–Zn batteries

Article Title: Toward scalable and direct CO₂ laser-assisted fabrication of binder-free NiO/Ni foam electrodes with high areal capacitance for supercapacitor and Ni–Zn battery applications

Article References: Toward scalable and direct CO₂ laser-assisted fabrication of binder-free NiO/Ni foam electrodes with high areal capacitance for supercapacitor and Ni–Zn battery applications. (n.d.). https://doi.org/10.1007/s11581-026-07585-x

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07585-x

Keywords: nickel oxide, nickel foam, CO₂ laser, binder-free electrode, supercapacitor, Ni–Zn battery, areal capacitance, energy storage, electrochemistry, nickel sulfate precursor, aqueous battery, laser processing

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