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: Shaalan, N. M., Ahmad, M. M., Aljaafari, A., Kumar, S., & El-Lateef, H. M. A. (2026). 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. Ionics. 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

Nickel oxide is a workhorse of modern materials science. In its bulk form it is a classic antiferromagnetic insulator, meaning its magnetic moments cancel each other out and it conducts electricity poorly. Yet when shrunk to the nanoscale, nickel oxide develops a range of useful behaviors: it catalyzes electrochemical reactions, senses gases, changes color under applied voltage, and stores charge through fast surface redox reactions. These properties have made it a popular electrode material for supercapacitors, devices that bridge the gap between batteries, which store a lot of energy but deliver it slowly, and conventional capacitors, which deliver power in a flash but hold little of it. Supercapacitors that rely on fast surface reactions, known as pseudocapacitors, are particularly promising for applications that demand rapid charge and discharge cycles, such as regenerative braking, grid buffering, and portable electronics.

The Indian team set out to tune nickel oxide by substituting magnesium atoms onto nickel lattice sites across a wide composition range, from 5 to 50 atomic percent magnesium. Magnesium is an interesting dopant choice because the magnesium ion carries the same +2 charge as nickel in nickel oxide and adopts a similar size, so it slots into the crystal lattice without introducing large amounts of charge-compensating defects. At the same time, magnesium doping is known to perturb the delicate magnetic order of nickel oxide, which normally arises from superexchange interactions mediated by oxygen atoms between nickel moments. By systematically varying the dopant level, the researchers could probe how composition influences crystal structure, magnetism, and electrochemical charge storage in one coherent study.

The synthesis itself is strikingly simple. The researchers placed the starting powders in a high-energy ball mill and milled them for 30 hours, a process in which hardened steel balls repeatedly fracture, cold-weld, and re-fracture the material, driving solid-state diffusion and forcing magnesium into the nickel oxide lattice at room temperature. The milled powders were then sintered at 500 degrees Celsius for 3 hours to relieve strain and stabilize the doped structure. This mechanochemical approach avoids the solvents, precursors, and lengthy reaction steps of solution-based synthesis, and it produces gram quantities of powder directly, which matters for any realistic electrode manufacturing process.

Structural characterization confirmed that the doping worked as intended. X-ray diffraction patterns showed that all compositions retained the face-centered cubic rock-salt structure of nickel oxide, and Rietveld refinement, a technique that fits a calculated diffraction profile to the measured one to extract precise lattice parameters and phase fractions, verified that the samples were single-phase solid solutions rather than mixtures of separate nickel oxide and magnesium oxide phases. The lattice parameter evolved systematically with magnesium content, consistent with successful substitution on the nickel sublattice. Maintaining a single crystalline phase across such a wide doping range is important because grain boundaries or secondary phases can scatter charge carriers, degrade magnetic coherence, and add parasitic resistance that undermines electrode performance.

The magnetic results are perhaps the most scientifically intriguing part of the study. Bulk nickel oxide is antiferromagnetic, yet all of the doped nanoparticle samples displayed moderate ferromagnetism at room temperature, with the saturation magnetization reaching a maximum of 6 electromagnetic units per gram at the highest doping level of 50 percent magnesium. The authors attribute this ferromagnetism to the coexistence of mixed nickel valence states, specifically Ni2+ and Ni3+, within the doped samples. Mixed valence in nickel oxides is well known to create charge-carrier-mediated exchange interactions that can tip the balance from antiferromagnetic order toward ferromagnetic alignment, and nanoscale effects such as broken exchange symmetry at particle surfaces amplify the response. Room-temperature ferromagnetism in a non-magnetic host oxide is the hallmark of the dilute magnetic oxide family of materials, which are candidates for spintronics, a technology that aims to manipulate electron spin as well as charge in devices.

On the energy storage front, the doped nanoparticles performed as pseudocapacitive electrodes with capacitance that climbed steadily with magnesium content. The specific capacitance values were 142 farads per gram for 5 percent doping, 162 farads per gram for 10 percent, 210 farads per gram for 30 percent, and 245 farads per gram for 40 percent magnesium. The best electrode, the 40 percent magnesium-doped sample, delivered a power density of 660.396 watts per kilogram and an energy density of 5.63 watt-hours per kilogram at a slow scan rate of 1 millivolt per second, demonstrating good pseudocapacitive behavior. These numbers place the ball-milled powders in a competitive range for nickel oxide-based electrodes, particularly given the simplicity of the synthesis. The trend with doping suggests that magnesium substitution increases the density of electrochemically active nickel sites or improves ion and electron transport within the powder, allowing more of the material’s theoretical charge storage capacity to be accessed during cycling.

Durability is where many pseudocapacitive metal oxide electrodes stumble, because repeated insertion and removal of ions from the electrolyte gradually pulverizes or dissolves the active material. The Mg-doped nickel oxide electrodes proved remarkably resilient: every doped composition retained 97 percent of its initial capacitance after 1000 charge-discharge cycles. That level of retention over a thousand cycles indicates that the mechanochemically synthesized particles, once sintered, form a mechanically and chemically stable framework for the surface redox reactions that store charge. For practical supercapacitors, which may endure hundreds of thousands of cycles, further longevity testing will be needed, but a 97 percent retention benchmark after 1000 cycles is a strong early indicator of robustness.

The study also connects to a broader research landscape in which doped nickel oxide nanostructures are being engineered for multiple applications simultaneously. Recent work has explored zinc, manganese, cobalt, iron, tungsten, and rare-earth dopants in nickel oxide for supercapacitors, photocatalysis, gas sensing, and electrochromic devices, while magnesium-doped nickel oxide has separately found roles as a hole transport layer in quantum dot light-emitting diodes and in photo-supercapacitor heterojunctions. What distinguishes the new study is the combination of a wide doping range, a solvent-free synthesis, and a three-way characterization of structure, magnetism, and electrochemistry in the same samples. That combination allows the authors to argue credibly that a single material platform could serve both energy storage and spintronic applications, depending on how the composition is tuned.

There remain caveats and open questions. The specific capacitances reported, while respectable, are below the highest values achieved by nanostructured nickel oxide composites incorporating conductive carbon scaffolds, and the energy density of 5.63 watt-hours per kilogram reflects the intrinsic limits of pseudocapacitive oxides tested as powder electrodes. The precise microscopic mechanism linking mixed nickel valence to the observed ferromagnetism would benefit from direct spectroscopic confirmation of the Ni3+ fraction, and the cycling data, while encouraging, cover a relatively short window by commercial standards. Nevertheless, the demonstration that a 30-hour ball mill and a modest 500-degree anneal can produce phase-pure, magnetically active, electrochemically durable doped nickel oxide is a meaningful result. If the mechanochemical route can be scaled to kilogram batches without losing performance, magnesium-doped nickel oxide could find itself competing for a place in next-generation supercapacitor electrodes and, more speculatively, in the spintronic devices of the future.

Subject of Research: Magnesium-doped nickel oxide nanoparticles synthesized by ball milling for supercapacitor electrodes and room-temperature ferromagnetism

Article Title: Structural, magnetic, and supercapacitor properties of Mg-doped NiO nanoparticles prepared by the ball milling method

Article References: Kisan, B., Das, R. K., Sarangi, T. K., Dash, B. B., Bhuyan, R. K., Kumar, S., Gautam, D., Kand, L., & Naik, K. K. (2026). Structural, magnetic, and supercapacitor properties of Mg-doped NiO nanoparticles prepared by the ball milling method. Ionics. https://doi.org/10.1007/s11581-026-07577-x

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07577-x

Keywords: nickel oxide, magnesium doping, nanoparticles, ball milling, supercapacitor, pseudocapacitance, ferromagnetism, energy storage, spintronics, X-ray diffraction, Rietveld refinement, mixed valence

The synthesis relied on the polyol method, a versatile wet-chemical technique in which ethylene glycol serves simultaneously as solvent and reducing agent. The researchers preheated the glycol to 160 degrees Celsius, then introduced silver nitrate together with polyvinylpyrrolidone, a polymer that caps the growing crystals and steers them into long, straight wires. Seed particles formed first, and anisotropic growth followed, yielding silver nanowires with diameters of roughly 60 to 75 nanometres and lengths on the micrometre scale. Zinc acetate solutions of two different concentrations, 0.1 and 0.3 molar, were then added to grow the zinc oxide coating, producing samples labelled Z1 and Z3. For the mixed-oxide variants, zinc acetate and nickel acetate were injected together, giving the ZNM1 and ZNM3 nanocables.

Scanning electron microscopy revealed how dramatically the shell chemistry reshapes the architecture. Pure silver nanowires displayed smooth surfaces and diameters up to about 75 nanometres, while zinc-coated cables thickened to 75–85 nanometres, their surfaces studded with cubic nanoparticles and spherical particles ranging from around 100 nanometres to a micron. Adding nickel pushed the diameters to 85–95 nanometres and produced a striking zoo of morphologies, including irregular hexagonal crystals, quadrangular pyramidal crystals and clustered spheres spanning one to three microns. The team attributes this heterogeneity to nickel’s influence on nucleation dynamics and to synergistic effects between the two oxide-forming metals that alter surface energy minimisation during growth.

Transmission electron microscopy confirmed the coaxial design at higher resolution. The images showed elongated one-dimensional structures with a crystalline metallic silver core and a continuous oxide shell, with uniform contrast along their lengths indicating homogeneous composition. At low precursor concentrations, isotropic shapes such as cubes and triangular bipyramids dominated, whereas higher concentrations favoured elongated rods and wires. Some samples showed partial fragmentation and aggregation attributed to mechanical stress during grid preparation, and the thickest cables reached diameters near 85 nanometres with lengths up to ten micrometres, sometimes bundling together with ultrathin companions attached.

X-ray diffraction established the crystallographic foundations of the composites. Peaks at 38.2 and 44.7 degrees corresponded to the (111) and (200) planes of face-centred cubic silver, with no impurity phases detected. Additional reflections at 31.82 and 34.33 degrees matched the (100) and (002) planes of crystalline zinc oxide. Applying the Debye–Scherrer equation gave average crystallite sizes of about 35 to 36 nanometres, and the analysis showed that crystallite size shrank as the zinc and zinc/nickel salt content increased. Because the silver ion radius of 114 picometres exceeds that of zinc at 74 picometres, substituting silver into the lattice expands the unit cell, and the measured lattice parameters tracked these substitutions. An intense peak at 38.02 degrees signalled anisotropic growth of silver along the (111) direction, with the nickel/zinc shell growing coaxially in the same phase, evidence of atomic-level alloying between the metals.

Optical measurements highlighted the plasmonic fingerprints of the silver core and the electronic tuning imposed by the shells. The bare nanowires showed sharp surface plasmon resonance peaks at 356 and 386 nanometres from the transverse mode, while the zinc-coated cables shifted these features, with a peak at 319 nanometres and a prominent band at 358 nanometres, and a slight redshift appearing as zinc concentration rose. Band gap energies fell steadily with increasing metal doping, from 3.220 electronvolts for Z1 down to 2.8 electronvolts for the most heavily doped mixed-oxide sample, a narrowing that reflects deliberate modification of the electronic structure. Photoluminescence spectroscopy added further nuance: band-edge emission sat at 380 nanometres for Ag@Zn and shifted marginally to 383 nanometres with nickel, while deep-trap emission linked to defect states moved from 522 to 513 nanometres. Crucially, the composite catalysts showed much weaker photoluminescence intensity than the bare wires, indicating that the silver cores suppress electron–hole recombination and lengthen the lifetime of photoexcited charge carriers, a property that directly benefits catalysis.

The catalytic showcase was the reduction of p-nitrophenol to p-aminophenol by sodium borohydride, a benchmark reaction for water treatment because p-nitrophenol is a persistent organic pollutant. In the untreated mixture, the yellow p-nitrophenolate ion absorbs strongly at 400 nanometres; as the reaction proceeds, this peak fades. The uncoated silver nanowires needed 44 minutes to complete the conversion, the zinc-coated cables cut this to 30 and 24 minutes for Z1 and Z3, and the nickel-containing composites performed best of all, finishing in 16 and 12 minutes for ZNM1 and ZNM3. A clear isosbestic point near 314 nanometres appeared in all spectra, a spectroscopic signature of a clean, direct conversion pathway. The team notes that these catalysts compare favourably with previously reported systems for the same transformation, and they emphasise that zinc offers a cheap, abundant and comparatively non-toxic alternative to more hazardous transition-metal catalysts.

Electrochemical testing painted an equally encouraging picture for energy storage. Cyclic voltammetry in potassium hydroxide electrolyte, using a three-electrode configuration with the nanocables deposited on nickel foam, revealed distinct redox peaks characteristic of pseudocapacitive behaviour. Bare silver nanowires produced current responses of roughly 20 microamperes with symmetrical peaks around the zero-current axis, corresponding to reversible silver oxidation and reduction. The zinc oxide coating raised the current density to about 35 microamperes, improving electron transfer kinetics, while the Ag@Zn/Ni composites delivered the highest response at approximately 60 microamperes, with a broad reduction peak near minus 0.8 volts and multiple oxidation peaks extending up to plus 1.4 volts, reflecting overlapping redox processes from silver, zinc oxide and nickel oxide. Electrochemical impedance spectroscopy, spanning frequencies from 10^-2 to 10^5 hertz, reinforced the story: the silver-coated composites showed the lowest equivalent series resistance, the smallest high-frequency semicircles indicating minimal charge transfer resistance, and shallow low-frequency slopes consistent with low Warburg resistance, all hallmarks of fast, efficient electron transport.

Taken together, the results argue that the whole of these nanocables exceeds the sum of their parts. The silver core supplies conductivity, plasmonic light harvesting and charge-separation assistance; the zinc oxide shell contributes wide-band-gap semiconducting behaviour, chemical stability and catalytic sites; and the nickel oxide component adds high redox activity that multiplies the pseudocapacitive response. Because the shell thickness and composition can be tuned simply by adjusting precursor concentrations, the platform offers a tunable route to bimetallic and mixed-oxide nanostructures without exotic equipment or scarce raw materials, and the polyol approach could plausibly be extended to other metal combinations. The authors suggest the nanocables could serve as electrodes for advanced electronic and energy storage devices, with potential reach into medical, environmental and fuel-cell technologies. For a field searching for ways to stretch precious silver further while squeezing more performance out of earth-abundant oxides, these cable-like hybrids offer a compelling blueprint.

Subject of Research: Synthesis and characterization of silver-core zinc/nickel oxide coaxial nanocables for catalytic and electrochemical applications

Article Title: Hybridized Ag@Zn/Ni nanocables: synergistic enhancements in optical, catalytic, and electrochemical behaviour

Article References: Sharif, S., Ahmad, Z., Choudhary, M. A., Irshad, M. A., Nisar, F., Al-Hussain, S. A., Irfan, A., & Zaki, M. E. A. (2026). Hybridized Ag@Zn/Ni nanocables: synergistic enhancements in optical, catalytic, and electrochemical behaviour. Journal of Saudi Chemical Society, 30(2), Article 21. https://doi.org/10.1007/s44442-026-00069-7

Image Credits: AI Generated

DOI: 10.1007/s44442-026-00069-7

Keywords: nanocables, silver nanowires, zinc oxide, nickel oxide, core-shell nanostructures, polyol method, p-nitrophenol reduction, pseudocapacitance, cyclic voltammetry, electrochemical impedance spectroscopy, surface plasmon resonance, photoluminescence

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

The research group, led by Lirui Sun and Zhaoyang Chen of the National Synchrotron Radiation Laboratory at the University of Science and Technology of China, together with Lidong Zhang and colleagues, prepared four catalysts under an identical protocol: pristine cerium dioxide, and the same oxide modified with iron, cobalt or nickel. Ceria is a fascinating material in its own right. Its fluorite crystal lattice can easily shed and reabsorb oxygen atoms, cycling between Ce4+ and Ce3+ oxidation states, which makes it a natural oxygen reservoir. In ammonia-SCR, that mobility is a double-edged sword. Lattice oxygen is needed to activate ammonia and nitric oxide, but if the oxygen is too aggressive it oxidises ammonia all the way to nitrogen dioxide or even nitrous oxide, destroying the selectivity that the reaction depends on.

The baseline results were sobering. Untreated cerium dioxide managed a peak nitrogen oxide conversion of just 14.83 percent at 300 degrees Celsius under a realistic oxygen-rich feed containing 0.5 percent NO, 0.5 percent NH3 and 5 percent O2. Worse, when the temperature rose to 350 degrees Celsius, conversion collapsed to 6.12 percent while the yield of nitrogen dioxide climbed to 24.92 percent. In other words, the bare catalyst was not merely inefficient — it was actively converting the desired reaction into over-oxidation, producing the very species that fast SCR chemistry needs only in carefully balanced amounts. Too much NO2 alongside insufficient NO conversion means the ammonia is wasted on side reactions rather than being stitched onto nitrogen oxide to form harmless nitrogen and water.

Adding iron changed the picture dramatically. The iron-modified ceria, dubbed FeCe, reached 79.8 percent nitrogen oxide conversion at 300 degrees Celsius and still delivered 75.7 percent at 350 degrees Celsius, while keeping nitrogen dioxide yield down to just 8.0 percent. That combination is the holy grail of this field: high activity and high over-oxidation resistance at the same time. Most catalysts trade one against the other — push the conversion up and the unwanted oxidation products follow. The FeCe sample broke that trade-off, sustaining strong performance across the temperature window where industrial flue gases typically sit.

The other two dopants told a more cautionary tale. Nickel modification shifted the activity maximum down to 250 degrees Celsius, where conversion peaked at 54.0 percent, but the catalyst fell off a cliff at higher temperatures, dropping to a mere 0.3 percent conversion at 350 degrees Celsius. Cobalt modification produced only a narrow low-temperature operating window before failing. Perhaps most striking was what the conventional characterisation techniques revealed. By the usual proxies — X-ray diffraction, high-resolution transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy — the nickel-modified sample displayed the strongest defect signatures of all three doped materials. By every standard metric of oxygen vacancy abundance, NiCe should have been the star of the show. Instead, it underperformed the iron catalyst above 250 degrees Celsius by a wide margin.

That paradox is the intellectual heart of the study, and the authors resolved it by looking more carefully at dopant speciation — the chemical form each metal actually adopts inside the ceria host. The three transition metals, despite sitting side by side in the periodic table, chose three entirely different fates. Iron dissolved into the ceria lattice, substituting for cerium atoms and generating oxygen vacancies deep in the bulk crystal. Nickel refused to incorporate and instead precipitated as discrete nickel oxide particles, concentrating vacancies at the NiO/CeO2 interface. Cobalt phase-separated into cobalt oxide, a strongly oxidising spinel phase with its own aggressive oxygen chemistry. Three metals, three architectures, three completely different ways of supplying and positioning reactive oxygen.

Density functional theory calculations then explained why location matters more than quantity. The lattice-substituted iron site combined the lowest oxygen vacancy formation energy among the tested configurations with the widest calculated free-energy separation between two competing reaction channels: the selective pathway in which activated ammonia couples with nitric oxide to form nitrogen, and the non-selective pathway in which lattice oxygen strips hydrogen from ammonia, driving over-oxidation. When the vacancy sits in the bulk lattice near an iron centre, the energetic landscape favours N–N coupling and penalises dehydrogenation. When vacancies cluster at an external interface, as in the nickel case, the local oxygen supply becomes too reactive, tipping the balance toward ammonia destruction at elevated temperatures — which is exactly why NiCe, despite its abundant defect signatures, fell apart above 250 degrees Celsius.

The implications reach well beyond this particular reaction. Oxygen vacancies have become the darling of defect engineering across catalysis, energy storage and electronics, and the field has largely operated on the assumption that more vacancies mean better performance. This study delivers a sharp corrective: vacancy concentration is a crude proxy, and vacancy location is the variable that actually governs the activity–selectivity balance. A catalyst bristling with interface vacancies can look superb under spectroscopic scrutiny and still fail in a reactor, while a lattice-doped material with fewer but better-placed defects can dominate. For ceria-based systems, the message is that dopants must be chosen not just for their electronic properties but for their willingness to enter the lattice rather than segregate out of it.

There is also a practical dimension. Vanadium-based SCR catalysts, typically vanadium pentoxide on titania with tungsten or molybdenum promoters, operate effectively only above roughly 300 degrees Celsius and suffer from vanadium toxicity and ammonia slip issues. A ceria–iron system that sustains nearly 80 percent conversion at 300 degrees Celsius with strong resistance to over-oxidation points toward vanadium-free formulations that could work closer to the source of emissions, where flue gases are cooler, reducing reheating costs. The work was supported by the National Natural Science Foundation of China and the Natural Science Foundation of Anhui Province, and the authors included collaborators from the China Automotive Technology and Research Center, suggesting an eye toward mobile-source applications where low-temperature operation is especially valuable.

What makes this study resonate is its methodological discipline. By preparing all four catalysts under one identical protocol and evaluating them under one identical feed, the team eliminated the confounding variables that plague much of the comparative catalysis literature. The combination of structural characterisation, careful activity testing and first-principles energetics produced a self-consistent story in which every observation — the collapse of bare ceria, the triumph of iron, the paradox of nickel, the narrow window of cobalt — follows from a single principle. Oxygen vacancies are not interchangeable widgets to be counted; they are positional players whose placement in the crystal determines whether they supply oxygen gently enough to build nitrogen bonds or aggressively enough to burn the reductant. As researchers pursue next-generation environmental catalysts, that distinction may prove to be the difference between a promising material and a deployable one.

Subject of Research: Dopant speciation and oxygen-vacancy location in Fe-, Co- and Ni-modified CeO2 catalysts for low-temperature NH3-SCR of nitrogen oxides

Article Title: Unraveling the Role of Dopant Speciation in Oxygen-Vacancy Location and Lattice-Oxygen Supply over Fe-, Co- and Ni-Modified CeO2 NH3-SCR Catalysts

Article References: Sun, L., Chen, Z., Xu, W., Zhang, L., & Li, Z. (2026). Unraveling the Role of Dopant Speciation in Oxygen-Vacancy Location and Lattice-Oxygen Supply over Fe-, Co- and Ni-Modified CeO2 NH3-SCR Catalysts. Catalysis Letters, 156(10), Article 288. https://doi.org/10.1007/s10562-026-05532-z

Image Credits: AI Generated

DOI: 10.1007/s10562-026-05532-z

Keywords: NH3-SCR, ceria, oxygen vacancies, dopant speciation, lattice oxygen, iron doping, nickel oxide, cobalt oxide, DFT calculations, nitrogen oxides, over-oxidation resistance, vanadium-free catalysts

The study, published in the Journal of Nanoparticle Research, was designed around a deceptively simple question: how does the copper fraction in a nickel oxide film change its ability to catalyze the methanol oxidation reaction in alkaline solution? The team deposited four compositions on fluorine-doped tin oxide glass, a transparent conducting substrate commonly used in photoelectrochemistry. A DC power source sputtered the nickel oxide target at a fixed 200 watts, while a separate radio-frequency power supply drove a copper target at 0, 40, 50, and 60 watts, corresponding to nominal copper contents of 0, 2.5, 4, and 7 percent. Everything else was held constant: a working pressure of 5 by 10 to the minus 3 torr, 400 seconds of deposition, 20 standard cubic centimeters per minute of argon, and a target-to-substrate distance of 14 centimeters. This kind of physical vapor deposition matters because it produces adherent, pinhole-free films whose composition and thickness can be dialled in precisely, unlike many solution-based routes where morphology is hard to reproduce.

Structural characterization showed that the copper was not forming a separate metallic phase. X-ray diffraction revealed only the cubic bunsenite phase of nickel oxide, with reflections from the (111), (200), and (220) crystal planes, and no peaks attributable to metallic copper. Instead, copper appeared to occupy interstitial and substitutional positions within the nickel oxide lattice, filling defects in the nonstoichiometric framework. The evidence was written into the peak shapes: the diffraction peaks broadened and weakened as copper content rose, and the average crystallite size, calculated with the Debye-Scherrer equation, shrank from 18.12 nanometers for pristine nickel oxide to 7.42 nanometers at 7 percent copper. Lattice strain climbed from 2.1 by 10 to the minus 4 to 5.31 by 10 to the minus 4, and the dislocation density rose nearly sevenfold, both signatures of a lattice that has been subtly disrupted by foreign atoms. Electron microscopy confirmed the trend, showing progressively rougher, more compact, and more agglomerated surfaces as the dopant level increased.

One consequence of the co-sputtering recipe deserves particular attention because it complicates the interpretation of catalytic data. Film thickness grew systematically with copper loading, from 53 nanometers for pristine nickel oxide to 90, 121, and 180 nanometers for the 2.5, 4, and 7 percent films. More material on the electrode naturally means more geometric current, so the researchers took the unusual and commendable step of normalizing their methanol oxidation currents in two additional ways: per unit of film thickness, and per unit of electrochemically active surface area estimated from double-layer capacitance measurements. The capacitance values rose from 0.226 to 0.44 millifarads per square centimeter across the composition series, yielding active surface areas between 5.65 and 11.12 square centimeters. Even after this careful normalization, the 7 percent copper film remained roughly 2.5 times more active than pristine nickel oxide, while the 2.5 and 4 percent films showed the highest currents per unit thickness and per active area respectively. The conclusion was nuanced: copper incorporation, enlarged active area, film growth, and improved interfacial kinetics all contributed, and no single factor explains the whole story.

Optical measurements pointed to a fundamental electronic reason for the improvement. Ultraviolet-visible spectroscopy combined with Tauc analysis showed that the optical band gap narrowed steadily as copper content increased, from 3.64 electron volts for pure nickel oxide to 3.24 electron volts at 7 percent doping. Band gap narrowing in doped nickel oxide is generally attributed to localized dopant states overlapping the band edges and to improved crystallization, and narrower gaps translate directly into better electronic conductivity through the film. For a p-type semiconductor like nickel oxide, which must shuttle holes and electrons between the current collector and the electrolyte interface during every catalytic cycle, that conductivity gain is not an academic nicety. It means less internal resistance, faster delivery of charge to surface reaction sites, and lower overpotentials, which is exactly what the electrochemical measurements went on to confirm.

Cyclic voltammetry in 1 molar sodium hydroxide exposed the redox machinery of the films. All four compositions showed anodic and cathodic peaks associated with the nickel(II) to nickel(III) and copper(I) to copper(II) couples, meaning that both metals contribute electroactive centers. Peak currents scaled linearly with the square root of the scan rate, indicating that hydroxide diffusion into the film pores, rather than some surface limitation, governed the redox process at the electrode-electrolyte boundary. When methanol was added, every film responded, but the doped films responded dramatically more, with anodic and cathodic current densities climbing in step with copper content. Onset potentials shifted to more negative values as methanol concentration rose from 0.25 to 3 molar, and the 7 percent copper film recorded the highest current density in 1 molar methanol, around 32 milliamperes per square centimeter.

Kinetic analysis tightened the picture. The team recorded linear sweep voltammograms at a deliberately slow scan rate of 5 millivolts per second, a quasi-steady condition that minimizes capacitive contributions from the nickel hydroxide to nickel oxyhydroxide transformation and yields Tafel slopes that reflect true faradaic kinetics. Pristine nickel oxide gave a slope of 178 millivolts per decade. Doping with just 2.5 percent copper dropped it to 127, and 7 percent copper brought it down to 120 millivolts per decade, a total reduction of about 32.5 percent. That final value corresponds to a charge-transfer coefficient of 0.5, consistent with the first electron transfer step dominating the reaction kinetics. Interestingly, the largest kinetic gain arrived at the lowest dopant loading, with the incremental benefit tapering off at 4 and 7 percent, suggesting the population of accessible surface redox sites begins to saturate. The authors attribute the enhancement to a bifunctional synergy: nickel centers cycle into the active nickel oxyhydroxide species that dehydrogenate methanol, while copper sites, present as mixed copper(I) and copper(II) states according to X-ray photoelectron spectroscopy, adsorb hydroxyl species at lower overpotentials and thereby strip carbonaceous intermediates from neighboring nickel sites before they can block them.

Electrochemical impedance spectroscopy, recorded at 0.6 volts in 1 molar sodium hydroxide with 1 molar methanol, backed this mechanism quantitatively. The fitted charge-transfer resistance decreased steadily with doping level, reflecting the greater density of redox-active nickel and copper sites on the film surfaces. A carbon monoxide stripping experiment delivered perhaps the most convincing evidence of poisoning resistance: the 7 percent copper film showed a clean stripping peak at 0.43 volts, and, strikingly, no reverse oxidation peak appeared during the backward scan, indicating negligible accumulation of adsorbed carbon monoxide intermediates. That absence of a backward peak is exactly the behavior fuel cell engineers want to see, because it means the catalyst surface stays clear and available for fresh fuel molecules rather than becoming choked with its own reaction byproducts.

Durability, the graveyard of many promising electrocatalysts, was tested on three fronts. Chronoamperometry at 0.6 volts for a full 12 hours showed only a 5.7 percent decline in current for the 7 percent copper film, with the small initial drop attributable to intermediate adsorption and local methanol depletion near the electrode surface. After 1000 cyclic voltammetry cycles the electrode retained 94.3 percent of its current, reaching 30.2 milliamperes per square centimeter, although the anodic oxidation feature shifted from roughly 0.40 to 0.49 volts. The authors interpret this shift not as degradation but as the gradual accumulation of adsorbed carbonaceous intermediates and reorganization of the surface oxyhydroxide layer, a reading supported by their post-mortem analyses. Inductively coupled plasma optical emission spectroscopy of the electrolyte after testing found nickel concentrations below the detection limit and copper at just 0.051 parts per million, and X-ray photoelectron spectra taken before and after operation showed the nickel and copper oxidation states essentially intact, confirming that the redox-active surface survives chemically.

What makes this work resonate beyond a single materials system is its recipe-like transferability. Rather than hunting for exotic compounds, the researchers demonstrated that a mainstream physical deposition technique, a cheap transition metal dopant, and careful normalization of electrochemical data can jointly push a simple nickel oxide film to performance levels that compete with far more elaborate catalysts. The band gap engineering, the bifunctional nickel-copper mechanism, and the documented poison tolerance together outline a practical roadmap for alkaline direct methanol fuel cells that sidestep platinum entirely. The authors point toward the logical next steps: integrating these optimized films into membrane electrode assemblies and testing them in full fuel cell stacks, where real operating conditions will judge whether laboratory elegance translates into engineered power. If it does, the humble nickel oxide lattice, nudged by a few percent of copper, may find itself at the heart of a new generation of liquid-fuel clean energy devices.

Subject of Research: Copper-doped nickel oxide thin film electrocatalysts for the methanol oxidation reaction in direct methanol fuel cells

Article Title: Tuning methanol oxidation activity: impact of Cu content on sputtered NiO thin film electrocatalysts

Article References: Salah, A. M., Hussein, M. R., Kotp, A. A., Farghali, A. A., & Abdel-wahab, M. S. (2026). Tuning methanol oxidation activity: impact of Cu content on sputtered NiO thin film electrocatalysts. Journal of Nanoparticle Research, 28(10), Article 250. https://doi.org/10.1007/s11051-026-06765-0

Image Credits: AI Generated

DOI: 10.1007/s11051-026-06765-0

Keywords: Cu-doped NiO, methanol oxidation reaction, direct methanol fuel cells, electrocatalysis, co-sputtering deposition, thin films, band gap engineering, Tafel analysis, alkaline electrolyte, nickel oxide, carbon monoxide tolerance, electrochemical impedance spectroscopy

The central problem the team set out to solve is a familiar one in electrochemistry. Nickel oxide, a transition metal oxide, carries an exceptionally high theoretical specific capacitance, meaning that in principle each gram of the material can store a large amount of charge through fast, reversible surface redox reactions in which nickel switches between oxidation states. In practice, however, pristine NiO is a poor electrical conductor. Electrons struggle to move through the oxide bulk and reach the active sites where charge storage occurs, so much of the theoretical capacity is never realized. Electrodes made from NiO alone also tend to degrade as repeated swelling and shrinking during cycling gradually destroys their structure.

To break through this bottleneck, the researchers synthesized the ternary hybrid using a two-stage route that combines hydrothermal synthesis with mechanical grinding and a solution-assisted physical mixing method. The hydrothermal step, in which reactions proceed in a sealed vessel above the boiling point of water, is a well-established way to grow crystalline metal oxide nanostructures with controlled morphology. Mechanical grinding and solution mixing then integrate the oxide with the two organic partners, producing a composite in which each component contributes a distinct function rather than merely diluting the others.

The logic of the three-way partnership is what makes the design compelling. Nickel oxide provides the redox engine, the sites of pseudocapacitive charge storage where fast faradaic reactions occur at or near the electrode surface. Polyaniline, a conducting polymer often abbreviated PANI, supplies the electrical wiring, offering a conductive pathway that lets electrons flow efficiently between active sites and the current collector. Cellulose, the abundant biopolymer that forms the structural skeleton of plants, contributes a flexible, porous network that keeps the electrode mechanically coherent, prevents aggregation of the active particles, and opens channels through which electrolyte ions can penetrate deep into the material. In effect, the composite behaves like a well-designed building: a strong frame, efficient wiring, and open corridors all working together.

The electrochemical results reported for the optimized NiO/Cellulose/PANI electrode are striking. At a scan rate of 10 millivolts per second in cyclic voltammetry, the electrode achieved a specific capacitance of 478.45 farads per gram, a figure that places it among the competitive performers for nickel oxide-based hybrid electrodes. Cyclic voltammetry measures how much charge the electrode can store as the applied voltage is swept back and forth, and the scan rate matters: slower sweeps allow ions more time to access every pore, while faster sweeps reveal how well the material keeps up under demanding conditions. A high capacitance at a moderate scan rate suggests that the porous cellulose network and the conductive polymer are genuinely improving ion and electron transport, not just adding mass.

Durability, often the Achilles heel of pseudocapacitive materials, also proved impressive. After 6000 charge-discharge cycles, the electrode retained 98 percent of its initial capacitance. That near-total retention over thousands of cycles indicates that the hybrid architecture successfully buffers the mechanical stresses and chemical degradation that normally erode performance. The cellulose scaffold appears to act as a stabilizing matrix, holding the NiO particles in place and accommodating the volume changes that accompany repeated redox reactions, while PANI maintains continuous electrical contact even as the structure flexes.

Perhaps the most consequential numbers come from the full energy-storage assessment. The electrode delivered an energy density of 37.98 watt-hours per kilogram at a power density of 825.36 watts per kilogram. Energy density describes how much energy the device can store, the property that determines how long it can power something; power density describes how quickly that energy can be delivered, the property that determines how fast it can charge or how hard it can push. Achieving nearly 38 watt-hours per kilogram while sustaining more than 800 watts per kilogram is a notable combination, because these two metrics usually pull against each other. Designs that maximize energy often sacrifice rate capability, and vice versa. The balanced performance here suggests the hybrid electrode can handle both rapid charge-discharge cycling and substantial energy delivery, exactly the profile needed for applications ranging from regenerative braking to grid frequency regulation and portable electronics.

The sustainability angle is more than a marketing flourish. Cellulose is among the most abundant renewable materials on Earth, and incorporating it into electrode architectures reduces reliance on purely synthetic or fossil-derived components while adding functionality that synthetic binders cannot match. Previous work has shown that biomass-derived carbons and cellulose-supported metal oxide arrays can serve as flexible, free-standing electrodes, and the present study extends that principle into a ternary design where the biopolymer is an integral part of the charge-storage mechanism rather than a passive filler. The synthesis route itself, relying on hydrothermal processing and simple mechanical and solution-based mixing, avoids exotic precursors and energy-intensive fabrication steps, which matters if such materials are ever to be manufactured at scale.

The broader context of this research is a field in rapid motion. Transition metal oxides, layered double hydroxides, sulfides, conducting polymers, and biomass-derived carbons have all been pressed into service as supercapacitor electrodes, and hybrid designs that combine two or three of these classes have repeatedly outperformed single-component materials. Metal-organic framework derivatives, MXene-hydrogel composites, and photo-assisted supercapacitor architectures represent parallel frontiers. What distinguishes the NiO/Cellulose/PANI work is its explicit attempt to pair high electrochemical performance with a sustainable materials platform, addressing both the technical and environmental dimensions of the energy-storage challenge in a single design.

There remain, of course, the usual caveats that separate laboratory electrodes from commercial devices. The reported measurements were obtained under controlled conditions, and translating a promising electrode into a full supercapacitor cell requires optimizing the counter electrode, the electrolyte, the separator, and the packaging, each of which imposes its own losses. Cycle life beyond 6000 cycles, performance at elevated temperatures, and behavior under mechanical stress in flexible formats all warrant further study. Nevertheless, the combination of high specific capacitance, exceptional capacitance retention, and a strong energy-power balance achieved with renewable cellulose and a scalable synthesis route marks this ternary hybrid as a serious candidate for next-generation energy storage. As the demand for fast-charging, long-lived, and environmentally responsible storage devices accelerates, designs that reconcile performance with sustainability, like the NiO/Cellulose/PANI electrode, are likely to define the direction of the field.

Subject of Research: A ternary NiO/Cellulose/PANI hybrid electrode material for high-performance sustainable supercapacitors

Article Title: Ternary hybrid electrode of NiO/Cellulose/PANI: a sustainable platform for high-performance supercapacitors

Article References: Otaif, H. Y., Alhashem, Z. H., Sadaf, S., Ahmed, I., Alam, M. W., & Iqbal, M. (2026). Ternary hybrid electrode of NiO/Cellulose/PANI: a sustainable platform for high-performance supercapacitors. Ionics. https://doi.org/10.1007/s11581-026-07534-8

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07534-8

Keywords: supercapacitors, nickel oxide, cellulose, polyaniline, hybrid electrode, energy density, specific capacitance, pseudocapacitance, energy storage, sustainable materials, hydrothermal synthesis, electrochemistry

The importance of nickel oxide in inverted, or p-i-n, perovskite solar cells is difficult to overstate. In this architecture, the light-absorbing perovskite layer sits atop a hole-transporting layer, and every photon-generated hole must pass cleanly through that buried interface before it can be collected. Nickel oxide is prized for its chemical stability, wide bandgap, deep valence band and low cost, but depositing it uniformly over large areas has always involved a painful trade-off. Solution-based chemical bath deposition can cover large, even textured substrates conformally, but the rapid, disorderly hydrolysis of nickel salts tends to produce films riddled with pinholes and aggregates. Vacuum techniques such as sputtering or atomic layer deposition offer denser films but are slower, more expensive and harder to marry with high-throughput manufacturing.

The Nankai-led team attacked the problem at the level of crystallization kinetics rather than after the fact. Their insight was to introduce potassium tartrate, a ligand that binds nickel ions into exceptionally stable coordination complexes in the deposition bath. By sequestering a fraction of the free nickel ions, the ligand suppresses the chaotic, uncontrolled aggregation that normally plagues chemical bath growth and halves the hydrolysis rate constant, slowing it to 0.124 liters per mole per minute. That seemingly modest number is the heart of the result: slower, more orderly crystallization gives the film time to nucleate evenly across the substrate and to grow into a dense, continuous layer rather than a patchwork of islands and voids.

The kinetic control pays off in a striking way at the nanoscale. The resulting films are composed of remarkably refined crystallites measuring just 4.8 nanometers. For most materials, smaller grains would sound like a disadvantage, but here the fine nanostructure is precisely the point. Shrinking the crystallites maximizes the density of grain boundaries reaching the surface, and each boundary terminates in hydroxyl groups. These hydroxyl terminations serve as robust chemical anchoring sites for self-assembled monolayers, the carbazole-based phosphonic acid molecules that have become the workhorses of modern perovskite photovoltaics. A denser carpet of anchoring sites allows the monolayer to form a chemically cohesive, defect-suppressed buried interface, where charge extraction is fast and non-radiative recombination is minimized.

The team backed this picture with extensive interfacial characterization and charge-carrier dynamics measurements on nickel oxide monolayer stacks, supported by density functional theory calculations and molecular dynamics simulations that probed the coordination chemistry and the energetics of monolayer attachment. The calculations and experiments together paint a consistent story: the potassium tartrate-regulated surface is not merely smoother, it is chemically better matched to the self-assembled monolayer, so the molecules graft uniformly instead of clustering on reactive patches. Fewer clustered molecules means fewer shunting pathways and fewer deep traps, which translates directly into higher open-circuit voltage and fill factor.

The device numbers speak for themselves. Champion inverted cells built on the treated nickel oxide reached a power conversion efficiency of 27.40 percent, and an independent certified measurement returned a reverse-scan efficiency of 27.35 percent, placing these single-junction cells among the very best inverted devices ever reported. More importantly for commercialization, the advantage survived scale-up. A 17.7-square-centimeter mini-module achieved 23.42 percent efficiency, and a substantially larger 81.5-square-centimeter module still delivered 21.97 percent. In the perovskite field, where efficiency typically collapses as area grows because coating non-uniformities and interconnect losses compound, retaining better than 22 percent on a module the size of a postcard is a genuine milestone.

Efficiency alone, however, has never been the sole barrier to market entry. Stability under continuous illumination and heat has haunted perovskite devices since their inception, and the buried interface is one of the most common sites of degradation, where ion migration and interfacial reactions quietly erode performance. Here too the coordination-regulated films excelled. Small-area devices retained 90 percent of their initial efficiency after 2,656 hours of operation, and the 17.7-square-centimeter mini-modules held more than 90 percent of their initial performance after 1,200 hours under the demanding ISOS-L-1I protocol, an internationally recognized stress test combining continuous illumination with elevated temperature and electrical bias. Such endurance figures suggest that the defect-suppressed buried interface is not just a transient efficiency boost but a structural improvement in device physics.

What makes the result particularly compelling from a manufacturing standpoint is that the underlying technique is inherently scalable. Chemical bath deposition is a low-temperature, low-cost, solution-based process that requires no vacuum equipment and can, in principle, coat substrates of arbitrary size and shape, including textured surfaces that evaporative methods struggle to cover. By solving the coverage-versus-reactivity trade-off inside the bath chemistry itself, the researchers have essentially upgraded the method from a laboratory curiosity to a credible industrial candidate. The approach is compatible with subsequent self-assembled monolayer deposition and standard perovskite coating steps, meaning it slots into existing p-i-n fabrication flows without requiring an architectural rethink.

The work also carries a broader lesson for the field. Much of the recent progress in perovskite photovoltaics has come from interfacial engineering, and the Nankai study demonstrates that the substrate beneath a self-assembled monolayer is not a passive bystander but an active determinant of how well that monolayer performs. Controlling the crystallization kinetics of the inorganic layer, right down to the density of surface hydroxyl groups, is a form of interface design that operates one level deeper than most molecular engineering campaigns. It hints that similar coordination-regulated strategies could improve other metal oxide transport layers, from tin oxide electron contacts to zinc-based alternatives, across both single-junction and tandem devices.

Challenges remain before perovskite modules based on this chemistry can leave the laboratory for the factory floor. Scaling from 81.5 square centimeters to full-sized panels will require maintaining the same kinetic control across even larger baths and faster throughput, and long-term field testing beyond accelerated laboratory protocols will be essential. Lead content, encapsulation and recycling logistics also loom over the entire perovskite enterprise. But by demonstrating certified 27.35 percent cell efficiency, 23.42 percent module efficiency and more than a thousand hours of stable module operation from a single, industrially friendly deposition process, the team has decisively narrowed the gap between what perovskites can do in principle and what they can do in production. The sun delivers more energy to Earth in an hour than humanity uses in a year; chemistry like this brings the devices needed to harvest it one large step closer to being cheap, durable and genuinely scalable.

Subject of Research: Coordination-regulated chemical bath deposition of conformal nickel oxide hole-selective layers for efficient and stable perovskite solar modules

Article Title: Scalable and conformal nickel oxide for efficient perovskite solar modules

Article References: Yang, H., Wang, Y., Li, H., Wu, Y., Li, S., Han, X., Wang, D., Ding, Z., Han, Y., Zheng, Q., Chen, L., Du, Z., Alshahrani, T., Chen, C., Wang, X.-Y., Jiang, Y., & Yuan, M. (2026). Scalable and conformal nickel oxide for efficient perovskite solar modules. Nature Photonics. https://doi.org/10.1038/s41566-026-02012-z

Image Credits: AI Generated

DOI: 10.1038/s41566-026-02012-z

Keywords: perovskite solar cells, nickel oxide, chemical bath deposition, self-assembled monolayers, hole transport layer, power conversion efficiency, solar modules, crystallization kinetics, buried interface, photovoltaic stability, potassium tartrate coordination, ISOS-L-1I protocol

The research team set out to answer a deceptively simple question: when hydrogen gas bubbles off a nickel electrode in an alkaline solution, which of the surface species that form on nickel is actually doing the catalytic work? Nickel electrodes in alkaline media are never chemically naked. Depending on the applied potential and local conditions, their surfaces can host nickel oxide, nickel hydroxide, and nickel hydride phases, each with distinct electronic structures and bonding geometries. For decades, researchers have debated whether these species are innocent bystanders, harmful blockers, or hidden active sites. Because real electrodes present a patchwork of all three, isolating their individual contributions has been extraordinarily difficult.

The breakthrough of the new work lies in its systematic approach to well-defined nickel surfaces. Rather than studying polycrystalline foams or nanoparticles, where grain boundaries and defects confound interpretation, the researchers prepared carefully controlled nickel surfaces and deliberately generated each candidate species under known conditions. By systematically varying the presence and coverage of nickel oxide, nickel hydride, and nickel hydroxide, and then measuring the hydrogen evolution activity of each configuration, they could assign catalytic roles with a clarity that previous ensemble measurements could not achieve. The strategy echoes a classic theme in surface electrochemistry: only when a surface is well defined can the link between structure and function be drawn unambiguously.

What emerged is a picture in which no single species can claim sole credit. Nickel oxide species, the team found, contribute to the reaction in ways that depend sensitively on their exact chemical state and distribution on the metallic surface. Nickel hydroxide, which forms readily in alkaline environments and has often been invoked as the key promoter of alkaline hydrogen evolution, plays a role that must be carefully separated from the contributions of the oxide and hydride phases. Meanwhile, nickel hydride, the species formed when adsorbed hydrogen penetrates the metal lattice or binds in hydride-like configurations, emerges as a central participant in the hydrogen formation chemistry itself. The study’s central achievement is showing how these three species interact and divide the labor of the reaction rather than acting in isolation.

The distinction matters enormously for the alkaline hydrogen evolution reaction because its mechanism differs fundamentally from the one that operates in acid. In acidic media, the reaction proceeds through adsorbed hydrogen atoms that form directly on the metal surface and combine into hydrogen molecules. In alkaline electrolytes, however, water itself is the proton source, so every hydrogen molecule produced requires a water molecule to dissociate on the surface, cleaving an O-H bond and liberating a hydroxide ion. This initial water dissociation step is widely regarded as the kinetic bottleneck on pure metals, and it is precisely where adjacent oxide or hydroxide species have been proposed to help, by offering oxygen-affine sites that cleave water while neighboring metallic sites assemble the hydrogen. The new results put this bifunctional picture on a much firmer experimental footing for nickel.

For the electrolyser industry, the implications are immediate. Alkaline water electrolysis is the most mature and lowest-cost electrolysis technology on the market, but its cathodes and anodes still trail the performance achievable with platinum-group catalysts. Nickel is already the workhorse electrode material in commercial alkaline electrolysers, prized for its corrosion resistance in concentrated potassium hydroxide and its reasonable activity. If engineers can now identify which surface species to stabilize—and in what proportion—they can rationally tune electrode preparation protocols, whether through surface oxidation treatments, controlled potential cycling, or the deliberate engineering of oxide-hydride interfaces, instead of relying on empirical trial and error. The study effectively converts a long-standing controversy into an engineering design principle.

The findings also carry weight for the broader search for precious-metal-free catalysts. Earth-abundant transition metals such as nickel, cobalt, iron, and molybdenum have all been explored as hydrogen evolution catalysts, and many of the most successful candidates are not pure metals at all but composites in which metallic domains coexist with oxide or hydroxide phases. The nickel study provides a conceptual template for deconvoluting such systems: prepare well-defined versions of each phase, measure their individual kinetics, and then interrogate their combinations. Applied across the periodic table, this methodology could accelerate the discovery of catalysts that match platinum’s performance at a fraction of the cost, a goal that would ripple through green hydrogen production, fuel cells, and carbon-neutral synthesis of fuels and chemicals.

There are also cautionary lessons in the results. Because nickel hydride participates directly in the reaction, the subsurface and bulk hydride chemistry of nickel electrodes deserves renewed attention, particularly under the strongly reducing potentials of cathodic operation where hydride formation is thermodynamically favored. Hydride formation can induce lattice strain, alter electronic properties, and even degrade electrode morphology over time, so understanding its catalytic role may simultaneously illuminate pathways to more durable electrodes. Similarly, the finding that oxide and hydroxide species make separable, state-dependent contributions suggests that the dynamic potential-dependent evolution of surface chemistry during electrolyser start-up, shutdown, and fluctuating renewable power input could shift which species dominates, with consequences for both efficiency and lifetime.

The study arrives at a moment when green hydrogen is scaling from demonstration projects to gigawatt deployments, and every millivolt saved at the cathode translates into real energy and cost savings at industrial scale. By systematically dissecting the individual roles of nickel oxide, nickel hydride, and nickel hydroxide on well-defined nickel surfaces, the researchers have replaced a murky, contested narrative with a mechanistically grounded one. The work does not end the search for better alkaline hydrogen evolution catalysts, but it decisively sharpens it: the target is no longer simply nickel, or nickel oxide, or nickel hydroxide, but the precisely engineered coexistence of all three. For a field racing to strip precious metals out of the hydrogen economy, that clarity may prove as valuable as any single catalyst.

Subject of Research: The individual roles of nickel oxide, nickel hydride, and nickel hydroxide surface species in the alkaline hydrogen evolution reaction on nickel electrodes.

Article Title: The role of individual nickel surface species in the hydrogen evolution reaction on nickel in alkaline electrolytes

Article References: Kozlica, D. K., Finšgar, M., Farinazzo Bergamo Dias Martins, P., Huš, M., Genorio, B., Connell, J. G., Martins, M., Hývl, M., Žibert, T., Andrina Varda, K., Osmić, A., Bele, M., Likozar, B., Tomc, B., Gaberšček, M., & Strmčnik, D. (2026). The role of individual nickel surface species in the hydrogen evolution reaction on nickel in alkaline electrolytes. Nature Catalysis. https://doi.org/10.1038/s41929-026-01605-9

Image Credits: AI Generated

DOI: 10.1038/s41929-026-01605-9

Keywords: hydrogen evolution reaction, nickel, alkaline electrolytes, water electrolysis, nickel oxide, nickel hydride, nickel hydroxide, electrocatalysis, green hydrogen, surface chemistry, precious-metal-free catalysts, Nature Catalysis