spinel oxide – Science

PEG Polymer Doubles as Dispersant, Template and Porogen in High-Entropy Oxide Supercapacitor Electrode

Neil Sanderson — Sat, 17 Oct 2026 14:28:28 +0000

High-entropy oxides (HEOs) have attracted considerable attention for energy storage applications because of their multi-principal synergistic effects and excellent structural stability. In this study, polyethylene glycol (PEG) was used as a surfactant to synthesize (CrMnFeCoNi)3O4 HEOs by tuning the molar ratio of PEG to metal cations (P/M). The results show that PEG plays three roles during synthesis, serving simultaneously as a coordinating dispersant, a structure-directing agent, and an in situ porogen. The optimized HEO (P/M = 4/5) exhibits a uniform nanoparticle morphology and a well-developed pore architecture, delivering a specific capacitance of 557.6 F g−1. Kinetic analysis further indicates that its pseudocapacitive behavior arises from a cooperative effect involving both capacitive-controlled and diffusion-dominated mechanisms. The assembled asymmetric supercapacitor device achieves an energy density of 64.2 Wh kg−1 at a power density of 375.3 W kg−1 and retains 81.3% of its capacitance after 10,000 charge/discharge cycles. These outstanding electrochemical properties highlight the promise of PEG-templated (CrMnFeCoNi)3O4 HEOs for advanced energy storage applications.

Subject of Research: PEG polymer shapes a five-metal high-entropy oxide into a porous supercapacitor electrode delivering 557.6 F g−1 and 64.2 Wh kg−1.

Article Title: PEG-mediated particle assembly and pore evolution in a Cr–Mn–Fe–Co–Ni spinel high-entropy oxide

Article References: Zeng, F., Xu, B., Jing, C., He, X., Li, C., & Li, G. (2026). PEG-mediated particle assembly and pore evolution in a Cr–Mn–Fe–Co–Ni spinel high-entropy oxide. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13928-w

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13928-w

Keywords: high-entropy oxide, supercapacitor, polyethylene glycol, energy storage, spinel oxide, pseudocapacitance, PEG-mediated, particle, assembly, pore, evolution, spinel

Molten Salt Corrosion Test Reveals Best Weld Filler for CFBC Boiler Super-Heater Pipes

Denise Maddox — Sat, 17 Oct 2026 00:33:55 +0000

The study of hot corrosion in welded superheater components sits at the intersection of metallurgy, electrochemistry, and plant engineering, and the findings from this investigation can be better appreciated when placed against the broader background of how molten salt attack develops on boiler steels. In circulating fluidized bed combustion systems, the flue gas carries ash particles rich in sodium, potassium, sulfur, and vanadium compounds. When these species deposit on superheater surfaces operating at temperatures near 770 degrees Celsius, they can form low-melting-point salt mixtures that remain liquid on the metal surface. The specific combination of sodium sulfate with vanadium pentoxide used in the thermogravimetric testing is a well-established laboratory surrogate for such deposits, because vanadium pentoxide reacts with sodium sulfate to form sodium vanadates whose melting points fall well below the metal surface temperature. Once a liquid film forms, it dissolves protective oxide scales through fluxing reactions, exposing fresh metal to accelerated oxidation in a cyclic process that can consume wall thickness far faster than dry oxidation alone would allow.

The choice of SA 335 P91 as the base material reflects its widespread adoption in modern thermal power stations. P91 is a modified 9 percent chromium, 1 percent molybdenum ferritic-martensitic steel that was developed to offer improved creep strength and oxidation resistance compared with earlier low-alloy grades, allowing higher steam temperatures and pressures and therefore better thermal efficiency. However, the welding of P91 introduces regions of very different microstructure within a single joint. The fusion zone solidifies from the molten filler, the heat affected zone experiences a thermal cycle that can transform the original tempered martensite, and the parent metal retains its normalized and tempered condition. Each of these regions has a distinct chromium content in solid solution, distinct precipitate distributions, and distinct grain sizes, all of which influence how a protective oxide scale nucleates and grows. This is why a comparative study that examines the parent metal alongside two different weldments is more informative than testing a single material condition in isolation.

The two filler metals compared in the work represent fundamentally different alloying philosophies. E9018 B9 is the covered-electrode counterpart of the P91 composition itself, designed so that the weld metal matches the base steel in chromium and molybdenum content and can sustain comparable creep performance. Its advantage is metallurgical compatibility, but its corrosion behavior is essentially that of a 9 percent chromium steel. ERNiCrMo-3, by contrast, is a nickel-based filler originally developed for demanding petrochemical and power generation service. With a matrix dominated by nickel and substantial additions of chromium, molybdenum, and niobium, it does not attempt to match the base steel composition; instead, it relies on the intrinsically superior oxidation resistance of nickel-rich alloys. Nickel oxides and nickel-containing spinels tend to form denser, more adherent scales than iron oxides, and nickel also has a lower tendency to form volatile or non-protective corrosion products in sulfate and vanadate environments.

The identification of nickel ferrite, NiFe2O4, as the protective spinel phase on the ERNiCrMo-3 fusion zone is consistent with a large body of high-temperature oxidation literature. Spinel oxides of the AB2O4 structure are valued in corrosion protection because their crystal structures can accommodate cation substitutions while remaining compact and slow-growing. Magnetite, Fe3O4, is itself a spinel, but when nickel substitutes for a portion of the iron, the resulting nickel ferrite has a lower concentration of cation vacancies and a reduced rate of outward cation diffusion, which slows scale growth. A thinner scale is mechanically more robust, less prone to cracking on thermal cycling, and presents a shorter diffusion path for inward penetration of corrosive species such as sulfur and vanadium compounds. The cyclic nature of the thermogravimetric testing, with fifty heating cycles, is particularly relevant here, because repeated thermal excursions are what cause brittle oxide scales to spall. A scale that survives fifty cycles with minimal mass loss and remains well adherent in cross-sectional examination has demonstrated genuine protective character rather than merely an initially fast-growing but non-adherent oxide.

The observation of blistering on the E9018 B9 weld zone deserves particular attention from a plant engineering perspective. Blistering in hot corrosion contexts generally indicates that corrosion products or trapped gas have accumulated at interfaces within the scale or between the scale and the substrate, generating local pressure and detachment. In vanadate-bearing environments, iron-rich oxides are susceptible to dissolution and reprecipitation cycles that disrupt scale integrity, and the resulting porous, layered scales can trap gaseous species. On an actual superheater tube, such blistered regions would be expected to spall during thermal transients such as boiler start-up and shutdown, progressively thinning the weld region. Because weld zones already carry residual stresses from the welding thermal cycle and may have slightly different creep properties than the parent tube, accelerated local corrosion at welds is a well-recognized failure location in superheater and reheater circuits. The finding that the SMAW joint degrades preferentially therefore aligns with field experience in which welds and heat affected zones are frequent sites of tube leaks.

The temperature of 770 degrees Celsius selected for the testing is meaningful in relation to CFBC operation. Circulating fluidized bed boilers are often promoted for their relatively low combustion temperatures, typically around 850 to 900 degrees Celsius in the furnace, which limits the formation of certain molten deposits compared with pulverized coal firing. However, superheater surfaces can run hotter than the furnace bed temperature depending on steam conditions and heat flux distribution, and metal temperatures approaching or exceeding 750 to 800 degrees Celsius place the material squarely in the regime where sodium vanadates and complex alkali sulfates become molten. The salt mixture of sodium sulfate with 60 percent vanadium pentoxide has a melting behavior that produces a liquid phase at the test temperature, ensuring that the corrosion mechanism studied is genuinely molten-salt fluxing rather than dry oxidation. This makes the laboratory results directly relevant to the deposit chemistry that superheater tubes encounter when firing fuels with appreciable vanadium content, such as certain heavy fuel oils, petroleum coke blends, and some biomass or waste-derived fuels.

The analytical techniques employed in the study each contribute a complementary piece of the corrosion picture. Thermogravimetric analysis provides kinetic information, revealing whether the oxidation follows parabolic behavior characteristic of diffusion-controlled protective scale growth, or faster linear kinetics indicative of non-protective scaling. Repeated cycling in the thermobalance also captures mass changes from spallation, which a single isothermal exposure would miss. Scanning electron microscopy with energy dispersive spectroscopy maps the morphology and elemental distribution of the corrosion products, distinguishing between compact scales, porous layers, and internal attack along grain boundaries. X-ray diffraction identifies the crystalline phases, allowing the distinction between simple iron oxides such as hematite and magnetite, mixed spinels such as nickel ferrite, and sodium or vanadium-containing reaction products that signal interaction between the molten salt and the scale. Cross-sectional imaging is especially valuable because it reveals scale thickness, adherence, and whether attack penetrates along prior austenite grain boundaries into the substrate, which is the mechanism by which hot corrosion compromises mechanical integrity even before measurable wall loss becomes severe.

From a practical standpoint, the recommendation to use ERNiCrMo-3 filler with the gas tungsten arc welding process carries implications for fabrication and maintenance practice in CFBC plants. Gas tungsten arc welding offers precise control of heat input and dilution, which matters because the composition of the fusion zone in a dissimilar weld depends on how much base metal is melted and mixed with the filler. Excessive dilution of a nickel-based filler with iron-rich P91 parent metal would reduce the nickel content of the fusion zone and could erode the very advantage that the filler is meant to provide. Controlled dilution, typically achieved with careful current settings and technique, preserves a nickel-rich fusion zone capable of forming the protective spinel. Shielded metal arc welding, while more portable and economical for field repairs, involves a flux-covered electrode whose slag chemistry and greater dilution variability can complicate achieving an optimal fusion zone composition, and the observed blistering suggests that in this corrosive service the SMAW joint with the ferritic filler is the weaker link.

The economic dimension of these findings should not be overlooked. Superheater tube replacement in a 70 MW unit involves planned outages, and unscheduled failures of welds can force entire unit trips with substantial replacement power costs. If a filler upgrade extends weld service life even modestly in vanadium-containing fuel service, the incremental consumable cost of a nickel-based filler is small relative to the avoided outage risk. Utilities operating CFBC boilers on fuels with elevated vanadium and sodium content may find that specifying nickel-based fillers for superheater welds, combined with regular inspection of weld zones during overhauls, offers a cost-effective reliability improvement. The study also underscores the value of laboratory cyclic hot corrosion testing as a screening tool: by reproducing deposit chemistry and thermal cycling in a controlled setting, candidate consumables can be ranked before plant trials, shortening the path from metallurgical research to operational decision-making in thermal power generation.

Subject of Research: Materials Science

Article Title: A comparative investigation on molten salt hot corrosion of GTA and SMA-welded super-heater pipes of 70 MW CFBC boilers

Article References: Pillai, L. R., Aravind, A., Dhanushwaran, R. V., Praveen, S. K., & Prabu, S. S. (2026). A comparative investigation on molten salt hot corrosion of GTA and SMA-welded super-heater pipes of 70 MW CFBC boilers. Scientific Reports. https://doi.org/10.1038/s41598-026-70579-2

Image Credits: AI Generated

DOI: 10.1038/s41598-026-70579-2

Keywords: hot corrosion, molten salt, P91 steel, GTAW, SMAW, CFBC boiler, ERNiCrMo-3, E9018 B9, spinel oxide, super-heater tubes, comparative, investigation

Coconut Shell Carbon Supercharges Copper Cobalt Oxide Supercapacitor Electrodes

Bethany Barker — Thu, 01 Oct 2026 07:57:50 +0000

Supercapacitors promise to bridge the stubborn gap between batteries, which store a lot of energy but charge slowly, and conventional capacitors, which charge in seconds but hold very little. The bottleneck has always been the electrode material: it must conduct electrons quickly, offer vast surface area for ions to dock onto, and survive tens of thousands of charge-discharge cycles without falling apart. A research team led by J. Bosco Franklin, J. Venkatesan, S. John Sundaram, and Kasinathan Kaviyarasu, publishing in Discover Electrochemistry, now reports that a humble waste product, discarded coconut shells, may hold a key ingredient for solving this puzzle. By blending copper cobaltite (CuCo2O4), a spinel-structured mixed metal oxide, with activated carbon derived from coconut shells, the researchers produced a composite electrode that nearly doubles the charge storage of the pristine oxide while dramatically cutting its internal resistance.

The choice of CuCo2O4 is grounded in solid electrochemical logic. As a binary transition metal oxide with a cubic spinel architecture, it hosts copper and cobalt cations on distinct lattice sites, each capable of switching between multiple oxidation states, Cu2+/Cu+ and Co3+/Co2+, during reversible Faradaic redox reactions. This rich redox chemistry underpins pseudocapacitance, the mechanism by which charge is stored through fast surface reactions rather than slow bulk diffusion. Compared with conventional cobalt oxides such as Co3O4, CuCo2O4 offers better electronic conductivity, and copper is both cheaper and less toxic than cobalt, an important consideration for any technology hoping to scale up. Yet pristine CuCo2O4 has well-known weaknesses: low surface area, a tendency for nanoparticles to clump together, sluggish ion diffusion through dense structures, and mechanical degradation as the material swells and shrinks during cycling.

The team’s solution was to marry the oxide to a porous carbon scaffold made from agricultural waste. Coconut shells were washed, dried, crushed, and carbonized at 900 degrees Celsius for four hours, yielding an activated carbon powder rich in micropores and mesopores and decorated with oxygen-containing functional groups that bond readily with metal oxide surfaces. The CuCo2O4 itself was synthesized through a sol-gel combustion route, with copper chloride and cobalt precursors chelated by citric acid, gelled, dried, and calcined at 600 degrees Celsius. The final composite was made by physically grinding equal weights of oxide and carbon in an agate mortar, a deliberately simple and low-cost procedure that could easily translate to industrial production.

Structural analysis confirmed the strategy worked at the nanoscale. X-ray diffraction showed sharp, high-intensity peaks matching the cubic spinel phase of CuCo2O4, with only a trace of CuO as a secondary impurity. When the activated carbon was added, the diffraction peaks broadened and weakened, and the average crystallite size shrank from 43.89 nanometers to 33.79 nanometers. That shrinkage matters: the disordered carbon framework physically restrains particle growth and aggregation during synthesis, leaving more electrochemically active sites exposed to the electrolyte. A broad reflection between 20 and 30 degrees in the composite pattern confirmed the amorphous, graphitic character of the biomass-derived carbon dispersed among the spinel nanocrystals.

The most striking transformation appeared in the surface chemistry. Nitrogen physisorption measurements revealed that pristine CuCo2O4 has a modest BET surface area of roughly 20 square meters per gram, with mesopores averaging 25.1 nanometers wide. The composite, by contrast, exploded to 562 square meters per gram, with an average pore width of just 1.9 nanometers and a Type I isotherm characteristic of microporous materials. In practical terms, the carbon scaffold multiplies the electrode’s ion-accessible real estate by a factor of nearly thirty, creating an interconnected network through which electrolyte ions can race rather than crawl. Infrared spectroscopy added further evidence of intimate coupling, showing new carbon-oxygen and aromatic carbon-carbon bands alongside the characteristic Co-O and Cu-O vibrations of the spinel framework.

Electrochemical testing in a three-electrode cell with 3 M potassium hydroxide electrolyte translated these structural gains into performance. Cyclic voltammetry showed broad redox peaks for both materials, but the composite enclosed a far larger current area, delivering 562.5 farads per gram at 5 millivolts per second, a 96 percent jump over the pristine oxide’s 287.5 farads per gram. Galvanostatic charge-discharge measurements were even more emphatic: at a current density of 1 ampere per gram, the composite achieved a specific capacitance of 643.75 farads per gram, against 389.06 farads per gram for CuCo2O4 alone. Even when the current was pushed fivefold to 5 amperes per gram, the composite retained 507.81 farads per gram, demonstrating the rate capability that fast-charging applications demand.

Perhaps the most revealing analysis came from Dunn’s method, which separates surface-dominated capacitive storage from diffusion-limited storage. For pristine CuCo2O4, capacitive contributions ranged from just 11 to 33 percent across the tested scan rates, meaning most of its charge was locked behind slow diffusion. The composite flipped that picture entirely, with capacitive contributions of 55 to 82 percent, confirming that the activated carbon network shifts the electrode toward fast, surface-controlled charge storage. Impedance spectroscopy reinforced the point: solution resistance fell from 8.21 ohms to 4.66 ohms, and charge-transfer resistance collapsed from 2725.45 ohms to 627.87 ohms, reflecting the porous carbon’s role in opening ion pathways and improving electron transport.

Energy and power metrics tell a similarly compelling story. The composite delivered 205.76 watt-hours per kilogram at a power density of 1797.90 watts per kilogram, and still held 162.24 watt-hours per kilogram at 8985.6 watts per kilogram. The pristine oxide managed only 124.5 watt-hours per kilogram initially and lost 42 percent of that at high power. Durability testing at 5 amperes per gram showed the composite retaining 90 percent of its capacitance after 5000 cycles, comfortably ahead of the pure oxide’s 82.5 percent. The authors attribute this resilience to the carbon matrix buffering the mechanical stresses of oxide expansion and contraction, while noting that energy densities calculated from three-electrode tests may not directly translate to full device performance.

What makes this work resonate beyond the laboratory is its sustainability angle. Coconut shells are an abundant, low-cost biomass residue across tropical regions, with high carbon yield and minimal inorganic contamination, making them an ideal feedstock for electrode-grade activated carbon. By pairing waste-derived carbon with a mixed metal oxide whose redox-active cations span multiple oxidation states, the study demonstrates that high-performance energy storage need not depend on exotic or expensive materials. Compared with a previously reported CuCo2O4/reduced graphene oxide electrode that achieved 291 farads per gram, the coconut-shell composite more than doubles that figure while sustaining 90 percent retention over five times as many cycles. As grid buffering, regenerative braking, and portable electronics all demand faster, tougher, and greener storage, this trash-to-treasure electrode offers a template worth watching.

Subject of Research: CuCo2O4/activated carbon composite electrodes for supercapacitor energy storage

Article Title: Enhanced electrochemical performance of CuCo2O4 and CuCo2O4/activated carbon composites for supercapacitor applications

Article References: Franklin, J. B., Venkatesan, J., Paul, J. F. J., Harini, S., Fathima, J. P. R., Sundaram, S. J., & Kaviyarasu, K. (2026). Enhanced electrochemical performance of CuCo2O4 and CuCo2O4/activated carbon composites for supercapacitor applications. Discover Electrochemistry, 3(1), Article 56. https://doi.org/10.1007/s44373-026-00143-0

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00143-0

Keywords: supercapacitors, CuCo2O4, activated carbon, coconut shells, pseudocapacitance, spinel oxide, energy storage, biomass-derived carbon, electrode materials, specific capacitance, electrochemical impedance, sustainable materials

Printable Tin Cobalt Oxide Ink Powers Supercapacitors and Sensors Alike

Denise Maddox — Sun, 13 Sep 2026 00:05:06 +0000

Researchers at the Manipal Institute of Technology, part of the Manipal Academy of Higher Education in India, have developed a single screen-printable conductive ink that can be used to fabricate three very different microelectronic devices: micro-supercapacitors for on-chip energy storage, humidity sensors, and electrochemical sensors capable of detecting pharmaceutical compounds. The work, published as an open-access paper in Advanced Composites and Hybrid Materials, addresses a persistent bottleneck in miniaturised electronics, where energy storage components and sensing elements are typically built from different materials using different, often expensive, fabrication routes. By formulating one ink that performs well in all three roles, the team has demonstrated a scalable and affordable platform for next-generation microdevices.

The active ingredient of the ink is a pseudocapacitive spinel oxide, tin cobalt oxide with the chemical formula SnCo2O4, combined with conductive carbon nanofibers. Spinel oxides of this kind are attractive for electrochemical applications because their crystal structure offers multiple accessible oxidation states, allowing fast and reversible redox reactions at the electrode surface. In an energy storage context, this pseudocapacitive behaviour means charge is stored not only electrostatically at the interface between electrode and electrolyte, as in a conventional double-layer capacitor, but also through faradaic charge-transfer reactions that can substantially increase the amount of energy packed into a given area. The carbon nanofibers serve as a highly conductive skeletal framework that threads through the oxide particles, providing continuous pathways for electrons and helping to anchor the active material mechanically.

Screen printing was chosen as the deposition technique because it is one of the most manufacturing-friendly methods available for printed electronics. In screen printing, a viscous paste or ink is forced through a patterned mesh onto a substrate, allowing large areas to be patterned quickly with minimal material waste and without the vacuum equipment or photolithography required by conventional microfabrication. The challenge lies in formulating an ink whose rheology, viscosity, and solids loading allow clean transfer through the mesh while retaining the electrochemical activity of the functional particles. The researchers optimised the composition of the SnCo2O4 and carbon nanofiber blend, identifying a formulation designated SC-3 that delivered the best balance of conductivity, printability, and charge-storage performance.

When printed as micro-supercapacitor electrodes, the SC-3 material exhibited both pseudocapacitive and electric double-layer capacitive charge-storage mechanisms, a hybrid behaviour that combines the high power and long cycle life of double-layer storage with the higher capacitance of faradaic materials. The printed electrodes achieved an areal capacitance of 673.8 plus or minus 3.1 millifarads per square centimetre, an energy density of 93.58 plus or minus 1.5 microwatt-hours per square centimetre, and a power density of 1.353 plus or minus 3.0 milliwatts per square centimetre. These figures were reported with a relative standard deviation below one percent across three replicate measurements, indicating a high degree of reproducibility in the printing process. For microscale energy applications, where the electrode area is measured in square centimetres or less, such areal metrics are the relevant benchmarks rather than gravimetric values.

The same ink proved equally capable when deployed in sensing devices. A humidity sensor printed from the SC-3 formulation showed excellent operational stability, fast response and recovery times of 38 and 56 seconds respectively, low hysteresis of 1.46 percent, and a wide detection range spanning relative humidity values from 11 to 97 percent. Low hysteresis is a particularly important figure of merit for humidity sensors because it reflects how consistently the sensor returns to its baseline resistance after exposure to moist and dry conditions, a property that determines whether repeated measurements can be trusted without recalibration. The wide dynamic range means a single printed sensor could operate reliably in environments as different as dry indoor air and near-saturated tropical conditions.

The third application demonstrated by the team is arguably the most medically significant. When the SC-3 material was used to modify a screen-printed electrode, abbreviated SPE, the resulting electrochemical sensor exhibited excellent behaviour in detecting naproxen, a widely used non-steroidal anti-inflammatory drug. The sensor operated across a broad drug concentration range from 1 micromolar to 500 micromolar, covering concentrations relevant to both pharmaceutical quality control and environmental monitoring of waterways, where accumulated drug residues have become an emerging concern. Long-term stability testing showed that the sensor could measure naproxen reliably in tablet samples and in synthetic urine, with a relative standard deviation of 3.53 percent, plus or minus 0.72, demonstrating practical analytical performance beyond idealised laboratory conditions.

The researchers attribute the multifunctional performance to the interplay between the carbon nanofiber framework and the redox-active SnCo2O4. The nanofibers create a percolating conductive network that lowers the overall resistance of the printed film, while the spinel oxide contributes abundant active sites for both faradaic charge storage and surface reactions involved in sensing. In the humidity sensor, the oxide surface likely adsorbs water molecules and facilitates proton conduction, while in the electrochemical sensor the redox-active oxide catalyses the electron-transfer reaction of naproxen at the electrode surface. A single material satisfying these distinct physical mechanisms is what makes the platform genuinely multifunctional rather than a collection of coincidental performances.

The broader significance of the work lies in how it tackles the shortcomings of conventional standalone energy storage and sensing devices. Traditionally, a designer building a self-powered sensing node would need to integrate a supercapacitor made of one material system with a sensor made of another, often requiring incompatible deposition processes, adhesion layers, and thermal treatments. A single ink that can be printed into any of these device architectures simplifies supply chains, reduces fabrication steps, and opens the door to fully printed integrated systems in which energy storage and sensing elements are deposited side by side on the same substrate in the same manufacturing run. This is precisely the kind of process integration that printed electronics and the Internet of Things have long demanded.

The study also carries implications for sustainability and cost. Tin and cobalt oxides are relatively abundant compared with some of the precious-metal catalysts used in high-end electrochemical sensors, and carbon nanofibers can be produced at scale. Because the ink is screen-printable at ambient conditions, it does not require energy-intensive vacuum deposition, and the additive nature of printing means far less material is wasted compared with etch-based patterning. The authors describe their formulation as a scalable, affordable, multifunctional conductive ink platform aimed squarely at next-generation miniaturised microelectronics, positioning it as a practical route from laboratory materials chemistry to manufacturable devices.

The research, led by Shilpa Shetty, Mohammad Saquib, Selvakumar M, and Ramakrishna Nayak at the Manipal Institute of Technology, was published open access on 11 September 2026 in Advanced Composites and Hybrid Materials, with Shetty supported by a Dr T. M. A. Pai Fellowship from the Manipal Academy of Higher Education. As wearable health monitors, environmental sensor networks, and self-powered microdevices proliferate, the demand for materials that can store energy and sense their environment within the same printed footprint will only grow. This single-ink strategy, validated across three distinct device classes with quantified performance metrics, offers a compelling template for how multifunctional materials can compress device fabrication into a single, scalable printing step.

Subject of Research: A screen-printable multifunctional conductive ink based on tin cobalt oxide decorated carbon nanofibers for energy storage and sensing devices

Article Title: A single screen-printable multifunctional active ink platform based on tin cobalt oxide decorated carbon nanofibers for energy storage and sensing applications

Article References: Shetty, S., Saquib, M., M, S., & Nayak, R. (2026). A single screen-printable multifunctional active ink platform based on tin cobalt oxide decorated carbon nanofibers for energy storage and sensing applications. Advanced Composites and Hybrid Materials. https://doi.org/10.1007/s42114-026-02070-5

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02070-5

Keywords: conductive ink, screen printing, tin cobalt oxide, carbon nanofibers, micro-supercapacitors, energy storage, humidity sensor, electrochemical sensor, naproxen detection, spinel oxide, printed electronics, sensors

MXene Dose Unlocks Faster Oxygen Evolution in Nickel Cobalt Oxide Catalysts

Gavin Prescott — Sat, 12 Sep 2026 14:57:30 +0000

The slowest step in the hydrogen economy may just have gotten a serious upgrade. In a study published in the journal Ionics, a team of researchers from India, Spain, Saudi Arabia and South Korea reports that a carefully measured pinch of a two-dimensional material known as MXene can transform an ordinary nickel cobalt oxide spinel into a remarkably efficient catalyst for the oxygen evolution reaction, the stubborn half-reaction that has long throttled the performance of water electrolyzers and rechargeable metal-air batteries. The work, led by Ashalatha Vazhayil and Nygil Thomas of Nirmalagiri College in Kerala, demonstrates that in electrocatalysis, as in cooking, the amount of an ingredient can matter as much as the ingredient itself.

The oxygen evolution reaction, or OER, is the demanding four-electron process by which water molecules are torn apart at an electrode to release oxygen gas. Because each water molecule must surrender four electrons and four protons in a sequence of energetically unfavorable steps, the reaction imposes a substantial extra voltage, called overpotential, on any electrolyzer. Every additional millivolt of overpotential translates directly into wasted electricity and higher-cost hydrogen. Precious metal oxides such as iridium dioxide perform well but are scarce and expensive, which is why the field has pressed hard on abundant alternatives such as first-row transition metal oxides, particularly the nickel cobalt spinel NiCo2O4, a compound prized for its flexible redox chemistry and its array of accessible nickel and cobalt active sites.

NiCo2O4 has a well-known weakness, however: it is a mediocre electrical conductor. Electrons generated or consumed at its active sites must fight their way through a resistive oxide lattice, slowing reaction kinetics and blunting performance. The new study confronts this bottleneck by interleaving the spinel with Ti3C2Tx MXene, a member of the family of two-dimensional carbides discovered in 2011. MXenes are produced by chemically etching away the atomic layers of a layered ceramic precursor, leaving behind single-atom-thick sheets of titanium carbide terminated with surface groups such as oxygen, hydroxyl and fluorine, the Tx in the formula. These terminations make the sheets hydrophilic and chemically versatile while preserving metallic-like conductivity, a combination that has made MXenes a favorite scaffold for energy materials.

The synthesis was deliberately simple. The researchers employed a hydrothermal route, growing NiCo2O4 in the presence of varying amounts of MXene nanosheets, ranging from none at all to 100 milligrams, yielding a series of composites labeled MXene@NCO-X, where X denotes the MXene loading. Hydrothermal synthesis involves sealed autoclaves in which aqueous precursors are heated well above the boiling point, allowing crystals to nucleate and grow on the dispersed MXene sheets. The resulting composites, examined by structural and surface characterization techniques including X-ray photoelectron spectroscopy, revealed that the spinel did not merely sit on the MXene surface but formed intimate interfacial contact with it, an electronic handshake that proved central to the catalyst’s behavior.

Among the series, one formulation stood out decisively. The composite containing 50 milligrams of MXene, designated MXene@NCO-50, required an overpotential of only 360 millivolts to drive a current density of 10 milliamperes per square centimeter in 1 molar potassium hydroxide electrolyte, a standard benchmark condition for alkaline water splitting. Its Tafel slope, the parameter that describes how quickly current rises with applied voltage and therefore how fast the reaction accelerates, was a lean 65.71 millivolts per decade. Both figures compare favorably with the pristine spinel and with the under- and over-loaded composites, marking an optimum in a landscape where too little MXene leaves the conductivity deficit uncorrected and too much buries or dilutes the spinel’s active sites.

The physical evidence pointed to a clear mechanism. Electrochemical impedance spectroscopy, which dissects the resistive and capacitive elements of an electrode interface, showed that MXene@NCO-50 possessed faster charge transfer kinetics than any of its siblings. Measurements of the double-layer capacitance, a proxy for the electrochemically active surface area, revealed that this sample also exposed the largest effective reaction area. Electron microscopy linked these electrochemical advantages to architecture: the optimized composite grew as well-defined nanorod architectures anchored on the conductive MXene sheets, an arrangement that simultaneously supplies abundant active sites and builds an unobstructed highway for electrons to reach them.

The authors attribute the outstanding activity to a synergistic interaction between the conductive MXene nanosheets and the NiCo2O4 spinel. In essence, the MXene solves the spinel’s conductivity problem while the spinel supplies the catalytic chemistry that the MXene alone lacks. The interfacial electronic interaction between the two phases can modulate the oxidation states and adsorption energies of nickel and cobalt centers, easing the binding of oxygen intermediates along the four-electron pathway. This composite design echoes a broader trend in the literature, where MXene hybrids with cobalt hydroxides, ferrites and other spinels have repeatedly shown that coupling two-dimensional carbides with transition metal oxides produces catalysts greater than the sum of their parts.

Durability, the perennial Achilles heel of non-precious OER catalysts operating in hot, corrosive alkaline media, also held up. The optimized catalyst demonstrated excellent electrochemical stability over prolonged operation, retaining its performance through extended electrolysis. For any envisioned electrolyzer or metal-air battery, such longevity matters as much as the headline overpotential, since catalyst dissolution and phase degradation during long-term current flow are the practical barriers that keep laboratory champions out of commercial stacks.

The significance of the study lies less in any single number than in the design principle it crystallizes: MXene concentration is a tunable dial for OER performance. Rather than discovering a new compound, the team systematically mapped how dosage reshapes morphology, conductivity and activity, and identified the sweet spot where synergy is maximized. As nations scale up green hydrogen production under tightening decarbonization targets, catalysts built from earth-abundant nickel, cobalt and titanium, assembled through a facile hydrothermal process with no exotic equipment, offer a credible path to cheaper electrolysis. The work highlights the promising potential of MXene and spinel oxide nanohybrids as advanced electrocatalysts for sustainable energy applications, and it gives the field a practical recipe: if you want faster oxygen evolution, count your MXene carefully.

Subject of Research: The influence of Ti3C2Tx MXene concentration on the oxygen evolution reaction performance of NiCo2O4 spinel electrocatalysts

Article Title: Tuning the oxygen evolution reaction performance: the influence of MXene concentration in NiCo2O4 catalysts

Article References: Vazhayil, A., C., S. A., Vazhayal, L., Thomas, J., Chicardi, E., Rokhum, S. L., Safra, I., Jeffery, A. A., & Thomas, N. (2026). Tuning the oxygen evolution reaction performance: the influence of MXene concentration in NiCo2O4 catalysts. Ionics. https://doi.org/10.1007/s11581-026-07506-y

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07506-y

Keywords: MXene, NiCo2O4, oxygen evolution reaction, electrocatalysis, water splitting, green hydrogen, spinel oxide, nanocomposite, Tafel slope, charge transfer, renewable energy, hydrothermal synthesis