The elegance of the design lies in pairing two materials with complementary chemistries. Manganese dioxide is a veteran of pseudocapacitor research: it is cheap, abundant, environmentally benign, and boasts a theoretical capacitance of roughly 1,370 farads per gram thanks to reversible Mn3+/Mn4+ redox reactions at or near its surface. But it has well-known Achilles heels. Its bulk is electrochemically nearly inaccessible, its electrical conductivity is poor, and it gradually dissolves and aggregates during repeated cycling. Prussian blue, the deep-blue iron hexacyanoferrate pigment first synthesized in the eighteenth century, brings exactly what manganese dioxide lacks. Its three-dimensional open framework of iron-nitrogen and iron-carbon coordination units, stitched together by cyanide bridges, creates interconnected channels through which electrolyte ions can migrate freely. More importantly, it hosts its own family of Fe2+/Fe3+ redox centers, adding a second, independent source of faradaic charge storage.

Fabrication followed a two-step sequence chosen for its industrial simplicity. First, strips of carbon cloth were activated in a hot mixture of nitric and sulfuric acid, which cleans the fibers and grafts oxygen-rich functional groups onto their surfaces, improving wettability and creating nucleation sites. The cloth was then sealed in an autoclave with acidified potassium permanganate solution and heated to 180 degrees Celsius for 24 hours, growing dense forests of manganese dioxide nanoneedles and nanorods directly on every fiber. In the second step, Prussian blue was electrodeposited onto the coated cloth by cyclic voltammetry in a solution of ferric chloride, potassium ferricyanide, hydrochloric acid, and supporting potassium chloride. The number of deposition cycles, varied from 15 to 100, became the tuning knob for how much Prussian blue loaded onto each electrode.

Microscopy revealed why the choice of 50 cycles proved decisive. With only 15 cycles, sparse Prussian blue particles dotted the carbon fibers, leaving most of the conductive network uncovered and the active material content too low. At 100 cycles, the opposite failure appeared: thick, cracked, agglomerated crusts of Prussian blue choked the porous architecture, blocking electrolyte diffusion and raising charge-transfer resistance. The PBMC-50 electrode, named for its 50 deposition cycles, hit the sweet spot, with a uniform, well-dispersed coating that preserved the interconnected fibrous framework of the cloth while maximizing the electroactive surface area. X-ray diffraction, performed on films grown on transparent conductive substrates to avoid interference from the carbon background, confirmed the coexistence of tetragonal alpha-MnO2 and face-centered cubic Prussian blue, with no impurity phases detected.

Electrochemical testing told a consistent story across every measurement technique. In a three-electrode configuration, the optimized PBMC-50 electrode delivered an areal capacitance of 636 millifarads per square centimeter at a modest current density of 0.7 milliamperes per square centimeter, and still retained 426 millifarads per square centimeter at 2 milliamperes per square centimeter. Cyclic voltammetry and galvanostatic charge-discharge measurements, which probe the electrode on different timescales, both independently identified PBMC-50 as the best performer, ruling out the possibility that the result was an artifact of a single method. Impedance spectroscopy added a mechanistic explanation: adding Prussian blue left the overall series resistance essentially unchanged, around 172.5 ohms, but sharply reduced interfacial charge-transfer resistance and produced a near-vertical low-frequency response with a phase angle approaching 80 degrees, a signature of efficient ion transport.

Kinetic analysis added a layer of nuance rarely reported for such electrodes. By separating the current response into surface-controlled capacitive and diffusion-controlled contributions, the researchers discovered markedly asymmetric behavior between the oxidation and reduction branches. The anodic b-value of 0.36 indicated a strongly diffusion-limited oxidation process, while the cathodic b-value of 0.66 pointed to a mixed regime. At the slowest scan rate of 2 millivolts per second, diffusion-controlled processes accounted for about 88 percent of the anodic charge and 77 percent of the cathodic charge, with surface-controlled contributions growing as the scan rate increased. This mixed, diffusion-influenced mechanism reflects the genuine bulk participation of the redox-active phases, a double-edged property that grants high capacity at moderate rates but limits the deepest active sites at very fast charging.

The practical payoff came when the team assembled complete devices. Using a polyvinyl alcohol-sodium sulfate gel electrolyte, they constructed six different symmetric and asymmetric all-solid-state supercapacitors and compared them head to head. The symmetric PBMC//PBMC configuration emerged as the clear winner, achieving an areal capacitance of 117 millifarads per square centimeter, more than four times that of the weakest configuration tested. After systematically mapping the voltage window with cyclic voltammetry and charge-discharge curves, the researchers settled on a wide operating range of 2.2 volts, extending from minus 1.4 to plus 0.8 volts. They deliberately avoided pushing to the highest voltage the device could technically tolerate, noting that beyond this range, polarization and incipient electrolyte oxidation begin to contaminate the response with parasitic, weakly reversible reactions.

The full-cell figures place the device among the competitive entries in the flexible supercapacitor field. The PBMC//PBMC device delivered a maximum areal energy density of 0.084 milliwatt-hours per square centimeter at a power density of 0.48 milliwatts per square centimeter, and held a capacitance of 31 millifarads per square centimeter even at a demanding 5 milliamperes per square centimeter. Endurance testing over 10,000 consecutive cycles at 7 milliamperes per square centimeter left 89.83 percent of the initial capacitance intact. Mechanical robustness proved equally impressive: capacitance retention measured at bending angles of 0, 90, and 180 degrees came in at 100, 99.14, and 98.67 percent respectively, meaning the device essentially did not notice being folded in half. Three devices wired in series successfully lit an array of ten red and yellow light-emitting diodes, and a single unit, light enough to rest on a plant leaf without bending it, demonstrated the ultralight character the design was after.

What distinguishes this work is not a single record-breaking number but the coherent integration of materials chemistry, electrode engineering, and device demonstration. By coupling manganese-based and iron-based redox systems on a conductive, mechanically resilient carbon cloth scaffold, the researchers eliminated the binders and insulating additives that typically degrade flexible electrode performance, while the Prussian blue framework simultaneously added redox capacity, improved ion pathways, and helped suppress the structural degradation that usually shortens manganese dioxide lifetimes. The hydrothermal-then-electrodeposition route uses inexpensive reagents, water-based processing, and standard laboratory equipment, making it a credible candidate for scale-up. As the market for wearables, electronic skin, medical sensors, and bendable displays continues to expand, electrode architectures of this kind, which balance energy density, durability, and manufacturability, may prove to be the quiet enabling technology behind the next generation of devices that flex with the human body.

Subject of Research: Binder-free Prussian blue-MnO2 heterostructure electrodes on carbon cloth for flexible solid-state supercapacitors

Article Title: Engineering Prussian blue-MnO 2 heterointerfaces on carbon cloth as binder-free electrodes for high-performance flexible solid-state supercapacitors

Article References: Moosavi, N., & Momeni, M. M. (2026). Engineering Prussian blue-MnO2 heterointerfaces on carbon cloth as binder-free electrodes for high-performance flexible solid-state supercapacitors. Results in Chemistry, 30, Article 103847. https://doi.org/10.1016/j.rechem.2026.103847

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103847

Keywords: flexible supercapacitors, Prussian blue, manganese dioxide, carbon cloth, binder-free electrodes, solid-state energy storage, pseudocapacitance, heterointerfaces, electrodeposition, wearable electronics, energy density, cycling stability

The technique, known as sequential dual-laser direct writing, builds on the well-established phenomenon of laser-induced graphene, or LIG. First reported in 2014, LIG formation relies on the fact that certain polymers, when swept by a focused infrared laser beam, do not simply burn away. Instead, their carbon backbone undergoes rapid localized photothermal conversion, reorganizing into a porous, conductive network of graphene sheets directly on the substrate. The process is one-step, mask-free, and can be carried out in ambient air, which is precisely why it has attracted so much attention for wearable sensors, micro-supercapacitors, and printed electronics.

What the Qingdao team recognized is that a single laser pass has inherent limitations. The energy distribution within a moving laser spot is Gaussian, hottest at the center and cooler at the edges, which produces uneven graphitization: some regions become well-formed conductive graphene while others remain partially carbonized or over-burned. By splitting the transformation into two sequential irradiation steps, the researchers allowed the material to graphitize more gradually and uniformly. The result, confirmed through microscopy and Raman spectroscopy, was a denser, more homogeneous graphene architecture with improved electrical continuity throughout the electrode.

The starting material is equally central to the story. The team used polyethersulfone, a robust engineering polymer rich in aromatic carbon and sulfur, as the precursor film. Crucially, they incorporated transition metal ions—cobalt and iron—into the polymer before laser writing. During laser exposure, these ions are simultaneously converted in situ into electrochemically active metal oxide species embedded within the growing graphene matrix. This one-step co-conversion eliminates the need for separate synthesis of active materials, current collector coatings, or conductive additives. The finished electrode is freestanding and binder-free: there is no polymer glue diluting conductivity, no metal foil current collector adding weight, and no slurry-casting step generating solvent waste.

The electrochemical payoff was substantial. The optimized cobalt-containing electrode, designated Co@PES-LIG, delivered an areal specific capacitance of 3800 millifarads per square centimeter at a current density of 1 milliampere per square centimeter, while its iron-based counterpart, Fe@PES-LIG, reached 1980 millifarads per square centimeter under the same conditions. Areal capacitance is the figure of merit that matters most for flexible and miniaturized devices, where the footprint rather than the mass of the electrode sets the design limit. Values in this range place the dual-laser electrodes among the more competitive LIG-based systems reported to date, and the improvement over single-pass processing underscores how much performance had been left on the table by conventional laser writing.

To demonstrate practical relevance, the researchers paired the two materials in an asymmetric supercapacitor, using the cobalt-based electrode as the cathode and the iron-based electrode as the anode. Asymmetric configurations exploit the different stable voltage windows of the two electrodes to extend the overall operating voltage of the cell beyond what either electrode could sustain alone. The assembled device operated at 1.8 volts in aqueous electrolyte—an unusually wide window for a water-based system, where most cells are limited to roughly 1.0 to 1.6 volts before water splitting consumes current and degrades performance.

The full device metrics are impressive for a fabrication method this simple. The asymmetric supercapacitor achieved an areal capacitance of 855 millifarads per square centimeter and an energy density of 125 microwatt-hours per square centimeter at a power density of 800 microwatts per square centimeter. Energy density has long been the Achilles heel of supercapacitors relative to batteries, so every improvement matters. Equally important for real-world use, the device retained 89.4 percent of its capacitance after 10,000 charge-discharge cycles, demonstrating that the in-situ-formed metal oxide phases and the surrounding graphene network can withstand repeated electrochemical cycling without rapid degradation.

The environmental and manufacturing implications are as compelling as the numbers. Because the entire electrode is written directly from a polymer film with two laser scans, the process requires no toxic solvents, no high-temperature furnaces, no vacuum deposition, and no multi-step materials synthesis. Laser direct writing is also digitally programmable: electrode geometry, interdigitated patterns for micro-supercapacitors, and device layouts can simply be drawn in software and written on demand. For flexible and wearable electronics—where devices must bend, stretch, and conform to skin or fabric—the freestanding nature of the electrodes is a particular advantage, since rigid current collectors and brittle binder networks are common points of mechanical failure.

The researchers point out that the strategy is efficient, simple, and environmentally benign, offering a general route for designing high-performance flexible energy storage. Because the dual-laser principle is not tied to any single metal ion, the approach could plausibly extend to other transition metal systems, opening paths to tailored pseudocapacitive chemistries written directly onto polymer substrates in a single integrated step. The work was supported by the Natural Science Foundation of Shandong Province, the Natural Science Foundation of Qingdao, and the Shandong Province Higher Educational Program for Young Innovation Talents. As demand grows for power sources that can be manufactured as easily as they are designed, sequential dual-laser writing of metal-ion-loaded polymers offers a persuasive glimpse of that future—one in which the electrode of a supercapacitor is not assembled at all, but simply drawn.

Subject of Research: Sequential dual-laser direct writing of binder-free laser-induced graphene composite electrodes for high-performance asymmetric supercapacitors

Article Title: Sequential dual-laser direct writing of binder-free electrodes for high-performance supercapacitors

Article References: Gao, H., Yang, L., Han, X., Peng, Z., Ge, L., & Sun, X. (2026). Sequential dual-laser direct writing of binder-free electrodes for high-performance supercapacitors. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13724-6

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13724-6

Keywords: laser-induced graphene, supercapacitors, dual-laser direct writing, binder-free electrodes, polyethersulfone, asymmetric supercapacitor, energy density, flexible electronics, transition metal oxides, energy storage, cobalt electrode, iron electrode

The study embarks on a critical examination of conventional electrode materials, which often rely on binders that can detract from overall electrochemical performance. By removing the binder layer, the researchers aim to enhance ionic and electronic conductivities, thus improving charge storage capacity and accelerating electrochemical reactions. This move aligns with the industry’s direction toward slimmer and more efficient energy sources capable of meeting modern demands.

Sonochemical-assisted chemical bath deposition is at the heart of this research. This technique utilizes ultrasound waves to agitate the solution during the deposition process, enhancing the interaction between the cobalt and nickel ions in the bath. The ultrasound generates localized high temperatures and pressures, leading to increased nucleation rates and better quality of the deposited film. This improved deposition technique promises to yield electrodes with superior structural integrity and electrochemical properties.

The significance of cobalt and nickel phosphate compounds in battery applications cannot be overstated. These materials excel due to their high theoretical capacity and favorable electrochemical characteristics. Cobalt’s role in battery technology has been well documented, while nickel introduces enhanced stability and efficiency during charge and discharge cycles. The synergistic effect of these two metals enhances energy density and prolongs battery lifespan, making them ideal candidates for advanced battery formulations.

The research meticulously describes the parameters of the sonochemical deposition process, which were fine-tuned to achieve optimal results. Key parameters such as temperature, deposition time, and concentration of reactants were all rigorously examined. Initial tests established a baseline for performance, with variations in these parameters providing insights into their influence on the composition and morphology of the electrodes.

A notable aspect of the study is the characterization techniques used to analyze the properties of the deposited films. Scanning electron microscopy (SEM) was employed to observe the surface morphology and structural features of the electrodes. The results indicated a uniform and dense surface, characteristic of high-quality films, leading to improved electrochemical properties. Additionally, energy-dispersive X-ray spectroscopy (EDX) was utilized to confirm the elemental composition, ensuring the successful incorporation of cobalt and nickel into the phosphate structure.

The electrochemical performance of the binder-free cobalt-nickel phosphate electrodes was evaluated using cyclic voltammetry and galvanostatic charge-discharge tests. The results showcased remarkable specific capacity and excellent rate capability, outpacing many conventional electrode materials. The electrode’s performance stability was also assessed, revealing minimal degradation over numerous charge-discharge cycles—a critical factor for practical applications.

The findings from Lei et al. carry significant implications for the future of battery technology. By providing a method to fabricate binder-free electrodes that can exhibit superior electrochemical properties, this research opens new avenues for the development of more efficient and sustainable energy storage solutions. The implications extend to electric vehicles and portable electronics, where the demand for high-performance batteries is ever-increasing.

This study is expected to inspire further research in the field of advanced electrode materials. By exploring different metallic combinations and deposition techniques, scientists can potentially uncover even more robust materials that meet the challenges posed by burgeoning energy demands. The experiment underscores the potential of sonochemical methods in synthesizing innovative materials for next-generation batteries.

In conclusion, Lei et al.’s work offers a promising glimpse into the future of battery technology through the optimized formulation of cobalt-nickel phosphate electrodes. The integration of sonochemical-assisted deposition techniques has demonstrated substantial improvements in electrochemical performance, paving the way for binder-free electrodes that could revolutionize the energy storage landscape. This research sets a precedent for future studies aiming to refine electrode materials, ultimately assisting in the transition to greener energy solutions.

As the world moves toward a more electrified future, the outcomes of this research will resonate through various sectors reliant on efficient energy storage. The advancement of lithium-ion technology, along with alternative chemistries that leverage the findings from this study, highlights the dynamic nature of battery research. With innovations continuously emerging from laboratories around the globe, the next generation of energy storage solutions is on the horizon, promising to enhance both consumer technology and renewable energy integration.

Subject of Research: Optimization of binder-free cobalt-nickel phosphate battery-type electrodes using sonochemical-assisted chemical bath deposition.

Article Title: Optimizing the formulation of binder-free cobalt–nickel phosphate battery-type electrode via sonochemical-assisted chemical bath deposition approach.

Article References: Lei, Q., Gerard, O., Guo, X. et al. Optimizing the formulation of binder-free cobalt–nickel phosphate battery-type electrode via sonochemical-assisted chemical bath deposition approach. Ionics (2025). https://doi.org/10.1007/s11581-025-06749-5

Image Credits: AI Generated

DOI: https://doi.org/10.1007/s11581-025-06749-5

Keywords: Cobalt-nickel phosphate, binder-free electrodes, sonochemical deposition, energy storage, electrochemical performance.