Prussian Blue Meets Manganese Dioxide in Flexible Supercapacitor Breakthrough

Wearable electronics have long been held back by one stubborn problem: batteries are rigid, heavy, and occasionally unsafe when bent, sweat on, or stitched into clothing. A research team at Isfahan University of Technology in Iran now reports a deceptively simple solution that could change how flexible gadgets store their energy. In a study published in Results in Chemistry, Negin Moosavi and Mohamad Mohsen Momeni describe a binder-free hybrid electrode built from Prussian blue, manganese dioxide, and ordinary carbon cloth that delivers some of the most balanced performance figures yet recorded for an all-solid-state flexible supercapacitor. Their device runs at a remarkably high 2.2 volts, survives 10,000 charge-discharge cycles with nearly 90 percent of its capacitance intact, and kept working flawlessly while being folded back on itself through 180 degrees.

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