The significance of the result lies in what it replaces. Conventional COF synthesis typically demands days of heating under aggressive acid- or base-catalysed conditions, extensive screening of solvents and temperatures, and careful matching of reaction conditions to each monomer combination. Even then, many products emerge with imperfect crystallinity or compromised porosity, the two properties that make COFs valuable for gas separation, catalysis, energy storage and proton conduction. The new strategy, by contrast, produces imide-, imine-, hydrazone- and sp2-carbon-linked COFs within hours, with high crystallinity and porosity, using a catalyst that can be recovered and used again.

Benzimidazole occupies a special position among organic molecules because it is amphiprotic: it can donate a hydrogen bond through its N-H group and accept one through its pyridine-like nitrogen. That dual character is the engine of the new method. Unlike conventional acid or base catalysis, which activates monomers by proton transfer, the benzimidazole catalysts engage monomers, intermediates and transition states simultaneously through explicit hydrogen-bonding interactions, lowering the energy barrier at every step of the polymerization rather than at just one.

The authors demonstrate the approach most thoroughly on imide-linked COFs, a class prized for its chemical robustness and its applications in batteries, sensing and carbon capture. In the prototypical TAPB-PMDA-COF, formed from a triamine and a dianhydride, the catalyst accelerates the imidization reaction while promoting its reversibility, so that the growing network can continuously repair defects and settle into the thermodynamically favoured crystalline state. Powder X-ray diffraction profiles of the resulting materials show sharp reflections and narrow full widths at half maximum, hallmarks of long-range order that typically require days of solvothermal treatment to achieve.

Control is a second virtue of the method. Because the catalyst acts through noncovalent interactions rather than stoichiometric consumption, the reaction outcome can be tuned simply by varying the catalyst-to-monomer ratio. This knob allows the team to balance reaction rate against error correction: too little catalyst leaves the system slow and kinetically trapped, while the right proportion drives rapid bond formation and rapid bond exchange in parallel, the combination that crystalline polymer growth requires. The same logic extends across linkage chemistries, as the team showed by preparing the imine-linked TPB-DMTP-COF, the hydrazone-linked COF-43 and the sp2-carbon-conjugated sp2c-COF-16 under the same catalytic regime.

Theoretical calculations by Hongde Yu and Thomas Heine at the Technical University of Dresden, performed with density functional theory, support this mechanistic picture. The computations indicate that hydrogen-bonding interactions with the catalyst stabilize the transition states of the linkage-forming reactions and lower activation barriers for both the forward and reverse directions. Reversibility is the crucial ingredient: a network that can break and remake its bonds while it forms is one that can anneal itself into crystallinity, whereas an irreversible polymerization locks in disorder.

Scalability has long been the Achilles heel of COF chemistry, because many celebrated syntheses yield only tens or hundreds of milligrams after days of reaction. The hydrogen-bonding protocol supports a 1,000-fold scale-up, and the catalyst itself can be reused, addressing both the cost and the waste streams that would otherwise accompany industrial production. The scaled materials retain the high crystallinity and porosity of their small-batch counterparts, suggesting that the catalytic mechanism is robust to the heat- and mass-transfer realities of larger reactors.

The practical payoff is illustrated by proton conduction, a property central to fuel cells and electrolyzers. COFs prepared by the new route achieve benchmark proton conductivity, consistent with the team’s earlier work showing that crystalline porous frameworks can serve as exceptional proton-conducting electrolytes when their pores are engineered with appropriate carrier chemistry. Because the hydrogen-bonding synthesis delivers frameworks with well-defined channels and high surface areas, the resulting membranes combine the structural order needed for efficient transport with the mechanical and chemical stability demanded by devices.

The strategy also draws on a distinguished lineage in organic chemistry. Explicit hydrogen-bonding organocatalysis, pioneered for enantioselective reactions by chemists such as Peter Schreiner and Eric Jacobsen, relies on small-molecule donors that activate substrates without transferring protons. Applying that philosophy to polymer crystallization is conceptually elegant: the same interactions that guide a single reaction’s transition state can, when applied throughout a growing network, guide the entire system toward order. The result is a synthesis that is simultaneously faster, milder and more general than the harsh protocols it replaces.

For a field whose promise has often outrun its practicality, the message is striking. A cheap, recyclable heterocycle, acting through nothing more exotic than hydrogen bonds, can now build some of the most sophisticated materials in chemistry in hours instead of days, at gram scale instead of milligram scale, and with the crystalline quality that applications demand. If the approach proves as general across monomer families as the initial results suggest, hydrogen-bonding catalysis may become the default route to covalent organic frameworks, and the porous architectures built from it may finally move from the pages of review articles into the membranes, electrodes and catalysts of working technology.

Subject of Research: Hydrogen-bonding organocatalysis for the rapid, scalable synthesis of crystalline covalent organic frameworks

Article Title: Synthesis of covalent organic frameworks through hydrogen-bonding catalysis

Article References: Ye, X., Tao, S., Yu, H., Heine, T., Shao, H., Mu, X., Liu, Y., Xu, H., Lin, M., & Jiang, D. (2026). Synthesis of covalent organic frameworks through hydrogen-bonding catalysis. Nature Synthesis. https://doi.org/10.1038/s44160-026-01180-8

Image Credits: AI Generated

DOI: 10.1038/s44160-026-01180-8

Keywords: covalent organic frameworks, hydrogen-bonding catalysis, benzimidazole, organocatalysis, porous materials, imide-linked COFs, crystallinity, proton conduction, polymer synthesis, Nature Synthesis, scale-up, reversible polymerization

The central component of any solid-state battery is the electrolyte, the medium through which charge-carrying ions shuttle between electrodes while electrons are forced around the external circuit. Liquid electrolytes dominate today’s commercial cells, but they bring well-documented problems: flammability, leakage, volatility, and complicated packaging. Solid polymer electrolytes promise a way around these hazards, yet many of the synthetic polymers used to make them, such as poly(vinyl alcohol) and polyacrylonitrile, are derived from petrochemicals and resist degradation. Biopolymer electrolytes offer an alternative route. Natural polysaccharides and plant-derived materials are renewable, inexpensive, and rich in oxygen-containing functional groups that can host mobile ions. Over the past decade, research groups have explored tamarind seed polysaccharide, iota-carrageenan, pectin, gellan gum, cellulose acetate, sodium alginate, agar, and even Moringa oleifera seeds as ion-conducting hosts. The new study adds a familiar garden herb to that growing roster.

The team’s method was deliberately simple. Leaves of Plectranthus amboinicus were processed and blended with ammonium nitrate, NH4NO3, in varying proportions using the solution casting technique, a low-energy process in which a dissolved mixture is poured into a mold and left to dry into a free-standing film. The resulting bio-membranes were then interrogated with a battery of characterization techniques: X-ray diffraction to probe their internal structure, differential scanning calorimetry and thermogravimetric analysis to assess thermal behavior, electrochemical impedance spectroscopy to measure ionic conductivity, linear sweep voltammetry to test electrochemical stability, and ion transport number measurements to confirm which charge carriers were actually moving.

The structural findings explain much of the material’s performance. X-ray diffraction revealed that the films were predominantly amorphous, meaning their molecular chains lacked the long-range ordered packing of a crystal. This matters because ion transport in polymer electrolytes proceeds through flexible, disordered regions: amorphous chains segment and rearrange with thermal motion, opening transient pathways through which small ions can hop. The most amorphous membrane, labeled PALN3, contained 1 gram of Plectranthus amboinicus leaf material complexed with 0.8 percent molecular weight of ammonium nitrate. In crystalline regions, by contrast, polymer chains are locked in place and ions are trapped or blocked. The amorphous character of the best composition thus set the stage for the conductivity results that followed.

And those results were striking. Electrochemical impedance spectroscopy showed that the PALN3 membrane achieved an ionic conductivity of 1.18 times ten to the minus two siemens per centimeter, a figure that places it among the highest values reported for biopolymer electrolyte systems. For context, many undoped biopolymer membranes conduct at rates six or more orders of magnitude lower. The ammonium nitrate salt is the key additive: when ammonium ions dissociate from nitrate counterions within the leaf-derived polymer matrix, they provide mobile proton carriers, while the salt disrupts chain packing and further suppresses crystallinity. The researchers also computed transport parameters using an equivalent circuit formalism developed by A. K. Arof, a widely used analytical approach that separates bulk, grain boundary, and electrode contributions from the impedance response.

Proton conduction itself is a fascinating and unusual branch of ion transport. Unlike lithium or sodium ions, which drag a solvation shell through the electrolyte in a vehicle-like mechanism, protons are far too small to exist freely in a condensed medium. Instead, they typically migrate through hydrogen-bonded networks via the Grotthuss mechanism, essentially relayed from one hydrogen-bonded site to the next, like a bucket brigade passing water along a line. Plant-derived polymers, dense with hydroxyl, ether, and carbonyl groups, are naturally rich in hydrogen-bonding sites, which is precisely why they make such effective proton hosts. Recent work in the literature, including studies published in Communications Chemistry, has focused on directly observing this proton transfer process, and the field increasingly recognizes biological and bioinspired materials as ideal scaffolds for engineering Grotthuss-type conduction.

Before a membrane can serve in a device, it must survive the electrochemical environment. The team’s thermogravimetric analysis established the material’s thermal stability window, while linear sweep voltammetry confirmed that the electrolyte remains electrochemically stable across the operating range of the cell. Ion transport number measurements verified that protons, rather than electrons or other ionic species, dominate the conduction, a crucial check because electronic leakage would cause self-discharge and render the membrane useless as a battery separator. With these criteria satisfied, the researchers selected the highest-conductivity PALN3 membrane as the electrolyte for fabricating a primary proton-conducting battery.

The assembled cell delivered an open-circuit voltage of 1.64 volts, a respectable figure for a proton battery built from a plant-based electrolyte, comparable to the nominal voltages of many conventional primary chemistries. The team then examined the battery under different load conditions to assess how the voltage and current output held up as the cell was asked to do real work. Load testing is where laboratory curiosities either prove their mettle or fall apart, since internal resistance and mass transport limitations typically cause voltage to sag under current draw. While the study reports the device as a primary, non-rechargeable cell, the demonstration completes the full chain from raw leaf to functioning electrochemical device, a pipeline that earlier work from the same research community has applied to Centella asiatica, Peltophorum pterocarpum, and Ocimum sanctus membranes.

The appeal of this approach extends beyond novelty. Plectranthus amboinicus is fast-growing, widely cultivated, and requires no exotic processing infrastructure, and ammonium nitrate is an inexpensive commodity chemical. Solution casting needs no high temperatures or vacuum systems, making the entire fabrication route accessible and low-carbon. At end of life, a biodegradable membrane avoids the persistent waste problems associated with synthetic polymer separators. None of this means herb-based proton batteries will displace lithium-ion in smartphones tomorrow; primary cells, energy density, cycle behavior, and scale-up all remain open questions, and the published abstract does not report long-term cycling data. But as a proof of concept, the work is compelling. It suggests that the next generation of safe, sustainable solid-state energy storage might be grown in a garden rather than refined from a mine, and that the humble oregano pot on a windowsill could one day share a lineage with the battery in your pocket.

Subject of Research: A plant-derived biopolymer electrolyte from Plectranthus amboinicus leaves and ammonium nitrate for proton-conducting solid-state batteries

Article Title: Development of biomaterial plectranthus amboinicus for proton conducting battery

Article References: Kowsalya, S., Prameela, P., Selvasekarapandian, S., & Devi, S. K. (2026). Development of biomaterial plectranthus amboinicus for proton conducting battery. Ionics. https://doi.org/10.1007/s11581-026-07569-x

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07569-x

Keywords: Plectranthus amboinicus, biopolymer electrolyte, proton conduction, ammonium nitrate, solid-state battery, solution casting, ionic conductivity, X-ray diffraction, electrochemical impedance spectroscopy, Grotthuss mechanism, primary battery, sustainable energy materials

The work began from a familiar frustration in electrolyte research. Proton-conducting polymers such as Nafion dominate commercial fuel cells, but they come with limits, including modest thermal stability and a hydrated architecture that is difficult to engineer at the atomic level. Metal-organic frameworks, covalent organic frameworks, graphene oxide and polyoxometalates have all been explored as alternatives, and their pore networks can indeed move protons quickly. The catch is that large, continuous pores that help protons can also let hydrogen gas sneak across the electrolyte, a phenomenon known as crossover that wastes fuel and degrades efficiency. Oxide ceramics, by contrast, are thermally robust and chemically tunable, but they are usually studied as dense, micrometer-scale bulk materials in which protons diffuse sluggishly through the grain interior, often trapped at defect sites, with correspondingly high activation energies.

The researchers’ strategy was to take an oxide and flatten it. They synthesized a family of layered compounds with the formula LiMM’O6, where M is tantalum or niobium and M’ is tungsten or molybdenum, built from corner-sharing TaO6 or NbO6 octahedra interleaved with lithium layers. Acid treatment swapped the lithium for protons, and an aqueous solution of tetrabutylammonium hydroxide then pried the charged layers apart into individual negatively charged nanosheets. Vacuum filtration of the resulting colloidal dispersion, confirmed by the telltale Tyndall light-scattering effect, produced free-standing, semi-transparent membranes in which the nanosheets are strongly oriented with their crystallographic c-axes perpendicular to the film. A final acid immersion replaced the bulky organic cations with protons, yielding the target HMM’O6 membranes. X-ray diffraction showed that the interlayer spacing in the membrane form of HTaWO6 expanded to 1.27 nanometers, substantially larger than the 0.92 nanometers of the parent powder, and thermogravimetric analysis revealed that the exfoliated membrane holds far more surface water than the bulk, a hint that hydration, and with it proton mobility, had been enhanced.

Impedance spectroscopy from 80 down to 40 degrees Celsius under fully humidified conditions told a striking story. Among the four compositions tested, the HTaWO6 membrane was the clear winner for cross-plane transport, reaching 1.7 millisiemens per centimeter at 80 degrees with an activation energy of just 0.224 electronvolts, small enough to indicate weak temperature dependence, a marked contrast to bulk oxide ceramics. When the team measured transport along the membrane plane, the picture inverted: the molybdenum-containing HTaMoO6 led with an in-plane conductivity of 0.20 siemens per centimeter at 80 degrees, actually surpassing commercial Nafion over much of the measured temperature range. Crucially, the ratio of in-plane to out-of-plane conductivity, the anisotropy, was only 28 for HTaWO6, roughly one order of magnitude, whereas HTaMoO6 and HNbMoO6 showed anisotropies of about 290-fold and 300-fold, squarely in the range typical of stacked nanosheet materials.

Before celebrating, the authors verified what was actually doing the conducting. Conductivity fell steeply as humidity dropped from 100 to 40 percent, consistent with a water-mediated proton mechanism. Switching the atmosphere from H2O to D2O raised the membrane’s resistance by a factor of 1.56 at 80 degrees, the classic H/D isotope effect that fingerprints proton transport. A water-vapor concentration cell produced an electromotive force close to the theoretical Nernst value, confirming that protons, not hydroxide ions, dominate the current. Together these tests established that the impressive cross-plane conduction in HTaWO6 is genuine proton conduction.

How does it compare with the competition? The 1.7 millisiemens per centimeter out-of-plane figure is 36 to 170 times higher than calcium niobate-based nanosheet membranes such as HCa2Nb3O10 and HCa2Nb2.5Ti0.5O10, and 124 to 381 times higher than strontium tantalate-based nanosheets. Part of the advantage comes from a low activation energy, comparable to the best strontium tantalates and far below the 0.38 to 0.65 electronvolts of the calcium niobates, and part comes from an unusually high pre-exponential factor in the Arrhenius relationship, which the authors attribute to the abundance of accessible conduction pathways in the curled morphology.

The morphology itself turned out to be the real surprise. Atomic force microscopy of the TBA/TaWO6 nanosheets revealed rod-like objects with heights of about 26 nanometers, far too tall for a single inorganic monolayer. High-angle annular dark-field scanning transmission electron microscopy resolved the mystery: the rods are nanotubes, formed when the flat nanosheets roll themselves up, with 63 percent of the observed sheets curled. The rolled cross-sections, about 27 nanometers tall and 39 nanometers wide, resemble flattened ellipses rather than perfect circles, which neatly explains why the anisotropy does not vanish entirely but merely shrinks to one order of magnitude. The team proposes that the tubular geometry shortens the effective diffusion path through the membrane thickness and provides continuous one-dimensional channels that bypass the interlayer barriers that cripple flat-sheet stacks. Composition matters, too: mixing tungsten and molybdenum in TaMo0.4W0.6O6 produced a mixture of flat and partially rolled sheets, showing that chemical composition governs the tendency to roll, even though the microscopic origin of the rolling remains unresolved. Meanwhile, the HNbWO6 sheets, which stayed flat but grew nanopores tens of nanometers across, also conducted well out-of-plane, echoing earlier observations in graphene oxide that nanopores offer extra cross-plane routes.

Fuel-cell tests translated the conductivity numbers into device performance. A 37-micrometer HTaWO6 membrane delivered an open-circuit voltage of 1.0 volt and, at 80 degrees, a maximum current density of 191 milliamperes per square centimeter and a power density of 41 milliwatts per square centimeter, several times better than the other three compositions. Thinning the membrane changed everything: at 18 micrometers the power density rose to 67 milliwatts per square centimeter, and at just 1 micrometer the cell reached 1.26 amperes per square centimeter and 294 milliwatts per square centimeter, with the open-circuit voltage holding at 1.00 volt, evidence of low gas crossover and good electronic insulation. Those figures exceed previously reported oxide nanosheet electrolytes by factors of dozens to hundreds. Post-mortem characterization showed the membrane’s crystal structure intact after testing, and the material resisted acid dissolution. A further boost came from treating the membrane with methanesulfonic acid, which widened the interlayer spacing, grafted sulfonic acid groups onto the sheets, improved water retention, and lowered interfacial resistance at the electrode. The membrane even operated at 100 degrees, albeit with reduced output as hydration fell away.

The broader lesson is that in two-dimensional ion conductors, geometry can matter as much as chemistry. By introducing curvature into planar nanosheets, the researchers reconciled the short diffusion lengths of nanoscale thickness with efficient cross-plane transport, a combination long thought to be out of reach for layered oxides. They argue the concept extends well beyond nanotubes to nanowires, nanospirals and nanofiber assemblies, and beyond protons to lithium, oxide-ion and hydride-ion conductors, any system where ions must move perpendicular to a stacked architecture. If morphology engineering proves general, the humble act of rolling a sheet could become a standard tool for designing the thin, stable, fast electrolytes that next-generation electrochemical devices demand.

Subject of Research: Morphology-engineered oxide nanosheet membranes for out-of-plane proton conduction in fuel-cell electrolytes

Article Title: Overcoming Out‐of‐Plane Conduction by Changing Nanosheet Morphology

Article References: Sakuda, Y., Hatakeyama, K., Yuji, A., Tsugawa, T., Ueno, K., Tomatsu, S., Utami, Z. D., & Ida, S. (2026). Overcoming Out‐of‐Plane Conduction by Changing Nanosheet Morphology. Advanced Science, Article e78017. https://doi.org/10.1002/advs.78017

Image Credits: AI Generated

DOI: 10.1002/advs.78017

Keywords: proton conduction, nanosheets, nanotubes, HTaWO6, fuel cells, oxide electrolytes, conductivity anisotropy, two-dimensional materials, exfoliation, impedance spectroscopy, morphology engineering, Advanced Science