The central challenge the researchers set out to solve is a familiar one in battery materials science. Graphite, the standard anode in commercial lithium-ion batteries, stores lithium ions between flat sheets of carbon, and its performance at very high charge rates is limited by how quickly ions can diffuse into the bulk of the material. Three-dimensional graphene — a porous, interconnected network of graphene sheets — has long been considered a promising alternative because it combines high electrical conductivity with an open framework that ions can access from many directions. But making 3D graphene is only half the battle. Its macroscopic shape, whether it forms granules, plates, or a continuous honeycomb, and its microscopic surface texture, particularly the abundance of tiny micropores, both strongly influence how fast lithium ions can reach the storage sites and how efficiently electrons can travel through the electrode. Until now, tuning these two features at different length scales has required multiple, often incompatible, processing steps.

The team’s solution is a metallothermic reduction strategy, in which a reactive metal strips the oxygen from CO2, leaving elemental carbon behind. The trick is that the choice of metal reductant — sodium, potassium, or magnesium — does more than simply liberate the carbon. It dictates the entire architecture of the resulting graphene. With magnesium as the reductant, the carbon condenses into a granulated structure. With potassium, it forms plate-like sheets. But with sodium, the reaction produces something far more interesting: a three-dimensional interconnected honeycomb framework, in which graphene walls branch and merge into a continuous conductive skeleton riddled with pores at the nanometre scale. In other words, simply swapping one alkali metal for another transforms the final material from a collection of particles into a fully connected, sponge-like network.

The sodium-derived honeycomb graphene, which the authors call Na-3DG, is the star of the study. It has a specific surface area of 765.5 square metres per gram — a vast internal area packed into a small mass — and, remarkably, 84.9 percent of its pore volume is in the micropore range, the smallest class of pores. This is unusual because most porous carbons distribute their pore sizes across a broad spectrum, mixing micropores with larger mesopores and macropores. Here, the micropores dominate, and that dominance turns out to be the key to the material’s ultrafast lithium storage. Micropores act as short-range windows through which lithium ions can penetrate the electrode surface directly, rather than having to snake their way through long, tortuous channels. The result is a dramatic reduction in the distance ions must travel and, consequently, in the time it takes to charge and discharge the cell.

But porosity alone is not enough. If the carbon network were interrupted — if the graphene sheets were broken, poorly connected, or contaminated with defects — electrons could not move quickly enough to keep up with the incoming ions, and the electrode would fail at high rates. To verify that the sodium route produces a truly continuous conductive network, the researchers turned to X-ray photoelectron spectroscopy, which probes the chemical bonding of the carbon atoms, and to four-probe conductivity measurements, which directly measure how well the material conducts electricity. The spectroscopy showed that Na-3DG retains a highly continuous network of sp2-hybridized carbon — the same bonding motif that gives pristine graphene its exceptional electron mobility. The conductivity measurements confirmed this: the intrinsic electrical conductivity of the material is 16.4 siemens per centimetre, a high value for a porous carbon. Electrochemical impedance spectroscopy, which measures the resistance a battery cell presents to alternating current, revealed a series resistance of just 1.8 ohms and a charge-transfer resistance of 70.9 ohms, both low figures that indicate electrons and ions can move through the electrode with minimal obstruction.

The researchers attribute the material’s exceptional performance to a synergistic effect between two structural features that work together rather than in isolation. The continuous three-dimensional conductive skeleton minimizes what is known as interparticle contact resistance — the electrical resistance that arises where separate particles of an electrode material touch one another. In conventional electrodes made of discrete particles, electrons must hop from particle to particle, and each junction adds resistance. In Na-3DG, because the graphene network is continuous, electrons can travel along uninterrupted pathways. Meanwhile, the abundant surface micropores provide short-range ion-penetration windows, allowing lithium ions to access the carbon surface from many directions at once. The combination — fast electron transport through a connected skeleton and fast ion transport through a microporous surface — is what enables the material to sustain such extreme charge rates without collapsing.

The electrochemical results bear this out. When tested as the anode in a lithium-ion half-cell, Na-3DG delivered more than 200 mAh per gram at a rate of 150C. To put that in perspective, a rate of 150C means the battery would be fully discharged in about 24 seconds — an extraordinary figure for any anode material, and one that approaches the limits of what ion transport physics allows. At a more moderate rate of 50C, the material retained 88.9 percent of its first-cycle capacity after 2,000 charge-discharge cycles, demonstrating not only speed but also durability. Long-term cycling stability is often the Achilles heel of high-rate anodes, because repeated insertion and removal of lithium ions can mechanically stress the material and degrade its structure. The fact that Na-3DG holds up over thousands of cycles suggests that its honeycomb framework is robust enough to accommodate the strain.

Beyond its immediate performance, the study carries a broader significance for how we think about carbon materials and the carbon cycle. The starting material is CO2 — a waste product and a greenhouse gas — and the product is a high-value carbon material with a precisely engineered structure. The authors describe this as a strategy for upcycling CO2 into hierarchical porous carbon, a term that captures the idea of transforming a low-value molecule into a material with sophisticated, multi-scale architecture. This is not the first time CO2 has been converted into graphene; previous work by some of the same researchers and by other groups has explored metallothermic and plasma-based routes. But the new study is distinguished by the degree of control it offers: by simply changing the metal reductant, the macroscopic morphology can be continuously tuned from granulated to plate-like to honeycomb, all within a single reaction. That level of morphological control, achieved in one step, is rare in materials synthesis and points toward a more general design principle for porous carbons.

The work also contributes to a growing body of research on fast-charging lithium-ion batteries, a field that has become one of the most active in energy storage science. Fast charging is widely seen as a critical enabler for electric vehicles, because the time it takes to recharge remains a major barrier to widespread adoption. The bottleneck, however, is not the battery’s total capacity but its ability to accept lithium ions quickly without triggering unwanted side reactions, such as lithium plating on the anode, which can degrade the cell and pose safety risks. Anode materials that can accommodate rapid ion insertion — like the honeycomb graphene described here — are therefore central to the fast-charging agenda. The study’s structural design principles, particularly the synergy between a continuous conductive skeleton and abundant surface micropores, offer a template that other researchers can apply to different carbon architectures and even to non-carbon materials.

For now, the material remains a laboratory demonstration, and translating it into commercial batteries will require scaling up the synthesis, integrating it into full cells with compatible cathodes and electrolytes, and validating its performance under realistic operating conditions. But the study’s message is clear and, in its own way, striking: the same molecule that drives climate change can be chemically reimagined as the backbone of a next-generation battery, provided the architecture is designed with the same care as the chemistry itself. By showing that a single reaction, guided by the choice of a metal reductant, can produce a 3D graphene with a honeycomb topology, an overwhelming micropore fraction, and a continuous sp2 carbon network, the researchers have not only advanced the state of the art in anode materials — they have also offered a glimpse of a future in which carbon capture and energy storage are not separate endeavours but two sides of the same molecular coin.

Subject of Research: Synergistic tuning of topology and microporosity in 3D graphene via direct CO2 conversion for ultrafast lithium storage

Article Title: Synergistic tuning of topology and microporosity in 3D graphene via direct CO2 conversion for ultrafast lithium storage

Article References: Wang, L., Wang, X., Wu, X., Luo, J., Liu, M., & Toan, S. (2026). Synergistic tuning of topology and microporosity in 3D graphene via direct CO2 conversion for ultrafast lithium storage. Ionics. https://doi.org/10.1007/s11581-026-07593-x

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07593-x

Keywords: Synergistic, tuning, topology, microporosity, graphene, direct, conversion, ultrafast, lithium, storage, scientific research

The research team, led by Wojciech Jerzak of AGH University of Krakow, pyrolyzed both materials at 700, 800 and 900 degrees Celsius in a fixed-bed reactor flushed with high-purity nitrogen. Each 1.5-gram sample was held at the target temperature for one hour, after which the resulting chars were ground, sieved and subjected to a battery of analytical techniques including Fourier-transform infrared spectroscopy, X-ray diffraction, X-ray fluorescence, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and nitrogen sorption analysis. Carbon dioxide uptake was then measured at 20 degrees Celsius across pressures ranging from 0.5 to 110 kilopascals.

The starting materials could hardly have been more different. Chicken manure, collected from a poultry farm in southern Poland, contained just 8 percent fixed carbon but a hefty 26.4 percent ash, along with 4.1 percent nitrogen. Onion peels from a processing facility in the Kuyavian-Pomeranian Voivodeship were richer in combustible material, with 56.4 percent volatile matter, 14.9 percent fixed carbon and a lignocellulosic structure containing substantial cellulose and hemicellulose. X-ray fluorescence showed that calcium oxide dominated the ash of both feedstocks, at 48.8 percent for the manure and 40.8 percent for the peels, but the manure also carried elevated potassium, phosphorus, magnesium and sulphur, while the peels were unusually rich in silica at 33.8 percent.

As pyrolysis temperature climbed, both feedstocks lost mass, moisture and volatile components while their ash fractions concentrated in the solid residue. Manure biochar ash content soared from 26.4 percent in the raw material to 65.2 percent at 900 degrees Celsius, while onion peel biochar ash rose from 14.9 to roughly 41.8 percent. Hydrogen contents in both biochars fell below 1 percent, and nitrogen in the manure chars dropped from 4.1 to between 1.1 and 1.8 percent, reflecting the thermal cracking of volatile compounds and the release of small nitrogenous molecules. Onion peel biochars, by contrast, concentrated carbon to around 50 to 52 percent, more than the manure chars managed, thanks to their lower initial mineral burden.

Spectroscopy traced the chemical evolution in fine detail. Infrared spectra showed the progressive disappearance of hydroxyl, aliphatic and carbonyl bands with rising temperature, signalling dehydration, decarboxylation and the growth of a condensed aromatic carbon matrix. Yet phosphate and carbonate signals persisted in the manure-derived chars, underscoring the thermal stability of their inorganic constituents. X-ray diffraction revealed dramatic mineral reorganisation: at 700 degrees Celsius the manure char held quartz, portlandite and rutile, but by 800 and 900 degrees Celsius the ash had transformed into calcium oxide, whitlockite-type calcium-magnesium phosphates, magnesite, oldhamite and eventually sulfoapatite. The onion peel chars followed a different path, developing graphitic carbon alongside quartz, kalsilite, sodium carbonate and, at the highest temperature, the stable alkali aluminosilicate sanidine.

Electron microscopy captured the morphological consequences. Manure biochars remained dense, heterogeneous aggregates with no well-defined pore network, their high mineral content apparently filling or masking the developing carbon porosity. The onion peel chars told a more elegant story: at 700 degrees Celsius they retained elongated, layered fragments of the original plant tissue, and at 800 degrees Celsius they developed a striking channel-like structure the authors liken to a fish skeleton, with aligned, interconnected spaces carved out by devolatilisation. At 900 degrees Celsius, however, that ordered architecture began to fragment and partially collapse, a warning that excessive heat can destroy the very structure adsorbent designers hope to build.

Porosity measurements quantified these visual impressions. The onion peel biochar produced at 900 degrees Celsius achieved the highest specific surface area of the entire study, 109.8 square metres per gram—more than three times that of its 800-degree counterpart and nearly 6.5 times that of the 700-degree sample—with micropores contributing up to 60 percent of the internal surface in the intermediate-temperature samples. Manure biochars reached more modest areas between 14.0 and 36.2 square metres per gram, but their average pore diameter also shrank steadily with temperature, indicating progressive micropore refinement.

The carbon dioxide adsorption results upended the expectation that bigger surface area always means better capture. Among the onion peel chars, the 700-degree sample—despite its modest 17 square metres per gram—delivered the highest uptake, 26.6 cubic centimetres per gram at 100 kilopascals, while the 900-degree sample with the largest surface area actually adsorbed less. The researchers attribute this to pore widening and a shrinking population of narrow ultramicropores, those cavities below 0.7 nanometres whose dimensions closely match the kinetic diameter of CO2 and which nitrogen adsorption at cryogenic temperatures cannot fully resolve. Residual oxygen-containing surface groups may also enhance CO2-surface interactions in the cooler char.

The manure biochars behaved in almost mirror-image fashion, with CO2 uptake rising steadily as pyrolysis temperature increased, tracking the growth of microporosity and surface area. But texture alone could not explain the performance of the 900-degree manure char, which captured substantial CO2 despite a smaller surface area than its onion peel rivals. X-ray diffraction and fluorescence pointed to the missing piece: calcium oxide and calcium-rich phosphate phases that furnish basic adsorption sites with a strong affinity for acidic CO2 molecules, potentially even fixing some of the gas chemically as carbonate or bicarbonate species. In these mineral-rich chars, capture is a partnership between physical pore-filling and mineral-assisted interaction.

The practical lesson is that biochar design must be matched to feedstock chemistry. For lignocellulosic wastes like onion peels, the goal should be preserving narrow micropores rather than maximising total surface area, and avoiding the pore widening and structural collapse that come with excessive heat. For manures, engineers should exploit the inherent calcium, magnesium and potassium phases that add a chemical dimension to capture. Converting two problematic wastes into tailored carbon sorbents in a single thermal step offers a double dividend—waste valorisation and carbon management—grounded not in exotic chemistry but in a careful reading of what heat does to the organic and mineral halves of agricultural residue.

Subject of Research: Thermal conversion of chicken manure and onion peels into biochars for carbon dioxide adsorption

Article Title: Effect of thermal treatment on the structure and CO2 adsorption capacity of biochar from chicken manure and onion peels

Article References: Effect of thermal treatment on the structure and CO2 adsorption capacity of biochar from chicken manure and onion peels. (n.d.). https://doi.org/10.1007/s10098-026-03598-2

Image Credits: AI Generated

DOI: 10.1007/s10098-026-03598-2

Keywords: biochar, pyrolysis, CO2 capture, chicken manure, onion peels, carbon adsorption, microporosity, mineral phases, waste valorisation, X-ray diffraction, Raman spectroscopy, surface area