The concept at the heart of the study is Power-to-Methane, an energy storage strategy in which surplus renewable electricity is used to make hydrogen through water electrolysis, and that hydrogen is then reacted with captured carbon dioxide to produce synthetic natural gas. Because existing gas grids, storage infrastructure and combustion appliances can all handle methane without modification, the approach offers a way to buffer intermittent wind and solar power at terawatt-hour scales. The critical bottleneck, however, is the catalyst. The methanation reaction—CO2 plus four hydrogen molecules yielding methane plus two water molecules—is thermodynamically favored at low temperatures but kinetically sluggish, requiring an efficient catalyst, typically nickel, to proceed at industrially meaningful rates. Conventional nickel catalysts are supported on metal oxides such as alumina or ceria, but researchers have increasingly turned their attention to carbonaceous supports, which offer high surface area, tunable porosity, resistance to acidic species and, crucially, a renewable origin when derived from biomass.

The Spanish team chose olive stones deliberately. Characterization of the raw material revealed an unusually favorable composition for a catalyst support: a volatile matter content of 79 percent by weight, a carbon content of roughly 55 percent by weight, and a notable inventory of inherent metals—potassium, calcium and sodium—that are known to influence both pyrolysis behavior and downstream catalytic activity. Rather than producing biochar through a two-step process of carbonization followed by activation, the researchers employed single-step pyrolysis in which zinc chloride was mixed directly with the biomass before heating. Zinc chloride is a classic chemical activation agent: during carbonization it promotes dehydration, inhibits tar formation, and carves out an extensive network of micropores and mesopores as the precursor is consumed. When the activating agent is subsequently washed away, it leaves behind a highly porous carbon skeleton whose texture reflects the conditions under which it was created.

The experimental design was systematic. The researchers varied the biomass-to-zinc chloride ratio across three levels—1:4, 1:6 and 1:8—and the activation temperature across three values: 400, 600 and 800 degrees Celsius. The results showed a clear trend. Increasing both the zinc chloride loading and the activation temperature raised the carbon content of the resulting biochars and dramatically expanded their surface area, which climbed from 403 square meters per gram at the mildest conditions to a remarkable 1,409 square meters per gram at the most aggressive. That figure places these waste-derived materials firmly in the territory of commercial activated carbons and far above many conventional catalyst supports. Enhanced porosity, in turn, translated directly into greater adsorption capacity, a property that matters for methanation because the reaction requires CO2 molecules to linger in proximity to the active nickel sites long enough to be activated and hydrogenated.

With a family of activated biochars in hand, the team deposited nickel onto them and evaluated the resulting catalysts in CO2 methanation. The interaction between nickel and a support is one of the most consequential parameters in heterogeneous catalysis: strong interactions anchor small, well-dispersed metal particles that resist sintering, whereas weak interactions allow atoms to migrate and coalesce into larger crystallites at elevated temperatures. Reduction studies on the olive-stone-derived catalysts revealed relatively weak nickel–support interactions, and nickel crystallite growth intensified as reduction and reaction temperatures rose. Interestingly, the zinc chloride activation also had an unexpected chemical consequence: the formation of nickel–zinc alloys alongside larger nickel particles. Zinc in close contact with nickel has been shown in other studies to modify the electronic structure of the active metal, and X-ray photoelectron spectroscopy confirmed that in these catalysts the electronic density around nickel was increased—a shift that the authors link to enhanced catalytic activity, since electron-rich nickel surfaces are better positioned to activate CO2 and hydrogenate the resulting intermediates.

The mechanistic picture that emerges from the study is one in which the methanation reaction proceeds primarily through carbon monoxide intermediates—denoted CO in the catalytic literature. In this pathway, CO2 adsorbs onto the nickel surface and is activated, either directly or via surface oxygen species, and is then progressively hydrogenated; the formation of a CO intermediate followed by its stepwise hydrogenation to methane is widely regarded as the dominant route over nickel catalysts. The authors identify CO2 activation and the subsequent hydrogenation steps as the critical bottlenecks, which explains why the increased electron density around nickel—and the improved adsorption capacity of the highly porous carbon supports—mattered for performance. The porous architecture of the biochar serves a dual function: it maximizes the exposed nickel surface available for adsorption and it channels reactant gases toward the active sites, while the carbon matrix itself moderates the electronic environment of the metal in ways that oxide supports cannot easily replicate.

Performance testing identified a clear winner among the prepared materials: a catalyst designated 10Ni-1:6-800, containing 10 percent nickel on a biochar activated with a 1:6 biomass-to-zinc chloride ratio at 800 degrees Celsius. This catalyst achieved a CO2 conversion of approximately 20 percent. While that figure is modest compared with the conversions achievable at higher pressures and temperatures over optimized industrial catalysts, the result must be read in context. The support is essentially free—a byproduct of olive oil production—synthesized in a single pyrolysis step without the sol-gel chemistry, calcination regimes or rare-earth promoters that inflate the cost of conventional catalysts. For a first-generation waste-derived material, the authors argue, the demonstration of meaningful catalytic activity establishes a genuine proof of concept and a foundation for optimization through nickel loading refinement, promoter addition and reaction condition tuning.

The findings sit within an active research lineage. Previous work has shown that biochars derived from wheat straw, almond shells, corn stover and coconut husk can all serve as catalyst supports for hydrogenation and methanation reactions, and the same Castilla-La Mancha group has previously demonstrated olive stone biochars as CO2 adsorbents and as supports for methanation in earlier publications. What distinguishes the new study is its systematic interrogation of two variables—activation agent concentration and activation temperature—that are often optimized only cursorily in biomass-to-catalyst pipelines. By quantifying how each parameter propagates through the material chain, from biochar texture to nickel dispersion and electronic state, and ultimately to catalytic conversion, the study provides a rational design map for anyone seeking to reproduce or improve the approach with other lignocellulosic feedstocks.

The broader implications extend beyond the laboratory. Activated carbon production worldwide still relies heavily on fossil-derived precursors such as coal and on energy-intensive activation processes, while catalyst manufacturers depend on mined alumina, titania and ceria. Substituting agro-industrial waste for these inputs addresses two environmental burdens simultaneously: it diverts residue from disposal or low-value combustion, and it reduces the embodied carbon of the catalysts needed for greenhouse-gas utilization technologies. The economics are particularly attractive in Mediterranean regions such as southern Spain, where olive stones accumulate in millions of tonnes annually at olive mills and are already collected as biomass fuel. Converting even a fraction of this stream into high-surface-area catalyst supports could anchor local circular economies around CO2 conversion plants, in which the same agricultural region supplies both the support material and, via biogenic CO2 from bioenergy or biogas upgrading, part of the carbon feedstock for synthetic methane production.

Challenges remain before such visions materialize. Weak nickel–support interactions, while beneficial in some respects, raise questions about long-term catalyst stability under sustained high-temperature operation, since particle sintering is a leading cause of deactivation. Carbon supports are also susceptible to gasification under methanation conditions in the presence of hydrogen at elevated temperatures, and the inherent alkali metals in olive stone ash could influence both activity and durability in ways that require extended lifetime testing to resolve. Nonetheless, the study demonstrates that the journey from an olive pit to a functioning CO2-to-fuel catalyst is not merely possible but chemically coherent, with every step—activation, nickel deposition, electronic modification and reaction mechanism—traceable and tunable. As Power-to-Methane projects scale up across Europe in pursuit of sector coupling and grid-scale renewable storage, catalysts grown from orchard waste may prove to be exactly the kind of unglamorous, abundant and inexpensive material that helps make carbon recycling economically real.

The researchers created a composite material by attaching cellulose-derived carbon quantum dots, known as CQDs, to CdS nanoparticles. In laboratory tests, the optimized catalyst generated 7,812.5 micromoles of hydrogen per gram during five hours of visible-light irradiation. Under the same conditions, unmodified CdS produced 4,633.5 micromoles per gram. The results, published in Sustainable Carbon Materials, suggest that a renewable carbon material can help solve one of the central problems in solar photocatalysis: keeping light-generated electrical charges apart long enough to drive useful chemical reactions.

Hydrogen is often described as an energy carrier rather than a primary energy source. It can be produced using electricity or sunlight and later used in fuel cells, industrial processes, or energy-storage systems. When consumed in a fuel cell, hydrogen produces water rather than carbon dioxide at the point of use. Photocatalytic hydrogen production is especially attractive because it seeks to use sunlight directly to power the chemical conversion of protons into hydrogen gas. However, the efficiency and durability of photocatalytic materials remain significant obstacles to practical deployment.

CdS is a promising photocatalyst because its relatively narrow bandgap allows it to absorb a substantial portion of visible light. When CdS absorbs photons with sufficient energy, electrons are promoted from the valence band to the conduction band, leaving positively charged holes behind. The excited electrons can reduce protons to form hydrogen, while the holes participate in oxidation reactions. The difficulty is that electrons and holes can rapidly recombine, releasing their energy as heat or light before they reach the surface. CdS can also suffer from photocorrosion, a process that gradually damages the semiconductor during illumination.

To modify the material, the researchers produced CQDs from cellulose through a hydrothermal process. Cellulose, the structural polymer found in plant cell walls, can be converted under heat and pressure into nanoscale carbon particles with electronic and optical properties that differ from those of bulk carbon. Microscopy showed that the CQDs averaged approximately 3.5 nanometers in diameter and were distributed on the surface of CdS nanoparticles. The attachment process preserved the general structure of the CdS while creating an interface where charge transfer could occur.

The resulting composites absorbed visible light more effectively than pure CdS and displayed slightly narrower bandgaps. The best-performing formulation, designated 12CQDs/CdS, had a bandgap of approximately 2.01 electron volts, compared with 2.05 electron volts for unmodified CdS. Although the numerical shift appears small, changes in band structure and interfacial electronic states can influence how efficiently a photocatalyst uses incoming photons and how readily excited electrons move through the material.

The clearest evidence of improved charge management came from electrochemical measurements. The optimized CQDs/CdS composite reached an average photocurrent density of 49.9 microamperes per square centimeter, nearly 20 times higher than the 2.63 microamperes per square centimeter measured for pure CdS. A higher photocurrent indicates that more photogenerated charges are reaching the electrode and participating in external electrical processes rather than recombining inside the catalyst. The composite also showed lower charge-transfer resistance, suggesting that electrons could move more readily across the CQD–CdS interface.

The researchers propose that the carbon quantum dots perform two related functions. First, they act as photosensitizers, helping the material harvest visible light. Second, they serve as electron acceptors that capture excited electrons from CdS and help transport them away from locations where recombination is likely. By improving spatial separation between electrons and holes, the CQDs leave more electrons available to reduce protons into hydrogen. This interfacial process is central to the performance increase: the carbon dots do not simply add more surface area, but actively influence the movement and lifetime of charge carriers.

The study also reveals why adding more of the carbon material is not necessarily better. When the CQD loading becomes excessive, the particles can cover active sites on the CdS surface, block the arrival of light, or hinder the movement of reactants and products. The strongest performance therefore depended on carefully controlling the amount of CQDs rather than maximizing their concentration. Even at the optimized composition, however, hydrogen production declined during repeated photocatalytic cycles. This decrease indicates that photocorrosion of CdS remains unresolved and could limit the material’s long-term usefulness. Protective surface layers, cocatalysts, engineered heterostructures, and further tuning of CQD surface chemistry may help improve stability. By combining an abundant biomass-derived material with a visible-light semiconductor, the work offers a relatively simple route toward more efficient photocatalysts while reducing reliance on noble metals and elaborate architectures.

Subject of Research: Cellulose-derived carbon quantum dots combined with cadmium sulfide for visible-light photocatalytic hydrogen production.

Article Title: Cellulose carbon quantum dots decorated CdS nanocatalyst for enhanced visible-light photocatalytic hydrogen evolution

News Publication Date: 8-Jun-2026

Web References: Sustainable Carbon Materials: https://www.maxapress.com/scm; DOI: https://doi.org/10.48130/scm-0026-0020

References: Wang Z, Changotra R, Dong G, Yang J, He QS. 2026. Cellulose carbon quantum dots decorated CdS nanocatalyst for enhanced visible-light photocatalytic hydrogen evolution. Sustainable Carbon Materials 2: e025. DOI: 10.48130/scm-0026-0020

Image Credits: Zijing Wang, Rahil Changotra, Guofa Dong, Jie Yang, and Quan Sophia He

Keywords

Photocatalysis, hydrogen evolution, carbon quantum dots, cellulose, cadmium sulfide, visible-light catalysis, renewable energy, solar fuel, nanomaterials, photocorrosion

A research team from several Chinese universities has reported a strategy for improving aqueous zinc-ion batteries, or AZIBs, by modifying an industrial form of manganese dioxide. The researchers found that mechanical treatment known as ball milling can remove oxygen atoms from the manganese dioxide crystal lattice, creating oxygen vacancies that significantly alter the material’s electronic and chemical behavior. Their findings suggest that a relatively inexpensive manufacturing process could transform commercially produced manganese dioxide into a more effective cathode for next-generation energy-storage systems.

Unlike lithium-ion batteries, AZIBs use positively charged zinc ions as the charge-carrying species. Zinc is abundant, inexpensive and already suitable for large-scale manufacturing. The batteries also employ water-based electrolytes containing mild acids or neutral salts rather than volatile organic solvents. This makes them far less prone to ignition and potentially safer for stationary storage installations, where batteries may be deployed in large numbers. However, the technology has been held back by the difficulty of developing cathodes that can rapidly and repeatedly accommodate zinc ions without suffering structural damage.

The team investigated electrolytic manganese dioxide, or EMD, an industrially manufactured material that is relatively cheap, abundant and capable of storing substantial amounts of energy. Manganese dioxide has long attracted attention as a battery electrode, but its limited electrical conductivity can slow electrochemical reactions. During repeated charging and discharging, the material may also undergo phase changes and structural distortion. These processes can promote manganese dissolution into the electrolyte, gradually reducing the battery’s reversible capacity and shortening its useful lifetime.

To address these limitations, the researchers subjected EMD powders to ball milling. In this process, heavy balls repeatedly collide with and shear the powder inside a rotating or vibrating container. The impacts can reduce particle size, introduce defects and modify the arrangement of atoms. In the researchers’ experiments, the mechanical energy was sufficient to drive lattice oxygen out of the manganese dioxide structure. The resulting oxygen vacancies left behind additional electrons and changed the local chemical environment around manganese atoms.

Measurements indicated that the oxygen content of the treated material declined from 68.93 percent to 61.17 percent, while the measured manganese content increased from 31.07 percent to 38.83 percent. The researchers interpreted this shift as evidence that oxygen vacancies had formed within the EMD lattice. These vacancies can improve electronic transport by creating pathways through which electrons move more readily. The modified material also displayed induced half-metallic behavior, in which electrons with one spin orientation conduct like those in a metal while electrons with the opposite spin experience insulating behavior.

The electronic changes were important because they affected how the cathode interacts with both zinc ions and protons. According to the study, oxygen vacancies shifted the energy positions of manganese d-bands and oxygen p-bands. These orbitals determine how strongly atoms bind incoming ions and how easily electrons move through the solid. By adjusting the balance between these interactions, the modified EMD reduced the tendency of zinc ions and hydrogen ions to become trapped at specific sites. That could allow the ions to enter and leave the cathode more smoothly during battery operation.

The researchers also calculated adsorption energies and migration barriers, which describe how strongly ions bind to a material’s surface and how much energy they need to move through its crystal structure. The ball-milled EMD showed more favorable ion-transport characteristics than untreated material, including lower barriers for zinc-ion and proton migration. Faster ion movement can accelerate charging and discharging, while more balanced binding energies can reduce the buildup of chemically immobile species. At the same time, the altered lattice appeared to limit the structural distortions that normally develop as EMD cycles between different chemical states.

The study, published in Nano Research Energy, presents defect engineering as a practical route for upgrading an existing industrial material rather than replacing it with a costly, laboratory-only compound. The researchers argue that the combination of oxygen vacancies and d- and p-band modulation addresses several weaknesses at once: poor conductivity, sluggish ion diffusion, ion trapping and structural instability. Although further work will be needed to evaluate long-term cycling, large-scale production and performance under commercial conditions, the ball-milling approach is attractive because it uses established mechanical processing and does not require elaborate synthesis. The results could help bring safer zinc-based batteries closer to use in grid storage, where affordability, material availability and fire safety may matter more than extreme energy density.

Subject of Research: Oxygen-vacancy engineering in industrial electrolytic manganese dioxide for aqueous zinc-ion battery cathodes

Article Title: Unveiling the action mechanism of synergistic d/p-band center modulation on the zinc storage capability of industrial-grade MnO₂ cathode

News Publication Date: 15-Jul-2026

Web References: https://doi.org/10.26599/NRE.2026.9120255

References: Nano Research Energy, “Unveiling the action mechanism of synergistic d/p-band center modulation on the zinc storage capability of industrial-grade MnO₂ cathode,” DOI: 10.26599/NRE.2026.9120255

Image Credits: Nano Research Energy, Tsinghua University Press

Keywords

Aqueous zinc-ion batteries, manganese dioxide, oxygen vacancies, ball milling, energy storage, battery cathodes, zinc-ion transport, defect engineering, renewable energy, grid-scale batteries

Published in Communications Earth & Environment, the study by J. Wesselkaemper, T. P. Hendrickson, S. J. Smith and colleagues examines how improvements in processing economics could change the outlook for lithium extraction from clay. Its central message is not that clay is already cheaper than conventional resources, but that the cost gap may be narrowed through optimization. That finding could give the battery industry access to a far broader geological resource base at a moment when concerns about supply, permitting and geopolitical concentration are intensifying.

Lithium-bearing clays are sedimentary materials in which lithium is incorporated into, or attached to, the structure of fine-grained minerals. Unlike the concentrated spodumene ores mined from hard-rock deposits, clay deposits generally contain lithium at lower concentrations and lock it into minerals that do not readily release the element. Unlike brines, where lithium is dissolved in water and can be brought to the surface for chemical separation, clay requires a sequence of physical and chemical treatments before lithium can be recovered.

That difference has historically made clay appear less attractive. Processing may require crushing and grinding the material, heating it to alter its mineral structure, mixing it with chemical reagents, leaching lithium into a solution and then separating impurities. The lithium-bearing solution must subsequently be purified and converted into a usable compound such as lithium carbonate or lithium hydroxide. Every stage consumes energy, water, equipment capacity and chemicals, while also generating residual solids and potentially contaminated process streams. If those costs are too high, a large geological resource may still be commercially irrelevant.

The study focuses on a crucial but sometimes overlooked distinction in resource economics: the size of a deposit does not determine whether it can support a viable mine. What matters is the cost of transforming the material into a saleable product, alongside recovery rates, infrastructure needs, environmental controls and the market value of lithium. By analyzing how processing costs influence competitiveness, the researchers highlight opportunities to improve the entire extraction chain rather than relying on a single technological breakthrough.

One important target is the amount of energy required to prepare clay for leaching. Heating can make lithium easier to extract by changing the arrangement of atoms within clay minerals, but thermal treatment can also become one of the most expensive and carbon-intensive parts of the operation. More efficient reactors, better heat recovery, optimized temperatures and improved control of particle size could reduce the energy needed per unit of lithium recovered. These changes would matter especially in regions where electricity or fuel costs are high, or where mining companies must limit greenhouse-gas emissions.

Chemical use is another major factor. In a leaching process, reagents dissolve lithium from the clay, but they may also dissolve unwanted elements such as iron, aluminum, magnesium or calcium. Removing those impurities can require additional chemicals and separation steps. A process designed to maximize lithium recovery without dissolving excessive amounts of other minerals could reduce both operating costs and waste. The researchers’ analysis points toward this kind of systems-level optimization, in which mineralogy, chemistry, equipment design and energy demand are evaluated together.

Clay resources could also offer strategic advantages that are not captured by a simple comparison of extraction costs. Deposits may be located closer to roads, railways, power networks or existing industrial facilities than some remote hard-rock mines or brine operations. Processing could potentially be integrated with regional chemical manufacturing, creating shorter supply chains for battery materials. At the same time, clay extraction is not automatically low-impact. Large-scale excavation can disturb landscapes, while chemical processing can generate waste and require substantial water. A commercially successful process would therefore need to demonstrate not only lower costs, but also reliable management of water, residues and emissions.

The comparison with brines and hard-rock ores is particularly important because each source has a different cost and environmental profile. Brine operations can use evaporation ponds or direct lithium extraction technologies, depending on the chemistry of the resource, but they may be affected by water scarcity, long production times and complex underground hydrology. Hard-rock mining can produce high-grade ore but requires intensive crushing, concentration and often high-temperature conversion. Clay sits between these categories: it may be abundant and widely distributed, yet technically challenging to process. The study indicates that targeted cost reductions could make that middle ground commercially meaningful.

The implications extend beyond one mining method or one battery market. If clay-derived lithium becomes competitive, manufacturers and governments could gain another option for diversifying supplies and reducing dependence on a limited number of producing regions. However, the research does not suggest that every clay deposit will become economic. Deposit-specific mineralogy, lithium concentration, water availability, energy prices, reagent supply and regulatory standards will determine whether a particular project succeeds. The most promising developments are likely to come from processes tailored to the chemistry of individual deposits rather than from a universal extraction recipe.

The broader lesson is that the future of lithium may depend as much on engineering efficiency as on geological discovery. The world already knows where many lithium-bearing materials are located; the challenge is converting them into battery-grade chemicals at a cost and environmental footprint that society can accept. By showing how processing optimization could improve the competitiveness of clay relative to brines and hard-rock ores, Wesselkaemper and colleagues add a potentially important pathway to the rapidly evolving lithium landscape. As demand for electrification accelerates, even resources once considered too difficult to process may become central to the race for the metal behind the battery boom.

Subject of Research: Lithium extraction from clay and the optimization of processing costs relative to brine and hard-rock sources.

Article Title: Optimization of processing costs could improve the cost-competitiveness of lithium extraction from clay relative to conventional sources of brines and hard rock ores.

Article References: Wesselkaemper, J., Hendrickson, T.P., Smith, S.J. et al. “Optimization of processing costs could improve the cost-competitiveness of lithium extraction from clay relative to conventional sources of brines and hard rock ores.” Commun Earth Environ (2026). https://doi.org/10.1038/s43247-026-03845-w

Image Credits: AI Generated

DOI: 10.1038/s43247-026-03845-w

Keywords: lithium extraction, clay, lithium processing, battery materials, brines, hard-rock ores, energy transition, critical minerals