Thermoelectric materials sit at the intersection of heat and electricity: when one side of such a material is hotter than the other, charge carriers diffuse from the hot region to the cold one, generating a voltage. The efficiency of this conversion is governed by a dimensionless figure of merit, ZT, which depends on the Seebeck coefficient, the electrical conductivity, and the thermal conductivity of the material. The problem, famously, is that these three quantities are entangled in awkward ways. Improving one often degrades another, which is why the best inorganic thermoelectrics — bismuth telluride and its relatives — are expensive, brittle, and often built from scarce or toxic elements such as tellurium, antimony, and lead.

Conducting polymers offer an appealing escape route. Polyaniline in particular is inexpensive, mechanically flexible, lightweight, and far less toxic than its inorganic rivals, and it can be synthesized by simple oxidative polymerization of aniline in water. Its weakness has always been modest thermoelectric performance: its electrical conductivity and Seebeck coefficient are individually unremarkable, and the power factor — the product of the Seebeck coefficient squared and the conductivity — has remained low. The new study attacks that limitation not by adding metal nanoparticles or carbon fillers, but by redesigning the polymerization chemistry itself with tailor-made ionic liquids.

Ionic liquids are salts that are liquid at or near room temperature, composed of bulky organic cations paired with organic or inorganic anions. Their defining virtues are negligible vapor pressure, high thermal stability, and an extraordinary capacity for structural tuning. In polymer synthesis they can play several roles at once: as solvents, as soft templates that steer the growing polymer into particular morphologies, and as dopants that insert counter-ions into the polymer backbone. Earlier work has shown that ionic liquids can drive polyaniline to form nanofibers and other nanostructures, and that adding ionic liquids to conducting polymer films can raise conductivity while preserving or even enhancing the Seebeck coefficient.

The research team, led by Mohamed Ali Mokrani of the Ecole Militaire Polytechnique in Algiers, together with colleagues at INSA Lyon and Université Paris-Est, took this idea further by employing peroxydisulfate-based ionic liquids as oxidants. Two variants were tested: EMImS₂O₈, built on the 1-ethyl-3-methylimidazolium cation, and BMImS₂O₈, based on the 1-butyl-3-methylimidazolium cation. Because the peroxydisulfate anion is itself a strong oxidizing agent, these ionic liquids could initiate the polymerization of aniline while simultaneously acting as structural modifiers, their bulky imidazolium cations interfering with the way polymer chains aggregate. A third ionic liquid, the Brønsted acidic HMImHSO₄, served as the dopant, protonating the emeraldine form of polyaniline to create mobile charge carriers.

The resulting composites were subjected to a battery of characterization techniques. Fourier-transform infrared spectroscopy and Raman spectroscopy confirmed the formation of the emeraldine salt phase and revealed interactions between the polymer and the imidazolium species, including hydrogen bonding of the kind previously documented between polyaniline and imidazolium salts. UV-Vis spectroscopy tracked the doping state of the polymer, X-ray diffraction probed its crystallinity and chain ordering, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy mapped the morphology and elemental composition of the composites. Together these measurements showed that the ionic liquids had substantially reorganized the polymer’s microstructure relative to polyaniline synthesized without them.

The thermoelectric measurements told the most compelling story. The composite prepared with the ethyl-substituted oxidant, PANI–EMImS₂O₈–HMImHSO₄, delivered an electrical conductivity of 106.97 S per meter at room temperature together with a Seebeck coefficient of 33.21 microvolts per kelvin. While the Seebeck coefficient remained moderate — as is typical for heavily doped conducting polymers — the combination produced a markedly improved power factor, the quantity that determines how much electrical power a thermoelectric leg of given geometry can deliver. The dimensionless figure of merit reached 5.76 × 10⁻⁴ at room temperature, approximately four hundred times the value measured for neat polyaniline synthesized under otherwise similar conditions.

The comparison with the butyl-substituted variant proved equally instructive. Changing only the alkyl chain length on the imidazolium cation altered the final thermoelectric performance, underscoring that the cation is not a passive spectator but an active participant in shaping chain packing, doping efficiency, and charge transport. This sensitivity to molecular architecture gives chemists a genuine design lever: by selecting cation size, anion chemistry, and dopant identity, they can tune the microstructure of the polymer at the nanoscale without ever changing its fundamental composition. The finding echoes the group’s earlier work on imidazolium ionic liquids in polypyrrole, in which the anionic moiety of the ionic liquid was shown to influence thermoelectric properties, and it aligns with broader evidence that ionic-liquid processing can simultaneously raise conductivity and Seebeck coefficient in polymers such as PEDOT:PSS.

It is important to keep the absolute numbers in perspective. A ZT of 5.76 × 10⁻⁴ is still far below the values of one to two that define state-of-the-art inorganic thermoelectrics, so nobody should expect polyaniline films to compete with bismuth telluride modules in high-power applications any time soon. But the relevant comparison for many emerging applications is not with power stations; it is with the alternatives for low-grade, distributed energy harvesting, where flexibility, processability, low cost, and mechanical compliance matter as much as raw efficiency. Flexible thermoelectric generators for wearable electronics, self-powered sensors, and coating of curved surfaces are exactly the niches where organic materials hold structural advantages that inorganic crystals cannot match.

The study also carries a broader message about how materials chemistry advances. Rather than searching for an entirely new polymer, the researchers showed that a rational, molecularly precise modification of a well-known synthesis route — swapping a conventional oxidant for an ionic liquid that doubles as a structural template — can multiply performance by orders of magnitude. The work was supported by the Ecole Militaire Polytechnique and the Ecole Nationale Préparatoire aux Etudes d’Ingéniorat, and its authors suggest that rationally designed ionic liquid systems offer a general route to tailoring the microstructure and optimizing the thermoelectric properties of conductive polymers. If subsequent studies can push the power factor further, perhaps by combining ionic-liquid templating with nanostructuring or hybrid fillers, the dream of wrapping waste-heat harvesters around engines, pipes, and even skin may come one flexible step closer to reality.

Subject of Research: Ionic liquid-assisted synthesis of polyaniline composites for enhanced thermoelectric performance

Article Title: Evaluation of thermoelectric performance of polyaniline-based peroxydisulfate ionic liquid composites

Article References: Mokrani, M. A., Bekkar Djelloul Sayah, Z., Chabane, H., Mekki, A., Bourenane Cherif, Y., Nedjar, L., Kaufa, M., Slimani, Z. Y., Livi, S., & Durastanti, J. F. (2026). Evaluation of thermoelectric performance of polyaniline-based peroxydisulfate ionic liquid composites. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13899-y

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13899-y

Keywords: thermoelectrics, polyaniline, ionic liquids, peroxydisulfate, conducting polymers, waste heat recovery, power factor, Seebeck coefficient, doping, energy materials, imidazolium, figure of merit

The water-harvesting side of the pairing relies on atmospheric water harvesting, or AWH, a technology that has attracted intense interest as a route to drinking water in arid regions without access to rivers, lakes, or desalination plants. Most AWH devices use porous sorbents that grab water vapor from ambient air overnight and then release it when heated, so the vapor can be condensed and collected. The bottleneck is regeneration: desorbing water from the sorbent requires a substantial input of heat, and nearly all practical designs have leaned on sunlight to supply it. That dependence ties water output to weather, daylight hours, and the intensity of solar irradiation, and it means the sorbent sits idle or underperforming whenever the sun is weak or absent. The new work asks a different question: if heat is needed anyway, why not borrow it from a source that is already producing it as a waste product?

The answer the researchers settled on is a metal-organic framework, a class of crystalline materials built from metal nodes connected by organic linkers into an extremely porous lattice. The specific sorbent chosen, MOF-303, is well known in the AWH literature for its strong affinity for water and its ability to uptake and release vapor in cycles. Crucially, the enthalpy of regeneration for this material, the amount of heat needed to drive water out of its pores, sits in a range that aligns closely with the thermal output of a battery under heavy discharge. That alignment is the heart of the symbiosis. When the battery discharges at currents between 12 and 20 amperes in the negative direction, the waste heat it generates is sufficient to push the MOF layer past its desorption threshold, triggering the release of captured water without any external heater or solar concentrator.

The experimental demonstration is striking in its specifics. Within 46 minutes of operation, the MOF sorbent layer exceeded 50 degrees Celsius, hot enough to liberate water vapor, which was then condensed and collected in a sealed setup. The released vapor represents water that was previously adsorbed from ambient air, meaning the device completes a full harvesting cycle powered entirely by energy that would otherwise have been thrown away. At the same time, the adsorption process on the sorbent acts as a heat sink for the battery: as water molecules bind within the MOF pores, they draw thermal energy out of the adjacent cell, passively stabilizing its temperature. The researchers measured a reduction in peak battery temperature of roughly 10 degrees Celsius, a meaningful margin in a field where every degree of overheating accelerates degradation and raises safety concerns.

The headline performance figure is a water production rate of 1.39 grams of water per gram of sorbent per day. To put that in context, the team reports that this represents a 117 percent increase over comparable solar-driven AWH systems. The improvement does not come from a better sorbent or a cleverer condenser; it comes from the fact that the heat supply is continuous and decoupled from the weather. A solar-driven harvester only regenerates while the sun is up and strong, whereas a battery-coupled harvester regenerates whenever the battery works, which in most applications is exactly when cooling is needed most. The thermal demands of the two systems are not merely compatible but complementary, each peaking precisely when the other can absorb it.

Behind the experiments sits a substantial computational effort. The team used finite-element simulations to model the heat transfer dynamics of the coupled system, validating the measured temperature profiles and water release behavior against the numerical predictions. These simulations also served a diagnostic purpose, allowing the researchers to identify the parameters that govern thermal efficiency in the integrated design: the thermal conductivity of the interface between cell and sorbent, the heat capacity of the assembly, and the kinetics of adsorption and desorption all emerge as levers that determine how much of the battery’s waste heat is actually captured and put to work. That kind of parametric map matters for anyone hoping to scale the concept beyond a laboratory prototype, because it indicates where engineering effort will pay off most.

The implications extend well beyond the specific pairing of MOF-303 and a lithium-ion cell. The authors frame the work as establishing a general closed-loop thermal cycle that repurposes energy-storage waste heat to power atmospheric water harvesting, and they suggest the strategy could enhance thermal efficiency across a variety of energy and environmental systems through internal heat recovery. Data centers, electric vehicle packs, grid-scale storage installations, and industrial electronics all generate large quantities of low-grade heat that is currently vented to the environment. Any of these could, in principle, host a sorbent layer that converts that heat into a useful output, whether water or something else, while simultaneously easing the cooling burden. The concept of symbiotic heat sharing turns what engineers call waste heat recovery from an add-on into a design principle.

There are also practical attractions for deployment in off-grid and resource-constrained settings. A device that produces water as a byproduct of energy storage requires no solar panel, no fuel, and no separate power supply for regeneration, which simplifies the system and reduces cost. In remote telecommunications towers, disaster relief camps, or military outposts where batteries are charged and discharged daily and drinking water is scarce, the same hardware could serve double duty. The passive nature of the cooling is equally significant: because the sorbent draws heat away through the adsorption process itself, there is no pump, fan, or compressor to fail, and the thermal management works even during power interruptions. The 10-degree reduction in peak temperature would translate directly into longer cycle life and improved safety margins for the cells.

Challenges remain before such systems reach commercial maturity. The study was conducted on laboratory-scale hardware, and scaling the thermal coupling from a single cell to a large battery pack, where heat distribution is far less uniform, will require careful engineering. The long-term stability of the MOF under repeated thermal cycling, its behavior in dusty or humid field environments, and the logistics of condensing and storing the harvested water all need attention. The published version of the paper is also an early-release, peer-reviewed accepted manuscript subject to further edits, so some quantitative details may be refined in the final record. Nevertheless, the core demonstration stands: the regeneration enthalpy of a well-chosen sorbent can be matched to the thermal output of a working battery, and the two systems can be made to serve each other. In a decade preoccupied with both energy efficiency and water scarcity, a technology that turns one problem into the solution for the other is exactly the kind of cross-disciplinary thinking the field has been waiting for.

Subject of Research: Thermally coupled MOF-based atmospheric water harvesting and battery thermal management

Article Title: Symbiotic heat sharing in MOF-based atmospheric water generators for battery thermal management and sorbent regeneration

Article References: Chen, W., Luo, M., Tan, Y., Yan, L., Liao, T., Liu, W., Liu, F., Chen, Z., Yao, J., Liang, X., Fang, Y., Wang, S., Ke, Y., Suwardi, A., Yuen, A. C. Y., Tan, S. C., & Ravi, S. K. (2026). Symbiotic heat sharing in MOF-based atmospheric water generators for battery thermal management and sorbent regeneration. Nature Communications. https://doi.org/10.1038/s41467-026-76774-z

Image Credits: AI Generated

DOI: 10.1038/s41467-026-76774-z

Keywords: atmospheric water harvesting, MOF-303, metal-organic frameworks, battery thermal management, waste heat recovery, sorbent regeneration, thermal symbiosis, energy efficiency, water-energy nexus, finite-element simulation, low-grade heat, Nature Communications

Nepal offers an unusually instructive setting for this kind of analysis. Although the country contributes just 0.08 percent of global greenhouse gas emissions, its industrial sector consumes 20 percent of national energy and produces 40 percent of the country’s net carbon emissions. Manufacturing is the largest contributor to both. Yet Nepal’s electricity grid is dominated by hydropower, giving it a carbon intensity of just 0.068 kilograms of CO2-equivalent per kilowatt-hour—a figure roughly 35 times lower in lifecycle terms than coal-fired electricity. That combination of an inefficient industrial base and an exceptionally clean grid creates what the researchers describe as a rare opportunity: electrifying fossil-fueled industrial heat in Nepal delivers far deeper emissions cuts than the same retrofit would in countries reliant on coal or natural gas, where studies have shown boiler electrification can sometimes increase emissions.

The research team, led by Adity Sapkota and colleagues, selected two representative facilities from each sector, deliberately choosing plants with contrasting energy profiles. The dairy facilities ran around the clock on grid electricity supplemented by diesel and biomass, processing between roughly 2,100 and 18,900 tons of milk products annually. The plastic plants produced high-density polyethylene pipes using almost exclusively electrical power, while the metal facilities cast aluminum utensils—one with an electric induction furnace, the other with fossil-fueled reverberatory and annealing furnaces burning waste oil, LPG, and diesel. Over the 2024/25 base year, the team deployed calibrated three-phase power quality analyzers, clamp meters, infrared thermometers, and thermal imaging cameras, logging electrical loads at hourly intervals and cross-checking results against twelve months of utility bills to within a 10 percent deviation.

The baseline measurements exposed substantial efficiency gaps. Nepalese dairy plants consumed 0.22 to 0.25 kilowatt-hours per kilogram of product—better than the national average of 0.3 to 0.58, but still two to four times higher than international best practice of 0.056 to 0.12. In the metal sector, the contrast was starker still: the fossil-fueled aluminum plant recorded a specific energy consumption of 9.17 kilowatt-hours per kilogram, far above the 1.65 to 5.69 range reported internationally, while its electrically driven counterpart performed at 1.18, better than comparable facilities abroad. Thermal efficiency testing revealed why. The dairy boilers operated within normal industrial ranges at 80 to 82 percent efficiency, but the oil-fired melting furnace managed only 21 percent and the LPG-fired annealing furnace a mere 17 percent, meaning most of the fuel’s energy escaped as waste heat rather than reaching the metal.

Motor systems emerged as a universal weakness. Across the 164 motors audited, average loading ranged from 52 percent in the metal facility to 64 percent in dairy—well below the 60 percent threshold at which motor efficiency and power factor begin to decline sharply. In the plastic plants, 60 percent of motors ran underloaded, and in the metal plant the figure reached 85 percent. The consequences were visible in the numbers: the extruder drive motors in the plastic facilities consumed 0.42 to 0.55 kilowatt-hours per kilogram, three to five times the benchmark range, because oversized motors churned at low load. Using the US Department of Energy’s MEASUR tool, the team calculated that upgrading motors to higher-efficiency units yields diminishing returns past a saturation point—95 percent efficiency for dairy and metal, 91 percent for plastic—beyond which replacement costs outweigh incremental savings.

The study then applied a three-tiered scenario framework to each facility: process optimization, electrification of thermal systems, and renewable energy integration. Under the first scenario, insulating steam lines and installing a desuperheater on the refrigeration system of the large dairy plant could recover 690 megawatt-hours annually, about 15 percent of total energy, and cut boiler fuel demand by 30 percent, saving roughly $100,000 per year. In the fossil-fueled aluminum plant, preheating combustion air with recuperators promised fuel savings of 43 percent, while preheating the charge material added another 25 percent—a combined 68 percent fuel reduction from relatively conventional engineering measures. In the plastic plants, where waste heat opportunities are inherently limited, insulating extruder barrel heaters and preheating polymer feedstock delivered a more modest 3 to 5 percent of facility energy.

Electrification produced the study’s most dramatic results. Replacing the diesel boiler at the large dairy plant with a 96 percent efficient electric boiler would pay for itself in six months and save $164,000 annually, while cutting facility emissions by up to 85 percent. Yet the same retrofit at the smaller dairy plant, which burns inexpensive firewood, yielded negative savings because wood and electricity cost nearly the same in Nepal—a finding the sensitivity analysis confirmed was robust even to a 20 percent rise in wood prices. In the metal sector, electrifying the inefficient melting and annealing furnaces could save nearly 60 percent of total facility energy and more than 90 percent of emissions, though the melting furnace’s financial case proved fragile, turning negative at discount rates above 8 percent. The lesson, the authors note, is that electrification’s viability hinges on the cost of the fuel being displaced.

Solar photovoltaic integration told a different story across the sectors. Hybrid systems pairing rooftop solar with lithium iron phosphate battery storage achieved renewable penetration of 15 to 90 percent depending on the facility, but battery capital and replacement costs accounted for more than half of total system expense, pushing the levelized cost of electricity to between $0.04 and $0.17 per kilowatt-hour. Only one facility, a plastic plant, recorded an LCOE below Nepal’s grid tariff of $0.068 per kilowatt-hour, and most hybrid configurations showed negative net present value with indefinite payback periods. Strip out the batteries, however, and the economics transform: PV-only systems achieved an LCOE of $0.02 per kilowatt-hour, repaid their capital within five years at every facility, and delivered positive NPV across the board. The battery remains technically necessary to replace diesel backup during grid instability, creating a gap between technical need and financial reality that the authors argue only concessional financing or capital subsidies can close.

Taken together, the results deliver a message that resists uniform technology prescription. Fossil-fuel-dependent dairy and metal plants achieved their largest energy and emissions reductions through heat recovery and electrification, while the electrically driven plastic facilities gained most from solar integration, offsetting up to 65 percent of grid dependence. The modeled emissions cuts of 50 to 90 percent from electrification vastly exceed what comparable retrofits achieve on fossil-dominated grids, underscoring that industrial decarbonization strategy must be matched to the carbon intensity of the electricity system. The authors caution that their findings rest on two facilities per sector from a single industrial cluster, with modeled rather than verified post-implementation outcomes, and they call for broader multi-facility studies. But the policy implications travel well beyond Nepal: mandatory audit programs, sector-specific benchmarks, targeted financing for capital-intensive retrofits, and grid investment to handle rising industrial demand are all prerequisites for turning audited potential into real-world emission cuts in developing economies.

Subject of Research: Cross-sectoral energy auditing and scenario-based decarbonization assessment of dairy, plastic, and secondary aluminum manufacturing facilities in Nepal

Article Title: Cross-sectoral energy audit and scenario-based decarbonization assessment of manufacturing industries in Nepal: A comparative study of dairy, plastic, and metal sectors

Article References: Sapkota, A., Paudel, S., Joshi, A., & Adhikari, B. (2026). Cross-sectoral energy audit and scenario-based decarbonization assessment of manufacturing industries in Nepal: A comparative study of dairy, plastic, and metal sectors. Results in Engineering, 32, Article 113191. https://doi.org/10.1016/j.rineng.2026.113191

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113191

Keywords: energy audit, industrial decarbonization, Nepal, electrification, solar photovoltaics, waste heat recovery, specific energy consumption, dairy processing, aluminum manufacturing, plastic extrusion, greenhouse gas emissions, energy efficiency

Researchers at TU Wien have now developed a method that makes the invisible visible, at least in the mathematical sense. Their work, published in the journal Applied Thermal Engineering, demonstrates how the complete internal temperature state of a packed-bed storage system can be precisely determined during operation using only a small number of strategically placed temperature sensors. The study, which carries the title ‘Observer-based thermocline tracking and heat transfer coefficient estimation in packed bed thermal energy storage systems’, is a striking example of what happens when control engineering meets energy technology. Rather than attempting to measure everything, the team exploits a detailed mathematical model of the storage process to infer the quantities that no sensor can practically reach. The model, in effect, supplements the information that the physical instrumentation cannot deliver, reconstructing the full spatial temperature distribution from sparse measurements taken at the tank’s boundary regions.

The heart of the challenge lies in a narrow transition zone called the thermocline. Inside a packed-bed storage unit, a hot region and a cold region coexist, separated by this relatively thin boundary layer where the temperature gradient is steepest. As the storage system charges and discharges, the thermocline migrates through the bed of particles, and its position, shape and stability directly determine how efficiently the system operates and how much of the stored energy can actually be extracted for useful work. A diffuse or poorly controlled thermocline means that hot and cold zones blur into one another, degrading the quality of the heat that can be delivered. Tracking this moving front in real time is therefore the key to intelligent operation, but doing so by direct measurement would require an impractically dense array of sensors threaded through the storage material.

Stefan Jakubek from TU Wien explains the practical obstacle plainly: a complete measurement of the spatial temperature distribution would demand a large number of sensors inside the storage system, and particularly given the high temperatures and harsh conditions found in industrial plants, this is technically complex and expensive. Thermocouples buried deep within a bed of hot particles must survive thermal cycling, mechanical stress and potentially corrosive or dust-laden gas flows, and every additional probe adds cost, complexity and another potential point of failure. The alternative pursued by the Vienna team is fundamentally different in philosophy. Instead of saturating the tank with instrumentation, they place a handful of sensors at positions chosen for their informational value and let a mathematical observer do the rest, continuously computing what the interior must look like given the measurements and the known physics of the process.

The technical machinery behind this achievement draws on several research fields at once. The team combines the modelling of distributed physical systems, in which temperature varies continuously across space and time, with mathematical model reduction, a technique that compresses an otherwise computationally heavy model into a leaner form suitable for real-time use. Crucially, the reduction is performed in a way that preserves the properties of the original model that are essential to describing how the thermocline moves through the tank. The researchers also apply optimal sensor placement, asking systematically at which positions a temperature sensor yields the greatest amount of information about the overall state of the storage unit. Control-theoretic state observation then fuses the model with the sensor data, while online parameter identification allows the algorithm to adapt itself to the actual behaviour of the plant as it evolves during operation.

The result is an estimation method that does more than reconstruct temperatures. It simultaneously estimates the heat transfer coefficient between the gas flowing through the bed and the solid storage material, a parameter that describes how effectively thermal energy passes between the two phases. Martin Kozek, one of the researchers involved, notes that this parameter enables the team to describe how effectively heat is transferred between gas and solid, and he adds that it opens up another interesting avenue of research. The significance of this second output is easy to underestimate, but it may prove just as valuable as the temperature reconstruction itself. Heat transfer is not a fixed property of a storage plant; it changes over the lifetime of the facility in ways that reflect its physical condition.

Consider, for example, what happens inside an industrial storage unit that is charged with waste heat carried by dust-laden gas flows. Over months and years of operation, fine particles carried by the gas can deposit on the surfaces of the storage material, gradually coating the very interfaces across which heat must pass. The consequence is a slow degradation of the heat transfer coefficient, which in turn erodes the performance of the entire storage system. Because the new method estimates this coefficient continuously and online, deviations from its expected behaviour can serve as an early warning sign of fouling or other internal changes. In this way, the same algorithm that supports energy-efficient operation also doubles as a diagnostic instrument, providing information on the condition of the plant and enabling a shift towards condition-based maintenance, in which servicing is triggered by the actual state of the equipment rather than by rigid schedules or by failures that have already occurred.

The project also illustrates the value of disciplinary collaboration within a single university. The Institute of Energy Technology and Thermodynamics at TU Wien contributes deep expertise in thermal energy systems and heat storage, while the Institute of Mechanics and Mechatronics complements it with methods from mathematical modelling, control engineering and process automation. The two institutes conduct their joint research as part of the Christian Doppler Laboratory for Digital Twins of Distributed Parameter Systems, a framework dedicated to learning, monitoring and optimising complex physical systems in real time. The phrase ‘digital twin’ captures the underlying idea well: a continuously updated computational replica of a physical asset, fed by sparse measurements and refined by physics-based modelling, that mirrors the state of the real system closely enough to support decisions without invasive inspection. For packed-bed storage, that twin now runs on a handful of sensors and a reduced-order model.

The broader implications for the energy transition are considerable. Recovering industrial waste heat is widely regarded as one of the most attractive levers for raising energy efficiency and cutting greenhouse gas emissions, because the energy has already been generated and would otherwise be lost. Packed-bed thermal energy storage is particularly interesting in this context because it uses inexpensive solid storage materials and air as the heat transfer medium, making it suitable for the high-temperature regimes typical of heavy industry. What has been missing is a practical way to know, at any instant, how much usable energy the tank holds and where its thermal front sits. By solving that observability problem with minimal instrumentation, the TU Wien method lowers a genuine barrier to deploying these systems in demanding industrial environments, where dense sensor networks are neither affordable nor durable.

Looking ahead, the combination of thermocline tracking and continuous heat transfer estimation points towards storage plants that largely manage themselves. A control system equipped with such an observer can optimise charging and discharging strategies in real time, maximise the fraction of stored energy that is actually recoverable, and flag maintenance needs long before performance visibly declines. The research, validated through computational simulation and modelling on a fluidised-bed test rig at the university, demonstrates that sophisticated estimation techniques once confined to aerospace and process control can be brought to bear on the unglamorous but essential task of storing industrial heat. In a warming world that must squeeze every useful joule out of the energy it already produces, learning to see inside a hot steel tank without opening it may turn out to be one of the quietly consequential advances of the decade.

Subject of Research: Observer-based state estimation for packed-bed thermal energy storage systems

Article Title: A glimpse inside – without actually looking inside

Article References: A glimpse inside – without actually looking inside. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: thermal energy storage, packed-bed storage, waste heat recovery, thermocline, state estimation, sensor placement, model reduction, heat transfer coefficient, digital twin, industrial energy efficiency, TU Wien, condition-based maintenance

The scientific foundation of the new device is the thermogalvanic effect, an electrochemical phenomenon in which a temperature gradient applied across a redox-active electrolyte generates a measurable voltage. In a conventional thermogalvanic cell, two electrodes are held at different temperatures while reversible oxidation and reduction reactions proceed at different rates at each electrode. The imbalance in reaction equilibria produces a difference in electrode potential, and the resulting thermovoltage can drive a current through an external circuit. Because the effect does not require boiling fluids, turbines, or mechanical motion, it is particularly attractive for harvesting low-grade heat, the diffuse thermal energy below roughly 100 degrees Celsius that is released by industrial processes, cooling operations, electronics, and even the human body. Converting such small temperature differences into useful electricity has long been difficult, and most existing approaches either deliver too little power or rely on expensive, resource-constrained materials.

That last point is where the new study makes its most distinctive contribution. Many high-performing thermogalvanic systems depend on metal-based redox couples, such as ferroferricyanide complexes, which raise questions about cost, resource availability, and environmental sustainability at scale. The researchers instead turned to lignin, the aromatic biopolymer that gives wood its rigidity and that accumulates in enormous quantities during chemical pulping. Lignin and its sulfonated derivatives are rich in phenolic structures, which include quinone and hydroquinone moieties. These functional groups are electrochemically active and can shuttle reversibly between oxidized and reduced states, making them natural candidates for a redox electrolyte derived entirely from renewable biomass. In effect, the researchers recognized that the very molecules paper mills discard are already equipped with the chemical machinery needed for thermoelectrochemical energy conversion.

To activate this machinery, the team combined lignosulfonate with ammonium persulfate, a strong oxidizing agent. The persulfate oxidizes a portion of the lignin-derived phenolic groups, establishing a redox couple between quinone and hydroquinone species within the solution. When a temperature gradient is applied across this liquid electrolyte, the temperature-dependent equilibria of these reversible reactions generate a thermovoltage between the electrodes. The researchers systematically optimized the composition of the liquid system and reported a Seebeck coefficient of 2.92 millivolts per kelvin, a figure that quantifies how much voltage the electrolyte produces per unit of temperature difference. For a waste-derived material, this performance is notable, and it established a promising baseline before the team moved to the more challenging task of immobilizing the electrolyte in a solid-like form.

Liquid electrolytes, however mobile and conductive, are awkward for practical devices. They can leak, evaporate, and require careful containment, which complicates the design of wearable, flexible, or integrated power units. The researchers therefore embedded their lignosulfonate-based electrolyte into a poly(vinyl alcohol) matrix using freeze-thaw gelation, a simple physical crosslinking process in which repeated freezing and thawing cycles induce the polymer chains to organize into a stable hydrogel network. The resulting quasi-solid material, designated LSAK/PVA, retains the redox-active lignin chemistry while gaining the mechanical robustness and form factor of a gel. This strategy follows a broader trend in energy materials research, in which functional liquids are gelled to combine electrochemical performance with the handling advantages of solids, but it is unusual in sourcing the entire redox system from an industrial waste stream.

The gel did not merely preserve the performance of the liquid; it improved on it. At an optimized lignosulfonate concentration, the LSAK/PVA thermogalvanic gel achieved a Seebeck coefficient of 4.3 millivolts per kelvin, substantially higher than the liquid precursor, along with a maximum output power density of 976 microwatts per square meter per square kelvin. To demonstrate that individual gel elements could be scaled into something practically useful, the researchers connected eleven units in series. Under a temperature difference of 40 kelvin, the series-connected device generated approximately 1.56 volts and delivered 1.75 microwatts of power, enough to operate small electronic devices such as a timer and a calculator. While these power levels are modest in absolute terms, they are meaningful for the growing ecosystem of low-power electronics, sensors, and Internet-of-Things nodes that require only microwatts to function and that could otherwise depend on batteries with limited lifetimes.

Perhaps the most conceptually elegant demonstration in the study involves the waste stream itself. Rather than treating black liquor merely as a source of lignosulfonate feedstock, the researchers showed that the material could directly harvest the heat released as hot black liquor cools. When heated black liquor was allowed to cool, the gel system generated an open-circuit voltage of about 45 millivolts during the cooling process. This result illustrates a circular scenario in which a single industrial by-product serves simultaneously as the active redox material of the energy converter and as the thermal source that drives it. Pulp mills handle black liquor at high temperatures as a matter of routine, and capturing even a portion of the thermal energy released during its processing, using a device built from the liquor’s own constituents, would add a new layer of value to an operation that already recovers significant energy by combustion.

The gel’s abilities extend beyond waste heat into solar energy harvesting, which broadens its potential deployment considerably. Under simulated sunlight with an irradiation intensity of 1 kilowatt per square meter, comparable to standard terrestrial solar conditions, the gel developed an internal temperature difference of approximately 25 kelvin and generated an open-circuit voltage of about 0.1 volt. The photothermal conversion relies on the gel’s ability to absorb sunlight and establish a thermal gradient across its thickness, which the thermogalvanic chemistry then translates into electricity. Stability is a critical concern for any device intended for continuous outdoor operation, and the researchers addressed this with a five-cycle test that showed stable voltage output across repeated illumination cycles. Encouragingly, the performance carried over from the laboratory to the field: an outdoor device exposed to natural sunlight produced a thermovoltage of 0.33 volts after 30 minutes of light exposure, indicating that the material can function under real, variable environmental conditions rather than only under carefully controlled lamps.

Taken together, the results sketch a material strategy with implications that reach well beyond the paper industry. The authors suggest that lignin-based thermogalvanic materials could provide a pathway for recovering otherwise underused low-grade thermal energy while simultaneously adding value to industrial biomass waste. In this framing, lignin is no longer merely a low-cost fuel or a feedstock for commodity chemicals but an active functional component in energy conversion devices. The approach aligns with the principles of waste valorization, in which residues are upgraded into products of higher economic and functional value, and it does so using abundant, metal-free chemistry that avoids the supply-chain and environmental concerns associated with many inorganic thermoelectric materials. If the performance of such gels can be further improved and their manufacture integrated into existing pulp mill operations, the dark by-product of papermaking could find a second life as a soft, sustainable material that quietly harvests the heat and sunlight that would otherwise simply dissipate.

Subject of Research: Lignin-based thermogalvanic gels from papermaking waste for heat and solar energy conversion

Article Title: Papermaking waste turned into a gel for harvesting heat and sunlight

Article References: Papermaking waste turned into a gel for harvesting heat and sunlight. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: thermogalvanic gel, lignin, lignosulfonate, black liquor, waste heat recovery, solar energy, thermogalvanic effect, biomass valorization, poly(vinyl alcohol), Seebeck coefficient, papermaking waste, redox electrolyte

The study, led by Shang Jiang and Peixin Zhu of the State Key Laboratory of Catalysis at the Dalian Institute of Chemical Physics, together with Yanting Liu and Dehui Deng, describes a coupled process the authors call seawater-to-hydrogen-and-water, or STHW. Rather than treating desalination and electrolysis as separate, serial industrial steps, the design folds them into a single thermally integrated loop. Low-grade waste heat released by the alkaline electrolyser—heat that would normally be dissipated into the environment as a loss—is captured and used to drive low-temperature distillation of seawater. The distilled water then serves two purposes simultaneously: it replenishes the electrolyser’s feedwater and supplies fresh water for external use.

The elegance of the approach lies in its thermodynamic bookkeeping. Alkaline water electrolysers typically convert only about 70 to 80 percent of their electrical input into the chemical energy of hydrogen, with the remainder appearing as heat. In conventional plants this heat is an inefficiency to be minimized. In the STHW architecture, it becomes an asset. Because low-temperature thermal desalination operates at modest temperatures and pressures, the electrolyser’s waste heat is sufficient to vaporize seawater and condense it as distillate. The researchers point out that the concept has surprisingly deep roots: a Swiss patent from 1928 already proposed generating distilled water in water electrolysis plants, but the idea never matured into an industrial demonstration—until now.

The team’s experimental campaign proceeded in two stages. First, a 20-kilowatt industrial pilot system ran for 100 consecutive days, producing 3.8 normal cubic meters of hydrogen per hour alongside 1.2 kilograms of fresh water per hour. That sustained, three-month trial is significant in a field where many seawater electrolysis claims rest on laboratory-scale electrodes tested for hours or days. Stability has historically been the Achilles heel of direct seawater electrolysis, in which chloride corrosion, competing chlorine chemistry, and precipitating magnesium and calcium hydroxides degrade catalysts and electrodes. By sidestepping direct seawater splitting altogether—distilling the water first, even if only within the same unit—the STHW process lets the electrolyser operate on effectively pure water, preserving the maturity and durability of conventional alkaline technology.

Scaling up, the researchers built a 250-kilowatt system that achieved 48 normal cubic meters of hydrogen per hour and 31.6 kilograms of fresh water per hour. Crucially, the integrated design delivered a 14.4 percent improvement in system electrical efficiency compared with running an alkaline electrolyser on fresh water alone. That gain comes from the dual dividend of waste heat recovery: the thermal energy recycled into distillation displaces electricity or fuel that a standalone desalination plant would otherwise consume, and the cogeneration of fresh water adds a sellable product without any additional primary energy input. In effect, the same electron entering the plant yields hydrogen, water, and a smaller thermal footprint than any of its competitors.

The engineering challenge was substantial. Integrating a thermal desalination stage with an industrial electrolyser required careful management of material flows, temperature gradients, and water balances. The team mapped the process feasibility and simplified the flowsheet so that seawater enters the distillation loop, vapor is condensed into product water, a portion is returned to the electrolysis stack, and brine is rejected—mirroring the mass flows of a compact combined heat-and-power plant, but with hydrogen and potable water as outputs. Figure-level analyses in the paper trace these material and energy streams, showing where heat exchangers recover the electrolyser’s reject heat and how the distillation unit maintains throughput across varying operating loads.

Direct seawater electrolysis, by contrast, has attracted enormous research attention in recent years, with notable demonstrations including a membrane-based seawater electrolyser published in Nature in 2022 and catalyst designs that adjust the local reaction environment to resist chloride attack. Yet a vocal segment of the electrochemistry community has questioned whether these approaches are economically meaningful, arguing in journals such as Joule and Energy and Environmental Science that hyping direct seawater splitting may actually hinder electrolyser development. The STHW results lend weight to that skepticism: instead of forcing electrolysis to endure the brutal chemistry of the ocean, the Dalian team’s process treats seawater as a resource to be purified, using free waste heat as the purification engine.

The economics appear to favor the coupled route decisively. A techno-economic analysis included in the study indicates that the STHW process is more profitable than the traditional tandem arrangement of desalination followed by electrolysis, in which a reverse-osmosis or electrodialysis plant is built, powered, and operated as a separate facility. The authors note that low-temperature thermal desalination avoids many of the membrane fouling, wetting, and scaling problems that plague membrane distillation, while the co-produced fresh water can offset local water demand—a valuable revenue stream or social benefit in arid coastal regions such as the Gulf states, where capital costs of desalination plants have long been a subject of intense study.

The implications ripple outward across the hydrogen economy. As countries draft national hydrogen strategies, water demand is emerging as a quiet constraint: the International Renewable Energy Agency has estimated that hydrogen production could require billions of cubic meters of water annually by mid-century, and analysts have urged the industry to mine nontraditional water sources rather than compete with agriculture and cities for freshwater. A 250-kilowatt demonstration is still far from the megawatt and gigawatt scales envisioned for export-oriented hydrogen hubs, but the architecture is inherently modular, built from two commercially proven unit operations—alkaline electrolysis and thermal distillation—rather than from experimental catalysts.

There remain engineering hurdles to confront on the path to commercialization. Long-term brine management, corrosion of distillation hardware, and the economics of waste-heat exchangers at larger scales will all require scrutiny, and the pilot results, while encouraging, cover a single 100-day campaign. Yet the demonstration marks a conceptual shift worth savoring: the same heat that engineers have spent decades trying to squeeze out of electrolysers has been recast as the driving force for a second product. In a world where 2.2 billion people lack safely managed drinking water and clean hydrogen remains stubbornly expensive, a machine that makes both from the sea—using energy that would otherwise warm the air—offers a rare and genuinely circular vision of the energy-water nexus.

Subject of Research: Coupled alkaline seawater electrolysis and low-temperature thermal desalination for co-production of hydrogen and fresh water

Article Title: A 250-kilowatt system for co-production of hydrogen and fresh water from seawater

Article References: Jiang, S., Zhu, P., Liu, Y., & Deng, D. (2026). A 250-kilowatt system for co-production of hydrogen and fresh water from seawater. Nature Energy. https://doi.org/10.1038/s41560-026-02130-6

Image Credits: AI Generated

DOI: 10.1038/s41560-026-02130-6

Keywords: hydrogen production, seawater electrolysis, desalination, alkaline water electrolysis, waste heat recovery, fresh water, Nature Energy, techno-economic analysis, green hydrogen, water-energy nexus, thermal distillation, industrial pilot system

The significance of the demonstration lies in its scale and integration. Laboratory reports of seawater electrolysis appear regularly, but few technologies have graduated beyond the bench. A 250 kW system is a meaningful industrial pilot size, large enough to expose engineering realities such as heat management, brine handling, corrosion and long-term stability that small laboratory cells simply never encounter. By designing the distillation and electrolysis stages as one thermally and hydraulically linked unit rather than two separately optimized plants, the researchers eliminated much of the parasitic energy burden and capital cost that normally separate seawater from the ultrapure water that conventional electrolyzers demand.

The underlying problem is well known to electrochemists. Alkaline water electrolyzers, among the most mature and durable electrolysis technologies, circulate a concentrated potassium hydroxide electrolyte and split water at nickel-based electrodes. They are robust against many impurities, yet the magnesium, sulfate and, above all, chloride ions in seawater wreak havoc. Chloride ions that reach the anode can participate in chlorine and hypochlorite evolution reactions that compete with oxygen evolution, corroding electrodes and membranes and contaminating the product gas. Precipitates of magnesium hydroxide and calcium carbonate can clog porous transport layers and poison catalyst surfaces. This is why virtually every commercial electrolysis installation relies on deionized water, often to resistivity specifications measured in megohm-centimeters.

Previous attempts to sidestep this requirement have taken two broad routes. One is direct seawater electrolysis, in which specially designed catalysts and membranes resist chloride chemistry; a prominent 2023 Nature Energy study demonstrated a self-driven system that suppressed chloride corrosion through in situ generated protective layers, and a 2026 follow-up by Jiang and colleagues advanced that line of work. The other route is upstream desalination, in which seawater is purified by reverse osmosis, membrane distillation or thermal processes before entering a standard electrolyzer. Each route carries penalties: direct seawater electrolysis remains constrained by catalyst durability and selectivity at industrially relevant current densities, while standalone desalination adds cost, complexity and energy demand that hydrogen producers have been reluctant to absorb.

The unified system described in the new report belongs to the second family but reframes its economics entirely. Vacuum distillation lowers the boiling point of water by reducing pressure, allowing evaporation at temperatures far below 100 degrees Celsius. Alkaline electrolysis stacks operate with substantial inefficiency: a portion of the electrical input inevitably degrades into heat at operating temperatures typically between 60 and 90 degrees Celsius. In conventional plants this heat is a nuisance, requiring cooling water and radiating away as waste. In the unified design, that same low-grade waste heat becomes the driving force for vacuum distillation of seawater. The electrolyzer effectively pre-heats and purifies its own feedwater, closing the loop between the two processes.

This thermal coupling yields several compounding benefits. The distillation step produces water of a purity suitable for direct injection into the alkaline electrolyte circulation loop, so the plant draws seawater rather than municipal fresh water, neutralizing objections from communities and regulators in water-stressed coastal regions. The concentrated brine byproduct can be managed as a manageable waste stream, and in principle carries value as a feedstock for salt and mineral recovery. Because no external steam boiler or electrically driven desalination train is required, the overall energy efficiency of hydrogen production improves relative to a conventional arrangement of separate desalination and electrolysis plants, and the system’s footprint shrinks accordingly.

The 250 kW demonstration matters because it interrogates the integration at a scale where heat balances become genuine engineering constraints rather than laboratory conveniences. At this size, the researchers could quantify how much of the stack’s waste heat is recoverable, how the vacuum distillation unit responds to the transient thermal profile of a real electrolyzer under variable renewable power, and how water quality, brine concentration and hydrogen output behave over sustained operation. Co-producing fresh water alongside hydrogen also opens a second revenue stream: a coastal hydrogen plant can double as a small desalination facility, supplying potable or industrial water to its host community and improving the project’s overall economics in ways that hydrogen sales alone cannot.

Analysts following the hydrogen sector have repeatedly emphasized that water availability is an underappreciated constraint on global electrolyzer deployment. The International Energy Agency’s Global Hydrogen Review has documented the rapid growth of announced electrolyzer capacity, much of it concentrated in coastal and arid regions such as Australia, the Middle East, Chile and North Africa, precisely where solar and wind resources are strongest and fresh water is scarcest. Policy frameworks, including those developed by Australian state agencies to manage water resources during extreme events, increasingly scrutinize industrial water withdrawals. A technology that converts seawater into both a clean fuel and fresh water directly addresses the resource conflict at the heart of the green hydrogen build-out.

Challenges remain before such unified plants can be considered commodity technology. Long-term materials compatibility is paramount: vacuum distillation vessels, heat exchangers and condensers must resist corrosion and scaling over thousands of hours, and the electrolyzer stack must tolerate the trace impurities that survive even high-quality distillation. Maintaining vacuum conditions adds mechanical complexity and pumping loads that must be optimized against the heat available from the stack. The economics will also hinge on the value assigned to the co-produced fresh water, which varies enormously by geography. Nevertheless, the demonstration that waste heat from alkaline electrolysis can drive vacuum distillation of seawater at the quarter-megawatt scale offers a credible, thermodynamically elegant answer to one of the hydrogen economy’s most persistent bottlenecks, and points the way toward hydrogen production that quenches water scarcity rather than deepening it.

Subject of Research: A unified system coupling alkaline water electrolysis with vacuum distillation to co-produce hydrogen and fresh water from seawater

Article Title: A unified distillation and electrolysis system

Article References: Love, J. G. (2026). A unified distillation and electrolysis system. Nature Energy. https://doi.org/10.1038/s41560-026-02136-0

Image Credits: AI Generated

DOI: 10.1038/s41560-026-02136-0

Keywords: green hydrogen, seawater electrolysis, vacuum distillation, alkaline water electrolysis, desalination, waste heat recovery, hydrogen economy, water scarcity, electrocatalysis, renewable energy, Nature Energy, co-production