In a finding that sounds more like kitchen alchemy than materials science, researchers in India have transformed the soot from a simple cotton wick burning in sesame oil into a high-performance electrode material for supercapacitors, using nothing more exotic than a household microwave oven. The study, published in Discover Electrochemistry, reports that a five-minute microwave treatment at just 110 degrees Celsius was enough to unlock a surface area of 686 square meters per gram in the carbon, more than seven times that of the untreated material, and to push the resulting device to a specific capacitance of 485 farads per gram with an energy density of 33.68 watt-hours per kilogram. For a material harvested from the inside of a covered steel vessel above an earthen lamp, those numbers are remarkable.
Supercapacitors occupy a unique niche in the energy storage landscape. Unlike batteries, which store charge in slow chemical reactions, electrochemical double-layer capacitors, or EDLCs, store energy physically, as ions from the electrolyte accumulate on the surface of porous carbon electrodes. That mechanism delivers exceptional power density, near-instant charge and discharge, long cycle life, and outstanding efficiency. The trade-off has always been energy density, which depends critically on how much electrolyte-accessible surface the electrode offers. Activated carbon remains the workhorse material for these devices, typically delivering specific capacitances between 100 and 500 farads per gram, and its appeal is amplified by the fact that it can be made from cheap, renewable agricultural waste such as corncob, rice husk, coconut shell, and orange peels.
The catch lies in the activation step. Conventional physical activation involves heating a carbon precursor above 700 degrees Celsius in steam or carbon dioxide, which selectively gasifies carbon atoms to open and widen pores. Chemical activation with agents such as potassium hydroxide, sodium hydroxide, or phosphoric acid generally achieves higher surface areas and more uniform pore distributions, but it still demands temperatures around 800 degrees Celsius, long processing times, and substantial energy input. Both routes carry environmental and economic penalties, and both offer limited control over the final pore architecture. Any method that can achieve comparable porosity at lower temperature, in less time, and with less energy would represent a meaningful advance for sustainable electrode manufacturing.
Microwave irradiation offers exactly that possibility, and the new study exploits it elegantly. Unlike conventional furnaces that heat from the outside in through conduction, microwaves couple directly with the carbon matrix through dielectric and conductive losses, producing rapid, volumetric, and selective heating. Localized hot spots form at conductive or defect-rich regions, and in this case at the interfaces between the carbon and the potassium hydroxide activator, which itself acts as a porogen and a microwave absorption medium. The result is accelerated etching, faster diffusion of the activating agent into the carbon interior, and the formation of well-defined micro- and mesoporous networks in minutes rather than hours, all while avoiding the structural collapse that prolonged conventional heating can cause.
The raw material itself is unconventional. The team, led by Poonam Mahendia and Ritu Jangra with senior author Suman Mahendia of Kurukshetra University, burned a 250-milligram cotton wick in an earthen cup lamp filled with sesame oil, covering it with a stainless steel vessel to trap the smoke. Sesame oil is rich in polyunsaturated fatty acids, containing roughly 40 to 50 percent linoleic acid and 33 to 44 percent oleic acid. During combustion, these long-chain triglycerides decompose through cracking, dehydrogenation, aromatization, and incomplete oxidation, generating soot-like carbon particles. The oil thus serves three roles at once: it supplies the carbon skeleton, its unsaturated fatty acids promote partial aromatization into defective, turbostratic carbon domains that are far more reactive toward potassium hydroxide etching than graphitized carbon, and the incomplete combustion leaves behind oxygen-containing surface groups that improve wettability in aqueous electrolytes and may contribute additional charge storage.
The synthesis route was deliberately simple. The black powder peeled from the vessel walls was first carbonized at 400 degrees Celsius for two and a half hours under nitrogen to yield what the researchers call bare carbon, with a modest surface area of 92.5 square meters per gram and a total pore volume of 0.13 cubic centimeters per gram. That material was then mixed with potassium hydroxide in a five-to-one ratio in deionized water, stirred for 24 hours, dried into a thick paste, and subjected to microwave heating at 110 degrees Celsius in convection mode at full 1200-watt power for just five minutes. Washing with dilute hydrochloric acid and water removed residual impurities, leaving the activated carbon, designated AA, with a surface area of 686 square meters per gram and a pore volume of 0.44 cubic centimeters per gram.
Characterization confirmed the transformation at every scale. Nitrogen adsorption isotherms showed that activation shifted the material toward a type IV profile with a larger hysteresis loop, indicating a higher proportion of mesopores, the ion-transport channels that complement the micropores responsible for double-layer formation and capacitance. X-ray diffraction revealed broad, low-intensity peaks near 23 and 43 degrees, signatures of highly disordered carbon, with the activated sample showing an expanded interlayer spacing of 0.39 nanometers compared with 0.37 nanometers before activation, both well above graphite’s 0.335 nanometers. That disorder, the authors note, reflects carbon layers separated by functional groups and structural defects, which create additional active sites for charge storage. Scanning electron microscopy completed the picture, showing layer-like carbon sheets with sparse porosity before activation and a well-developed pore structure throughout the sample afterward.
The electrochemical results are where the five-minute treatment truly pays off. Cyclic voltammetry produced nearly rectangular curves characteristic of ideal double-layer behavior, with specific capacitances of 300 farads per gram for the activated material against just 18 farads per gram for the untreated carbon at 10 millivolts per second. Galvanostatic charge-discharge testing at 1 ampere per gram delivered the headline figure of 485 farads per gram, along with an energy density of 33.68 watt-hours per kilogram at a power density of 628.23 watts per kilogram in 6 molar potassium hydroxide electrolyte. Impedance spectroscopy showed a low charge-transfer resistance of 0.3 ohms, far below the 2.06 ohms of the untreated device, indicating fast charge transport and excellent electrode-electrolyte contact. Cycling stability proved equally convincing: after 5000 charge-discharge cycles at a demanding 20 amperes per gram, the device retained 84 percent of its capacitance with 100 percent coulombic efficiency.
To demonstrate practical viability, the researchers connected three identical devices in series, since aqueous electrolytes limit single cells to roughly one volt before water begins to dissociate. The stack operated stably across the 1-to-2-volt and 2-to-3-volt windows and powered a red light-emitting diode for about 65 seconds, a small but tangible proof that lamp soot from a kitchen microwave can do real electrical work. The series combination did show an increased internal resistance of 10.22 ohms, a reminder that device integration still poses engineering challenges, but the overall performance compares favorably with literature values for microwave-activated carbons, including silkworm-excrement-derived carbon at 322 farads per gram, paper-waste carbon at 237 farads per gram, and food-waste aerogels at 316 farads per gram with 16.3 watt-hours per kilogram.
What makes this work resonate beyond its numbers is the radical accessibility of the process. The precursor costs pennies, the activation step runs at 110 degrees Celsius instead of 800, and the total microwave exposure is measured in minutes, translating directly into energy and time savings over conventional thermochemical routes. As the demand for grid buffers, regenerative braking systems, and portable electronics grows, so does the incentive to find electrode materials that are cheap, abundant, and environmentally benign. Turning the soot of a sesame-oil lamp into a 485-farad-per-gram electrode suggests that the path to sustainable energy storage may sometimes run through the most humble corners of the household, one five-minute microwave pulse at a time.
Subject of Research: Microwave-assisted synthesis of activated carbon from cotton and sesame oil combustion soot for supercapacitor electrodes
Article Title: Microwave-assisted synthesis of activated carbon from aerobic combustion of cotton in sesamee oil for high performance supercapacitor
Article References: Mahendia, P., Jangra, R., Karakoti, M., Sinha, O. P., Sahoo, N. G., Srivastava, A., Rana, S., & Mahendia, S. (2026). Microwave-assisted synthesis of activated carbon from aerobic combustion of cotton in sesamee oil for high performance supercapacitor. Discover Electrochemistry, 3(1), Article 52. https://doi.org/10.1007/s44373-026-00139-w
Image Credits: AI Generated
DOI: 10.1007/s44373-026-00139-w
Keywords: activated carbon, supercapacitor, microwave-assisted activation, sesame oil, cotton soot, biomass-derived carbon, energy storage, porosity, electrochemical double-layer capacitor, potassium hydroxide activation, specific capacitance, sustainable materials
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Bethany Barker. (October 1, 2026). Lamp Soot From Sesame Oil Turns Into a Five-Minute Microwave Miracle for Supercapacitors. Scienmag. https://scienmag.com/lamp-soot-from-sesame-oil-turns-into-a-five-minute-microwave-miracle-for-supercapacitors/
Bethany Barker. “Lamp Soot From Sesame Oil Turns Into a Five-Minute Microwave Miracle for Supercapacitors.” Scienmag, 1 October 2026, https://scienmag.com/lamp-soot-from-sesame-oil-turns-into-a-five-minute-microwave-miracle-for-supercapacitors/. Accessed 1 October 2026.
Bethany Barker. “Lamp Soot From Sesame Oil Turns Into a Five-Minute Microwave Miracle for Supercapacitors.” Scienmag. October 1, 2026. https://scienmag.com/lamp-soot-from-sesame-oil-turns-into-a-five-minute-microwave-miracle-for-supercapacitors/
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Tags: activated carbonbiomass-derived carbonbiomass-derived carbon energy storagecotton sooteco-friendly supercapacitor electrode fabricationelectrochemical double-layer capacitorelectrochemical properties of soot-based electrodesenergy density improvement in supercapacitorsenergy storagefast charge/discharge supercapacitorshigh surface area carbon materials from soothousehold microwave energy storageinnovative energy storage materials from natural sourcesmicrowave processing of carbon materialsmicrowave-assisted activationmicrowave-treated carbon for supercapacitorsporositypotassium hydroxide activationsesame oilsesame oil soot supercapacitor electrodespecific capacitancesupercapacitorsustainable electrode materials from household wastesustainable materials
