The story begins with one of the most abundant and cheapest starting materials imaginable. Fresh Bauhinia variegata flowers were gathered from the campus of P P Savani University in Surat, washed thoroughly with tap water, double-distilled water and ethanol, and dried first in the sun and then overnight at about 100 degrees Celsius. The dried petals were ground into a fine powder and mixed with zinc chloride in a one-to-two weight ratio, then left for a full month to allow deep impregnation. Zinc chloride activation is a well-established chemical route to porous carbon: during subsequent high-temperature treatment it promotes dehydration, aromatization and the development of an extensive pore network throughout the carbon matrix.

Carbonization itself took place in a tubular furnace under a continuous flow of nitrogen gas. The temperature was ramped from room temperature to approximately 900 degrees Celsius at a controlled 5 degrees Celsius per minute and held there for thirty minutes, driving off oxygen-containing surface groups and locking in the porous architecture. After natural cooling, the blackened product was crushed, washed with concentrated hydrochloric acid to strip out residual activating agent and inorganic impurities, and rinsed repeatedly with hot deionized water until the filtrate reached a neutral pH. X-ray photoelectron spectroscopy confirmed the thoroughness of this purification: no zinc signal appears in the spectra, because at 900 degrees Celsius zinc species largely volatilize thanks to the element’s high vapor pressure, and any survivors were dissolved away during the acid wash.

The innovation that elevates this work beyond routine biomass carbonization is the manganese doping step. Rather than relying on simple soaking, the team dispersed the activated carbon in ethanol and added manganese(III) oxide corresponding to a 2 weight percent manganese loading, then subjected the suspension to 70 minutes of high-intensity probe sonication at 750 watts and 20 kilohertz in pulsed mode. Acoustic cavitation, the rapid formation and collapse of microscopic bubbles in the liquid, generates intense local temperature and pressure spikes that drive precursor particles into the carbon pores and anchor them to the surface with unusual uniformity. Ethanol was replenished periodically during treatment to compensate for evaporation, and the dried powder was subsequently annealed at 450 degrees Celsius under nitrogen for three hours to strengthen the metal-carbon interactions and stabilize the manganese species.

The spectroscopic fingerprints of the resulting Mn-doped activated carbon, abbreviated Mn-AC, tell a convincing story. High-resolution XPS of the C 1s region shows peak broadening relative to the pristine material, evidence of increased surface functionalization after manganese loading. The O 1s spectrum deconvolutes into components assigned to Mn-O-C bonding near 530.0 electron-volts, surface hydroxyl groups near 531.6 electron-volts, and highly oxygenated species near 533.5 electron-volts, reflecting the strong metal-carbon interactions forged during sonication. The Mn 2p region displays the characteristic 2p3/2 and 2p1/2 doublet, confirming coexisting Mn3+ and Mn4+ oxidation states on the carbon surface. Scanning electron microscopy revealed the complementary morphological shift: smooth, compact, plate-like structures in the pristine carbon give way to a roughened, granular, nodular texture after doping, with energy-dispersive X-ray mapping confirming that carbon, oxygen and manganese are distributed evenly across the framework without agglomeration.

With the material characterized, the team fabricated two symmetric electrochemical double-layer capacitor cells using a gel polymer electrolyte composed of poly(vinylidene fluoride-co-hexafluoropropylene) and the ionic liquid 1-ethyl-3-methylimidazolium tricyanomethanide. Electrode slurries containing 90 weight percent active material and 10 weight percent binder were drop-cast onto graphite sheets to a thickness of 50 to 80 micrometers, with a mass loading of roughly 1 milligram per square centimeter. Electrochemical impedance spectroscopy measured from 100 kilohertz down to 10 millihertz delivered the first clear verdict: the Mn-AC cell achieved a specific capacitance of 20 farads per gram at low frequency, compared with 15 farads per gram for the undoped carbon. The authors attribute the gain to increased density of polar surface functionalities and adsorption sites, improved electrolyte wetting and ion accessibility within the pores, and additional fast surface redox contributions from the manganese species.

Cyclic voltammetry reinforced the picture. After identifying an optimized window of minus one to plus one volt, the researchers swept scan rates from 5 to 100 millivolts per second. The Mn-AC cell produced CV profiles that were noticeably more rectangular than those of the pristine device, a hallmark of superior double-layer formation, and the calculated specific capacitances at 5 millivolts per second were 13.20 and 8.59 farads per gram respectively. Galvanostatic charge-discharge testing added the durability data: the pristine carbon delivered about 2 farads per gram at 1 milliampere with an energy density of 0.38 watt-hours per kilogram and a power density of 1160 watts per kilogram, while Mn-AC reached approximately 9.80 farads per gram, an energy density of 1.42 watt-hours per kilogram and a power density of 1020 watts per kilogram. Crucially, both cells remained roughly stable over 10,000 charge-discharge cycles.

The second act of the study is arguably the more striking. Counter electrodes are a critical and often expensive component of dye-sensitized solar cells, which conventionally rely on platinum. Here the researchers coated layers of AC and Mn-AC onto fluorine-doped tin oxide glass, paired them with titanium dioxide working electrodes sensitized with N719 dye, and sandwiched a previously reported PEO-KI/I2-EMImSCN polymer electrolyte between them. Under one-sun illumination from a solar simulator, the Mn-AC device nearly doubled the power conversion efficiency of the pristine-carbon cell, driven primarily by a substantial increase in short-circuit current density while open-circuit voltage and fill factor stayed comparable. The improvement points to enhanced electrocatalytic activity toward the iodide-triiodide redox reaction and faster charge transfer at the electrode-electrolyte interface, both direct consequences of manganese incorporation.

The broader context makes the result notable. Recent literature has seen explosive interest in biomass-derived carbons, from machine-learning-guided designs predicting surface areas near 2822 square meters per gram and capacitances around 322 farads per gram, to nitrogen- and phosphorus-doped porous carbons achieving energy densities approaching 49 watt-hours per kilogram. Flower-derived carbons in particular have proven versatile, serving as dye adsorbents, carbon dioxide capture media and aptasensor substrates. What this study adds is a demonstration that a modest, sonochemically delivered transition-metal dose can simultaneously upgrade a carbon’s capacitive behavior and its electrocatalytic performance, without sacrificing the porous framework or requiring scarce, costly noble metals. The authors caution that excessive manganese loading could block pores and hinder ion transport, an effect not specifically investigated here, and that no systematic optimization of manganese content was performed.

The ionic liquid electrolyte deserves its own mention. Unlike volatile, flammable organic solvents, ionic liquids are essentially non-volatile salts that remain liquid below 100 degrees Celsius, offering wide operating voltage windows and a highly ionized environment. The team’s earlier work identified EMImTCM as particularly well suited to both supercapacitor and dye-sensitized solar cell platforms, and pairing it with a PVdF-HFP gel matrix here produced a mechanically robust, safer electrolyte suited to flexible device concepts. Looking forward, the authors suggest that polymer-based electrolytes, tuned through further doping and composite formation, could push device performance well beyond what aqueous-electrolyte systems reported in most prior literature achieve. For now, the takeaway is simple and compelling: a tree that dots the streets and gardens of South Asia sheds flowers that, with a zinc chloride bath, a blast of nitrogen and seventy minutes of ultrasound, become a genuine dual-purpose energy material.

Subject of Research: Sonochemically manganese-doped activated carbon derived from Bauhinia variegata flowers for supercapacitor and dye-sensitized solar cell electrodes

Article Title: Sonochemically manganese doped activated carbon from Bauhinia variegata for dual energy application

Article References: Punetha, V. D., Dhapola, P. S., Singh, P. K., Matiyani, M., Singh, R., Kumar, S., & Pathak, V. (2026). Sonochemically manganese doped activated carbon from Bauhinia variegata for dual energy application. Discover Electrochemistry, 3(1), Article 71. https://doi.org/10.1007/s44373-026-00159-6

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00159-6

Keywords: activated carbon, Bauhinia variegata, manganese doping, sonochemical synthesis, supercapacitor, dye-sensitized solar cell, biomass-derived carbon, ionic liquid electrolyte, energy storage, electrocatalysis, XPS, gel polymer electrolyte

The heart of the advance is a battery built around disulfur dichloride, S2Cl2, a sulfur-containing compound in which sulfur sits at a higher oxidation state than the elemental sulfur used in traditional lithium–sulfur cells. Rather than cycling sulfur between its elemental form and lithium sulfide through the conventional two-electron pathway, the new chemistry reversibly converts lithium sulfide, Li2S, back into disulfur dichloride through a three-electron sulfur redox process. That extra electron transfer per sulfur atom is the key to unlocking both a higher cell voltage and a greater storage capacity, since the total energy a battery delivers is the product of its voltage and the charge it can move.

The numbers reported by the team are striking. At room temperature, 25 degrees Celsius, and a moderate discharge rate of 0.2C, the average operating voltage of the cell rises from approximately 2.05 volts in a conventional lithium–sulfur configuration to 2.54 volts. The sulfur-specific capacity increases by 58 percent relative to standard sulfur chemistry. Taken together, these gains translate into an electrode-level specific energy exceeding 1,700 watt-hours per kilogram, a figure far beyond what today’s commercial cathodes can achieve, and the cells sustain this performance over more than 100 charge–discharge cycles.

Achieving reversible high-valence sulfur chemistry has proven notoriously difficult in the past, and the reasons illuminate why this result matters. When chemists have attempted to push sulfur into higher oxidation states using halogens such as chlorine, two obstacles have consistently emerged. First, chloride species in typical electrolytes bind strongly to lithium ions, tying up the charge carriers needed for the battery to function. Second, halogen-mediated reactions tend to consume the electrolyte itself, degrading the cell from the inside out and destroying reversibility over repeated cycles. The new work demonstrates that both problems can be overcome with a carefully designed liquid medium.

The enabling technology is a free-chloride-rich ionic liquid electrolyte, a class of molten salts that remain liquid at or near room temperature and consist entirely of ions. Unlike conventional solvent-based electrolytes, this ionic liquid keeps chloride anions in an unbound, or free, state rather than locking them to lithium cations. In this configuration, the electrolyte does far more than simply conduct ions between the electrodes. It functions as an ionic mediator, actively participating in the redox chemistry that shuttles sulfur between its low-valence and high-valence states, while contributing only a minor share of the measured capacity itself.

The researchers support their electrochemical measurements with an extensive suite of characterization techniques, including synchrotron X-ray absorption spectroscopy performed at beamline 8-BM of the National Synchrotron Light Source II at Brookhaven National Laboratory, X-ray photoelectron spectroscopy, in situ Raman spectroscopy and galvanostatic intermittent titration. Molecular dynamics simulations, conducted with custom force field parameters and code that the team has released openly on Zenodo, provide atomistic insight into how the phase-separated ionic-liquid structure stabilizes the chloride-mediated reaction pathway. Together, these tools confirm that the conversion between lithium sulfide and disulfur dichloride is genuinely reversible across repeated cycles.

The implications for energy storage are considerable. Lithium–sulfur batteries are attractive not only for their theoretical energy density but also for their supply chain: sulfur is a byproduct of petroleum refining and is available in quantities that dwarf the demand of any conceivable battery market. Raising the operating voltage by nearly half a volt may seem like a modest increment, but because energy scales directly with voltage, this single improvement multiplies the practical energy output of every gram of active material in the cell. Combined with the capacity boost from three-electron redox, the approach could move lithium–sulfur technology from a laboratory curiosity toward a genuine competitor for electric vehicles, grid storage and aerospace applications.

The research also reframes how battery scientists think about electrolytes. For most of the history of electrochemistry, the electrolyte has been treated as a passive component, chosen primarily for its stability and ionic conductivity. Here, the electrolyte is an active chemical participant, engineered with precision so that its chloride content mediates sulfur oxidation without parasitic consumption. This concept of an electrolyte that serves as a reaction mediator while remaining substantially intact echoes strategies explored in other emerging chemistries, including lithium–chlorine, lithium–sulfur dioxide and lithium–sulfur hexafluoride systems, but the authors show that their formulation achieves a rare combination of high voltage, high capacity and sustained reversibility.

Significant engineering challenges remain before cells of this type could leave the laboratory. The performance was demonstrated at the electrode level rather than in fully optimized pouch or cylindrical formats, and scaling ionic-liquid electrolytes to mass production will require attention to cost, viscosity and low-temperature behavior. Nevertheless, the demonstration of more than 100 stable cycles at an electrode-level specific energy above 1,700 watt-hours per kilogram establishes a new benchmark for sulfur-based batteries and offers the field a compelling proof of concept: that pushing sulfur to higher oxidation states, long considered a dead end because of irreversible halogen side reactions, can be made practical when the electrolyte is designed as an ally rather than a bystander.

As the global demand for high-energy, low-cost batteries intensifies, breakthroughs of this kind underscore how much untapped potential remains in some of chemistry’s most abundant elements. By coaxing a single sulfur atom to give up or take on three electrons instead of two, and by recruiting chloride ions as willing chemical partners rather than destructive interlopers, the University of Maryland-led team has shown that even the oldest rival to lithium-ion technology still holds surprises. The work was funded in part by the US Department of Energy’s Basic Energy Sciences program and its Vehicle Technologies Office, and the authors report no competing financial interests.

Subject of Research: Chloride-mediated three-electron sulfur redox chemistry in rechargeable lithium–disulfur dichloride batteries using a free-chloride-rich ionic liquid electrolyte

Article Title: Lithium–disulfur dichloride batteries

Article References: Zhang, N., Zhang, J., Zhang, W., Wang, Z., Zhao, C.-X., Li, A.-M., Liu, Y., Xia, K., Mesirow, C., Yang, Y., Lucht, B. L., Hu, E., Ji, X., Jiang, D.-E., Xu, J., & Wang, C. (2026). Lithium–disulfur dichloride batteries. Nature Energy. https://doi.org/10.1038/s41560-026-02120-8

Image Credits: AI Generated

DOI: 10.1038/s41560-026-02120-8

Keywords: lithium-sulfur batteries, disulfur dichloride, ionic liquid electrolyte, sulfur redox chemistry, energy density, chloride mediator, lithium sulfide, high-voltage batteries, electrolyte design, polysulfide shuttling, rechargeable batteries, Nature Energy