Supercapacitors charge in seconds and batteries store vast amounts of energy, but no single device has ever managed to do both at once. A team of researchers from India, China, South Korea, Saudi Arabia and Thailand now reports a promising step toward closing that gap. In a study published in the Journal of Materials Science, the group synthesized petal-like nanostructures of bismuth sulfide (Bi2S3) and demonstrated that these flower-shaped particles can serve as the workhorse positive electrode in a supercapattery, an emerging hybrid device that combines the battery-like ability to store large amounts of charge with the supercapacitor-like ability to deliver it rapidly. The work stands out not only for its impressive performance numbers but also for the depth of its explanation: the team paired meticulous electrochemical experiments with density functional theory (DFT) simulations to reveal, atom by atom, why the device works best in one particular electrolyte.
The choice of material is deliberate. Bismuth sulfide is an earth-abundant, environmentally benign semiconductor that has attracted growing attention as an electrode material for energy storage. Its layered orthorhombic crystal structure, built from covalently bonded Bi2S3 ribbons held together by weaker van der Waals forces, offers open channels along which ions can migrate, making it naturally suited to intercalation-based charge storage. Previous studies have produced Bi2S3 in the form of nanorods, nanowires, nanoflowers and nanoflakes using solvothermal, chemical bath and spray methods, and several groups have reported respectable supercapacitor performance from composites that pair the sulfide with graphene, carbon nitride or nickel foam. What has been missing, the authors argue, is a systematic understanding of how the electrolyte itself, not just the material, controls the charge storage process.
To build their electrode material, the researchers turned to hydrothermal synthesis, a technique that grows crystals from aqueous precursors inside a sealed, heated vessel. Under the right combination of temperature, time and precursor chemistry, the reaction self-assembles Bi2S3 into petal-like nanopetals, which the team abbreviates BSNP. This flower-like architecture is more than aesthetic. The petals create a high surface-area scaffold with abundant exposed active sites, short diffusion pathways for ions and open voids that accommodate the volume changes that occur as charge is stored and released. Such morphological engineering is a central strategy in modern electrode design, because electrochemical reactions happen only at surfaces and interfaces; the more accessible surface a material presents to the electrolyte, the more charge it can store and the faster it can deliver it.
The heart of the experiment is a comparison across three alkaline electrolytes: 2 M solutions of lithium hydroxide (LiOH), sodium hydroxide (NaOH) and potassium hydroxide (KOH). All three contain the same charge-carrying hydroxide ion, but they differ in the size and hydration behavior of their cations, and those differences ripple through every aspect of electrode kinetics. When the team tested BSNP as the positive electrode in each solution, the results were striking. In 2 M KOH, the nanopetals delivered a gravimetric capacity of 797.9 coulombs per gram at a scan rate of 1 millivolt per second, outperforming the same material in LiOH and NaOH. In other words, simply swapping the electrolyte cation from lithium or sodium to potassium unlocked a substantially larger fraction of the material’s theoretical storage capability.
Why would potassium ions give bismuth sulfide an edge? The answer, the researchers show, lies in the electronic and ionic interplay at the material’s surface. Using DFT calculations, they probed how hydroxide species interact with the Bi2S3 lattice under each electrolyte condition. Orbital hybridization analysis revealed favorable overlap between the electronic states of the surface and the adsorbed species in the KOH case, while Bader charge analysis quantified the electron transfer between them. Charge density difference maps and electron localization function analysis visualized where electrons accumulate and deplete during adsorption, painting a consistent picture: the potassium-containing environment promotes stronger, more favorable electronic coupling at the Bi2S3 surface, which lowers the energetic barriers for the redox reactions that store charge. This computational evidence aligns neatly with the electrochemical data, giving the performance claims a mechanistic foundation rather than leaving them as empirical observations.
Kinetic analysis added another layer of insight. Applying Dunn’s method, a widely used technique that separates the capacitive (surface-controlled) and diffusion-controlled contributions to charge storage from cyclic voltammetry data measured at different scan rates, the team confirmed that diffusion-dominated processes govern the behavior of the BSNP electrode. That finding matters because it places the material firmly in the battery-type category rather than the purely capacitive one. Battery-type electrodes store charge through faradaic reactions, in which ions insert into the crystal lattice and electrons transfer to or from the metal centers, allowing much more charge to be packed per gram than in the electrostatic double-layer storage that characterizes carbon-based supercapacitor electrodes. It is precisely this battery-like positive electrode, paired with a capacitive negative electrode, that defines the supercapattery architecture.
To prove the concept at the device level, the researchers assembled an asymmetric supercapacitor (ASC) in which the BSNP nanopetals served as the positive electrode and activated carbon, a classic high-surface-area capacitive material, served as the negative electrode. The two electrodes were balanced in mass and charge so that each could operate within its stable voltage window, maximizing the overall cell voltage. The finished device achieved a gravimetric capacity of 209.76 coulombs per gram at a current density of 1 ampere per gram and, more importantly for real-world applications, an energy density of 46.61 watt-hours per kilogram. That figure sits well above what conventional symmetric supercapacitors typically deliver and approaches the lower range of lithium-ion batteries, while retaining the rapid charge-discharge capability and long cycle life that batteries struggle to match.
The significance of the electrolyte comparison extends beyond this particular material. Electrolyte engineering is often treated as an afterthought in electrode research, yet the ionic radius, mobility, hydration shell and desolvation energy of the charge carriers fundamentally shape how deeply ions can penetrate an electrode and how quickly redox reactions proceed. Potassium ions, being larger than lithium and sodium ions in their bare form but less strongly hydrated in aqueous solution, can shed their water shell more easily and interact more directly with electrode surfaces. The present study demonstrates that this seemingly subtle difference can translate into hundreds of coulombs per gram of additional capacity, a lesson that applies to the entire family of transition metal and post-transition metal sulfides under investigation for supercapatteries.
There are, of course, hurdles between a laboratory cell and a commercial device. Aqueous supercapatteries are inherently limited to modest cell voltages by water’s electrochemical stability window, and the long-term cycling stability, rate capability at high current densities and mechanical robustness of sulfide electrodes must be validated over thousands of cycles before such devices could power phones or grid buffers. The authors note that their data are available upon reasonable request, inviting the community to build on the results, and the combination of hydrothermal scalability, inexpensive raw materials and water-based processing gives the approach a credible path toward practical manufacturing. The work was supported by the Ongoing Research Funding Program at King Saud University, with additional support from the University of Kerala.
What makes this study a compelling piece of the energy storage puzzle is its methodological completeness. Rather than reporting a capacity number in isolation, the team connected morphology, electrolyte chemistry, electronic structure and device performance into a single coherent narrative, using DFT not as decoration but as a genuine explanatory tool. As the world races to decarbonize electricity grids and electrify transport, hybrid devices that blend the best of batteries and supercapacitors could fill critical niches, from regenerative braking and renewable energy smoothing to portable electronics that charge in minutes. Petal-like bismuth sulfide, coaxed into existence in a simple hydrothermal reactor and tuned by nothing more exotic than the right potassium hydroxide bath, may prove to be one of the quiet building blocks of that future.
Subject of Research: Electrolyte-dependent charge storage in hydrothermally synthesized petal-like Bi2S3 nanostructures for supercapattery electrodes
Article Title: Electrolyte-dependent charge storage in hydrothermally synthesized petal-like Bi2S3 nanostructure: experimental and DFT insights
Article References: Mottammal, D., Thomas, S. A., Cherusseri, J., Arumugam, D., Pallavolu, M. R., Fatehmulla, A., Ramasamy, S., Parasuk, V., & Rajendran, D. N. (2026). Electrolyte-dependent charge storage in hydrothermally synthesized petal-like Bi2S3 nanostructure: experimental and DFT insights. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13692-x
Image Credits: AI Generated
DOI: 10.1007/s10853-026-13692-x
Keywords: bismuth sulfide, supercapattery, asymmetric supercapacitor, hydrothermal synthesis, DFT calculations, potassium hydroxide electrolyte, battery-type electrode, energy density, charge storage kinetics, nanopetals, aqueous electrolytes, energy storage materials
Tags: aqueous electrolytesasymmetric supercapacitorbattery-type electrodebismuth sulfidecharge storage kineticsDFT calculationsenergy densityenergy storage materialsHydrothermal synthesisnanopetalspotassium hydroxide electrolytesupercapattery
