The study, led by S. Ramesh of Rajalakshmi Engineering College with colleagues B. Sathyasri, B. Yuvaraj, and S. Hanish Anand, set out to combine two abundant bio-waste streams into a single functional material. The first ingredient is Eleusine coracana straw, the residue of finger millet, a staple cereal grown widely across India and Africa. The researchers isolated microfibers from the straw through an alkali treatment, a chemical process that dissolves lignin, hemicellulose, and other amorphous components, leaving behind a cleaner, stronger cellulosic fiber network. The second ingredient is activated biocarbon derived from soy hulls, the fibrous outer coating of soybeans that is typically discarded as low-value agricultural residue. By heating the hulls through pyrolysis and then applying chemical activation, the team produced a porous, carbon-rich material whose conductive architecture is essential for intercepting electromagnetic waves.

Neither ingredient alone would bond well to the polymer chosen as the matrix, poly(vinyl alcohol), or PVA, a water-processable, biodegradable synthetic polymer prized for its film-forming ability and chemical versatility. Natural fibers tend to be hydrophilic and poorly compatible with many matrices, while biocarbon particles can clump together rather than dispersing evenly. To overcome this, the researchers treated both reinforcements with 3-glycidoxypropyltrimethoxysilane, commonly abbreviated GPTMS. This silane coupling agent acts as a molecular bridge: one end carries methoxy groups that can anchor to hydroxyl-rich surfaces such as cellulose fibers and carbon, while the other end carries an epoxy group that can interact with the PVA backbone. The result is a covalently assisted interface that improves load transfer between filler and matrix and keeps the conductive carbon uniformly distributed throughout the film.

The composites themselves were fabricated by solution casting, a straightforward and scalable technique in which the polymer and fillers are dissolved or dispersed in a solvent, cast into a mold or onto a substrate, and dried into a solid film. By systematically varying the amount of biocarbon loading, the team produced a series of hybrid composites and then subjected them to a comprehensive battery of tests covering mechanical strength, dielectric behavior, internal morphology, and electromagnetic shielding effectiveness. This multi-property characterization is what allows the work to stand out, because a shielding material that crumbles under stress or delaminates in service is of little practical value regardless of how well it absorbs microwaves.

The mechanical results tell a coherent story of reinforcement. As biocarbon loading increased, tensile strength, tear strength, and Shore D hardness all improved significantly, meaning the films became stronger, more resistant to ripping, and harder at the surface. At the same time, elongation at break decreased, the classic trade-off of particulate and fiber reinforcement: stiffer fillers restrict the polymer chains from stretching, so the material sacrifices ductility in exchange for strength and rigidity. Scanning electron microscopy provided the visual evidence for why this happens. Fracture surfaces of the composites showed rough, irregular topographies rather than clean, smooth failure planes, a signature of enhanced fracture resistance, and the improved adhesion between fiber and matrix confirmed that the GPTMS treatment was doing its job of transferring stress across the interface.

The dielectric measurements revealed the electromagnetic heart of the material. With increasing reinforcement loading, both the dielectric constant and the dielectric loss of the composites rose. This is exactly what a shielding designer wants to see. The dielectric constant reflects how much electric charge a material can store and polarize, while dielectric loss measures how effectively that stored energy is converted into heat rather than re-radiated. In the composites, higher loading increases the mobility of charge carriers within the conductive biocarbon network and simultaneously multiplies the number of internal interfaces between carbon, fiber, and polymer. These interfaces give rise to interfacial polarization, also known as Maxwell-Wagner-Sillars polarization, in which charges accumulate at boundaries between phases with different conductivities and permittivities, storing electromagnetic energy and dissipating it as heat.

The headline result concerns shielding effectiveness, quantified in decibels and measured in the J-band spanning 10 to 12 gigahertz, a microwave region relevant to radar, satellite communications, and high-frequency wireless systems. The best-performing formulation, designated P4, achieved a total shielding effectiveness of 38.3 dB. To put that number in perspective, a material with 20 dB shielding blocks 99 percent of incident radiation, and 30 dB blocks 99.9 percent; at 38.3 dB, only a few hundredths of one percent of the incoming wave survives. Critically, the team decomposed the total into its two components: absorption shielding effectiveness of 30.8 dB and reflection shielding effectiveness of 7.5 dB. This ratio matters enormously for real-world deployment, because reflective shields bounce radiation back into the environment, potentially causing secondary interference with neighboring devices, whereas absorptive shields convert the energy harmlessly into heat within the material itself.

The researchers attribute this absorption-dominated behavior to a synergistic trio of mechanisms. First, the conductive biocarbon networks dispersed through the PVA film interact with the electric and magnetic components of the incoming wave, inducing currents that dissipate energy. Second, the abundant heterointerfaces throughout the composite drive interfacial polarization, trapping charges and converting field energy into thermal motion. Third, the porous, irregular geometry of the activated biocarbon and the fibrous architecture of the millet straw promote multiple internal reflections: waves that enter the material bounce repeatedly between surfaces and fillers, lengthening the propagation path and giving the absorption mechanisms repeated opportunities to attenuate the signal before it can exit. This layered attenuation cascade is the same design principle found in anechoic chambers and stealth coatings, here achieved with kitchen-table agricultural waste.

What makes the study resonate beyond the laboratory is its sustainability arithmetic. Traditional EMI shields embed mined metals and energy-intensive synthetic carbon materials in thermoset matrices that are nearly impossible to recycle. The PVA-based composite, by contrast, is water-processable, uses a biodegradable matrix, and derives both of its functional fillers from crop residues that farmers currently burn or discard. Finger millet straw and soy hulls are produced on enormous scales in agricultural economies, meaning the feedstock is cheap, renewable, and geographically distributed. The solution casting route requires no high-temperature presses or vacuum metallization, further lowering the embodied energy of the final product. For consumer electronics manufacturers facing tightening right-to-repair and recyclability regulations, a shielding film that can be processed from aqueous solution and built from waste biomass is an increasingly attractive proposition.

There are, of course, hurdles between a laboratory demonstration and a commercial shielding gasket or enclosure liner. The trade-off between stiffness and ductility will need tuning for applications that demand flexibility, long-term environmental durability and humidity resistance of PVA-based films must be validated, and production-scale consistency of biocarbon quality from variable agricultural feedstocks remains an open question. Yet the fundamental demonstration is compelling: by pairing silane-treated natural microfibers with activated waste-derived biocarbon in a green polymer, the Chennai-based team has shown that absorption-dominated, broadband microwave shielding does not require exotic nanomaterials or metallic foils. As the electromagnetic spectrum grows ever more crowded and the environmental cost of electronics comes under scrutiny, materials like this finger millet and soy hull composite suggest that the answer to electromagnetic pollution may be growing in the fields rather than mined from the ground, turning one of agriculture’s leftovers into one of electronics’ essential defenses.

Subject of Research: Biomass-derived biocarbon and Eleusine coracana straw microfiber reinforced PVA composites for electromagnetic interference shielding

Article Title: Investigation of biomass derived biocarbon, and Eleusine coracana straw microfiber reinforced PVA composite for EMI shielding application

Article References: Investigation of biomass derived biocarbon, and Eleusine coracana straw microfiber reinforced PVA composite for EMI shielding application. (n.d.). https://doi.org/10.1007/s00289-026-06742-6

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06742-6

Keywords: EMI shielding, biocarbon, PVA composite, Eleusine coracana, soy hulls, GPTMS silane treatment, solution casting, dielectric properties, absorption shielding, J-band, agricultural waste, sustainable materials

To understand why this matters, it helps to recall how a dye-sensitized solar cell actually works. In these devices, light is absorbed by dye molecules attached to a nanostructured titanium dioxide photoanode. Excited electrons are injected into the titanium dioxide and travel through an external circuit to the counter electrode. Meanwhile, the oxidized dye is regenerated by an electrolyte, usually containing the iodide-triiodide redox couple, which itself must be regenerated at the counter electrode. The counter electrode therefore has to catalyze the reduction of triiodide back to iodide efficiently; if it does not, the whole cycle stalls and the cell’s fill factor and efficiency suffer. Platinum has been the benchmark catalyst for this reaction because of its exceptional activity and stability, but it is scarce, expensive and increasingly unattractive for mass-market deployment.

The search for platinum alternatives has become one of the most active corners of dye-sensitized solar cell research. Over the past decade, researchers have explored transition metal sulfides, selenides, nitrides, carbides and oxides as catalytic counter electrode materials, often pairing them with conductive carbon scaffolds such as graphene, carbon nanotubes or activated carbon. The logic is straightforward: the catalyst provides the electrochemical activity, while the carbon provides the electrical conductivity and surface area needed to shuttle electrons and expose active sites to the electrolyte. Ferrites—mixed metal oxides with the general formula MFe2O4—have emerged as promising candidates because they combine reasonable electrocatalytic activity with chemical stability and low cost.

The new study, led by D. Sengeni of C.K. College of Engineering and Technology in Cuddalore, Tamil Nadu, with colleagues from several Chennai institutions, takes this approach a step further by sourcing the carbon scaffold from renewable agro-food waste rather than from commercially produced activated carbon. The team converted Bean Curd Stick waste into porous biocarbon and then combined it with nickel ferrite, NiFe2O4, a spinel oxide in which nickel and iron ions occupy the crystal lattice in a way that supports electrocatalytic activity. The novel aspect of the study, according to the authors, is precisely this utilization of renewable agro-food waste as a conductive carbon matrix to fabricate a high-performance ferrite-carbon hybrid electrode.

Structural and compositional analyses confirmed the successful formation of the NFO@BC composite, while microscopic studies revealed the uniform anchoring of NiFe2O4 nanoparticles on the porous biocarbon surface. That uniformity is not merely cosmetic. In hybrid counter electrodes, the distribution of catalyst particles across the conductive scaffold determines how effectively electrons can reach active sites. If the ferrite particles cluster together, large portions of the carbon surface remain catalytically inert and the electrolyte cannot access much of the catalyst. Uniform anchoring, by contrast, means that nearly every ferrite nanoparticle is electrically connected to the carbon network and simultaneously exposed to the iodide-triiodide electrolyte, maximizing the density of accessible electrocatalytic sites.

One of the most striking quantitative results from the study comes from Brunauer-Emmett-Teller, or BET, surface area analysis, which revealed a specific surface area of 286.7 square meters per gram for the NFO@BC composite. For an electrode material, that is a substantial figure, and it has direct electrochemical consequences. A high surface area provides abundant accessible electrocatalytic sites and improved contact with the electrolyte, allowing the triiodide reduction reaction to proceed rapidly at the electrode-electrolyte interface. Porosity also matters for ion transport: the pores within the biocarbon matrix create pathways through which the electrolyte can penetrate the electrode, shortening diffusion distances and reducing the charge-transfer resistance that would otherwise limit current output.

The authors attribute the enhanced photovoltaic performance of their cells to the synergistic effect of the conductive biocarbon and the electrocatalytically active NiFe2O4. This division of labor is the central design principle of the hybrid. The biocarbon, derived from biomass, acts as a three-dimensional conductive network that collects electrons arriving from the external circuit and distributes them across the electrode. The nickel ferrite nanoparticles, dispersed across that network, serve as the catalytic workhorses where the triiodide ions are actually reduced. Neither component alone would perform as well: bare biocarbon lacks the catalytic activity of the ferrite, while bare nickel ferrite suffers from the modest electrical conductivity typical of spinel oxides. Together, they address each other’s weaknesses.

The broader context of this work is the push to commercialize dye-sensitized solar cells, which the authors identify as the motivation for developing inexpensive, effective and sustainable platinum-free counter electrodes. Dye-sensitized cells are attractive for applications where conventional panels struggle—indoor lighting, building-integrated photovoltaics, and devices that benefit from semi-transparency and flexibility. But every cost component counts. Platinum loading on a counter electrode may seem like a small fraction of a cell’s material budget, yet at the scale of gigawatt production the price of platinum becomes prohibitive, and its supply chain carries significant environmental and geopolitical burdens. Replacing it with a material synthesized from food waste and abundant iron and nickel compounds changes that calculus fundamentally.

The choice of Bean Curd Stick waste also fits into a growing body of research on biomass-derived carbons for energy devices. Biomass precursors are attractive because they are renewable, widely available and often rich in the heteroatoms that can enhance the catalytic properties of the resulting carbon. Previous work by some of the same research community has examined heteroatom doping in Bean Curd Stick-derived porous carbon for platinum-free counter electrodes, and other groups have used bamboo-derived activated carbon in similar ferrite composites. The present study extends this line of inquiry by demonstrating that the biocarbon matrix can host nickel ferrite nanoparticles uniformly, creating a composite whose texture and chemistry are both favorable for triiodide reduction.

The implications reach beyond a single laboratory result. If hybrid electrodes of this kind can be produced reliably from waste streams, dye-sensitized solar cells could move closer to the cost profile that made them famous after their invention by Brian O’Regan and Michael Grätzel in 1991. The study also illustrates a broader trend in materials science: the convergence of waste valorization and clean energy technology, where one environmental problem—food waste—is enlisted to solve another, the cost and scarcity of critical materials in renewable energy hardware. The authors conclude that NFO@BC stands out as a low-cost, sustainable and efficient platinum-free counter electrode for dye-sensitized solar cell applications, and their results suggest that the humble tofu stick, of all things, may have a role to play in the solar panels of the future.

Subject of Research: Pt-free dye-sensitized solar cell counter electrodes based on NiFe2O4 and biomass-derived biocarbon

Article Title: Development of NiFe2O4@Biocarbon hybrid counter electrode for efficient Pt-free dye-sensitized solar cells

Article References: Sengeni, D., Vinayagam, P., Karuppiah, S., Velmurugan, V., Bindhu, M., & Sevvanthi, S. (2026). Development of NiFe2O4@Biocarbon hybrid counter electrode for efficient Pt-free dye-sensitized solar cells. Ionics. https://doi.org/10.1007/s11581-026-07557-1

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07557-1

Keywords: dye-sensitized solar cells, counter electrode, NiFe2O4, biocarbon, platinum-free, Bean Curd Stick waste, nickel ferrite, biomass-derived carbon, triiodide reduction, photovoltaics, BET surface area, agro-food waste