Beach Plant Extract Yields Copper Ferrite Nanoparticles for Supercapacitor Electrodes

A team of researchers in India has found a way to turn a hardy coastal shrub into a key ingredient for next-generation energy storage. By using leaf extract from Pemphis acidula, a mangrove-associated plant that thrives in salty, rocky shorelines, scientists at Saveetha Institute of Medical and Technical Sciences in Chennai synthesized copper ferrite (CuFe₂O₄) nanoparticles through a hydrothermal route and demonstrated that the resulting material performs impressively as a supercapacitor electrode. The study, published in the journal Ionics, reports a specific capacitance of roughly 688.7 farads per gram at a scan rate of 10 millivolts per second, along with capacitance retention of 91.6 percent after 5,000 charge–discharge cycles. Those figures place the green-synthesized material among the competitive performers in the crowded field of transition-metal oxide electrodes, and they do so using a synthesis chemistry that avoids many of the toxic reagents traditionally employed to make ferrite nanoparticles.

The appeal of copper ferrite lies in its crystal chemistry. CuFe₂O₄ adopts the cubic spinel structure, in which copper and iron cations occupy interstitial sites within a close-packed oxygen lattice. This arrangement supports reversible redox reactions at the electrode surface, the fundamental process behind pseudocapacitive charge storage. Unlike battery-type materials that store charge through bulk phase changes, pseudocapacitive electrodes shuttle ions to and from near-surface sites, enabling rapid charge and discharge cycles. Ferrites in general, and copper ferrite in particular, have attracted attention because they combine good electrochemical activity with low cost, earth-abundant constituents, and useful magnetic properties. The challenge has always been synthesis: conventional routes often require high temperatures, harsh reducing agents, or surfactants that leave residues and complicate scale-up.

That is where the plant extract comes in. Pemphis acidula leaves are rich in phenolics and flavonoids, polyphenolic compounds known to act as natural reducing and stabilizing agents. In the Chennai team’s procedure, the leaf extract serves double duty: its biomolecules reduce the metal precursors and simultaneously cap the growing nanoparticles, limiting agglomeration and helping to control particle size and shape. The researchers combined the extract with copper and iron salt solutions and processed the mixture hydrothermally, a technique that uses water at elevated temperature and pressure inside a sealed vessel to drive crystal growth. Hydrothermal synthesis is prized for producing well-crystallized oxide phases at relatively modest temperatures, and pairing it with a biological capping agent gives the method an unusually green profile.

Characterization confirmed that the approach worked as intended. Ultraviolet–visible spectroscopy showed a distinctive absorption peak at 316.28 nanometers, and Tauc analysis of the absorption data yielded a narrow direct band gap of 2.29 electronvolts. A band gap in that range signifies strong absorption in the visible portion of the spectrum, a property that could prove useful beyond energy storage, since narrow-gap metal oxides are often candidates for photocatalytic applications. X-ray diffraction verified the formation of phase-pure cubic spinel CuFe₂O₄, with the characteristic diffraction planes of the spinel lattice appearing clearly and without contaminating secondary phases. Phase purity matters enormously for electrode performance, because impurity phases can add dead weight, block ion pathways, or introduce parasitic reactions that degrade cycling stability.

Infrared spectroscopy added further confirmation. Fourier-transform infrared measurements identified the characteristic metal–oxygen stretching vibrations of the ferrite lattice, with the combined Cu–O and Fe–O bands appearing at 605.2 wavenumbers per centimeter. Field-emission scanning electron microscopy then revealed the morphology: polyhedral nanoparticles with only minimal agglomeration, a direct benefit of the phytochemical capping during synthesis. Elemental mapping performed alongside the imaging showed that copper, iron, and oxygen were distributed uniformly across the particles, indicating that the spinel composition was consistent throughout the material rather than segregated into separate copper-rich or iron-rich domains. Uniform elemental distribution supports consistent electrochemical behavior, since every region of the electrode participates equally in the redox chemistry.

The electrochemical evaluation formed the heart of the study. Using cyclic voltammetry, the researchers measured a specific capacitance of approximately 688.7 farads per gram at a scan rate of 10 millivolts per second, a high value for a single-phase ferrite electrode. Galvanostatic charge–discharge testing, which charges and discharges the electrode at a constant current, gave a specific capacitance of 574.7 farads per gram at a current density of 1 ampere per gram. The modest gap between the two figures is typical, since different techniques probe different time scales and surface access, but both numbers indicate that a large fraction of the material’s theoretical capacity is being accessed under realistic operating conditions.

Kinetic analysis offered insight into how the electrode stores charge. By examining how the peak currents in the voltammetry data scale with scan rate, the team extracted a b-value of 0.596. In this framework, a b-value of 1 would indicate purely surface-controlled capacitive behavior, while a value of 0.5 would indicate fully diffusion-limited processes. The measured value of 0.596 therefore points to charge storage that is predominantly diffusion-controlled pseudocapacitive in character, meaning that ions from the electrolyte must diffuse into the near-surface regions of the nanoparticles to participate in the redox reactions. This mechanistic picture helps explain both the high capacitance and the way performance changes with rate, and it gives future researchers a handle for optimizing the material, for instance by engineering porosity or particle size to shorten diffusion distances.

Stability, often the Achilles heel of metal oxide electrodes, proved to be a strength here. After 5,000 galvanostatic charge–discharge cycles, the electrode retained 91.6 percent of its initial capacitance. For a pseudocapacitive oxide, where repeated ion insertion and extraction can gradually pulverize the active material or dissolve metal ions into the electrolyte, retention above 90 percent over thousands of cycles is a meaningful benchmark. The structural integrity of the polyhedral particles, combined with the stabilizing influence of residual biomolecular capping, likely contributes to this durability. Electrochemical impedance spectroscopy completed the assessment, probing the resistance and charge-transfer behavior at the electrode–electrolyte interface and supporting the overall picture of an electrode whose kinetics are well suited to fast, repeated cycling.

The broader significance of the work lies in its convergence of two trends. On one side, supercapacitors are increasingly seen as complements to batteries in applications that demand rapid charge acceptance, long cycle life, and tolerance to temperature extremes, from regenerative braking systems to grid buffering of renewable power. On the other, green synthesis routes are moving from curiosity to practical necessity as the nanomaterials industry confronts the environmental footprint of its own manufacturing. A process that uses a coastal plant abundant in tropical shorelines, water-based hydrothermal chemistry, and no specialized toxic reagents addresses both concerns at once. The Chennai group’s results suggest that the humble Pemphis acidula leaf, better known for its role in coastal ecosystems and traditional medicine, can serve as a chemical workhorse for clean energy materials. If the performance holds up in full-device testing and at larger synthesis scales, beach shrubs and supercapacitors may turn out to be an unexpectedly productive pairing.

Subject of Research: Green hydrothermal synthesis of copper ferrite nanoparticles for supercapacitor energy storage

Article Title: Hydrothermal method of copper ferrite nanoparticles synthesized using Pemphis acidula leaf extract for energy storage application

Article References: Hydrothermal method of copper ferrite nanoparticles synthesized using Pemphis acidula leaf extract for energy storage application. (n.d.). https://doi.org/10.1007/s11581-026-07563-3

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07563-3

Keywords: copper ferrite, Pemphis acidula, green synthesis, hydrothermal method, nanoparticles, supercapacitor, energy storage, pseudocapacitance, spinel structure, electrode materials, electrochemistry, band gap