Sustainable AgFeO2–carbon nanohybrids derived from agricultural waste for high-performance supercapacitors in alkaline environments and multifunctional biomedicine

Abstract

Energy is a basic need in today's world, and there is a demand for renewable energy storage technologies. Supercapacitors (SCs) are a well-known type of storage device that can meet these needs. Delafossite minerals (ABO₂) have garnered much attention lately as potential materials in electrochemical energy storage technologies. In this study, sustainable AgFeO₂ hybrid nanocomposites integrated into biomass-derived carbon substrates were synthesized via co-precipitation and hydrothermal techniques for dual-function energy storage and biomedical applications. Structural analysis using X-Ray Diffraction (XRD) confirmed the preservation of the delafossite AgFeO₂ phase, exhibiting crystallite sizes of 6.51 nm for AgFeO₂–CNT and 7.43 nm for AgFeO₂–AC. Morphology studies via Scanning Electron Microscopy (SEM) revealed AgFeO₂ nanoparticles anchored onto granule-like CNT frameworks, creating textured hierarchical surfaces that significantly enhance charge transmission. Fourier transform infrared (FT-IR) spectroscopy analysis verified composite formation as indicated through characteristic bands at 3280 cm⁻¹ (hydroxyl/amine), 1563 cm⁻¹ (CC sp²), and 515/457 cm⁻¹ (Ag–O/Fe–O). Furthermore, X-ray Photoelectron Spectroscopy (XPS) revealed the presence of a mixture of Fe(II)/Fe(III) states and Ag–O/Fe–O coordination, indicating an abundance of active surface redox sites. Magnetic studies using a Vibrating Sample Magnetometer (VSM) demonstrated weak ferromagnetism (M_s = 2.34 × 10⁻³ emu g⁻¹) suitable for magnetic separation. In electrochemical evaluations using 2 M KOH electrolyte, an AgFeO₂–CNT electrode delivered a superior specific capacitance value of 970.8 F g⁻¹ at 8 A g⁻¹ outperforming the AgFeO₂–AC electrode (935.3 F g⁻¹) at the same current densities. The incorporation of CNTs into the AgFeO₂ lattice resulted in a larger CV integrated area and lower internal resistance, indicating superior electrochemical capacitance and faster ion-diffusion rates. Long-term stability tests revealed 82.75% capacitance retention for the AgFeO₂–CNT electrode after 6000 cycles. A fabricated asymmetric device exhibited high operational stability (52.90% retention over 5000 cycles) and excellent coulombic efficiency. Superior to the AgFeO₂–AC system, the AgFeO₂–CNT hybrid achieved a remarkable energy density of 109.21 Wh kg⁻¹ while maintaining a power density of 3599.67 W kg⁻¹, validating its efficacy as a sustainable and high-rate electrode material for advanced energy applications.