<i>Psidium guajava</i> mediated synthesis of Mn ₂ O ₃ /Mn ₃ O ₄ and MnO ₂ –CNT nanohybrids for high-performance supercapacitor applications

This study presents a sustainable approach for the Psidium guajava mediated synthesis of aqueous extract based-Mn2O3/Mn3O4 and ethanolic extract based-MnO2 nanoparticles (NPs), and their nanocomposites (NCs) with 3, 6 and 9 % carbon nanotubes (CNTs). The XRD patterns revealed cubic Mn2O3, tetragonal Mn3O4 and orthorhombic/monoclinic MnO2 phases. FE-SEM analysis showed nanosheets, polymorphic, and spherical morphologies. Mn2O3/Mn3O4 showed a lower band gap (2.96 eV) compared to MnO2 (3.52 eV), which was further decreased to 2.77 eV in Mn2O3/Mn3O4@CNT3% contributing to its exceptional electrochemical performance. The NMs were tested for their electrochemical performance using galvanostatic charge-discharge (GCD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Among all the nanomaterials, the Mn₂O₃/Mn₃O₄@CNT-3% composite had the highest specific capacitance of 1176 F g−1 at a current density of 1 A g−1 and a power density of 60.8 W kg−1, with a low charge-transfer resistance of 12 Ω, demonstrating its strong potential for practical supercapacitor applications.