Electronic structure, local coordination, and defect insights of aloe vera-derived NiO for supercapacitor applications

Green-synthesized nanomaterials are gaining increasing attention as sustainable electrode candidates for energy storage. Here, Aloe vera-assisted synthesis was employed to fabricate defect-rich NiO nanopyramids with superior electrochemical properties. Synchrotron XRD (SXRD) confirmed the formation of phase-pure crystalline NiO, while synchrotron x-ray absorption spectroscopy (XAS) provided detailed insights into hybridization of Ni-3d and O-2p orbitals, Ni oxidation state and the local coordination environment. Optical studies revealed a wide bandgap, compared to bulk NiO, accompanied by defect-related emissions. X-ray photoemission spectroscopy (XPS) analysis further demonstrated mixed Ni 2+ /Ni 3+ oxidation states with significant oxygen-vacancy contributions. This work addresses a key gap in the existing literature on Aloe vera-derived NiO by integrating UV-Vis/PL, synchrotron-based XAS, and XPS analyses with electrochemical evaluation to establish a comprehensive correlation between the electronic structure, local coordination environment, defect characteristics, and charge-storage behaviour of the material. Electrochemical investigations revealed diffusion-controlled pseudocapacitance, with the electrode delivering high specific capacitances of 674, 468 and 358 F g − 1 at current densities of 0.5, 4, and 10 A g − 1 , respectively, demonstrating high-rate capability. These results demonstrate that Aloe vera-derived NiO, with its defect-engineered electronic structure, is a sustainable and high-performance electrode material for next-generation hybrid supercapacitor applications.