Green synthesis of MnO₂ using Calendula officinalis and Tilia cordata extracts for application in supercapacitors

Green synthesis of MnO₂ was carried out using natural extracts of Tilia cordata (TC) and Calendula officinalis (CO). Utilizing the transmission electron microscopy, powder X-ray diffraction, and UV–Vis spectra techniques confirmed the successful synthesis of α-MnO₂. The BET analysis showed that the CO-derived material has a larger surface area and appropriate mesoporous structure. The obtained synthesized materials were assembled in asymmetric supercapacitor test cell, with a polymer membrane serving as a separator and an electrolyte. The prepared CO-MnO₂ demonstrates excellent capacitance and energy characteristics and seems to be a promising electrode material for the development of environmentally friendly solid-state supercapacitors.