Synergistic enhancement of binder-free MnO ₂ electrodes through morphological control and graphene oxide integration for high performance supercapacitors

This research focuses on synthesizing MnO 2 via a one-step hydrothermal method and evaluating its electrochemical performance for supercapacitor applications. MnO 2 was directly coated on a Ni foam substrate to create binder-free electrodes. Varying hydrothermal conditions altered the morphology and crystallinity of MnO 2 , with semi-crystalline structures formed at intermediate temperatures and times-exhibiting enhanced charge storage due to higher surface area and active sites. SEM analysis revealed diverse morphologies, including particulate, spherical and rod-like structures. Among the samples, M2 (synthesized at [Formula: see text]C for 8[Formula: see text]h) showed the best performance, achieving a specific capacitance (C sp ) of 780[Formula: see text]Fg[Formula: see text] with energy and power densities of 39.99[Formula: see text]Whkg[Formula: see text] and 0.29[Formula: see text]kWkg[Formula: see text], respectively. To further improve performance, M2 was combined with varying concentrations of graphene oxide (GO). The M2-5GO composite electrode delivered a high C sp of 1145[Formula: see text]Fg[Formula: see text], an energy density of 58.06[Formula: see text]Whkg[Formula: see text] and maintained 94.6% capacitance over 5000 cycles. The enhanced performance was attributed to the synergistic effect offered by a higher surface area of MnO 2 and the layered structure of GO. Analysis indicated that while M2 relied mainly on diffusive charge storage, while GO addition increased capacitive contribution by 11%. The study demonstrates MnO 2 has a potential for high-performance supercapacitors, especially when used with GO. Furthermore, M2-5GO was used to develop a symmetric two-electrode device. Electrochemical characterization of the device revealed that it possessed C sp of 333[Formula: see text]Fg[Formula: see text] at 1[Formula: see text]mVs[Formula: see text] with energy and power density of 44.42[Formula: see text]Whkg[Formula: see text] and 0.50[Formula: see text]kWkg[Formula: see text], respectively, at 1[Formula: see text]Ag[Formula: see text] current density.