Double-layered nano-composite of copper-manganese oxide/rGO-palladium for asymmetric supercapacitors

We developed composite electrode materials by depositing reduced graphene oxide (rGO) and palladium (Pd)-integrated CuMn₂O₄ onto Ni-foam substrates using a facile, binder-free hydrothermal method. This work aimed to enhance the specific capacitance of CuMn₂O₄ electrodes for compact energy storage devices. The addition of rGO contributed electric double-layer capacitance (EDLC) and improved conductivity, while Pd acted as a redox catalyst, further boosting the electrochemical performance of CuMn₂O₄. The rGO and Pd effectively suppressed the agglomeration of CuMn₂O₄ nanostructures, transforming their morphology from nano-worms to nano-sheets and doublet nano-sheets. The optimized CMrGP composite electrode achieved a remarkable specific capacitance of 12.3 F/cm² (Cv = 76.6 F/cm³; C = 1.70 mA/cm³) at 8 mA/cm² within a 0–0.5 V potential window, driven primarily by diffusion-controlled mechanisms. An asymmetric supercapacitor device was fabricated using CMrGP as the positive electrode and activated carbon (AC) as the negative electrode. This device delivered a specific capacitance of 1.22 F/cm² and an energy density of 0.433 mWh/cm³ at a power density of 4 mW/cm² (5 mA current). It demonstrated excellent cycling stability, retaining 93.6 % of its initial capacitance and 91 % coulombic efficiency after 27,000 charge-discharge cycles.