In the present investigation, we have synthesized samarium (Sm) nanoparticles (NPs) and anchored them onto the surface of CuO:CoO nanostructure (NS) by utilizing a simple chemical precipitation method. Nanostructures (NS) were characterized utilizing powdered X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron spectroscopy (SEM), transmission electron spectroscopy (TEM), UV–visible spectroscopy (UV–Vis), and Brunauer–Emmett–Teller (BET) studies. Resulting Sm_x CuO: CoO (x = 1%, 5%, 10%, and 12%) NS were investigated for their anomalous electrical and supercapacitive behavior. NS energy storage performance was experimentally determined using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). Sm_10%CuO:CoO exhibited better electrochemical response than other samples and showed a maximum specific capacitance of 283.6 F/g at 0.25 A/g in KOH electrolyte. However, contrary to our expectation, NS displayed rectifying nature in I-V, intercalative nature in C-V, and polaronic permittivity in all concentrations of Sm₂O₃ doping as compared with undoped CuO:CoO NS. The outstanding properties of Sm_x CuO:CoO NS are attributed to the synergy of high charge mobility of Sm NPs, leading to significant variation in dielectric permittivity, current–voltage (I-V) response, capacitance–voltage (C-V) behavior, with the formation of Sm³⁺ ionic cluster. The clusters lead to a change in dipole moment creating a strong local electric field. Additionally, a CR2032 type symmetric supercapacitor cell was fabricated using Sm_10%CuO:CoO, which exhibited a maximum specific capacitance of 67.4 F/g at 0.1 A/g. The cell was also subjected to 5000 GCD cycles where it retained 96.3% Coulombic efficiency.

Graphical Abstract