<p>Sm–Co–MWCNT composite is synthesized via co-precipitation method, in which Sm-doped cobalt nitrate is integrated with multi-walled carbon nanotubes (MWCNT) and subsequently annealed to form a crystalline Sm–Co oxide-based electrode material. Analysing the structure and morphology of the sample, it was further investigated as a potential electrode for supercapacitor. The electrode demonstrated a specific capacitance of 931 Fg^− 1 at 10 mV s^− 1. It is ascribed to the uniformly anchored Sm-doped Co₃No₃-type framework on the MWCNT network, enhanced defect-rich interfacial sites, improved electrical pathways, and rich redox activity of Co²⁺/Co³⁺ couples facilitated by Sm³⁺-induced oxygen vacancies. An aqueous asymmetric supercapacitor device (ASC) was designed with Sm–Co–MWCNT (positive electrode) and activated carbon (negative electrode). Electrochemical performance of the product, based on CV, GCD and EIS studies revealed an energy density of 9.6 Wh kg^− 1 and a power density of 3456 Wkg^− 1. Sm–Co–MWCNT//AC delivered quasi-rectangular cyclic voltammograms, near-triangular galvanostatic charge–discharge profiles, low internal resistance, and good rate capability, while retaining about 85% of its initial capacitance after 5000 cycles, demonstrating excellent long-term stability.</p>