<p>This study reports the synthesis of pristine α-MnO₂, Sn-modified α-MnO₂, and Sn @ Eu₂O₃-modified α-MnO₂ nanocomposites via a chemical precipitation method followed by calcination. Structural and surface chemical changes induced by Sn and Eu₂O₃ incorporation were systematically analysed. XRD results are consistent with the tetragonal α-MnO₂ phase, with weak reflections corresponding to cubic Eu₂O₃, indicating heterojunction formation rather than complete lattice substitution. XPS analysis reveals the coexistence of Mn³⁺/Mn⁴⁺ redox couples along with Sn⁴⁺ and Eu³⁺ species, confirming successful modification and defect generation. Optical and magnetic measurements provide supporting evidence for modification-induced electronic structure modulation and defect-related disorder. Electrochemical performance was evaluated in a three-electrode configuration using cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. The Sn @ Eu₂O₃-modified α-MnO₂ electrode exhibits improved pseudocapacitive behaviour, enhanced specific capacitance, and reduced charge-transfer resistance compared to pristine α-MnO₂. The improved performance arises from the combined effects of Sn-induced enhancement of electronic conductivity and Eu₂O₃-assisted defect-mediated ion diffusion, enabling simultaneous improvement in charge-transfer kinetics and electroactive surface accessibility. Electrochemical analysis reveals a significant enhancement in pseudocapacitive behaviour under alkaline conditions. However, these findings are restricted to electrode-level assessments conducted within a three-electrode configuration.</p>