<p>Regulating charge-storage behaviour in perovskite oxides through isovalent rare-earth substitution offers an effective route to improve pseudocapacitive performance. In this work, Bi_1−xGd_xFeO₃ (x = 0-0.25) electrodes were developed to investigate the influence of Gd³⁺ substitution on the structural evolution and electrochemical response of BiFeO₃-based perovskites. XRD analysis confirmed that Gd³⁺ incorporation preserves the rhombohedral perovskite framework while inducing lattice contraction, crystallite refinement, and microstrain. TEM and HRTEM analyses revealed platelet-/flake-like nanoscale morphology with crystalline lattice features characteristic of rhombohedral BiFeO₃. BET analysis further showed a progressive increase in specific surface area and pore volume after Gd³⁺ substitution, indicating improved electrolyte-accessible interfaces. These structural and microstructural changes are correlated with improved electrochemical accessibility and reduced interfacial charge-transfer resistance. Electrochemical measurements demonstrated that the optimized Bi_0.75Gd_0.25FeO₃ electrode exhibits enhanced pseudocapacitive behaviour, delivering a maximum specific capacitance of 854&#xa0;F g^− 1 at 3&#xa0;A g^− 1 along with good rate capability and cycling stability. Kinetic analysis indicated mixed diffusion-controlled Faradaic and pseudocapacitive charge-storage contributions, while EIS analysis revealed reduced charge-transfer resistance after Gd³⁺ substitution. These results indicate that the enhanced pseudocapacitive response of Bi_0.75Gd_0.25FeO₃ arises from the coupled contribution of crystallite refinement, lattice distortion, increased BET surface area, enlarged pore volume, improved electrolyte accessibility, and reduced interfacial charge-transfer resistance.</p>