Erbium-substituted LaFeO₃ perovskite nanoparticles for pseudocapacitive energy storage applications

LaFeO₃ perovskites are promising candidates for supercapacitor electrodes, yet their performance is limited by low ionic conductivity and restricted active surface area. In this work, Er³⁺ was introduced at the A-site of LaFeO₃ to increase defect concentration and improve ion transport within the perovskite lattice. Nanoparticles with compositions of La_1-x Er _x FeO₃ (x = 0, 0.1, 0.2, and 0.3) were synthesized using a sol-gel auto-combustion method and characterized by XRD, SEM, TEM, and XPS to establish structural refinement, morphological evolution, and defect chemistry. Among all compositions, La_0.8Er_0.2FeO₃ delivered the highest specific capacitance of 288.2 F g^-1 at 5 mV s^-1 and 201.4 F g^-1 at 2 A g^-1. XPS revealed a significant increase in defect concentration, accompanied by the formation of Fe²⁺ via electron transfer from O^2- ions, consistent with enhanced defect-assisted charge transport. Shortened oxygen diffusion pathways arising from reduced bond lengths further contributed to improved ionic mobility. The Ragone analysis indicated that the Er-doped composition exhibits superior energy and power densities compared to pristine LaFeO₃. These results establish Er substitution as an effective strategy for defect engineering in LaFeO₃, enabling improved charge-storage behavior and positioning Er-doped LaFeO₃ as a strong candidate for next-generation pseudocapacitive energy-storage applications.