Holmium-induced lattice engineering of SmFeO3 perovskite nanoparticles for high-performance symmetric supercapacitors in redox-active KI/KOH electrolyte

This study presents Ho-doped SmFeO 3 nanoparticles synthesized via citrate combustion to enhance supercapacitor performance through lattice engineering. Characterization confirmed that Ho 3+ substitution induces compressive microstrain and a refined nanoscale structure. Electrochemical evaluations in a symmetric two-electrode configuration utilizing a KI + KOH redox-active electrolyte demonstrated a significant enhancement in charge storage. Notably, the optimized Sm 0.9 Ho 0.1 FeO 3 electrode exhibited a superior specific capacitance of 115 F g −1 at 1 A g −1 , compared to 62.4 F g −1 for the pristine sample. This improvement is attributed to the synergistic effect of Ho-induced lattice strain, which increases the number of active sites and the faradaic contribution of the I − − /I 3 − redox couple. The device delivered a maximum energy density of 23 Wh kg −1 at a power density of 2400 W kg −1 . Furthermore, the Sm 0.9 Ho 0.1 FeO 3 electrode exhibited exceptional cycling durability, with 102% capacitance retention after 10,000 cycles, owing to improved ionic transport and structural stability. This work provides new insights into lattice engineering and the integration of redox electrolytes to advance perovskite-based supercapacitors.