Ni-doped LSFC perovskite oxides for enhanced electrocatalytic performance toward oxygen evolution and oxygen reduction reaction

This study systematically investigates the role of Ni doping on La 0.5 Sr 0.5 Fe 0.8 Cu 0.2 O 3 for electrochemical oxygen reactions by substituting Fe sites. Glycine-assisted sol–gel method followed by annealing at 900 °C is used to synthesize La 0.5 Sr 0.5 Fe 1−x Ni x Cu 0.2 O 3 (where x = 0.0–0.8). Electrocatalytic activity of La 0.5 Sr 0.5 Fe 1−x Ni x Cu 0.2 O 3 was investigated by linear sweep voltammetry, cyclic voltammetry and electrochemical impedance spectroscopy analysis in a 0.1 M KOH electrolyte. The results indicate that La 0.5 Sr 0.5 Fe 0.4 Ni 0.4 Cu 0.2 O 3 exhibits excellent oxygen evolution reaction performance (onset overpotential 346 mV and Tafel slope 69.47 mV/dec), and La 0.5 Sr 0.5 Fe 0.2 Ni 0.6 Cu 0.2 O 3 shows excellent oxygen reduction reaction (Tafel slope 185.68 mV/dec). Lower values of Tafel slope as well as onset potential for La 0.5 Sr 0.5 Fe 0.4 Ni 0.4 Cu 0.2 O 3 compared to undoped La 0.5 Sr 0.5 Fe 0.8 Cu 0.2 O 3 signify enhanced reaction kinetics and higher charge transfer. La 0.5 Sr 0.5 Fe 0.4 Ni 0.4 Cu 0.2 O 3 catalyst maintained a nearly constant current throughout the 5 h chronoamperometric test, demonstrating good electrochemical stability. The synthesized materials were characterized using powder X-ray diffraction with Le Bail profile fitting to analyse phases. Size, surface morphology and elemental composition were analysed by Field-emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (FESEM) analysis. Among all compositions, La 0.5 Sr 0.5 Fe 0.4 Ni 0.4 Cu 0.2 O 3 shows the highest OER activity and La 0.5 Sr 0.5 Fe 0.2 Ni 0.6 Cu 0.2 O 3 shows good ORR activity. Further, La 0.5 Sr 0.5 Fe 0.4 Ni 0.4 Cu 0.2 O 3 was examined by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) to investigate its oxidation states and detailed morphology. The improved performance after Ni substitution is associated with reduced particle size (as per FESEM analysis), increased electrochemical surface area, and changes in the surface electronic environment.