Fe-based double perovskite with Zn doping for enhanced electrochemical performance as intermediate-temperature solid oxide fuel cell cathode material

Abstract

This study aims to investigate the implications of transition-metal Zn doping at the B-site on the crystal structure, average thermal expansion coefficient (TEC), electrocatalytic activity, and electrochemical performance of LaBaFe₂O_5+δ by preparing LaBaFe_2−xZn_xO_5+δ (x = 0, 0.05, 0.1, 0.15, 0.2, LBFZ_x). The X-ray diffraction (XRD) results show that Zn²⁺ doping does not change the crystal structure, the unit cell volume increases, and the lattice expands. The X-ray photoelectron spectroscopy (XPS) and mineral titration results show that the oxygen vacancy concentration and Fe⁴⁺ content gradually increase with the increase in doping amount. TEC decreases with the increase in Zn²⁺ doping amount, and the TEC of LBFZ_0.2 is 11.4 × 10⁻⁶ K⁻¹ at 30–750 °C. The conductivity has the best value of 103 S cm⁻¹ at the doping amount of x = 0.1. The scanning electron microscopy (SEM) images demonstrate that the electrolyte CGO(Gd_0.1Ce_0.9O_1.95) becomes denser after high-temperature calcination, and the cathode material is well attached to the electrolyte. The electrochemical impedance analysis shows that Zn²⁺ doping at the B-site can reduce the (R_p) polarization resistance, and the R_p value of the symmetric cell with LaBaFe_1.8Zn_0.2O_5+δ as cathode at 800 °C is 0.014 Ω cm². The peak power density (PPD) value of the anode-supported single cell is 453 mW cm⁻², which shows excellent electrochemical performance.