Tailoring the catalytic activity of PrBaFe₂O_5+δ cathode material with non-transition metal In-doping for solid oxide fuel cells

Double perovskite PrBaFe₂O_5+δ (PBF) is a promising cathode material for solid oxide fuel cell (SOFCs) due to the favorable catalytic activity and superior electrochemical stability. Herein, to further tailor the oxygen-ion transport kinetics and electrochemical performance, unlike the typical approach through using higher valence, non-transition metal In³⁺ ion doping is initially investigated to partially replace Fe³⁺/Fe⁴⁺ site, forming the compositions of PrBaFe_2−xIn_xO_5+δ (PBFInx, x = 0, 0.05, 0.1, and 0.15). Xray diffraction (XRD) analysis indicates that PBFInx exhibit satisfactory chemical and thermal compatibility with the gadolinia-doped ceria (GDC) electrolyte. Expectedly, the polarization resistance (Rp) of PBFIn_0.1 cathode is decreased by approximately 40 % and an anode-supported single cell with PBFIn_0.1 cathode yields a 36 % higher peak power density (PPD) at 800 °C compared to that of PBF. Moreover, the single cell using PBFIn_0.1 as the cathode can be operated stably at 0.4 A cm⁻² for more than 50 h without obvious performance degradation. In addition, the X-ray photoelectron spectroscopy (XPS) results confirm that the low-valence state In³⁺ introduced into PBF have a positive impact on the oxygen vacancy concentration and boost the oxygen reduction reaction (ORR) activity, thus significantly enhancing the electrochemical performance of the PBF cathode. The results show that the non-transition metal In³⁺ ion doping is an effective method to improve the performance of the PBF cathode for SOFCs.