. (a) XRD patterns of L_xSFNM (x=0-0.4) powder calcined at 1000 ℃ in air for 5 h and (b) corresponding magnified patterns within 2θ=31°-35°

. TGA analysis of L_xSFNM in air

. Electricity conductivities of L_xSFNM at 650-800 ℃ in (a) air and (b) 50% CO-50% CO₂

. (a) Cross-sectional SEM image of the tri-layer symmetrical structure of “porous|dense|porous” LSGM and (b) high magnification view of symmetrical cell, and (c) high-magnification view of impregnated L_0.3SFNM catalyst

. Nyquist plots of impedance data measured with L_xSFNM at 800 ℃ in (a) air and (c) 50% CO-50% CO₂; (b, d) DRT curves of impedance data shown in (a, c)

. Measured polarization resistances versus the temperature reciprocal in (a) air and (b) 50% CO-50% CO₂

. (a) I-V curves and (b) impedance spectra measured at the 1.5 V of a single electrolyte-supported electrolysis cell with L_0.3SFNM at different temperatures with inset in (b) showing corresponding enlarged spectrum of the cell with L_0.3SFNM at 800 ℃, (c) current densities with varied La_xSFNM anodes at 1.5 V under different temperatures, and (d) short-term stability test of the symmetrical SOECs with L_0.3SFNM electrode, operating under 800 ℃ at an applied voltage of 1.3 V