La_0.5Ba_0.5CuxFe1_−xO_3−δ as cathode for high-performance proton-conducting solid oxide fuel cell

La_0.5Ba_0.5Cu_xFe_1−xO_3−δ (0 ≤ x ≤ 1) perovskite was investigated as a cathode for a protonic solid oxide fuel cell (H-SOFC) using BaZr_0.1Ce_0.7Y_0.2O_δ (BZCY) electrolyte. A maximum electric conductivity (76.84 S cm⁻¹ at 700 °C) was achieved in the air at the composition of La_0.5Ba_0.5Cu_0.4Fe_0.6O_3−δ. Comparing to La_0.5Ba_0.5CuO_3−δ (LBC), the increase in Fe content increased the D_chem (1.07x10⁻⁵ to 1.74x10⁻⁵ cm² S⁻¹) and K_chem (1.12x10⁻¹⁰ to 3.01x10⁻¹⁰ cm² S⁻¹) at La_0.5Ba_0.5Cu_0.2Fe_0.8O_3−δ (LBCF28) but decreased the proton conductivity from 7.5 to 4.3 mS cm⁻¹. Either Fe doping in LBC or Cu doping in La_0.5Ba_0.5FeO_3−δ increased the thermal expansion coefficient (TEC), but a low TEC among samples with mixed cations was achieved at La_0.5Ba_0.5Cu_0.5Fe_0.5O_3−δ (LBCF55) (16.12 ppm K⁻¹). LBC suffered from superficial decomposition in the ambient air, causing an ohmic resistance loss of the full cell on Ni(O)-BZCY support. A high initial cell performance (820 mW cm⁻²) can be achieved for the cell with LBCF55 and LBCF28 cathode but the latter was unstable under a cathodic bias owing to the increase in ohmic resistance owing to the production of intermediate layer between electrode and electrolyte. With better stability than LBCF28 and higher performance than LBC, LBCF55 was regarded as a viable cathode material for H-SOFC. This work explores systematically the behavior of a perovskite with mixed Cu and Fe cations as a cathode for H-SOFCs.