La0.5Ba0.5CuxFe1−xO3−δ as cathode for high-performance proton-conducting solid oxide fuel cell

• La 0.5 Ba 0.5 Cu x Fe 1−x O 3−δ is used as a cathode for H-SOFC on BZCY electrolyte. • Thermal expansion, oxide-ion and proton conductivity varies with the Cu/Fe ratio. • An initial power density exceeding 820 mW cm −2 is obtained at 700 °C. • Increase in the ohmic rather than polarization resistance dominates the degradation. La 0.5 Ba 0.5 Cu x Fe 1−x O 3−δ (0 ≤ x ≤ 1) perovskite was investigated as a cathode for a protonic solid oxide fuel cell (H-SOFC) using BaZr 0.1 Ce 0.7 Y 0.2 O 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 0.5 Ba 0.5 Cu 0.4 Fe 0.6 O 3−δ . Comparing to La 0.5 Ba 0.5 CuO 3−δ (LBC), the increase in Fe content increased the D chem (1.07x10 −5 to 1.74x10 −5 cm 2 S −1 ) and K chem (1.12x10 −10 to 3.01x10 −10 cm 2 S −1 ) at La 0.5 Ba 0.5 Cu 0.2 Fe 0.8 O 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 0.5 Ba 0.5 FeO 3−δ increased the thermal expansion coefficient (TEC), but a low TEC among samples with mixed cations was achieved at La 0.5 Ba 0.5 Cu 0.5 Fe 0.5 O 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.