Ba0.95La0.05Fe0.8Zn0.2O3-δ cobalt-free perovskite as a triple-conducting cathode for proton-conducting solid oxide fuel cells

A triple-conducting Ba0.95La0.05Fe0.8Zn0.2O3-delta (BLFZ) cobalt-free perovskite was evaluated as cathode for proton-conducting solid oxide fuel cells based on BaZr0.1Ce0.7Y0.1Yb0.1O3-delta (BZCYYb) electrolyte. BLFZ had a cubic perovskite structure and good chemical compatibility with BZCYYb electrolyte at temperatures below 1100 degrees C. The average thermal expansion coefficient of BLFZ is 20.4 x 10(-6) K-1 at 30 degrees C-1000 degrees C. The polarization resistance (R-p) of BLFZ decreased from 2.072( ) Omega cm(2) in air to 1.334 Omega cm(2) in wet air (3% H2O) at 600 degrees C due to the introduction of water. The single-cell power density with BLFZ-30 wt%BZCYYb composite cathode reached 329 mW cm(2) at 750 degrees C, and the corresponding R-p is 0.083 Omega cm(2). Based on the impedance and distribution of relaxation time analyses, proton diffusion and incorporation to the electrolyte lattice (H-ad(+)(Ni) -> H+ (surface, electrolyte) and H+ (surface, electrolyte) -> H+ (bulk, electrolyte)) were the rate-limiting steps above 650 degrees C, whereas the oxygen incorporated into the lattice (O2-(BLFZ) -> O2- (bulk, electrolyte)) and proton bulk diffusion to the triple-phase boundary (H+(bulk, electrolyte) -> H+(TPB)) were the rate-limiting steps below 650 degrees C. The single cell with BLFZ-30 wt% BZCYYb composite cathode showed good stability at 700 degrees C during a 100-h test.