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

A triple-conducting Ba 0.95 La 0.05 Fe 0.8 Zn 0.2 O 3−δ (BLFZ) cobalt-free perovskite was evaluated as cathode for proton-conducting solid oxide fuel cells based on BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3−δ (BZCYYb) electrolyte. BLFZ had a cubic perovskite structure and good chemical compatibility with BZCYYb electrolyte at temperatures below 1100 °C. The average thermal expansion coefficient of BLFZ is 20.4 × 10−6 K−1 at 30 °C-1000 °C. The polarization resistance (R p) of BLFZ decreased from 2.072 Ω cm2 in air to 1.334 Ω cm2 in wet air (3% H 2 O) at 600 °C due to the introduction of water. The single-cell power density with BLFZ–30 wt%BZCYYb composite cathode reached 329 mW cm2 at 750 °C, and the corresponding R p is 0.083 Ω cm2. Based on the impedance and distribution of relaxation time analyses, proton diffusion and incorporation to the electrolyte lattice (H a d + (N i) → H + (s u r f a c e , e l e c t r o l y t e) and H + (s u r f a c e , e l e c t r o l y t e) → H + (b u l k , e l e c t r o l y t e)) were the rate-limiting steps above 650 °C, whereas the oxygen incorporated into the lattice (O 2 − (B L F Z) → O 2 − (b u l k , e l e c t r o l y t e)) and proton bulk diffusion to the triple-phase boundary (H + (b u l k , e l e c t r o l y t e) → H + (T P B)) were the rate-limiting steps below 650 °C. The single cell with BLFZ–30 wt% BZCYYb composite cathode showed good stability at 700 °C during a 100-h test. [ABSTRACT FROM AUTHOR]