A cobalt-free Pr₆O₁₁–BaCe_0.2Fe_0.8O_3-δ composite cathode for protonic ceramic fuel cells with promising oxygen reduction activity and hydration ability

Oxygen reduction and proton conduction originated from hydration are two key steps in the cathode process of protonic ceramic fuel cells. In this work, Pr₆O₁₁ is impregnated into a cobalt-free BaCe_0.2Fe_0.8O_3-δ cathode, resulting in an improved activity of lattice oxygen and a moderate enhancement of the electrical conductivity, both of which are beneficial for charge transfer, the rate-determining step of oxygen reduction process at the cathode. The polarization resistance of bare BaCe_0.2Fe_0.8O_3-δ cathode for oxygen reduction is 0.115 Ω cm² at 700 °C, which is reduced significantly to 0.039 Ω cm² with the addition of 30 wt% Pr₆O₁₁. Besides, the hydration ability of the cathode is also improved with Pr₆O₁₁, and thus the combination of proton and oxygen is facilitated. A single cell with 30 wt% Pr₆O₁₁-70 wt% BaCe_0.2Fe_0.8O_3-δ composite cathode exhibits the highest maximum power density of 1406 mW cm⁻² at 700 °C. The composite cathode also shows a good stability.