La-Doped Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ Air Electrodes with Enhanced Performance and Stability for Reversible Protonic Ceramic Cells

Reversible protonic ceramic cells (R-PCCs) have attracted intense attention, as they can operate efficiently for both power generation and fuel production. The practical application of R-PCCs is, however, limited by the poor catalytic activity and stability of the air electrode. Here, we report a novel electrochemical catalyst of 10 mol.% La tailored Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ, showing improved stability under typical R-PCCs working conditions. XRD patterns confirm that La_0.1Ba_0.4Sr_0.5Co_0.8Fe_0.2O_3-δ maintains the cubic structure after heat treatment in humid air (3% H₂O) at 700 °C for 100 hours. In addition, the assembled full cells using this novel material as air electrode catalyst present outstanding performance. At 700°C, the peak power density reaches 650 mW cm^-2 (fuel cell mode); and in electrolysis mode the maximum current density reaches 1840 mA cm^-2 at 1.5 V. We speculate that the much-improved stability and electrochemical performance of the La_0.1Ba_0.4Sr_0.5Co_0.8Fe_0.2O_3-δ air electrode may result from the higher electronegativity of La, which is beneficial for reducing the basicity and improving the chemical stability in acidic atmospheres; from the smaller ionic radius of La, which can alleviate the lattice distortion of BSCF; and from the stronger interaction between La and lattice oxygen inhibiting the structural degradation caused by Sr segregation.