La-Doped Ba0.5Sr0.5Co0.8Fe0.2O3−δ Air Electrodes with Enhanced Performance and Stability for Reversible Protonic Ceramic Cells

Reversible protonic ceramic cells (R-PCCs) have attracted intensive 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 substituted Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3− δ , showing improved stability under typical R-PCCs working conditions. XRD patterns confirm that La 0.1 Ba 0.4 Sr 0.5 Co 0.8 Fe 0.2 O 3− δ maintains the cubic structure after heat treatment in humid air (3% H 2 O) at 700 °C for 100 h. 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 0.1 Ba 0.4 Sr 0.5 Co 0.8 Fe 0.2 O 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.