An Active and Stable Cobalt-Free Ruddlesden-Popper Nd0.8Sr1.2Ni1-xFexO4±δ Air Electrode for Reversible Proton-Conducting Solid Oxide Cells

Reversible proton-conducting solid oxide cells (R-PSOCs) are considered to be one of the most promising devices for efficient power generation and hydrogen production. However, the requirement of high catalytic activity for fast oxygen reduction/evolution reaction (ORR/OER) and durability under high steam concentration of air electrode materials remains the major challenge for the practical application of R-PSOCs. Here, a series of cobalt-free Ruddlesden-Popper perovskite of Nd0.8Sr1.2Ni1-xFexO4 +/-delta are reported with mixed conductivity for enhanced ORR/OER kinetics. The R-PSOCs with an optimal Nd0.8Sr1.2Ni0.7Fe0.3O4 +/-delta air electrode show a high peak power density of 1.28 W cm(-2) in the fuel cell mode and a promising current density of 3.24 A cm(-2) at 1.3 V in the electrolysis cell mode at 700 degrees C. In addition, the R-PSOCs show favorable stability under the fuel cell, electrolysis, and reversible modes for hundreds of hours. This work demonstrates that the Ruddlesden-Popper materials can be utilized as suitable air electrodes for R-PSOCs.