An Active and Stable Cobalt‐Free Ruddlesden–Popper Nd_0.8Sr_1.2Ni_1‐xFe_xO_4±δ Air Electrode for Reversible Proton‐Conducting Solid Oxide Cells

Abstract 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 Nd_0.8Sr_1.2Ni_1‐xFe_xO_4±δ are reported with mixed conductivity for enhanced ORR/OER kinetics. The R‐PSOCs with an optimal Nd_0.8Sr_1.2Ni_0.7Fe_0.3O_4±δ 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 °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.