An efficient and robust triple-phase nanocomposite air electrode for reversible proton ceramic fuel cells

Reversible protonic ceramic fuel cells (R-PCFCs) have attracted much attention because of their favorable energy conversion and storage technologies. However, the poor thermo-mechanical compatibility of the widely used cobalt-based electrodes with the electrolyte has greatly hindered the development of R-PCFCs. In this study, Pr_xBa_1-xCo_0.4Ce_0.4Y_0.2O_3-δ was prepared as an air electrode for R-PCFCs using in situ self-assembly technique. BaCo_0.75Y_0.25O_2.55 (BCoY), PrBaCo₂O_5.68 (PBC) and BaCe_0.8Y_0.2O_2.9 (BCeY) phases were formed. Among them, BCoY phase and PBC phase are good conductors of oxygen ions and electrons, BCeY phase is a good conductor of protons. The in situ self-assembly of these three phases promote the proton and oxygen ion conduction and transport, increase the active sites of ORR/OER, and further accelerate the ORR/OER reaction. The composite nano-electrode cells prepared by in situ self-assembly have an area specific resistance of 0.082 Ω·cm²at 700 ℃, and exhibit good performance in both fuel cell mode (FC) and electrolytic cell mode (EC), with a specific power density of 1.098 W cm⁻² at 700 ℃ and a current density of −1.45 A cm⁻² at 1.3 V and 700 ℃. The thermal expansion coefficient (TEC) of the electrode is 13.5 × 10⁻⁶ K⁻¹ which matched with that of electrolyte (∼14 × 10⁻⁶ K⁻¹). This effectively solves the problem of thermodynamic incompatibility between cobalt-based electrodes and electrolytes. This study provides a new strategy to achieve the thermo-mechanical stability compatibility between cobalt-based electrodes and electrolytes through one-step in situ self-assembly.