High‐Entropy Driven Self‐Assembled Dual‐phase Composite Air Electrodes with Enhanced Performance and Stability for Reversible Protonic Ceramic Cells

Abstract Reversible proton ceramic cells (R‐PCCs) offer a transformative solution for dual functionality in power generation and energy storage. However, their potential is currently obstacles by the lack of high‐performance air electrodes combining high electrocatalytic activity with durability. Here, an innovative air electrode composed of high‐entropy driven self‐assembled xNiO‐Pr_0.2La_0.2Ba_0.2Sr_0.2Ca_0.2Fe_0.8Ni_0.2−xO_3−δ (N‐XFN) composites is presented, which result from the unique lattice distortion effects inherent in high‐entropy perovskites. The experimental results coupled with density functional theory (DFT) calculations verify that the lattice distortion at the high‐entropy A‐site significantly induces NiO nanoparticles exsolved from the B‐site, promoting the formation of a biphasic composite structure that dramatically increases the electrochemical active sites. Remarkably, R‐PCCs using the N‐XFN composite air electrode achieve an impressive peak power density of 1.30 W cm⁻² in fuel cell mode and a current density of ‐2.52 A cm⁻² at 1.3 V in electrolysis mode at 650 °C. In addition, the cells show excellent stability with reversibility over 830 h, including 500 h in electrolysis mode and 330 h in reversible operation at 650 °C. This research provides important insights into the design of high‐entropy perovskites, paving the way for advanced R‐PCCs technology.