Quantitative Interface Engineering Framework for High‐Performance and Durable Protonic Ceramic Electrochemical Cells

ABSTRACT Protonic ceramic electrochemical cells (PCECs) are promising energy conversion devices for efficient power generation and green hydrogen production, offering improved thermodynamic efficiency, material compatibility, and long‐term stability at lower operating temperatures (400°C–600°C) compared to conventional solid oxide electrochemical cells. However, further improvements of PCECs are hindered by the substantial interfacial resistance originating from structural discontinuities at the electrode/electrolyte interface. In this study, we present a multilayered electrode architecture in which the particle size and distribution are independently tailored for bulk and interface electrodes. The interface electrode with smaller and more uniformly dispersed particles significantly enhances the contact coverage and specific surface area, resulting in a simultaneous reduction in both ohmic and polarization resistances. The optimized cell exhibits a remarkable peak power density of 1.04 W/cm 2 in the fuel cell mode and a current density of 0.69 A/cm 2 at 1.3 V in the electrolysis cell mode at 500°C along with excellent thermal and electrochemical durability. This study demonstrates a simple and scalable interface engineering strategy that does not require the use of a complicated fabrication process, providing a practical pathway for the development of high‐performance and durable PCECs suitable for operation under demanding conditions.