Supplementary information files for "Driving superionic transport in high-entropy oxide/fluorite heterostructure electrolytes for boosting fuel cell performance"

Supplementary files for article "Driving superionic transport in high-entropy oxide/fluorite heterostructure electrolytes for boosting fuel cell performance"<br><br>Compared with conventional ionic electrolyte-based solid oxide fuel cells, mixed ionic-electronic conductor (MIEC) electrolytes enable high power at relatively low temperatures. Here, we design a hybrid ionic-electronic conductor electrolyte based on p-n heterojunctions: a layered perovskite-type high-entropy oxide (La_0.2Pr_0.2Nd_0.2Sm_0.2Sr_0.2)₂CuO₄ (HEO) as the p-type semiconductor combined with the n-type fluorite Nd_0.05Ce_0.95O_2−δ (NDC). This study marks their first application in fuel-cell electrolyte composites. The multielemental composition of the HEO tailors the electronic structure to stabilize the interfacial charge dynamics and enhance ionic conduction via lattice disorder, which reduces the migration barriers. Integration with NDC induces band bending at heterogeneous interfaces and synergistically improves the carrier dynamics. In this heterostructure, the built-in electric field generated by the Fermi-level alignment suppresses electron penetration while driving ion/proton transport; concurrently, interfacial charge compensation induces oxygen vacancy formation, synergistically enhancing superionic conduction. Consequently, systematic optimization of HEO-NDC mass ratios combined with multiscale characterization identifies the 3HEO:7NDC composite as optimal, achieving a peak power density of 995.3 mW cm⁻² with an open-circuit voltage (OCV) of 1.067 V at 550 °C and approximately 50-h stability. This study demonstrates a new strategy for the development of HEO-based hybrid conductor electrolytes.<br> © Elsevier B.V, CC-BY-NC-ND 4.0<br>