Surface-interface engineered proton transport via hybrid structures: A new horizon beyond conventional solid-state ionics

Crystalline and amorphous oxides have long vied for supremacy in fast-ion conduction; crystals offer ordered pathways but suffer from grain-boundary drag, while amorphous hosts provide abundant defects but lack directional guidance. Here, we deploy a previously unexploited scheme: an interface-engineered in Y 0.15 Al 0.85 O (Y15-AO) heterophase electrolyte that guides surface proton conduction across a defect-flexible amorphous matrix, yielding a conductivity of 0.17 S cm −1 and achieving a peak power density of 0.99 W cm −2 with an OCV of 1.11 V at 550 °C, outperforming undoped amorphous alumina (a-Al 2 O 3 ). HRTEM directly visualizes a hybrid architecture with amorphous nanoscale surface crystallinity in Y15-AO, while a-Al 2 O 3 shows a single-phase, fully amorphous structure. The mechanism was validated experimentally and theoretically using ab-initio calculations with the VASP code, modeling single-phase amorphous and amorphous-surface crystalline structures. In the hybrid structure, the interfacial advantage at Y-modified surfaces/interfaces manifests as strongly exothermic proton incorporation ( E bind =−1.83 eV to −2.07 eV) and a reduced proton migration barrier of 0.56–0.69 eV. These values, which are lower than those in any single-phase counterpart, align with experimentally measured low activation energy of 0.28 eV. The predicted vacancy stabilization strongly agrees with XPS O 1s shifts and the EPR defect-center signal. DRT/EIS deconvolves with surface-guided conduction processes, yielding the minimum resistance. TGA shows the stability of heterophase structure far above the operational window (400–550 °C) of the electrolyte. Collectively, these results establish interface-guided proton transport in a hybrid structure, where protons migrate through the amorphous network while nanocrystalline surfaces lower migration barriers and connect transport pathways, enabling a novel design blueprint for fast-ion conductors at low/intermediate temperatures.