High Proton Conductivity in <i>x</i> CuO/(1‐ <i>x</i> )CeO ₂ Electrolytes Induced by CuO Self‐Nucleation and Electron‐Ion Coupling

Operating within the 300-500 °C range, low-temperature solid oxide fuel cells (LT-SOFCs) enable efficient and sustainable energy conversion, addressing the limitations of conventional high-temperature SOFCs. However, achieving >0.1 S cm^-1 ionic conductivity in electrolytes remains challenging. Here, a novel approach utilizing CuO self-nucleation and electron-ion (E-I) coupling in xCuO/(1-x) CeO₂ (CCO) semiconductor ionic membranes (x = 0-0.4) is presented. At the optimal 0.2CuO/0.8CeO₂ composition, ionic conductivity exceeds 0.15 S cm^-1, driven by E-I coupling at the CuO/CeO₂ heterojunction. This coupling creates a built-in electric field (BIEF) via interfacial charge transfer, facilitating ion transport by lowering the activation energy for ion migration. The dual-conduction pathway enabled by E-I coupling not only facilitates electronic transfer and ionic transport but also optimizes charge transfer kinetics, achieving exceptional power densities of 750-900 mW cm^-2 at 500-550 °C and 78 mW cm^-2 at 300 °C. Density functional theory (DFT) calculations further validate the role of Cu²⁺ and Ce⁴⁺ valence states in generating interfacial charge transfer and enhancing ionic mobility. This innovative approach positions CuO/CeO₂ as a state-of-the-art electrolyte, building the critical conductivity-performance gap in LT-SOFCs. This study pioneers LT-SOFC innovation by leveraging E-I coupling and electrode-electrolyte synergy, unlocking superior ion transport and practical applicability.