Breaking the three phase boundary constraint in NO sensors via a 3D heterogeneous LSCF-NiO-YSZ composite sensing electrode

Conventional sensing of nitrogen oxide (NO) is based on charge transfer reactions that occur exclusively at the triple-phase boundaries (solid electrolyte/sensing electrode/NO, TPBs). Here, an interface-engineered strategy is proposed to overcome this limitation by constructing a bidirectional mixed ionic-electronic conducting (MIEC) architecture. By modifying a porous YSZ scaffold with NiO to introduce an electron-conducting phase, a mixed conductive heterogeneous porous framework, NiO-YSZ, was formed. Subsequently, La 0.8 Sr 0.2 Co 0.2 Fe 0.8 O 3-δ (LSCF) active sensing phase was incorporated into this framework via an impregnation method, ultimately resulting in a 3D composite sensing electrode (LSCF-NiO-YSZ) that possesses both ionic and electronic conductivity. This design expands the active site region beyond TPBs and enables more efficient charge transfer. The influence of YSZ/NiO mass ratios was systematically examined, and sensors based on NiO-modified YSZ exhibited markedly higher response values and improved sensitivity compared to pristine YSZ. The optimal composition (YSZ/NiO = 5:5) delivered a sensitivity of 10.29 °·decade −1 with excellent reproducibility and selectivity at 500°C and 0.1 Hz. These results highlight interface conduction engineering as an effective route for achieving high-performance impedancemetric NO sensors.