On-Chip Construction of Hierarchically Macro-/Mesoporous Cerium Oxide/Pt Gas Sensitive Film for Ultrasensitive Detection of Trace Oxygen

Hierarchically porous structure is extremely favorable for many applications, including heterogeneous catalysis, chemical sensing, and energy conversion and storage. In these applications, controllable synthesis and assembly of transition metal oxide materials with tailored hierarchically porous structure and chemical microenvironments are highly desired but challenging. Herein, uniform mesoporous cerium oxide (mCeO₂) microspheres functionalized with Pt nanoparticles (NPs) were designed via efficient nanoemulsion approach and used to construct hierarchical macro-/mesoporous CeO₂/Pt film on micro-electromechanical system (MEMS) chips. The resultant functional chip-based devices have controllable porous structure and rich highly accessible active Pt–CeO₂ interfaces, and thus they exhibit outstanding performance as oxygen sensors with an unprecedented low limit of detection (LOD, 7.16 ppm), high sensitivity at a relatively low working temperature (250°C). Finite element analysis, density functional theory calculations, and in situ characterizations reveal that, such an excellent performance is mainly due to the favorable mass transfer and gas–solid interface interaction, the oxygen spillover effect enabled by the nanosized Pt, and the enhanced catalytic reaction causing the dramatic change of electronic resistance of the sensing layer in oxygen atmosphere. Finally, a smart gas sensing module capable of real-time precise detection of oxygen was fabricated, demonstrating the possibility for commercial application.