Passivation-Enhanced Mixed-Potential Cu-MOF Sensor for ppb-Level H2S Detection and Real-Time Food Freshness Evaluation

Precise detection of hydrogen sulfide (H 2 S), a key spoilage marker in premium foods, is essential for maintaining both flavor and safety. However, conventional sensors often struggle to achieve high sensitivity, stability, and low power consumption simultaneously. Here, we report a mixed-potential type gas sensor based on Cu-MOF sensing electrode, K 2 Fe 4 O 7 solid electrolyte, and Au reference electrode for rapid and non-destructive food freshness evaluation. The sensor achieves an ultra-low detection limit (LOD) below 5 ppb at room temperature via a two-electrode response mechanism, addressing the stringent requirements of premium food quality control. To improve stability, an electrode passivation strategy was introduced to suppress the formation of inactive sulfate deposits, extending repeatability from 22 to 66 cycles (change rate within 10%). Replacing Cu-MOF with CuO, its stability significantly improved after passivation, confirming the strategy’s general applicability. We further developed a portable H 2 S monitoring system capable of real-time freshness tracking, showing a strong correlation with early spoilage. This work demonstrates a generalizable stabilization strategy for mixed-potential type H 2 S sensors and provides a practical, non-destructive platform for freshness grading in premium food supply chains.