Highly Sensitive and Stable CeLaCuO/Ni-BTC MOF-Based Humidity Sensor for Plant Monitoring

Herein, we report a high-performance humidity sensor based on oxygen-vacancy-rich CeLaCuO integrated with a porous Ni-BTC metal-organic framework (MOF). Compared with the single CeLaCuO and Ni-BTC sensors, the CeLaCuO/Ni-BTC composite sensor exhibits a higher response value (24% @ 32% relative humidity (RH)), lower hysteresis (0.465%RH), faster response/recovery time (24.5/47.8 s), and enhanced long-term stability (<2.6% over 60 days). Moreover, it achieves a high sensitivity of S ≈ 1.35/%RH with excellent linearity (R² = 0.9868) across 11-63% RH and demonstrates a very low temperature cross-sensitivity between 25 and 100 °C (<0.35%). These improved performance properties are attributed to abundant oxygen vacancies (Ov) in the CeLaCuO structure that provide active sites for water adsorption and H⁺/H₃O⁺ species generation for fast ionic conduction. The high-surface-area Ni-BTC framework enhances water uptake and facilitates efficient charge transfer at the oxide-MOF interface. The lab-fabricated composite sensor also demonstrates real-world applicability in a microclimate chamber for monitoring the microclimate surrounding the Fragaria ananassa (strawberry) plant, where lower humidity (<60%) can cause plant stress and reduce yield. The proposed sensor placed on the plant shows a good response for various humidity levels at 43%, 51%, and 63% RHs, respectively. Moreover, the results show that, at 63% RH, plants exhibited optimal transpiration, allowing efficient water and nutrient uptake, resulting in healthy leaf morphology with minimal stress. Thus, the proposed sensors hold strong potential as next-generation real-time humidity sensors with practical applications in agriculture, smart greenhouses, environmental monitoring, and indoor climate control.