Cobalt–Nitrogen Bonding for Triggering the Low-Power Dual Detection of NO2 and NH3 by Mixed-Valence Co2+ and Co3+.

The real-time detection of harmful gases like NO₂ and NH₃ is crucial for smart agriculture and the noninvasive diagnosis of kidney, liver, lung, and heart diseases. However, sensing these gases and understanding the primary sensing mechanisms can be challenging since the nitrogen site of NO₂ or NH₃ is the primary site that binds the sensing crystallite. Herein, we designed and fabricated low-cost sensors for dual NO₂ and NH₃ sensing using a nanodevice-on-chips sensor (NDCS) with mixed-valence Co₃O₄ (Co²⁺ and Co³⁺). Co₃O₄–NDCS detects NO₂ and NH₃ at low power, room temperature, and 70% relative humidity. It also exhibits stable, recoverable, and reproducible sensing performance for NO₂ and NH₃, comparable to several high-performance sensors. The dual sensing performances are closely related to two distinct Co sites (Co²⁺ and Co³⁺) in the Co₃O₄ crystal. Co²⁺ could host the nitrogen atom of either NO₂ or NH₃ to form Co–N bonding, which is preferable to NO₂ detection. Meanwhile, the N atom could replace one of the six oxygen atoms coordinating with Co³⁺ to form Co–N bonding, favorable to NH₃ detection. Looking forward, the strategy proposed here makes it possible to fabricate high-performance gas sensors with the desired nanostructures and known sensing mechanisms. [ABSTRACT FROM AUTHOR]