Humidity‐Enhanced Chemoresistive Sensor Performance in a p‐Type Spinel Metal Oxide

Humidity strongly reduces the sensitivity of most chemoresistive‐type gas sensors, restricting their applicability in environmental monitoring, health diagnostics, and robotic olfaction. Intense research efforts have tried to enhance humidity resistance by, for instance, reducing the adsorption of hydroxyl species on chemoresistors through surface functionalization, compositional or structural optimization, and heterojunction formation. Here, we demonstrate that humidity‐related hydroxyl species can also increase sensing performance by improving molecular reception and catalytic oxidation of analytes. In the example of p‐type spinel ZnMn ₂ O ₄ , we observed a ~60% increase in response to parts‐per‐billion level acetone concentrations under humidity compared to dry conditions. By integrating X‐ray absorption spectroscopy, in situ IR spectroscopy, and isotopically labeled chemisorption analysis, we demonstrate that surface‐adsorbed hydroxyl groups play an active role in analyte oxidation. Notably, oxidation product formation rates were up to an order of magnitude higher under humid conditions compared to dry conditions. These findings advocate a more differentiated discussion of the role of humidity in chemoresistive gas sensors, as surface engineering may not only aim to mitigate its effects but can leverage it to overcome present frontiers in sensitivity and detection limit.