Hydrogen Gas Sensing Performances of -Type MnO Nanosystems: The Role of Built-in MnO/Ag and MnO/SnO Junctions.

Among oxide semiconductors, -type MnO systems have been exploited in chemo-resistive sensors for various analytes, but their use in the detection of H, an important, though flammable, energy vector, has been scarcely investigated. Herein, we report for the first time on the plasma assisted-chemical vapor deposition (PA-CVD) of MnO nanomaterials, and on their on-top functionalization with Ag and SnO by radio frequency (RF)-sputtering, followed by air annealing. The obtained MnO-Ag and MnO-SnO nanocomposites were characterized by the occurrence of phase-pure tetragonal α-MnO (hausmannite) and a controlled Ag and SnO dispersion. The system functional properties were tested towards H sensing, yielding detection limits of 18 and 11 ppm for MnO-Ag and MnO-SnO specimens, three orders of magnitude lower than the H explosion threshold. These performances were accompanied by responses up to 25% to 500 ppm H at 200 °C, superior to bare MnO, and good selectivity against CH and CO as potential interferents. A rationale for the observed behavior, based upon the concurrence of built-in Schottky (MnO/Ag) and - junctions (MnO/SnO), and of a direct chemical interplay between the system components, is proposed to discuss the observed activity enhancement, which paves the way to the development of gas monitoring equipments for safety end-uses.