Hydrogen gas sensing properties of WO3 sputter-deposited thin films enhanced by on-top deposited CuO nanoclusters

Hydrogen Gas Sensing Performances of p-Type Mn3O4 Nanosystems: The Role of Built-in Mn3O4/Ag and Mn3O4/SnO2 Junctions

“…A process which decreases the hole concentration and the HAL thickness, resulting, in turn, in an increase of the measured resistance [5,[16][17][18]42,43]. Finally, upon switching off the gas pulse, the sensor surface is again in contact with air, and the original situation is restored, with a recovery of the pristine HAL width [30,31,41].…”

“…Nonetheless, the enhanced hydrogen detection efficiency of Mn 3 O 4 -based nanocomposites with respect to bare manganese oxide is likely due to the concurrence of additional cooperative phenomena. For both Mn 3 O 4 -Ag and Mn 3 O 4 -SnO 2 systems, the higher content of oxygen defects at the composite surface with respect to bare Mn 3 O 4 (see the above XPS data and Figure S2), as well as the exposure of a high density of heterointerfaces, can in fact supply active sites for a more efficient chemisorption of both oxygen and analyte molecules, which, in turn, boosts the resulting gas responses [4,8,[16][17][18]30,43]. In addition, the intimate component contact enabled by the adopted preparation route, yielding a good intergranular coupling, enables a proficient exploitation of their chemical interplay [38,44,48], related to the synergistical combination of materials with different catalytic activities [10,27,37,41,47].…”

“…In this broad scenario, a key role is played by the early recognition of molecular hydrogen (H 2 ), a zero-emission and clean fuel, with a high energy density of ≈130 MJ×kg −1 [2,7], which has emerged as a future energy source for transportation, industrial and residential applications [8][9][10]. Nevertheless, since H 2 is colorless, odorless and highly flammable, the detection of hydrogen leakages at concentrations lower than hazardous levels [11][12][13][14] is extremely critical towards the emergence of a future hydrogen economy [7,8,[15][16][17][18][19].…”

“…Beside tailoring the system morphology [25,26,33,39], a proficient way to enhance the functionality of bare Mn 3 O 4 gas sensors involves their sensitization with suitable metal/oxide agents [8,18,35,[42][43][44]. The ultimate aim of this strategy is the exploitation of synergistical chemical and electronic effects, in order to obtain improved performances at moderate working temperatures, an issue of key importance for the development of low power consumption devices [4,37,41].…”

“…As prototypes for the two categories, in this work our attention has been focused on the use of Ag, a potential catalyst promoting the reactions involved in the sensing process [45][46][47][48][49], and of SnO 2 , by far one of the most investigated metal oxides for gas sensing applications, endowed with high electron mobility and gas sensitivity [10,13,25,26,50]. In particular, the occurrence of Schottky (Mn 3 O 4 /Ag) or p-n (Mn 3 O 4 /SnO 2 ) junctions between the system components can indeed enhance the modulations of the space charge region, and of the measured electrical resistance, ultimately yielding improved sensing performances thanks to electronic effects [18,26,33,43].…”