Abstract
Among oxide semiconductors, p-type Mn3O4 systems have been exploited in chemo-resistive sensors for various analytes, but their use in the detection of H2, 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 Mn3O4 nanomaterials, and on their on-top functionalization with Ag and SnO2 by radio frequency (RF)-sputtering, followed by air annealing. The obtained Mn3O4-Ag and Mn3O4-SnO2 nanocomposites were characterized by the occurrence of phase-pure tetragonal α-Mn3O4 (hausmannite) and a controlled Ag and SnO2 dispersion. The system functional properties were tested towards H2 sensing, yielding detection limits of 18 and 11 ppm for Mn3O4-Ag and Mn3O4-SnO2 specimens, three orders of magnitude lower than the H2 explosion threshold. These performances were accompanied by responses up to 25% to 500 ppm H2 at 200 °C, superior to bare Mn3O4, and good selectivity against CH4 and CO2 as potential interferents. A rationale for the observed behavior, based upon the concurrence of built-in Schottky (Mn3O4/Ag) and p-n junctions (Mn3O4/SnO2), 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.
Highlights
The reliable detection of hazardous/flammable gases is of key importance in a variety of fields, encompassing disease diagnosis, environmental monitoring and human health protection [1,2,3,4,5,6]
The main focus of the present investigation was directed at elucidating the structural, compositional and morphological characteristics of the target materials and their interplay with the resulting sensing performances in hydrogen detection. The latter were investigated at a fixed humidity level as a function of the operating temperature, with particular regard to the role exerted by the formation of metal-oxide (Mn3O4/Ag) or oxide-oxide (Mn3O4/SnO2) junctions
It is worthwhile highlighting that the optimal operating temperature for H2 detection by the present materials (200 ◦C for Mn3O4-SnO2 systems) was lower than the ones reported for Mn3O4 [35], MnO2 [8], CuO [3,17,29], Co3O4 [16], NiO [9], NiO-ZnO [43], NixCo3-xO4 [16], BiFeO3 [7] and CuO-WO3 sensors [18]
Summary
The reliable detection of hazardous/flammable gases is of key importance in a variety of fields, encompassing disease diagnosis, environmental monitoring and human health protection [1,2,3,4,5,6]. 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] In this context, the present study is devoted to the fabrication of Mn3O4-based chemo-resistive sensors for H2 detection, sensitized through the on-top deposition of selected metal and metal oxide activators. The main focus of the present investigation was directed at elucidating the structural, compositional and morphological characteristics of the target materials and their interplay with the resulting sensing performances in hydrogen detection The latter were investigated at a fixed humidity level as a function of the operating temperature, with particular regard to the role exerted by the formation of metal-oxide (Mn3O4/Ag) or oxide-oxide (Mn3O4/SnO2) junctions. Acaftrerriepdroeuptairnaotirodne,retxo-esnitsuurtehethremcaolntvrerastimonenoftsMinOa2irinattoaptheamsep-peruarteuMreno3Of 44[0504]◦aCnfdotro1sthabwileizreetchaerried out inoobrtdaienretdoneannsoumreatehreiaclos ninvevrieswionofogfaMs sneOns2iningttoespths a[1s9e,-4p8u].re Mn3O4 [54] and to stabilize the obtained nanomaterials in view of gas sensing tests [19,48]
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