Superior Hydrogen Sensing Property of Porous NiO/SnO2 Nanofibers Synthesized via Carbonization

Abstract

In this paper, the porous NiO/SnO2 nanofibers were synthesized via the electrospinning method along with the carbonization process. The characterization results show that the pristine SnO2-based nanofibers can form porous structure with different grain size by carbonization. The hydrogen gas-sensing investigations indicate that the NiO/SnO2 sensor exhibits more prominent sensing properties than those of pure SnO2 sensor devices. Such enhanced performance is mainly attributed to the porous nanostructure, which can provide large active adsorption sites for surface reaction. Moreover, the existence of p-n heterojunctions between NiO and SnO2 also plays a key role in enhancing gas-sensing performances. Finally, the H2 sensing mechanism based on the NiO/SnO2 nanocomposite was proposed for developing high-performance gas sensor devices.

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

“…Conversely, as concerns Mn3O4-SnO2, a maximum-like response behavior was observed, the best operating temperature being 200 °C. Such a response trend, in line with previous reports regarding H2 detection by other metal oxides [7,9,17,19,29,43,64], suggested the occurrence of a steady equilibrium between hydrogen adsorption and desorption at 200 °C, whereas an increase of the working temperature resulted in a predominant analyte desorption [27,33,55,64,65]. The lower value of the optimum operating temperature for Mn3O4-SnO2 in comparison to Mn3O4-Ag is in line with the more efficient SnO2 → Mn3O4 electron transfer (see the above XPS data).…”

“…As a consequence, HAL variations upon contact of the sensor with gaseous H 2 produce higher responses by increasing the registered resistance modulations [38,44]. An analogous phenomenon occurs for Mn 3 O 4 -SnO 2 systems (Figure 7b; HAL thickness = 12.4 nm, see the Supporting Information), although in this case the SnO 2 → Mn 3 O 4 electron flow is triggered by a different phenomenon, i.e., the presence of p-n Mn 3 O 4 /SnO 2 junctions [32,33,37,[41][42][43]55].…”

“…X-ray diffraction (XRD) patterns were recorded at room temperature using a Bruker (Billerica, MA, USA) D8 Advance X-ray diffractometer with a Cu Kα X-ray source (λ = 1.54 Å) operated at 40 kV and 40 mA, employing an incidence angle of 1.0 • . The average crystallite dimensions were calculated by means of the Scherrer equation [29,33,36,55].…”

“…Taken together, these results highlighted the formation of nanocomposites in which the single components maintained their chemical identity, and enabled us to discard the formation of ternary phases, in line with XRD results. The deconvolution of O1s photopeaks ( Figure S2) revealed the concurrence of two distinct bands at BE = 530.0 eV, resulting from lattice oxygen in Mn3O4, Ag(I) oxide (Mn3O4-Ag) or SnO2 (Mn3O4-SnO2) [14,31,38,60,61], and 531.6 eV, assigned to oxygen species adsorbed on surface O defects [4,41,51,52,55]. The contribution of the latter component to the overall O1s signal increased from ≈36.0 %, for bare Mn3O4, to ≈58.0 %, for the functionalized specimens, indicating a parallel increase of the oxygen defect content.…”

“…To account for the performance increase yielded by composite systems, it is necessary to consider the mechanism of hydrogen detection by the target p-type materials, which can be described as follows. Upon air exposure prior to contact with the target analyte, oxygen molecules undergo chemisorption processes, yielding the formation of various species [6,9,29,36,43,55], among which O − is the prevailing one in the present working temperature interval [14,17,30,33]:…”