Elsevier

Applied Surface Science

Volume 506, 15 March 2020, 144971
Applied Surface Science

Full Length Article
Ultra thin NiO nanosheets for high performance hydrogen gas sensor device

https://doi.org/10.1016/j.apsusc.2019.144971Get rights and content

Highlights

  • Unstacked & ultra thin 2-D NiO nano sheets synthesis via hydrothermal route.

  • High response and good selectivity towards H2 gas at 250 °C.

  • NiO sensor operates in low H2 concentration 10–150 ppm at 250 °C.

  • NiO sensor exhibits excellent transient gas response and stability.

  • Understanding of H2 sensing mechanism of p-type NiO sensor.

Abstract

Unstacked two dimensional (2-D) NiO nanosheets are synthesized via easy surfactant-free hydrothermal chemical route. NiO sensor is investigated for high performance and selective hydrogen (H2) gas sensing properties. Structural analysis is carried out using XRD pattern. The morphology of NiO is confirmed by using FESEM and TEM micrographs. Atomic state and elemental composition are analyzed by recording XPS and EDS spectra respectively. NiO sensor exhibited a high gas response of 191% for 150 ppm H2 concentration at 250 °C operating temperature with response time 150 s. The lowest H2 detection is observed at the concentration of 10 ppm having the gas response of 22%. The H2 response of NiO sensor was tested at different operating temperatures as well as gas concentrations. The dynamic gas response and sensor stability were recorded and analyzed. The sensing mechanism of NiO sensor was discussed.

Introduction

On the verge of vanishing fossil fuels, hydrogen gas is one of the promising renewable energy sources because of its supreme properties such as zero-emission, easy production, and renewability [1], [2]. Hydrogen molecule having lower density ~0.09 g/L and very small size of the order ~0.289 nm which enable easy risk of leakage [3]. The basic characteristics of hydrogen gas include colourless, odorless and not detectable by human nose, this makes potential threats of fire accident above 4 vol% [4]. In order to avoid such hydrogen gas fire accident during its production, storage, and transportation, there is immediate requirement of the highly sensitive gas sensor working at lower temperatures [5].

Nanomaterials play vital role in various applications such as supercapactors, catalysis and gas sensors [6], [7], [8], [9], [10], [11], [12]. Resistive gas sensors using semiconducting metal oxide nanostructures such as SnO2, ZnO, CuO, CdO, WO3, TiO2, and NiO have been reported over the years owing to advantages viz small dimension, cost-effective, simple operation and electronic processing with good compatibility [5], [13], [14], [15], [16], [17], [18], [19]. Among these semiconducting sensing materials, p-type (NiO) sensors are relatively less ~9.41% focused [20]. The remarkable properties NiO such as high electrical conductivity, wide bandgap, non-toxicity, reproducibility, great sensitivity, and chemical stability made it the potential sensor material [21]. The ultra thin nanosheets are a two-dimensional nanostructure that provides high surface area as well as number of active sites for gas adsorption along with continuous charge transportation [22]. There are several synthesis routes reported for NiO nanostructures formation such as co-precipitation [23], sol-gel [24], atomic layer deposition [25], hydrothermal [26], microwave-assisted [27]. However, hydrothermal chemical route has good control to obtain various high-quality nanostructures [28], [29], [30]. Various NiO morphologies have been reported in gas sensing applications viz nanowires (NWs), nanoparticles (NPs), nanoflower (NF), nanorods (NRs), nanotubes (NTs), [31], [32], [33], [34], [35]. however ultra thin nanosheets 2-D structure of NiO has not been studied for high-performance hydrogen sensing application according to our best of the information.

In the present research findings, surfactant-free NiO nanosheets structures were synthesized using the versatile hydrothermal chemical route, further characterization performed using sophisticated instruments techniques such as XRD, FESEM, EDS, TEM, UV–Visible spectroscopy, and XPS. Structural parameters of NiO nanosheets material (i.e. average crystallite size (D), inter-planar distance (d), dislocation density (δ), texture coefficient (TC), micro-strain (ε), and stacking fault (SF)) were estimated by XRD analysis. Resistance variation of NiO nanosheets sensor as a function of applied temperature and stabilization curve was recorded. The gas response of NiO nanosheets sensor was studied at different operating temperatures as well as gas concentrations. The transient sensor response for H2 gas sensing and selectivity was tested and analyzed. The schematics for sensing mechanism is presented and stability of NiO sensor is also confirmed.

Section snippets

Experimental

The NiO nanosheets were synthesized using the easy hydrothermal chemical route. A 0.6 mM Nickel nitrate solution and 1.8 mM sodium hydroxide solution were prepared using 60 mL de-ionized (D.I.) separately. These two solutions were mixed dropwise and left for magnetic stirring (30 min) at 600 rpm. This prepared solution was poured into Teflon lined autoclave and provided heat at a temperature of 200 °C up to 10 h. The obtained precipitate was washed using D.I. water several times. The collected

Structural properties

The pattern of X-Ray diffraction for the sensor material is presented in Fig. 1(a). It is confirmed from JCPDS card no. 047-1049 matching that sensor material formed the face-centered cubic (FCC) structure of NiO [37]. The structural properties of the sensor material such as crystal size, dislocation densities, and texture coefficient have a remarkable influence on the gas sensing properties of semiconducting metal oxide sensors [38], [39], [40], [34]. Hence detailed investigation of the

Conclusions

In summary, a surfactant-free synthesis of 2-D unstacked NiO nanosheets structures was carried out using via chemical hydrothermal method. The structural parameters investigation of NiO particles was performed in details and corresponding analysis carried out using XRD technique. Nanosheets like structures without agglomeration were revealed from FESEM and TEM images. The electrical properties of NiO material recorded to study semiconducting nature. The high gas response and selectivity were

Declaration of Competing Interest

The authors declared that there is no conflict of interest.

Acknowledgments

The present research work was financially supported by National Leading Research Laboratory Program via the National Research Foundation (NRF-2016R1A2B2016665) of Korea funded by the Ministry of Science, ICT and Future Planning.

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