Low temperature and fast response hydrogen gas sensor with Pd coated SnO2 nanofiber rods

doi:10.1016/j.ijhydene.2019.12.152

International Journal of Hydrogen Energy

Volume 45, Issue 11, 28 February 2020, Pages 7234-7242

https://doi.org/10.1016/j.ijhydene.2019.12.152 Get rights and content

Highlights

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A novel Pd coated SnO₂ nanofiber rods was synthesized.
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Pd was dispersed on the surface of SnO₂, which improved the H₂ sensing properties.
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Gas sensing mechanisms of the Pd coated SnO₂ NFRs were proposed.

Abstract

In this work, we introduced a structure of Pd coated SnO₂ nanofiber rods (NFRs) prepared by electrospinning and magnet sputtering. Pd was first deposited on the obtained nanofibers as a catalyst and then fully dispersed during the resulting of SnO₂ to improve the hydrogen response. The gas sensing tests showed the palladium enhanced the hydrogen response at low temperature (160 °C). When the hydrogen gas concentration was 100 ppm, the limit of detection (LOD) of sensor was as low as 0.25 ppm and the response time was as short as 4 s. Moreover, Pd coated SnO₂ also had excellent hydrogen selectivity and repeatability. The gas sensor was suitable for the detection of hydrogen in low-temperature environment. This work provided a new method for the low temperature hydrogen gas sensor with a fast response and low LOD.

Graphical abstract

The unique Pd doped SnO₂ nanofiber rods (NFRs) show enhanced sensing properties to hydrogen, providing a novelty method to fabricate low temperature, fast response and low LOD gas sensors for hydrogen.

Introduction

Hydrogen has been used in vast quantities in industrial manufacture due to its immense potential as an alternative renewable clean fuel. However, as a colorless and odorless gas, the early signs of its leakage are difficult to detect which presents serious safety concerns because hydrogen is highly flammable with a large diffusion coefficient (0.61 cm²/s), a broad combustion limit range (4–75%), a wide explosion limit range (18–59%) and small ignition energy (0.02 mJ). Therefore, there is a growing interest in accurate and rapid detection of hydrogen, and developing real-time monitoring and early warning of leakage technologies for safety production of hydrogen. Particularly, hydrogen sensors with a low LOD and fast response have attracted extensive attention [1].

SnO₂, a n-type semiconductor metal oxide, has been extensively employed in electrode modification, solar cells and especially gas sensing because of its resistance response to some reducing gases, including H₂, H₂S, C₂H₂ and C₂H₄. Usually, SnO₂ based hydrogen sensors are advantageous since it can provide great response and stability [2], but their wide application is still limited by high optimum temperature and long response time [2,3]. Currently, the existing technologies to deal with above undesirable characteristics are divided into two major categories: one is to boom the number of gas adsorption/desorption channels by controlling the nano-morphology of SnO₂ [[4], [5], [6], [7], [8], [9], [10]]. SnO₂ sensors with different morphologies have been developed by Shen's group, such as nanofilms, nanorods, and nanowires. Gas sensing tests showed that the increase in response as well as the decreases in response time and optimum operating temperature could be attributed to the larger effective surface area, indicating that morphology modification is an effective method for the performance enhancement of SnO₂ sensor [6]. The other strategy is to dope noble metals into SnO₂, e.g. Pd [[11], [12], [13], [14], [15], [16], [17]], Au [[18], [19], [20], [21], [22]], Eu [23], Ru [[24], [25], [26]] and Pt [[27], [28], [29], [30]] or carbon material [[31], [32], [33]], among which Pd [[34], [35], [36], [37], [38], [39], [40]] is particularly interesting because of its high catalytic activity and enhanced sensitivity to H₂, reducing the response time and optimum temperature of sensors. Chu Manh Hung et al. successfully lowered the hydrogen optimum operating temperature to 150 °C by preparing Pd doped SnO₂ nanofibers via thermal chemical vapor deposition (CVD) method [34], but other targets such as response time, detect limit and response (R_a/R_g) required further improvements. Wang's group synthesized SnO₂-composite Pd nanoparticles via solvothermal method, which displayed good performance on response time [38] while unwanted optimum operating temperature was at least 200 °C.

Herein, we report a facile method to prepare Pd coated SnO₂ nanofiber rods (NFRs) by magnetron sputtering and electrospinning, a promising method for fabricating nanostructures. The Pd coated SnO₂ NFRs showed promoted hydrogen sensing response and hydrogen selectivity due to the ravine-like sub-structure morphology formation during the annealing process. Moreover, we investigated the sensing behavior of various nanostructures, and our work exhibited advantages over others in response, detect limit, response time and selectivity.

Section snippets

Experimental section

A detailed schematic demonstration of the materials preparation is shown in Fig. 1.

Structure and morphology

The surface morphology and nanostructure of Pd coated SnO₂ NFRs during preparation was observed by SEM. Fig. 3a and b clearly shows the morphology of the intermediate products after electrospinning. During electrospinning, the product solidified to form continuous and evenly distributed nanofibers due to solvent volatilization, as exhibited by Fig. 3a. Fig. 3b shows the smooth surface of nanofibers with diameter of approximately 200 nm. The main component of nanofiber - SnCl₂·2H₂O was gradually

Conclusion

In conclusion, we demonstrate a Pd coated SnO₂ NFRs prepared by electrospinning and magnet sputtering. The sensor exhibited an excellent enhanced hydrogen sensing response to 100 ppm hydrogen: (1) the optimal working temperature lowered from 310 °C to 160 °C; (2) the maximum hydrogen response increased by 2.5 times compared to pure sample from 11.5 to 28.5 at their respective optimum temperatures; (3) the response time significantly reduced, which is only 4 s; (4) the repeatability test proved

Acknowledgements

This work is supported by the National Natural Science Foundation of China [U1537211], Fundamental Research Funds for the Central Universities [2019CDXYDQ0010], Chongqing Municipal Human Resources and Social Security Bureau [CX2017041], National “111” Project of the Ministry of Education of China [B08036] and National Key Basic Research Program of China (973 Program) [2015CB251003].

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