Elsevier

Carbon

Volume 81, January 2015, Pages 54-62
Carbon

Chemically modified graphene/PEDOT:PSS nanocomposite films for hydrogen gas sensing

https://doi.org/10.1016/j.carbon.2014.09.023Get rights and content

Abstract

In this study, we report the preparation of chemically modified graphene/(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) nanocomposites and their application in hydrogen (H2) gas sensing materials. The aqueous dispersions of graphene oxide (GO) and reduced graphene oxide (rGO) nanosheets were synthesized and further doped into the solution of PEDOT:PSS in dimethylsulfoxide (DMSO). Both the GO/PEDOT:PSS and rGO/PEDOT:PSS composite devices showed a decrease in the resistance upon hydrogen exposure at room temperature. The GO/PEDOT:PSS, a strong p-type material, formed by rectifying contact with tungsten was evaluated for the H2 gas sensing and identified as a contact-controlled type. The rGO/PEDOT:PSS, a weak n-type material, forming an ohmic contact with tungsten was investigated for its H2 gas sensing and identified as a body-controlled type.

Introduction

Hydrogen (H2) gas sensors, the devices that produce an electrical signal upon exposure to H2 gas, have received considerable attention for their potential applications in energy supply security and nuclear reactor safety [1]. Various materials including metals [2], metal oxides [3], [4], nanocarbons [5], [6], [7], [8], [9], and conducting polymers [10], [11] have been used for the sensing of hydrogen gas. Among these, conducting polymers have significant advantages compared to other material systems regarding the chemical versatility and ease of solution processing [12]. Upon exposure to H2, the electrical properties of conducting polymers can be altered via redox reactions and charge transfer.

The doping of conducting polymers with nanocarbon materials is expected to enhance their sensing properties owing to a maximum surface-to-volume ratio of the nanocarbon fillers. Among various nanocarbon materials, graphene nanosheets, consisting of a single layer of sp2-bonded carbon atoms, have attracted considerable scientific interest owing to their excellent thermal, mechanical, and electronic properties [13]. Because of its two-dimensional structure with a large specific surface area for molecular adsorption and excellent electrical conductivity, graphene could serve as a promising material for gas sensing. Even though pure graphene is not sensitive to hydrogen [14], chemically modified graphene (CMG) and its derivatives such as graphene oxide (GO) and reduced graphene oxide (rGO) have been reported for their potential applications in H2 gas sensing [15], [16]. In particular, GOs exhibited several sensing mode according to their degree of reduction. By the controlled reduction, the amount of the surface oxygen functional groups on the GO was controlled, thus ambipolar sensing behavior was observed [7], [8], [9], [17].

The formation of hybrid materials consisting of the CMGs and conducting polymer is expected to be a promising approach for the fabrication of H2 gas sensing materials with a higher sensitivity operating at room temperature. In this study, nanocomposite films consisting of poly(3,4-ethylene-dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) and GOs or rGOs were studied for their use as hydrogen gas sensors. The GO/PEDOT:PSS and rGO/PEDOT:PSS composited exhibited opposite H2 sensing behavior, and the maximum sensitivity of 4.2% was observed for the GO/PEDOT:PSS composite with a recovery and response times of ∼25 s (100 ppm H2).

Section snippets

Materials

Graphite flakes (Median size 7–10 μm, 99.0%) were purchased from Alfa Aesar; PEDOT:PSS solution was purchased from HeraeusClevios GmbH (Clevious™ PH1000); sulfuric acid (H2SO4) was purchased from PFP (Matsunoen, 98.08%); hydrochloric acid (HCl, 36.46%) was purchased from Daejung Chemicals. KMnO4 (99.0%), p-hydrazinobenzene sulfonic acid hemihydrate, hydrogen peroxide (H2O2), and phosphoric acid (H3PO4, 98.0%) were purchased from Sigma–Aldrich, and dimethyl sulfoxide (DMSO, 99.0%) was purchased

Results and discussion

Fig. 2 shows the XRD patterns of the graphite flakes (a), as-prepared GO (b), and rGO (c). For the natural graphite flakes, the XRD spectrum showed a tall narrow peak at 2θ = 26.6°, indicating a d-spacing of 0.335 nm between the two graphite sheets. For GO, the sharp peak at ∼2θ = 10.4° corresponded to an interlayer spacing of ∼0.87 nm. This interlayer distance was attributed to the formation of hydroxyl, epoxy, and carboxyl groups on the surface of the carbon network [20]. After the reduction, the

Conclusion

In conclusion, we investigated the H2 gas sensing properties of the hybrid materials consisting of CMGs and PEDOT:PSS at RT. Compared to the pure PEDOT:PSS, the CMG/PEDOT:PSS hybrid system exhibited more promising sensing behavior on H2 gas. The sensing behavior of the rGO/PEDOT:PSS composite sensor indicates that the sensing material is a n-type, and the device is a body-controlled type device. In comparison, the sensing behavior of the GO/PEDOT:PSS composite sensor indicates that the device

Acknowledgments

This study was supported by the RIC Program of Ministry of Trade, Industry and Energy and the LINC Program of Ministry of Education at Woosuk University, the KIST Institutional Program (2Z04260), and a Grant from the Converging Research Center Program funded by the Ministry of Science, ICT, and Future Planning Technology (2013K000414), Korea Research Council for Industrial Science and Technology (Grant B551179-13-01-01).

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    The authors contributed equally to this work.

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