Investigation of the H₂O Sensing Mechanism of DC-Operated Chemiresistors Based on Graphene Oxide and Thermally Reduced Graphene Oxide

Abstract

Graphene oxide (GO) is a promising material for H 2 O vapour sensing. However, H 2 O sensing mechanisms are still under investigation especially in the case of thermally reduced GO. To this purpose, planar devices were fabricated by spincoating graphene oxide on glass substrates. Ultra high response to H 2 O was recorded but poor repeatability and stability over time were also noted. Three different degrees of thermal reduction were applied to improve material stability. An inverse change of resistance was observed for reduced graphene oxide compared to pure graphene oxide upon interaction with H 2 O. The sensing mechanisms that govern GO and reduced GO behaviour were studied based on DC measurements. In the case of GO, strong ionic conductivity was proposed whereas in the case of reduced GO mixed electronic/ionic with the leading mechanism affected by H 2 O percentage in air, degree of material reduction and sensor working temperature. Finally, it was found that by promoting one sensing mechanism over the other, improved operating humidity range of the sensor can be achieved.

Ethanol Sensors Based on Porous In2O3 Nanosheet-Assembled Micro-Flowers

“…Gas sensors like electronic noses can detect and monitor gas to prevent safety accidents [ 5 ]. In recent decades, in order to obtain better gas sensitivity, researchers have made a variety of gas sensors such as semiconductor sensors [ 6 , 7 ], infrared sensors [ 8 ], electrochemical sensors [ 9 ], thermal conductivity sensors [ 10 ], solid electrolyte sensors [ 11 ], and so on. Among them, gas sensors made by semiconductors, especially metal oxide semiconductors (MOS), have attracted extensive attention due to their advantages of environmental protection, simple preparation, low cost, and good stability [ 12 , 13 , 14 ].…”

Structure and Property Evolution of Graphene Oxide Sheets during Low-Temperature Reduction on a Solid Substrate

“…It is reported that the apparent thermal reduction of GO starts at temperatures above 130 or 150 °C, , but mild thermal annealing procedures that drive the phase transformation of GO are at 50 and 80 °C . As a result, the onset temperature for reduction may be overlapped with the working temperatures, and exploring the property evolution of GO at these temperatures is crucial for the long-term stability of the graphene-based materials or devices. , In addition, the oxygen functional groups make the graphene-based materials hydrophilic for dispersion in water. Tracking the structure and property evolution of GO during low-temperature reduction will facilitate controlling of the preserved oxygen content and dispersion in water for applications such as in nanofluids …”

“…These multifunctional applications largely rely on the reduction processes which are used to control the evolution of sp 2 -hybridized structures and then tailor the electronic, ,, optical, − thermal, and mechanical properties of GO. Among various reduction techniques, thermal reduction offers a simple and safe way to tune and enhance the properties. , Compared to many of the thermal methods which are assisted by high temperatures (>200 °C), , vacuum, microwave, or reducing agent vapors, , the low-temperature (≤200 °C) thermal treatments under ambient conditions provide an economically effective and easily controllable procedure. , …”

“…In ambient conditions, ubiquitous water is permanently trapped in low-temperature thermal-reduced GO and can be confined at interfaces and microscopic pores. , Water plays a crucial role in the functional groups constantly by developing and transforming on GO sheets. − Compared to bulk water, water confined at interfaces features significantly different characteristics and determines various aspects in materials science. ,, In previous reports, environmental water vapor effects on GO properties are mainly in leading electrical behavior changes, − so that GO can be used in humidity-sensing , and moist-electric power generators . However, water effects on the evolution process of GO on a solid substrate under ambient conditions are not well-tracked previously.…”

“…Among various reduction techniques, thermal reduction offers a simple and safe way to tune and enhance the properties. 3,12 Compared to many of the thermal methods which are assisted by high temperatures (>200 °C), 2,12 vacuum, 13 microwave, 4 or reducing agent vapors, 14,15 the low-temperature (≤200 °C) thermal treatments under ambient conditions provide an economically effective and easily controllable procedure. 2,16 Many of the remarkable properties of graphene-based materials, such as electronic and opto-electronic characteristics, stability over time, and dispersion in aqueous media, are related to the evolution of GO during low-temperature reduction that can modulate the oxygen functional groups attached to the surface.…”