Hydrogen sensors are of increasing importance in connection with the development and expanded use of hydrogen gas as an energy carrier and as a chemical reactant. There are an immense number of sensors reported in the literature for hydrogen detection and in this work these sensors are classified into eight different operating principles. Characteristic performance parameters of these sensor types, such as measuring range, sensitivity, selectivity and response time are reviewed and the latest technology developments are reported. Testing and validation of sensor performance are described in relation to standardisation and use in potentially explosive atmospheres so as to identify the requirements on hydrogen sensors for practical applications.

Hydrogen Sensors - A review

Graphene, a single, one-atom-thick sheet of carbon atoms arranged in a honeycomb lattice and the two-dimensional building block for carbon materials, has attracted great interest for a wide range of applications. Due to its superior properties such as thermo-electric conduction, surface area and mechanical strength, graphene materials have inspired huge interest in sensing of various chemical species. In this timely review, we discuss the recent advancement in the field of graphene based gas sensors with emphasis on the use of modified graphene materials. Further, insights of theoretical and experimental aspects associated with such systems are also discussed with significance on the sensitivity and selectivity of graphene towards various gas molecules. The first section introduces graphene, its synthesis methods and its physico-chemical properties. The second part focuses on the theoretical approaches that discuss the structural improvisations of graphene for its effective use as gas sensing materials. The third section discusses the applications of pristine and modified graphene materials in gas sensing applications. Various graphene modification methods are discussed including using dopants and defects, decoration with metal/metal oxide nanoparticles, and functionalization with polymers. Finally, a discussion on the future challenges and perspectives of this enticing field of graphene sensors for gas detection is provided.

Recent advances in graphene based gas sensors

Palladium-Based Nanomaterials: Synthesis and Electrochemical Applications

Recent progress in applications of graphene oxide for gas sensing: A review

Optical fibers have been involved in the area of sensing applications for more than four decades. Moreover, interferometric optical fiber sensors have attracted broad interest for their prospective applications in sensing temperature, refractive index, strain measurement, pressure, acoustic wave, vibration, magnetic field, and voltage. During this time, numerous types of interferometers have been developed such as Fabry-Perot, Michelson, Mach-Zehnder, Sagnac Fiber, and Common-path interferometers. Fabry-Perot interferometer (FPI) fiber-optic sensors have been extensively investigated for their exceedingly effective, simple fabrication as well as low cost aspects. In this study, a wide variety of FPI sensors are reviewed in terms of fabrication methods, principle of operation and their sensing applications. The chronology of the development of FPI sensors and their implementation in various applications are discussed.

https://www.mdpi.com/1424-8220/14/4/7451/pdf-vor

Chronology of Fabry-Perot interferometer fiber-optic sensors and their applications: a review.

The utilization of novel comb copolymer phthalocyanine (Pc) thin films as sensitive layers for microwave gas sensors at room temperature under exposure to various volatile organic compounds are presented. The microwave gas sensors are based on an interdigital capacitor fabricated in a microstrip line technique with adequate layers and dimensions. The developed sensors were tested for acetone, ethanol and methanol in the range of 0–200 ppm with special emphasis to the range of 0–25 ppm. The presented sensors will be used as a part of a microsystem for exhaled breath analysis, i.e. diabetes biomarkers detection. All the measurements are carried out at room temperature. The obtained results confirmed the possibility of utilization the microwave Pc-based sensors for exhaled acetone measurements.

Microwave-based sensors with phthalocyanine films for acetone, ethanol and methanol detection

Transition metal oxides covered Pd film for optical H2 gas detection

The paper deals with investigations concerning the construction of sensors based on a quartz crystal microbalance (QCM) containing a TiO2 nanostructures sensor layer. A chemical method of synthesizing these nanostructures is presented. The prepared prototype of the QCM sensing system, as well as the results of tests for detecting low NO2 concentrations in an atmosphere of synthetic air have been described. The constructed NO2 sensors operate at room temperature, which is a great advantage, because resistance sensors based on wide gap semiconductors often require much higher operation temperatures, sometimes as high as 500 °C. The sensors constructed by the authors can be used, among other applications, in medical and chemical diagnostics, and also for the purpose of detecting explosive vapours. Reactions of the sensor to nitroglycerine vapours are presented as an example of its application. The influence of humidity on the operation of the sensor was studied.

https://www.mdpi.com/1424-8220/15/4/9563/pdf

A Study of a QCM Sensor Based on TiO2 Nanostructures for the Detection of NO2 and Explosives Vapours in Air

An interdigital capacitor with resonant frequency fres ≈ 8.6 GHz coated by comb polymer Pc-based thin film as a sensitive layer was investigated under exposure to different concentrations of various VOCs, such as: acetone, ethanol, methanol, isopropanol, butanol and ethylbenzene in a 0–25 ppm concentration range. The measurement system has been significantly simplified due to measurement of the reflection coefficient at a single frequency f0 = 8 GHz, at which the sensor exhibits the largest change in reflection coefficient's magnitude. For the reflection coefficient's measurement a new six-port reflectometer has been developed, which provides an enhanced measurement accuracy for the measurements of reflection coefficients having small magnitudes. The developed detector based on microwave measurements can be utilized in a portable exhaled breath analyzers.

Six-port microwave system for volatile organic compounds detection

The paper presents a resistance structures with sensor layers based on nanostructures elaborated on the base of TiO2 and ZnO. The structures were tested concerning their sensitivities to the effects of nitrogen dioxide in the atmosphere of synthetic air. The TiO2 and ZnO nanostructures played the role of sensor layers. Investigations have proved that the elaborated resistance structures with TiO2 and ZnO layers are sensitive to the presence of NO2 in the atmosphere of synthetic air. The resistance of the structure amounted to about 20Ω in the case of ZnO structures and to about 200Ω in the case of TiO2 structures. The investigations confirmed that resistance structures with ZnO and TiO2, exposed to the effect of nitrogen dioxide in the atmosphere of synthetic air changes their resistances relatively fast. This indicates that such structures might be practically applied in sensors of nitrogen dioxide ensuring a short time of response.

/pdf/gas-sensors-based-on-nanostructures-of-semiconductors-zno-49xdi4ebwu.pdf

Erwin Maciak

Papers

Microwave-based sensors with phthalocyanine films for acetone, ethanol and methanol detection

Transition metal oxides covered Pd film for optical H2 gas detection

A Study of a QCM Sensor Based on TiO2 Nanostructures for the Detection of NO2 and Explosives Vapours in Air

Six-port microwave system for volatile organic compounds detection

Gas sensors based on nanostructures of semiconductors ZnO and TiO2