A survey and analysis of experimental hydrogen sensors

In order to ascertain the applicability of hydrogen sensors to aerospace applications, a survey was conducted of promising experimental point-contact hydrogen sensors and their operation was analyzed. The techniques discussed are metal-oxide-semiconductor or MOS based sensors, catalytic resistor sensors, acoustic wave detectors, and pyroelectric detectors. All of these sensors depend on the interaction of hydrogen with Pd or a Pd-alloy. It is concluded that no single technique will meet the needs of aerospace applications but a combination of approaches is necessary. The most promising combination is an MOS based sensor with a catalytic resistor

Recent Advances in Optical Hydrogen Sensor including Use of Metal and Metal Alloys: A Review

Optical sensing technologies for hydrogen monitoring are of increasing importance in connection with the development and expanded use of hydrogen and for transition to the hydrogen economy. The past decades have witnessed a rapid development of optical sensors for hydrogen monitoring due to their excellent features of being immune to electromagnetic interference, highly sensitive, and widely applicable to a broad range of applications including gas sensing at the sub-ppm range. However, the selection of hydrogen selective metal and metal alloy plays an important role. Considering the major advancements in the field of optical sensing technologies, this review aims to provide an overview of the recent progress in hydrogen monitoring. Additionally, this review highlights the sensing principles, advantages, limitations, and future development

Design And Fabrication Of Chemiresistor Typemicro/nano Hydrogen Gas Sensors Usinginterdigitated Electrodes

Hydrogen sensors have obtained increased interest with the widened application of hydrogen energy in recent years. Among them, various chemiresistor based hydrogen sensors have been studied due to their relatively simple structure and well-established detection mechanism. The recent progress in micro/nanotechnology has accelerated the development of small-scale chemical sensors. In this work, MEMS (Micro-Electro-Mechanical Systems) sensor platforms with interdigitated electrodes have been designed and fabricated. Integrating indium doped tin dioxide nanoparticles, these hydrogen sensors showed improved sensor characteristics such as sensitivity, response and selectivity at room temperature. Design parameters of interdigitated electrodes have been studied in association with sensor characteristics. It was observed that these parameters (gap between the electrodes, width and length of the fingers, and the number of the fingers) imposed different impacts on the sensor performance. In order to achieve small, robust, low cost and fast hydrogen micro/nano sensors with high sensitivity and selectivity, the modeling and process optimization was performed. The effect of humidity and the influence of the applied voltage were also studied. The sensor could be tuned to have high sensitivity (105), fast response time (10 seconds) and low energy consumption (19 nW). Finally, a portable hydrogen instrument integrated with a micro sensor, display, sound warning system, and measurement circuitry was fabricated based on the calibration data of the sensor

Recent Advances and Challenges of Nanomaterials-Based Hydrogen Sensors

Safety is a crucial issue in hydrogen energy applications due to the unique properties of hydrogen. Accordingly, a suitable hydrogen sensor for leakage detection must have at least high sensitivity and selectivity, rapid response/recovery, low power consumption and stable functionality, which requires further improvements on the available hydrogen sensors. In recent years, the mature development of nanomaterials engineering technologies, which facilitate the synthesis and modification of various materials, has opened up many possibilities for improving hydrogen sensing performance. Current research of hydrogen detection sensors based on both conservational and innovative materials are introduced in this review. This work mainly focuses on three material categories, i.e., transition metals, metal oxide semiconductors, and graphene and its derivatives. Different hydrogen sensing mechanisms, such as resistive, capacitive, optical and surface acoustic wave-based sensors, are also presented, and their sensing performances and influence based on different nanostructures and material combinations are compared and discussed, respectively. This review is concluded with a brief outlook and future development trends

SYNTHESIS, STRUCTURE, PROPERTIES AND APPLICATIONS OF NANOPOROUS SILICON AND PALLADIUM

Nanoporous (np) materials with pore size below 100 nano-meters exist naturally in biological and mineral structures, and synthetic np materials have been used industrially for centuries. Np materials have attracted significant research interest in recent decades, as the development of new characterization techniques and nanotechnology allow the observation and design of np materials at a new level. This study focuses on two np materials: nanoporous silicon (np-Si) and nanoporous palladium (np-Pd). Silicon (Si), because of its high capacity to store lithium (Li), is increasingly becoming an attractive candidate as anode material for Li ion batteries (LIB). One significant problem with using Si as an anode is the large strain that accompanies charge-discharge cycling, due to swelling of the Si during Li insertion and deinsertion. Np-Si offers a large amount of free volume for Li absorption, which could allow the anode material to swell without cracking. A new method to fabricate thin films of high-purity (100% Si content) np-Si, which is promising as an anode material for LIB, is demonstrated and discussed in this study. Microstructural characterization, chemical analysis, battery performance testing and mechanical behavior of thin film np-Si are discussed here. Palladium (Pd) is considered an ideal and reliable hydrogen sensor and storage material, due to its fast response and selectivity for hydrogen gas. This research not only demonstrates a method to fabricate np-Pd thin films, but also proposes a method to fabricate bulk np-Pd. The uniformly crack-free and sponge-like np-Pd thin film provides high sensitivity to low concentrations of H2, showing promise as a hydrogen sensor material. Stress changes during hydrogenation/dehydrogenation were measured using wafer curvature. For bulk np-Pd, ultra-fine pore sizes were achieved by electrochemically dealloying bulk PdNi alloy. Mechanical behavior of bulk np-Pd was studied using in-situ transmission electron microscopy (TEM). Scanning electron microscopy (SEM) and x-ray diffraction were also used to characterize the structure and morphology of np-Pd. This doctoral research has involved the optimization of fabrication conditions and investigations of microstructural evolution during processing, yielding an improved understanding of the properties, mechanical behavior and potential applications of np-Si and np-Pd

Fabrication characterization of nanostructured Pt and Pt-Ag Alloys, and Investigation of their Hydrogen Gas sensing properties

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Mevcut tez çalışması, platin (Pt) ve platin-gümüş (Pt-Ag) alaşım ince filmlerin hidrojen gaz algılama özelliklerini incelemiştir. Pt ve PtAg filmler cam alttaş üzerine magnetron sputter tekniği ile kaplanmıştır. Her biri farklı kalınlığa sahip Pt filmler (2-50 nm) RF sputtering yöntemi kullanılarak hazırlanmıştır. Kaplama sırasında filmlerin kalınlık kontrolü sputter sistemi içerisinde bulunan piezoelektrik sensörle yapılmıştır. Çalışmada ayrıca, 3 nm PtxAg1-x (x: 0.95, 0.90, 0.80 ve 0.50) ince filmler co-sputtering yöntemi kullanılarak kaplanmıştır. Pt ve PtAg alaşım filmlerin yapısal karakterizasyonları X-ışını kırınımı (XRD), taramalı elektron mikroskobu (SEM), X-ışını fotoelektron spektroskopisi (XPS) ve enerji dağılımlı X-ışını spektroskopisi (EDX) teknikleri ile yapılmıştır. Pt ve PtAg filmlerin kaplama kalınlığına, sıcaklığa ve konsantrasyona bağlı hidrojen duyarlılıkları incelenmiştir. Pt ve PtAg ince filmlerin sıcaklığa bağlı direnç değişimleri ve gaz ölçümleri ise kuru hava ve hidrojen ortamında 30 oC ile 200 oC arasında değişen sıcaklıklarda test edilmiştir. Böylece Pt ve PtAg sensörler için en iyi çalışma performansları belirlenmiştir. Elde edilen sonuçlar, üretilen Pt ince film sensörlerde direncin sıcaklıkla doğru orantılı, kaplama kalınlığı ile ters orantılı olacak biçimde değişiklik gösterdiğini ortaya koymaktadır. Pt ince film sensörlerin % 0.1 - % 1 konsantrasyon aralığında hidrojen gazına duyarlılıkları incelenmiştir. Pt ince filmler arasında, 2 nm Pt filmin 30 oC' de ve kuru hava ortamında en iyi duyarlılık performansı gösterdiği görülmüştür. Pt ince film sensörlerin en iyi cevap süresine ise oldukça yüksek sıcaklıklarda ulaştığı saptanmıştır. PtAg sensörlerin H2 duyarlılıkları 25 ppm – 1000 ppm hidrojen konsantrasyon aralığında incelenmiştir. PtAg ince film sensörlerin direnç ve duyarlılığı sıcaklığın artması ile birlikte artmıştır. PtAg sensörleri arasında en iyi çalışma performansı ise 3 nm Pt0.80Ag0.20 sensör için 150 oC'de görülmüştür.This thesis presented hydrogen (H2) sensing properties of platinum (Pt) and platinum-silver (Pt-Ag) thin films. Pt and PtAg films were deposited on glass substrate by magnetron sputter technique. The Pt thin films with different thickness (2-50 nm) were prepared using RF sputtering method. The thicknesses of the films were controlled by a piezoelectric sensor placed in sputter system at the same time of coating process. On the other hand in this study, 3 nm PtxAg1-x (x: 0.95, 0.90, 0.80 and 0.50) thin films were coated by co-sputtering technique. The structural properties of Pt and PtAg alloy films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) techniques. Hydrogen sensing properties of the Pt and PtAg films were investigated depending on film thickness, temperature and concentration. Temperature dependent resistances and the gas measurements of the Pt and PtAg thin films were studied under a dry air flow and hydrogen ambient at a temperature range from 30 °C to 200 °C. Thus the best working performances of Pt and PtAg sensors were detected. The results showed that the resistance is directly proportional with temperature, and inversely proportional with the thickness of Pt thin film sensors. The H2 sensing properties of Pt thin film sensors were examined in the concentration range of 0.1 % - 1 % H2. Among the results for Pt thin films, it was revealed that the Pt thin film with 2 nm thickness exhibited the best sensing performance to H2 at 30 °C under dry air flow. The best response time was obtained at high temperatures for Pt thin film sensors. H2 sensitivity of PtAg sensors were also investigated in the concentration of 25 ppm - 1000 ppm H2. The resistances and the sensitivities of PtAg thin film sensors were increased with enhancing the temperature. Among the results for PtAg sensors, 3 nm Pt0.80Ag0.20 sensor showed the best sensitivity properties at 150 oC

Fibre optic hydrogen sensing for long term use in explosive environments

Hydrogen is an explosive and flammable gas with a lower explosive limit of just 4% volume in air. It is important to monitor the concentration of hydrogen in a potentially hazardous environment where hydrogen may be released as a by-product in a reaction or used as a principal gas/liquid. A fibre optic based hydrogen sensor offers an intrinsically safe method of monitoring hydrogen concentration. Previous research studies have demonstrated a variety of fibre optic based techniques for hydrogen detection. However the long-term stability of the hydrogen sensor and interrogation system has not yet been assessed and is the focus of this study. In the case of sensor heads being permanently installed in-situ, they cannot be removed for regular replacement, making long-term stability and reliability of results an important feature of the hydrogen sensor. This thesis describes the investigation and characterisation of palladium coated fibre optic sensor heads using two designs of self-referenced refractometer systems with the aim of finding a system that is stable in the long term (~6 months). Palladium was the chosen sensing material owing to its selective affinity for absorbing hydrogen. Upon hydrogen absorption, palladium forms a palladium- hydride compound that has a lower refractive index and lower reflectivity than pure palladium. The refractometers measured the changes in the reflectivity to enable calculation of the concentration of hydrogen present. A low detection limit of 10ppm H2 in air was demonstrated, with a response time of 40s for 1000ppm H2 in air. A further aspect to sensor stability was investigated in the form of sensor heads that had a larger area for palladium coverage. Hydrogen induced cracking in palladium is a common failure mechanism. A hypothesis is presented that a larger sensor area can reduce the probability of catastrophic failure resulting from cracks, which may improve the predictability of the sensor’s performance. Two sensor head designs have been proposed – fibre with a ball lens at the tip and fibre with a GRIN lens at the tip, both of which potentially offer a larger area than the core of a singlemode optical fibre. The limit of detection and response times of the sensor heads were characterised in hydrogen. For long term stability assessment of the sensor head and the interrogation unit, the system was left running for a period of 1 to 4 weeks and the noise and drift in the system was quantified using an Allan deviation plot

Graphene-Based Junction Devices for Hydrogen Sensors

Graphene is quite a robust material for sensing hydrogen and other gases at room temperature as well as at elevated temperatures with high efficiency. This chapter deals with different junction devices based on graphene for hydrogen sensing. Graphene has excellent electronic attributes that make it suitable for gas sensor devices. However, till date, the research on graphene-based junction devices is not many. In this chapter, we present different types of graphene junction devices suitable for hydrogen sensing. Hydrogen sensor response of these junctions is analyzed, and the sensing mechanism is presented. The temperature- and atmosphere-dependent inversion of n-type to p-type conductivity in graphene is highlighted for hydrogen sensing. Moreover, the two dimensional nature of graphene makes it very convenient for device miniaturization. This chapter provides relevant information on the growth of graphene, the fabrication of different graphene junction devices, and hydrogen sensor applications. Also, the sensor-related concerns such as cross-sensitivity, signal drift, stability, and interference of humidity during hydrogen sensing are thoroughly discussed in this chapter

Design and manufacture of functional titanium–palladium devices for the activation of anti-cancer prodrugs

National health organisations and authorities have reported an increment in death cases due to cancer. To overcome this issue and improve the survival rate, it is needed to find new clinical methods, early diagnoses techniques and treatments. Radiation and chemotherapy have been used for years to treat cancer. However, these types of treatments have serious side effects such as hair loosing, the mortality of healthy cells and other organs. A new treatment based on prodrugs therapy is in development with the intention to reduce these side effects or to replace the harmful treatments completely. Prodrug treatments need an activation agent, i.e. a catalyst, to convert the prodrug delivered to the cancerous cells to an active drug in-situ. Metals such as palladium can be used as a catalyst to activate the prodrug in targeted cancer cells. In this PhD study, the research was divided into two major aspects. The first aspect was to design and manufacture a catalyst carrier with specific properties and specifications such as biocompatibility of the materials used as the carrier, suitable mechanical properties to withstand physiological loads and conditions, and cost efficiency of the production. Two different manufacturing methods were used, Powder Metallurgy technique and Arc Melting technique, to achieve the optimal fabrication method. The carriers were characterised via XRD, SEM, EDS, DSC methods and mechanical tests to ensure the carrier meets the requirements. In the second stage, the carriers were coated with Palladium in its metallic state (i.e. Pd0). The coating was required to meet the requirements of being unalloyed, pure and free of any contamination, and its deposition cost and time effective. Four coating methods were employed. Powder Metallurgy technique and sintering (with and without space holder), Magnetron Sputtering, Pulsed Laser Deposition and Supersonic Beam Cluster Deposition methods were used to apply Palladium coating onto the carriers. The coating was characterised by XPS, XRD, FIB, XRF, SEM, EDS, biochemical and in-situ biological tests. The results obtained confirmed that the devices achieve high biocompatibility of the materials, and an excellent superelasticity can withstand the loads inside the human body. Also, the Magnetron sputtering methods as a coating method demonstrated it is the most effective for achieving a uniform and long-lasting deposited layer. The devices were able to activate a clinically approved prodrug.</div

Carbon-Based Nanomaterials for (Bio)Sensors Development

Carbon-based nanomaterials have been increasingly used in sensors and biosensors design due to their advantageous intrinsic properties, which include, but are not limited to, high electrical and thermal conductivity, chemical stability, optical properties, large specific surface, biocompatibility, and easy functionalization. The most commonly applied carbonaceous nanomaterials are carbon nanotubes (single- or multi-walled nanotubes) and graphene, but promising data have been also reported for (bio)sensors based on carbon quantum dots and nanocomposites, among others. The incorporation of carbon-based nanomaterials, independent of the detection scheme and developed platform type (optical, chemical, and biological, etc.), has a major beneficial effect on the (bio)sensor sensitivity, specificity, and overall performance. As a consequence, carbon-based nanomaterials have been promoting a revolution in the field of (bio)sensors with the development of increasingly sensitive devices. This Special Issue presents original research data and review articles that focus on (experimental or theoretical) advances, challenges, and outlooks concerning the preparation, characterization, and application of carbon-based nanomaterials for (bio)sensor development