Different Concentrations Of Hydrogen Research Articles

Quasi-distributed optical fiber hydrogen leakage detecting system based on bus chain topology structure

Micro-mirror optical fiber hydrogen sensors have the advantages of compact structure and fast demodulation speed. All-optical sensor networks consisting of micro-mirror optical fiber hydrogen sensors are essentially necessary across the hydrogen value chain. A bus chain topology structure hydrogen leakage detecting system based on micro-mirror sensors is proposed and experimentally demonstrated. A compensating optical path with constant power supply is introduced, and the power dissipation scheme is theoretically and experimentally proposed by designating the splitting ratios of the splitters array. By constructing such a network with twenty micro-mirror hydrogen sensors, the system has been experimentally verified with good repeatability and stability under different concentrations of hydrogen. By employing this bus chain topology strategy, a quasi-distributed optical fiber hydrogen leakage detection system with micro-mirror hydrogen sensors array is realized. It will provide a promising solution with high feasibility on multi-point leakage detecting in hydrogen infrastructures.

A novel method for hydrogen synthesis in natural gas reservoirs

Hydrogen has been proven as a promising energy resource for a clean and sustainable future. However, the complete replacement of conventional hydrocarbon energy sources poses a challenge due to their widespread industrial utilization. Despite the gradual depletion of petroleum and natural gas reserves, they continued to serve as primary energy sources for many decades. But what if we could repurpose these hydrocarbons? Currently, fossil fuels that are both non-renewable and environmentally unfriendly are directly used for energy generation. Instead, we could convert hydrocarbons into a significantly cleaner alternative – hydrogen. This process implies in situ hydrogen generation even before hydrocarbons are recovered from a reservoir without releasing greenhouse gases into the atmosphere. In this context, we explore the conversion of methane into hydrogen in the gas reservoir with zero oil saturation via steam methane reforming initiated by in situ gas combustion. In the experimental model, different rock porous media were utilized and the process parameters such as temperature and the steam-to-methane ratio were varied. The outcome reveals a range of variations, each yielding different concentrations of hydrogen produced depending on these adjustable parameters. Our findings suggest the incredible potential for underground hydrogen generation in natural gas reservoirs. This approach holds great promise as a leading candidate for the foreseeable future, benefiting from the synergy of the fossil fuel industry and an innovative hydrogen production technology.

Monte-Carlo simulations on H2 adsorption in kaolinite nanopore in the presence of CO2 and CH4 gases

Hydrogen is being explored as a potential future energy source, but the effective storage of hydrogen in geological formations especially in clay-rich formations requires a significant understanding of its interaction mechanisms. In this study, we use Grand canonical Monte-Carlo (GCMC) simulations to investigate the H2 adsorption on kaolinite minerals in the presence of CO2 and CH4. Furthermore, we assess the average adsorption energy, Henry coefficient, and RDFs of hydrogen. In this study, at first, the CO2 adsorption is computed and validated with the published data. Later, different concentrations of hydrogen are introduced in the system to investigate the competitive adsorption of CO2/H2 mixture with kaolinite. Following that, we evaluate the pure H2 and the competitive H2/CH4 mixture adsorption. These simulations are carried out under elevated geological pressures and high-temperature conditions. The results show that the pressure increases while temperature reduces the hydrogen adsorption causing a rise in the average adsorption energy. This results in a decrease in Henry coefficient, and, consequently, a decrease in the overall hydrogen adsorption capacity. The results also reveal that increasing the concentration of CO2 and CH4 significantly reduces hydrogen adsorption. This phenomenon is driven by the high intermolecular attraction of CO2 and CH4 with the kaolinite surface. Such high affinity creates a strong adsorption layer, impeding the contact of hydrogen with the kaolinite surface. In addition, the contribution of all kaolinite atoms towards hydrogen adsorption is competitive with a slightly higher contribution by silicon. Our work provides significant insights into hydrogen interaction with the clay-rich mineral and reveals H2 adsorption mechanisms in the presence of both CO2 and CH4.

CFD modelling of hydrogen and hydrogen-methane explosions – Analysis of varying concentration and reduced oxygen atmospheres

This paper evaluates the predictive capabilities of the advanced consequence model FLACS-CFD for deflagrations involving hydrogen. Two modelling approaches are presented: the extensively validated model system originally developed for hydrocarbons included in FLACS-CFD 22.1 and a Markstein number dependent model implemented in the in-house version FLACS-CFD 22.1 IH. The ability of the models to predict the overpressure and the flame arrival time for scenarios with different concentrations of hydrogen, and thus different Lewis and Markstein numbers, is assessed. Furthermore, the effect of adding methane or nitrogen on overpressure for different regimes of premixed combustion are investigated. The validation dataset includes deflagrations in the open or in congested open areas and vented deflagrations in empty or congested enclosures. The overpressure predictions by FLACS-CFD 22.1 IH are found to be more accurate than those obtained with FLACS-CFD 22.1 for scenarios with varying hydrogen concentrations and/or added nitrogen or methane in the mixture. The predictions by FLACS-CFD 22.1 IH for lean hydrogen mixtures are within a factor of 2 of the values observed in the experiments. Further development of the model is needed for more accurate prediction of deflagrations involving rich hydrogen mixtures as well as scenarios with other fuels and/or conditions where the initial pressure or temperature deviate significantly from ambient conditions.

Stabilization of liquid water‐in‐oil emulsions by modifying the interfacial interaction of glycerol monooleate with aqueous phase ingredients

AbstractGlycerol monooleate (GMO)‐stabilized liquid water‐in‐vegetable oil emulsions are difficult to stabilize due to the desorption of GMO from the water‐vegetable oil interface toward the oil phase. This work improved the stability of GMO‐stabilized liquid 20 wt% water‐in‐canola oil (W/CO) emulsion by modifying the dispersed aqueous phase composition with hydrogen bond‐forming agents. As a control, 20 wt% water‐in‐mineral oil (W/MO) emulsion was also utilized. Different concentrations of hydrogen bond‐forming agents (citric acid (CA), ascorbic acid (AA), low methoxyl pectin (LMP)) with and without salts (sodium chloride (S) or calcium chloride (Ca)) were added to the aqueous phase before emulsification, which enhanced emulsifier binding to the water–oil interface. W/CO emulsion without any aqueous phase additive destabilized instantly, whereas W/MO emulsion stayed stable during the week‐long observation. The addition of hydrogen bond‐forming agents and salts significantly improved emulsion stability. LMP, with many hydrogen bond‐forming groups, was able to provide the highest emulsion stability after 7 days in both oils compared to AA, CA and their mixtures with S. Emulsions with both oils formed weak gels due to the formation of an extensive network of water droplet aggregates. Overall, the hydrogen bond‐forming agents interacted with GMO at the interface, thereby favoring their presence at the water droplet surface and significantly improving the stability of liquid W/CO emulsions. The knowledge developed in this research can be useful in utilizing GMO to stabilize liquid water‐in‐oil emulsions without using any fat crystal network.

Modeling and Analysis of a Thermophotovoltaic Integrated Self-Powered Furnace

This work investigates the energy efficiency and carbon reduction potential of self-powered residential building heating equipment using a thermodynamic modeling approach. An integrated thermophotovoltaic power module and residential scale furnace system (40,000 Btu/h) were modeled and studied in detail to assess the influence of different design configurations on primary energy efficiency. Operational characteristics such as total power generation, electrical efficiency, and heat recovery were examined in a self-powered system configuration. A sensitivity analysis was conducted to determine the influence of the electric grid’s carbon dioxide footprint (carbon intensity) and the cost of electricity on the environmental, as well as the economic, benefit associated with the self-powered configuration. Compared with a traditional furnace powered by an electric grid at a carbon intensity of 0.5 kg CO2eq/kWhEL, the self-powered furnace was shown to decrease the annual carbon dioxide emissions by approximately 550 kg (~75% reduction), while also saving more than USD 200 in utility expenses, annually. Additionally, the carbon emission reduction potential of blending different concentrations of hydrogen in natural gas fuel was also studied.

Angular-dependent interatomic potential for large-scale atomistic simulation of the Fe-Cr-H ternary system

The recently developed angular-dependent potential for pure iron was advanced to the interatomic potential of the Fe-Cr-H ternary system. The new potential allows to simulate Fe-Cr alloys for a wide range of compositions and different concentrations of hydrogen. The angular-dependent format of the model and the development procedure based on the machine learning approach allow to achieve a favorable balance between the computation cost and the reliability of the created parametrization. As part of potential validation, we performed a large number of tests of both the binary metallic alloys and hydrogen interactions. The applicability of the potential is demonstrated by large-scale simulations of hydrogen diffusion in the vicinity of crystal defects.

In vivo microelectrode monitoring of real-time hydrogen concentration in different tissues of rats after inhaling hydrogen gas

Medical effects of hydrogen have been reported in many studies. Due to difficulties in measuring hydrogen concentration in vivo after intake and high explosive risks of hydrogen, studies about dose-response relationships and tissue concentrations of hydrogen are few. Here, for the first time, we monitored real-time hydrogen concentrations in different tissues in rats including brain, liver, spleen, kidney, thigh muscle, inguinal white adipose tissue, and gonadal white adipose tissue after inhaling different concentrations of hydrogen (4%, 42%, and 67%) using an electrochemical sensor. Hydrogen concentrations in the same tissue showed a dose-dependent response. The equilibrium concentration values were highest in the brain and lowest in the thigh muscle. The saturation and desaturation curves changed more slowly in the thigh muscle and white adipose tissues than in other tissues. These results provide fundamental information for the selection of hydrogen dose applications in basic research and clinical trials. The experiments were approved by the Laboratory Animal Ethics Committee of Shandong First Medical University & Shandong Academy of Medical Sciences (No. 2020-1028) on March 18, 2020.

Enhanced gas sensing and photocatalytic activity of reduced graphene oxide loaded TiO2 nanoparticles

In the present study, we have evaluated the gas sensing and photocatalytic activity of reduced graphene oxide (rGO) conjugated titanium dioxide (TiO2) nanoparticles (NPs) formed by the hydrothermal method. The as-synthesized rGO-TiO2 nanocomposite were characterized for the physicochemical properties such as the nature of crystallinity, functionalization, and morphology by making use of the powder X-ray diffraction, Fourier transform-infrared spectroscopy, and scanning electron microscopy, respectively. On testing the gas sensing properties, we found that the rGO-TiO2 nanocomposite can serve as the chemoresistive-type sensor because of its sensitivity and selectivity towards different concentrations of hydrogen and oxygen at room temperature conditions. However, the rGO-TiO2 sensor’s response and recovery speed towards hydrogen and oxygen needs further optimization. Test of photocatalytic activity of TiO2-rGO catalyst for the removal of two model contaminant dyes, RhB and MB showed effective removal, with respective degradation percentages of about 80 and 90% within the first 50 min of irradiation under visible light irradiation. Besides, MB was more effectively degraded using TiO2-rGO than pure TiO2 during the first 30 min of irradiation and this enhanced activity can be attributed to the increased capacity of light absorption, the efficiency of charge carriers separation, and the specific surface area maintained by the rGO-TiO2 nanocomposite to effectively utilize the photo-generated holes (h+) and superoxide radicals (O2−), responsible for the degradation of the dye. Based on the overall analysis, the formation of rGO-TiO2 nanocomposite can significantly improve the gas sensing and photocatalytic properties of TiO2 NPs and thus can be potential for practical applications in future nanotechnology.

Quantitative analysis of the synergistic effect of Au nanoparticles on SnO2-rGO nanocomposites for room temperature hydrogen sensing.

Hydrogen detection devices based on gold-tin oxide/reduced graphene oxide (Au-SnO2/rGO) nanohybrids were fabricated by combining a hydrothermal method with sputter coating. The gas sensing performance of the Au-SnO2/rGO sensor was investigated under different concentrations of hydrogen from 0.04% to 1% at room temperature, which indicated a notable sensitive response even for 0.04% hydrogen. The activation energies of hydrogen adsorption/desorption were extracted via Arrhenius analysis which revealed the acceleration effect of gold dopants. This acceleration led to a faster response and recovery during hydrogen sensing. The activation energy analysis provided a more comprehensive understanding on the gas sensing mechanism. A hydrogen detection handheld device is demonstrated by integrating the sensor chip with a portable digital meter for direct readout of test results.

Design and Development of Instrumentation for Remote Detection of Hydrogen Using Metal Oxide Sensor

Indigenous instrumentation setup was designed, developed and demonstrated for remote detection of hydrogen using metal oxide (MO) sensors. The metal oxide sensor was developed to sense the low concentration of hydrogen. The hardware developed was based on a function generator configuration and uniquely designed to give low excitation voltage across the sensor to improve the life of the sensor and reduces the number of components. The data acquisition software was developed to collect the sensor response in PC remotely. The hardware was calibrated, tested with standard resistance and found to give an accuracy of ±0.5% and high stability and reliability. The sensor response towards hydrogen was measured by the instrument. Different features of sensor response viz., sensitivity, response time and recovery time were studied towards different concentrations of hydrogen at optimized temperature.

The first-principles study of nH-VSn complex: impurity effects on p-type SnO monolayer.

As a rare typical p-channel layered oxide semiconductor, two-dimensional tin monoxide has attracted great attention due to its wide promising applications in nano-electronics. Using the first-principles calculation, we studied the effects of multi-hydrogen-tin/oxygen vacancy complex impurities on the electronic properties of the p-type monolayer SnO. The calculation results indicated that O vacancy (VO) is a donor and Sn vacancy (VSn) acts as a double acceptor. VSn should be the source of p-type in undoped SnO in an O-rich environment. When hydrogen is introduced, the more stable nH-VSn (n = 1, 2, and 3) complex defects can be formed. These complex impurities can affect the p-type SnO monolayer in the following three main ways: (i) the p-type H-VSn compensates the deeper acceptor level of VSn and enhances the majority carrier mobility. (ii) The more stable 2H-VSn neutralizes the p-type dopant nature of VSn and H-VSn. (iii) The 3H-VSn converts the defect to be an n-type dopant. Our results indicated that limitation of hydrogen is necessary for the preparation of high-quality p-type two-dimensional SnO, as a small amount of hydrogen produces positive effect on p-type SnO; however, the higher concentration of hydrogen is destructive to the p-type character of monolayer SnO.

Palladium-coated narrow groove plasmonic nanogratings for highly sensitive hydrogen sensing.

In this paper, we propose novel plasmonic hydrogen sensors based on palladium coated narrow-groove plasmonic nanogratings for sensing of hydrogen gas at visible and near-infrared wavelengths. These narrow-groove plasmonic nanogratings allow the incident light to be coupled directly into plasmonic waveguide modes thereby alleviating the need for bulky coupling methods to be employed. We carried out numerical simulations of the palladium coated narrow-groove plasmonic nanogratings using rigorous coupled wave analysis (RCWA). When palladium is exposed to varying concentrations of hydrogen gas, palladium undergoes phase transition to palladium hydride (PdHx), such that there are different atomic ratios ‘x’ (H/Pd) of hydrogen present in the palladium hydride (PdHx) depending on the concentration of the hydrogen gas. RCWA simulations were performed to obtain the reflectance spectral response of the Pd coated nanogratings in both the absence and presence of hydrogen, for various atomic ratios ‘x’ (x ∼ 0.125 to 0.65) in palladium hydride (PdHx). The results of the RCWA simulations showed that as the dielectric permittivity of the palladium (Pd) thin film layers in between the adjacent walls of the plasmonic nanogratings changes upon exposure to hydrogen, significant shifts in the plasmon resonance wavelength (maximum Δλ being ∼80 nm for an increase in the value of the atomic ratio ‘x’ from 0 to 0.65) as well as changes in the differential reflection spectra are observed. The structural parameters of these Pd coated narrow groove nanogratings—such as the nanograting height, gap between the nanograting walls, thickness of the palladium layer, periodicity of the nanogratings—were varied to maximize the shift in the plasmon resonance wavelength as well as the differential reflectance when these nanostructures are exposed to different concentrations of hydrogen (i.e. for different atomic ratios ‘x’ in PdHx).

Remarkably enhanced H2 response and detection range in Nb doped rutile/anatase heterophase junction TiO2 thin film hydrogen sensors

Hydrogen sensors combining wide detection range and high response, that can operate at room temperature, are urgently demanded for monitoring different concentrations of hydrogen on a single device. Here, a novel one-step hydrothermal method is reported to construct Nb doped rutile/anatase TiO2 heterophase junctions for a highly sensitive H2 sensor. The Nb concentration in the solvent plays an important role for the heterophase juncton self-assemble, and the reaction time determines the surface morphology giving either a rutile TiO2 nanorod decorated anatase form, or a Nb doped rutile/anatase TiO2 bi-layer structure. An inverse dependence of the detectivity on H2 concentration is obtained as theoretically predicted but previously not experimentally verified for the high concentration region at low temperatures. The H2 concentration detection range is remarkably expanded, extending from 1 ppm to 12000 ppm for nanorod decorated film. The H2 response at 1 ppm is significantly enhanced to 22.5%, and reaches 98.9% in 8000 ppm H2 for the bilayer structure. The remarkablely extended detection range is the result of the massive accumulation of reactive pre-absorbed O2− on the surface due to the Nb doping, and the significantly enhanced response at room temperature results from the joint contributions of pre-absorbed O2−, film compactness and the heterophase junction. Moreover, Nb doped rutile/anatase TiO2 heterophase juncton films show high stability and humidity resistance for hydrogen sensing.

Molecular‐Scale Modeling and Multiscale Experiments on the Elastic Properties of HR‐2 Steel Affected by Hydrogen

Austenitic stainless steel is used in hydrogen containers. The hydrogen embrittlement has drawn much attention. In this paper, in situ measurement by neutron stress spectrometer and neutron scattering is carried out during quasi‐static tensile tests. Based on the information at the micro‐ and macro‐scale obtained through these measurements, a molecular‐scale simulation system with different numbers of grain boundaries is established. With the Tersoff potential parameters fitted by Kuopanportti, the change rates of the elastic modulus and yield limit of the steel with different concentrations of hydrogen can be calculated.

Response of TiO2/MWCNT/B2O3 gas sensor to hydrogen using different organic binder

A binder influences the sensitivity, resistivity and optimal operating temperature of a gas sensor, which plays an important role in gas sensing. This work compared the sensitivity of the TiO2/MWCNT/B2O3 gas sensor to hydrogen with the addition of different organic binders, namely linseed oil and ethyl cellulose, to TiO2/MWCNT/B2O3 paste. Both pastes were deposited on alumina substrate using the screen-printing method and annealed at 500 °C. The sensing films of gas sensor, OBL and OBE were characterized by field emission scanning electron microscopy (FESEM), Energy dispersive x-ray (EDX), X-ray diffraction (XRD) Raman Spectroscopy and Brunauer-Emmett-Teller (BET). The gas sensors were also exposed to different concentrations of hydrogen (100–1000 ppm) at various operating temperature (100 °C, 200 °C and 300 °C). The obtained results revealed that ethyl cellulose-based gas sensor achieves better sensitivity, whereas linseed oil-based gas sensor has better conductivity and recovery characteristic.

PO-133 Effects of different concentrations of hydrogen on oxidative stress in rats with high intensity exercise

Objective Exercise-induced oxidative stress is due to the massive increase in free radicals caused by strenuous exercise, which exceeds the ability of self-clearing. It is one of the main causes of sports injury and sports fatigue. Eliminating excessive production of free radicals is the key to alleviating exercise induced oxidative damage. Therefore, the purpose of this study is to study the effect of hydrogen on exercise-induced oxidative damage, to explore its possible mechanism and to explore the best dose of hydrogen with different concentrations.
 Methods 40 male SD rats (200±20g) were randomly divided into five groups(n=8):sedentary, exercise control, low concentration hydrogen with exercise(H1), medium concentration hydrogen with exercise(H2), high concentration hydrogen with exercise(H3). The rats performed high-intensity exercise for 4 weeks, except the sedentary. rats that with Low, medium and high concentration hydrogen were placed in a hydrogen atmosphere with a concentration of 0.5%, 1% and 1.5% for 1 h immediately after each exercise (keeping the concentration of oxygen and nitrogen in the environment the same as those in the air). The rats were weighed weekly during the experiment. The next day after 4 weeks of training, the samples were collected, and the contents of total superoxide dismutase (T-SOD), catalase (CAT), total antioxidant capacity (T- AOC) and malondialdehyde (MDA) were determined respectively.
 Results The weight of exercise control was significantly lower than sedentary in the third and fourth weeks of exercise (P<0.05). Compared to sedentary rats, there was no significant difference in the weight of rats between H1, H2 and H3 group. The contents of T-AOC, CAT and T-SOD in exercise control were significantly higher than those in sedentary (P<0.05). The content of CAT in H2 group was significantly decreased compared with exercise control (P<0.01). Compared with exercise control, the T-AOC and T-SOD in the H2 group showed a downward trend but no statistical difference (P>0.05), there was no significant difference between the above indexes, compared with sedentary. In addition, there was no difference in T-SOD and CAT content between H1 group and exercise control; Compared with exercise control, there was no significant difference in T-SOD, T-AOC and CAT in H3 group. At the MDA level, each exercise group increased significantly compared with the sedentary (P<0.05), and the MDA levels in the H1, H2, and H3 groups were decreased compared with the exercise control, but there was no statistical difference.
 Conclusions It can be seen from the above results that different concentrations of hydrogen intervention can improve the weight loss of rats after intensive exercise. More importantly, the dosage and effect of 1% concentration of hydrogen is easier to remove the excessive radicals produced by intense exercise in the body, avoid the aggravation of oxidative stress, and have very good therapeutic effect. It provides a theoretical basis for the further study of the application of hydrogen in exercise oxidative damage.

Inhalation of Hydrogen of Different Concentrations Ameliorates Spinal Cord Injury in Mice by Protecting Spinal Cord Neurons from Apoptosis, Oxidative Injury and Mitochondrial Structure Damages

Background/Aims: Hydrogen selectively neutralizes reactive oxygen species (ROS) and ameliorates various ROS-induced injuries. Spinal cord injury (SCI) is a serious injury to the central nervous system, and secondary SCI is closely related to excessive ROS generation. We hypothesized that hydrogen inhalation ameliorates SCI, and the mechanism of action may be related to the protective effects of hydrogen against oxidative stress, apoptosis, and mitochondrial damage. Methods: Mechanically injured spinal cord neurons were incubated with different concentrations of hydrogen in vitro. Immunofluorescence staining and transmission electron microscopy were used to confirm the protective effects of hydrogen. ROS and related proteins were detected with dihydroethidium fluorescence staining, enzyme-linked immunosorbent assays, and western blotting. Terminal deoxynucleotidyl transferase dUTP nick end labeling assays, flow cytometry, and western blotting were used to detect neuronal apoptosis. ATP concentrations, Janus Green B staining, and mitochondrial permeability transition pore (mPTP) status were assessed to investigate mitochondrial damage. RNA sequencing was performed to screen potential target genes of hydrogen application. Hydrogen was administered to mice after spinal cord contusion injury was established for 42 days. The Basso Mouse Scale (BMS) and footprint analyses were used to assess locomotor functions, and immunofluorescence staining of the injured spinal cord segments was performed to detect oxidative stress status. Results: Spinal cord neurons were preserved by hydrogen administration after mechanical injury in a dose-dependent manner. ROS generation, oxidative stress injury-related markers, and the number of apoptotic neurons were significantly reduced after hydrogen treatment. The ATP production and mPTP function in injured neurons were preserved by hydrogen incubation. The expression levels of Cox8b, Cox6a2, Cox7a1, Hspb7, and Atp2a1 were inhibited by hydrogen treatment. BMS scores and the footprint assessment of mice with SCI were improved by hydrogen inhalation. Conclusions: Hydrogen inhalation (75%) ameliorated SCI in vivo and attenuated neuronal mechanical injuries in vitro, and its protective effect on spinal cord neurons was exerted in a dose-dependent manner. The underlying mechanisms included reducing ROS generation and oxidative stress, inhibiting neuronal apoptosis, and restoring mitochondrial construction and function. Cox8b, Cox6a2, Cox7a1, Hspb7, and Atp2a1 were identified as potential target genes of hydrogen treatment.

Addressing the selectivity issue of cobalt doped zinc oxide thin film iso-butane sensors: Conductance transients and principal component analyses

Iso-butane (i-C4H10) is one of the major components of liquefied petroleum gas which is used as fuel in domestic and industrial applications. Developing chemi-resistive selective i-C4H10 thin film sensors remains a major challenge. Two strategies were undertaken to differentiate carbon monoxide, hydrogen, and iso-butane gases from the measured conductance transients of cobalt doped zinc oxide thin films. Following the first strategy, the response and recovery transients of conductances in these gas environments are fitted using the Langmuir adsorption kinetic model to estimate the heat of adsorption, response time constant, and activation energies for adsorption (response) and desorption (recovery). Although these test gases have seemingly different vapor densities, molecular diameters, and reactivities, analyzing the estimated heat of adsorption and activation energies (for both adsorption and desorption), we could not differentiate these gases unequivocally. However, we have found that the lower the vapor density, the faster the response time irrespective of the test gas concentration. As a second strategy, we demonstrated that feature extraction of conductance transients (using fast Fourier transformation) in conjunction with the pattern recognition algorithm (principal component analysis) is more fruitful to address the cross-sensitivity of Co doped ZnO thin film sensors. We have found that although the dispersion among different concentrations of hydrogen and carbon monoxide could not be avoided, each of these three gases forms distinct clusters in the plot of principal component 2 versus 1 and therefore could easily be differentiated.

Surface Acoustic Wave Sensors for Hydrogen and Deuterium Detection.

A delay-line-type surface acoustic wave (SAW) sensor based on a zinc oxide (ZnO) sensitive layer was developed. Two types of sensitive layers were obtained: ZnO nanowires and ZnO thin films, both deposited using laser methods (VLS-PLD and PLD, respectively) onto quartz substrates. The responses of sensors with two different nanowire lengths (300 and 600 nm) were compared with those of sensors with thin films of different thicknesses (ca. 100 and 200 nm) to different concentrations of hydrogen and deuterium. The experimental results revealed a high response at low concentrations and a rapid saturated response for nanowires, but a low response at low concentrations and a linear response to much higher gas concentrations for the thin-film-based SAW sensors.