H2 Gas Concentration Research Articles

Thermal decomposition-assisted, aspect ratio controlled ZnO nanorods towards highly selective H2 gas detection

ZnO nanostructures with various aspect ratios have been synthesized for H2 gas detection applications. The thermal-decomposition method was employed at different annealing temperatures (350, 450, and 550 °C) and its impact on various shapes/sizes of ZnO nanostructures is demonstrated. Thermal decomposition performed at 350 °C exhibited a maximum (∼6.25) aspect ratio among them. Its capability of H2 sensing was also observed to be maximum by realizing ∼483% of sensor response at 180 °C under H2 gas concentration of 80 ppm. The sensor response is ∼3 times (∼177%) and ∼9 times (∼53%) higher at ZnO nanostructure synthesized at 350 °C than at 450 °C, and 550 °C, respectively. The higher sensor response has been attributed to the increased availability of active surface area for adsorption/desorption of gas molecules. ZnO@350 nanostructure showed significantly higher selectivity towards H2 gas than other target chemical inputs. We have also studied H2-induced metallization on the surface of ZnO nanostructures which plays an important role for improving the selectivity and sensor response. This study provides insight into the role of aspect-ratio-controlled shape/sized ZnO in improving H2 gas sensing.

Enhanced hydrogen gas sensing performance with Ag-doped WO3 thin film

The paper reports the fabrication of a device, based on the thin film of Ag-doped WO3 nanoparticles, to enhance the hydrogen gas sensing performance. The synthesis of thin films of pristine and Ag-doped WO3 nanoparticles were carried out using the single-step hydrothermal method, followed by the spin coating deposition process. The characterization of the samples was carried out with XRD, FESEM, TEM, FTIR and UV–vis spectroscopy. The consistent pattern observed from the microstructure analysis of data from XRD, UV–vis spectrometer and FTIR validates effective incorporation of Ag into the WO₃ structure. The XRD patterns confirmed the formation of the monoclinic phase of WO3 nanoparticles. The crystallite size and the value of band gap decreased on increasing the Ag doping percentage in WO3. This reduction with Ag-doping could be attributed to the proper substitution of the W with Ag due to their similar sizes. The gas sensing performances of the fabricated sensing devices were analyzed by exposing different concentrations of hydrogen gas ranging from 12.5 ppm to 75 ppm. The device based on the thin film of Ag-doped WO3 performed much better than the device based on the thin film of pristine WO3 nanoparticles. The device with 4% Ag-doped WO3 showed the best sensor response of 98 % for 75 ppm H2 gas concentration with response and recovery time of 76 and 100 s, respectively at 100 °C. The improved response of the device with Ag doping compared to the pristine device could be attributed to the better charge transfer, more defect creation, and the ability of Ag to work as a catalyst to make reaction kinetics faster. The selectivity of the device was tested using the oxidizing and reducing gasses of NO2, H2, and NH3 at 100 °C for 75 ppm gas concentration. The recorded response of the device for NO2, H2, NH3 were 38%, 98%, and 43%, respectively.

Influence of H2 on the properties of NiOxHy thin films deposited by reactive direct current magnetron sputtering for electrochromic devices

This study aims to optimize the deposition condition of Nickel hydroxide (NiOxHy) films for electrochromic devices by adjusting the H2 gas concentration during the reactive direct current magnetron sputtering. The influence of H2 content on the crystallinity, chemical composition, optical properties, and electrochromic behavior of the NiOxHy films was thoroughly investigated. In the absence of H2 gas in the sputtering system, the Nickel oxide (NiOx) film was obtained as confirmed by the X-ray diffraction results. However, introducing the H2 gas resulted in the formation of NiOxHy film, accompanied by a decrease in the film crystallinity. Fourier transform Infrared spectra were employed to confirm the presence of hydroxyl groups in the as-deposited NiOxHy films. X-ray photoelectron spectroscopy was employed to examine the influence of H2 content on the optical properties of the NiOxHy film. Additionally, it offered valuable insights into the film's chemical composition during the transition from a dark to a transparent state. Our findings revealed that increasing the H2 gas content enhanced the transmittance of NiOxHy films. Here, the optimal H2 flow ratio of 50 % was found to yield a high transmittance of 77.43 % (T550) along with the highest charge density, an optical density changed value of 0.84, and a coloration efficiency value of 83.67 cm2/C. These findings clearly illustrate the substantial influence of H2 concentration on the properties of NiOxHy films, particularly in relation to their application in electrochromic devices.

Natural catalysis-based clean hydrogen production from shale oil: An in-situ conversion enabled by electromagnetic heating

Employing electromagnetic(EM)-assisted catalytic heating to produce hydrogen (H2) directly from petroleum reservoirs is an emerging technology for decarbonizing fossil fuel industry. Transforming hydrocarbons to clean H2 in situ will enable pure hydrogen extraction to surface while simultaneously sequestering carbon underground with the assistance of downhole hydrogen membrane separation technology. Here, we aim to characterize the role of shale rocks in enhancing EM heating and catalyzing shale oil conversion to hydrogen as natural catalysts under EM irradiation. Flow-through experiments are well designed and conducted in a customized microwave reactor system. We also identified for the first time that shale rocks exhibit a “thermal runaway” (TR) phenomenon which occurs at a temperature of 280 °C. After TR happens, the energy needed for heating shale samples to a high enough temperature is significantly reduced under EM irradiation. Further, we identified that metal-rich minerals in shale rocks play an evident natural catalytic effect on shale oil conversion to hydrogen. As a result, hydrogen with a percentage of 1 mol.% starts to be generated at a measured temperature of 253–421 °C in the presence of shale rocks and is a dominant gas in the generated gas products at high temperatures. The highest production rate and concentration of H2 gas are 178 sccm and 77 mol.% from the conversion of 0.4 g of shale oil, respectively. Importantly, CO2 generated during the process is negligible. This work lays a foundation for leveraging the abundant shale rocks and their natural catalytic effect for more efficient, cost-effective, in-situ hydrogen production directly from shale reservoir via the EM-assisted catalytic heating technology we recently proposed.

Fixation of air nitrogen to ammonia and nitrate using cathodic plasma and anodic plasma in the air plasma electrolysis method

AbstractThe fixation of nitrogen (N2) from the air into ammonia (NH3) and nitrate (NO3−) is usually conducted using the Haber–Bosch process, which requires the raw material of hydrocarbons for hydrogen (H2), which has a large amount of energy but produces high CO2 emissions. An environmentally friendly and energy‐saving alternative is the air plasma electrolysis method, which can be used to synthesize NH3 and NO3− under ambient conditions. In this study, this method was used to inject air into the plasma zone in a K2SO4 electrolyte solution to produce N2 fixation compounds. The results showed that the use of cathodic plasma promoted the formation of NH3 but suppressed NO3− production. The optimal air injection rate was achieved at 0.6 L.min−1 and an electrical power of 452 W, with a total fixed N2 of 51.66 mmol. The highest formation of NO3− in cathodic plasma was obtained in 35 min, with a value of 29.92 mmol, and 2.57 mmol NH3 was achieved at 60 min. The high concentration of H2 gas, which is a by‐product of this process, can contribute to increasing the use of Haber–Bosch green technology in the production of NH3.

Photoacoustic Spectroscopy-Based Breath Analysis for SIBO.

Breath hydrogen (H2) and methane (CH4) monitoring play an important role in the diagnosis of gastrointestinal disorders, such as lactose intolerance and small intestinal bacterial overgrowth (SIBO). In this paper, the photoacoustic spectroscopy method is used for H2 gas and CH4 gas detection. We present a novel approach for H2 gas concentration measurement, which is the linear relationship between the resonant frequency of breath carbon dioxide (CO2) and the H2 concentration in a resonant photoacoustic cell. Experimental results show that the minimum detectable limits of H2, CH4, and CO2 are calculated to be 8.86, 0.56, and 145.14 ppm, respectively, which can meet the requirements of breath diagnosis.

Preparation of tungsten-doped zinc oxide thin films by co-sputtering for micro-gas sensing devices

Synthesis of a good nanostructure is a vital part in regards to achieving proper gas sensing characteristics. In this study, Tungsten (W) doped ZnO nanostructure is synthesized on micro electro mechanical systems (MEMS) device by co-sputtering process. Appropriate doping concentration to the sensing material is crucial for sensing properties, therefore, 5 different doping concentrations ranging from 0% W to 4% W to the ZnO structure are developed. The structural properties of all the W doped ZnO samples were characterized by Scanning electron microscope (SEM), X-Ray diffraction (XRD) analysis and Energy-dispersive X-ray spectroscopy (EDS) analysis. Sensing properties were calculated with different concentrations of H2 gas ranging from 20 ppm to 100 ppm. All of the W doped ZnO sensors were tested for H2 gas at working temperatures varying from 100 °C to 300 °C to detect the optimal doping concentration and optimal working temperature. At 150 °C, 3% W doped ZnO revealed 67% gas sensing response for 100 ppm H2 gas. Selectivity test with 5 different gases displayed that W doped ZnO sensor has good selectivity over H2 gas at 150 °C.

Thermoelectric Detection of H2 Gas Based on Exothermic Absorption by Pd

The thermoelectric hydrogen (H2) gas sensor using PCB (Printed Circuit Board) technique was developed based on the exothermic absorption of H2 by a palladium (Pd) film coated on a thermocouple. A cascade connection of two thermocouples composed of copper (Cu) and constantan (55% nickel and 45% Cu) was used to detect the exothermic absorption of H2 by Pd. The differential thermoelectric voltage output between the two thermocouples (with and without the Pd film) increased linearly with the H2 gas concentration in a 2.0–50 vol% ambient atmosphere. Standard deviations (SD) for 8 measurement cycles are typically 1.1% at 4 vol% H2, 0.81% at 6 vol% H2, and 1.9% at 8 vol% H2, respectively. The differential thermoelectric voltage output can be detected from 2.0 vol% H2 atmosphere. The ambient temperature fluctuations on the measurement was also effectively reduced using the cascade connection of two thermocouples. Calibration line of H2 concentration calculated by the least square method is linear and standard error (SE), 0.44 vol%, is smaller than measured value.

Nanostructured Diamond Composites for Multifunctional Sensing Applications

We report studies of multifunctional, nanostructured diamond composites that were fabricated using chemical vapor deposition (CVD) techniques. Grain sizes from micrometer, to submicron, nano, and ultrananocrystalline diamond (UNCD) were controlled by varying CH4, hydrogen, and argon gas concentrations during the syntheses. Scanning electron microscopy (SEM) and Raman scattering spectroscopy were used to investigate the morphologies, composites, and crystallinities of the films. Four multifunctional sensor prototypes were designed, fabricated, and tested, based on the four diamond materials of different grain sizes. The responses of the four prototypes to either pollution gas or UV light illumination were systematically investigated at different operating temperatures. Experimental data indicated the obtained UNCD composite from the low-cost simple CVD fabrication technique appeared to have very good sensitivities when exposed to low concentrations of H2 or NH3 gas with a decent response and fast recovery time. Furthermore, highly induced photocurrents from both microdiamond- and UNCD-based prototypes to deep UV illumination were also demonstrated, with responsivities up to 2750 mA/W and 550 mA/W at 250 nm wavelength, respectively. Overall, the fabricated UNCD prototypes displayed a good balance in performance for multifunctional sensor applications in terms of responsivity, stability, and repeatability.

Effect of Voltage Source Differences on Hydrogen Gas Production by Electrolysis-photocatalysis Reactor Systems

We have evaluated the process of watersplitting into hydrogen gas. Electrolysis-photocatalysis reactor is used to harvest hydrogen gas through water splitting, a combination of electrolysis and photocatalysis reactions. The concentration of hydrogen gas (H2) is detected by the MQ-8 sensor and the number of bubbles is calculated. Evaluation of watersplitting is done by varying the DC voltage source (3V, 6V, 9V, 12V). We found the highest concentration of H2 gas was produced at 12 volts 616300 ppm for 600 seconds, The largest increase from the photocatalyst-electrolysis reaction combination was found to be 182017 ppm. Here we observe a linear increase in hydrogen with increasing voltage which results in a faster electrolysis process. But what is most interesting is the increase in H2 during the simultaneous electrolysis-photocatalysis process. the combined reaction has increased the amount of hydrogen greater than the sum of the photocatalytic and electrolysis reactions taking place separately. It is most likely that a mutually reinforcing reaction occurs so that the overall activation energy of the system becomes smaller in the process of dissociating water into hydrogen.

TiO2–CU Thin Film Material for Optical Hydrogen Gas Sensor Applications

Purpose: Several scientific researches are underway to investigate the possibility of using various green energies. Hydrogen gas is a candidate of such research, since its use as a fuel in automobiles releases pure water, a recyclable biproduct. But, the leakages of the gas are detrimental to its application due to its low auto ignition energy of 20 μj, wider air flame limit of 4-75 % and high flame velocity of 3.46 ms-1. This study involved fabrication of an optical gas sensor for sensing the leakage levels of hydrogen gas to a surrounding.
 Methodology: Titanium dioxide thin films of thicknesses 47.7, 56.2, 82.3, 100.4 and 120.5 nm were deposited on both microscope and FTO glass slides using DC magnetron sputtering technique and characterized as primate and annealed at 400 and 500oC. Copper (Cu) catalytic layers of 5.6, 10.2, 17.3 and 21.0 nm were deposited using EDWARDS AUTO 306 Magnetron sputtering system on an optimized 100.4 nm TiO2 sample, annealed at 400oC. Optical properties were deduced from transmittance and absorbance spectra measured using 1800 Shimadzu spectrophotometer in the optimum range of 280-800 nm through simulation. The optical behavior of the films was generated using SCOUT software and analyzed using ORIGIN 9.1 64-bit software.
 Results: The energy band gap decreased with material thickness from 4.2±0.05 eV for 47.7 nm film to 3.9±0.05 eV for 100.4 nm films. 120.5 nm films showed higher energy gap of 4.0±0.05 eV. Transmittance decreased with increase in thickness probably due to agglomeration of film particles. The energy gap of the 100.4 nm, TiO2 thin films annealed at 400oC was 3.9±0.05 eV. This is a material quality of the anatase phase. The copper surface layer increased absorption in the higher wavelength region. The energy band gaps were reduced from 3.9 to 3.8±0.05 eV with increased coverage. Self-limiting at 17.3 nm copper overlayer realized increased energy gap to 4.1±0.05 eV. A lower energy band gap range of 3.9-3.8±0.05 eV was realized when FTO substrates were used. The transmittance decreased with increased H2 gas concentration. The optical energy gap reduced from 4.1±0.05 eV in 0 ccm to 3.9±0.05 eV in 50 ccm of hydrogen gas concentration. The sensitivity increased from 0.3 % in 0ccm to 3.9 % in 50 ccm hydrogen gas concentration. An average sensitivity of 2.0 % was realized for films fabricated on FTO substrate. This is higher than 1.7 % reported earlier. The material gas sensing potential was done at room temperature. The fabricated sensor material showed higher sensitivity and lower temperature operation and is furthermore, expected to be cheaper and safer
 Unique Contribution to Theory, Policy and Practices: Though, in order to realize a more portable stand-alone gas sensor, an investigation on an ideal photon type source that incorporates the material is recommended. Further, extension of this study on structure and morphology of the film is essential to understand its sensing behavior.

Localized Liquid Zones Assisted Highly Crystalline Single-Wall Carbon Nanotube Sheets: Implications for Conducting Shields in Coaxial Cables

The electrical conductivity of carbon nanotube (CNT) macro assemblies can be influenced by their crystallinity. Herein, we present the synthesis of high-quality SWCNT sheets for which an appropriate optimization parametric research of synthesis temperature, precursor flow rate, and H2 flow rate was carried out in this approach. It was found that highly crystalline SWCNT sheet (IG/ID = 180.3) was synthesized by floating catalyst chemical vapor deposition technique at 12 mL/h precursor flow rate and 1000 sccm H2 flow rate. Three distinct Raman laser wavelengths (514, 532, and 785 nm) were used to study the as-synthesized sheet, and the maximum calculated IG/ID ratio was found to be 180.3 (@ λ = 514 nm). Due to high concentration of H2 gas, the number of localized liquid zones or CNT nucleation sites increased which has an impact on both the quality as well as the diameter of CNTs. The I–V characteristics of CNT sheet were studied via four-probe technique, yielding a measured value of electrical conductivity of 9.21 × 106 S/m. Further, the R-T measurement showed the positive temperature coefficient up to the 108 K which indicates the metallicity of as produced CNT sheets. These highly conducting SWCNT sheets are the best solution for a wide range of applications in many fields, including conducting shields in coaxial cables, flexible and nano scale electrical and electronic devices, displays, biosensors, field-effect transistors and gas sensing materials.

Hydrogen gas sensing feature of polypyrrole nanofibers assisted by spinel ZnMn2O4 microspheres in dynamic conditions

In this report, spinel ZnMn2O4 microspheres (ZMO) were synthesized via a hydrothermal method. Then nanocomposites based on DBSA doped-Polypyrrole nanofibers assisted by various wt% of ZMO (PZMs) have been synthesized by a chemical polymerization method. The results showed the formation of microspherical morphology for the tetragonal phase of the ZMO, and the decoration of the ZMOs with DBSA doped-Polypyrrole nanofibers in the nanocomposites with high specific surface area and porosity. The H2 gas sensing properties of the PZMs films were investigated under different concentrations of H2 gas at room temperature, ambient pressure (1 atm), and relative humidity (35%) for the first time. The results showed as the wt% of metal oxide increased from 5 to 30%, the gas sensing response decreased from 1.32 to 1.09, while tres increased from 108 to 143 s, respectively, toward 15,000 ppm H2 gas. A sample with 5 wt% ZMO (PZM5) showed not only the best response and tres between the samples at dynamic conditions but also excellent long-term stability after 6 months with about 3% variation than the initial experiment. Different percentages of humidity presented a change (1.3–11.3)% in the results of gas sensing response at H2 gas different concentrations. The suitable response and tres at dynamic situations along with significant long-term stability and good selectivity offer our hand-made sensing layers as a reliable device for H2 gas sensing with a broad-wide application. Finally, the possible mechanism of the H2 sensing in the PZMs was discussed in detail.

Effects of H2/N2 on CO2 hydrate film growth: Morphology and microstructure

The addition of small-molecules gases such as H2/N2 can significantly improve CO2-CH4 hydrate replacement efficiency. However, the physical/chemical mechanism behind this phenomenon is not completely clear. Since CO2-CH4 hydrate replacement is the sequential process of CH4 hydrate decomposition and CO2 hydrate reformation, the microscopes and Raman spectroscopy were combined to clarify the effects of H2/N2 gas on CO2 hydrate film growth. The experimental results showed that H2 gas significantly affected the initial morphology, thickening and compactness of CO2 hydrate films. With the increase of H2 gas concentration, the size of the initial single hydrate crystal increased, the granulation phenomenon weakened, and hydrate films became rougher after thickening. Raman experiments showed that the presence of H2 made the CO2 hydrate film looser, which was conducive to the sustainability of hydrate growth. However, their growth rates did not change monotonously with the H2 concentration. We consider that H2 played roles in reducing the local CO2 gas concentration, slowing down the CO2 supply rate to the reaction interface, and delaying the time of the gas pores being blocked by further formed CO2 hydrate. N2 gas could also play the similar roles as H2 gas, however, due to its participation in CO2/N2 mixed hydrate formation, the growth of hydrate film changed adaptively. The results obtained are not only important for understanding the mechanism of CH4 hydrate replacement by CO2 and small molecule mixed gas, but also referential for other hydrate technologies involving mixed hydrate formation.

Chemically controlled megasonic cleaning of patterned structures using solutions with dissolved gas and surfactant

Acoustic cavitation is used for megasonic cleaning in the semiconductor industry, especially of wafers with fragile pattern structures. Control of transient cavitation is necessary to achieve high particle removal efficiency (PRE) and low pattern damage (PD). In this study, the cleaning performance of solutions with different concentrations of dissolved gas (H2) and anionic surfactant (sodium dodecyl sulfate, SDS) in DIW (DI water) on silicon (Si) wafers was evaluated in terms of PRE and PD. When only DIW was used, PRE was low and PD was high. An increase in dissolved H2 gas concentration in DIW increased PRE; however, PD also increased accordingly. Thus, we investigated the megasonic cleaning performance of DIW and H2-DIW solutions with various concentrations of the anionic surfactant, SDS. At 20 ppm SDS in DIW, PRE reached a maximum value and then decreased with increasing concentration of SDS. PRE decreased slightly with increasing concentrations of SDS surfactant when dissolved in H2-DIW. Furthermore, PD decreased significantly with increasing concentrations of SDS surfactant in both DIW and H2-DIW cases. A high-speed camera setup was introduced to analyze bubble dynamics under a 0.96 MHz ultrasonic field. Coalescence, agglomeration, and the population of multi-bubbles affected the PRE and PD of silicon wafers differently in the presence of SDS surfactant. We developed a hypothesis to explain the change in bubble characteristics under different chemical environmental conditions.

Development and investigation of the flexible hydrogen sensor based on ZnO-decorated Sb2O3 nanobelts

Hydrogen is regarded as the next-gen fuel for vehicles to avoid the emission of toxic gases, which needs a continuous monitoring of the concentration level. In the design of the H2 sensor, especially of flexible type, a sensing layer will be blended, which affects the sensing performance of the device. Based on this concern, the present investigation is carried out to understand the effect of the bending angle toward the sensing performance of bare and ZnO (n-type)-decorated Sb2O3 (p-type) nanobelt–based sensors for hydrogen gas. The sensing element was prepared by the thermal chemical vapor deposition followed by the drop-casting method. Furthermore, the role of the zinc precursor (molar concentration—1 M–3 M) on the preparation of ZnO-decorated Sb2O3 nanobelts was studied. Various techniques were used to confirm the formation of ZnO-decorated nanobelts such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), and Fourier transform infrared spectroscopy (FTIR). From these analyses, 1 M concentration of the zinc precursor shows uniform distribution of nanoparticles over the surface of Sb2O3 nanobelts. However, agglomeration was observed when the concentration of the zinc precursor increases from 1 M to 3 M. Later, the prepared nanobelts were deposited on the OverHead Projector (OHP) sheet by the doctor blade method for sensing hydrogen gas at 100 °C at a concentration of 1000–3000 ppm. In addition to it, the effect of the substrate bending angle (0°, 45°, 60°, and 90°) was analyzed at a fixed concentration of H2 gas (1000 ppm). From this study, it is clear that the highest sensing response was achieved for 1 M decorated nanobelts compared with bare as well as other concentrations because of uniform distribution of nanoparticles on the surface of nanobelts. Moreover, the prepared sample demonstrates better sensing performance with the bending of substrates, which suggests that the prepared sensor could be used for flexible electronic devices. The prepared nanobelts show a good H2 gas–sensing response even with bending of the substrates. The work suggests that the prepared sensor is applicable for flexible electronic devices.

Generation of high-pH groundwaters and H2 gas by groundwater–kimberlite interaction, northeastern Ontario, Canada

ABSTRACT We report new isotopic data for H2 and CH4 gases and Sr for groundwater collected from Jurassic Kirkland Lake kimberlites in northern Ontario, Canada. Groundwaters interacting with kimberlites have elevated pH (up to 12.4), are reducing (Eh as low as the H2-H2O couple), are dominated by OH− alkalinity, and have non-radiogenic (mantle) 87Sr/86Sr values (∼0.706–0.707). Most significantly, the highest pH groundwaters have low Mg, high K/Mg, and are associated with abundant reduced gases (H2 ± CH4). Open system conditions favor higher dissolved inorganic carbon and CH4 production, whereas under closed system conditions low DIC, elevated OH− alkalinity, and H2 production are enhanced. Hydrogen gas is isotopically depleted (δ2HH2 = −771 to −801‰), which, combined with δ2HH2O, yields geothermometry temperatures of serpentinization of 5–25 °C. Deviation of H2-rich groundwaters (by up to 10‰) from the meteoric water line is consistent with Rayleigh fractionation during reduction of water to H2. Methane is characterized by δ13CCH4 = −35.8 to −68‰ and δ2HCH4 = −434‰. The origin of CH4 is inconclusive and there is evidence to support both biogenic and abiogenic origins. The modeled groundwater–kimberlite reactions and production of elevated concentrations of H2 gas suggest uses for diamond-production tailings, as a source of H2 for fuel cells and as a carbon sink.

Anodic Performance of BaO-Added Ni/SDC for Solid Oxide Fuel Cell Fed With Dry CH4

SOFCs fed with dry H2 and CH4 fuels were examined using 20 wt% Ni/SDC and 0.2 wt% BaO-added 20 wt% Ni/SDC [Ni(BaO)/SDC] anodes. The i–v characteristics of the cells in H2 and CH4 resulted in a higher output produced by CH4 fuel compared to that produced by H2 fuel in both anodes. In both fuels, better anode characteristics were obtained for Ni(BaO)/SDC. Consequently, the anodic performance was in the order of Ni(BaO)/SDC in CH4 > Ni/SDC in CH4 > Ni(BaO)/SDC in H2 > Ni/SDC in H2. A significant carbon deposition was observed in the Ni/SDC anode in CH4, but the carbon deposition observed in Ni(BaO)/SDC was less. From the DC electrical resistance measurement of the anode films, a remarkable decrease in resistance was observed in Ni/SDC due to the carbon deposition after CH4 exposure. The resistance of Ni(BaO)/SDC was higher than that of Ni/SDC and did not change even after CH4 exposure because of the less carbon deposit. The high dispersibility of Ni particles was confirmed in both anodes and was particularly remarkable in Ni(BaO)/SDC. The highest anodic performance in Ni(BaO)/SDC was attributed to the high Ni dispersibility which might promote CH4 decomposition by producing less carbon deposit. It was speculated that the higher cell output in CH4 than that in H2 is due to the locally high concentration of H2 and/or CO gas on the anode surface by the promotion of CH4 decomposition.

Controlled Megasonic Cleaning of Patterned Structures Using Solutions with Dissolved Gas and Surfactant

Acoustic cavitation is used for megasonic cleaning in the semiconductor industry, especially of wafers with fragile pattern structures. Control of transient cavitation is necessary to achieve high particle removal efficiency (PRE) and low pattern damage (PD). In this study, the cleaning performance of solutions with different concentrations of dissolved gas (H2) and anionic surfactant (sodium dodecyl sulfate, SDS) in DIW (DI water) on silicon (Si) wafers was evaluated in terms of PRE and PD. When only DIW was used, PRE was low and PD was high. An increase in dissolved H2 gas concentration in DIW increased PRE; however, PD also increased accordingly. Thus, we investigated the megasonic cleaning performance of DIW and H2-DIW solutions with various concentrations of the anionic surfactant, SDS. At 20 ppm SDS in DIW, PRE reached a maximum value and then decreased with increasing concentration of SDS. PRE decreased slightly with increasing concentrations of SDS surfactant when dissolved in H2-DIW. Furthermore, PD decreased significantly with increasing concentrations of SDS surfactant in both DIW and H2-DIW cases. A high-speed camera setup was introduced to analyze bubble dynamics under a 0.96 MHz ultrasonic field. Coalescence, agglomeration, and the population of multi-bubbles affected the PRE and PD of silicon wafers differently in the presence of SDS surfactant. We developed a hypothesis to explain the change in bubble characteristics under different chemical environmental conditions.

Sensitive H2 gas sensors based on SnO2 nanowires

Sensitive H2 gas sensors are highly desirable for the prediction and early-warning of H2 leakage. Low-dimensional nanostructures of metal oxide semiconductor emerge as promising materials candidates, but it remains a challenge to preserve the nanostructures in the real sensors. In this work, we demonstrated highly sensitive H2 gas sensors based on porous network of SnO2 nanowires that exhibited ultrasmall diameter ∼ 2 nm. Colloidal SnO2 nanowires synthesized via a solvothermal process were drop-coated onto the commercial alumina substrates, followed by in-situ annealing treatment at 350 °C to remove the surface ligands. The sensors exhibited sensitive response with linear dependence on the H2 gas concentration ranging from 2 ppm to 100 ppm when operated at 250°C. Typically, the sensor had a response of 13 toward 40 ppm of H2, with the response and recovery time being 15 s and 31 s, respectively. To further improve the sensor performance, Palladium doped SnO2 nanowires were thoroughly investigated. It’s shown that, the operating temperature of the sensor decreased from 250 °C to 150 °C after Pd doping, and the response and recovery time decreased to 6 s/3 s. The superb sensitivity was attributed to the enhanced gas reception, electron transport as well as utility factor owing to the network nanostructure of ultrathin SnO2 nanowires and catalytic activity of Pd, according to theoretical calculation and adsorption kinetics studies. Combined with the excellent solution processability, the colloidal SnO2 nanowires are potentially attractive for next-generation gas sensors with lower power consumption and integration with silicon-based substrates.