Hydrogen Gas Flow Research Articles

Ligand-Linked Nanoparticles-Based Hydrogen Gas Sensor with Excellent Homogeneous Temperature Field and a Comparative Stability Evaluation of Different Ligand-Linked Catalysts.

This paper presents a thermoelectric gas microsensor with improved stability where platinum nanoparticles linked by bifunctional ligands are used as a catalyst. The sensor design provides a homogeneous temperature field over the membrane, an important factor for the long-term stability of the catalyst. A comprehensive study of heat transfer from the chip is performed to evaluate the convection heat loss coefficient and to understand its effect on the homogeneity of the temperature field in a real-time situation. The effect of highly heat-conductive thermopiles is also analyzed by comparing the temperature distribution and power consumption with a thermoresistive sensor of the same dimensions and materials. Despite the thermopiles, the thermoelectric sensor gives better temperature homogeneity and consumes 23% less power than the thermoresistive sensor for 90 °C average temperature on the membrane. A comparative stability analysis among ligand-linked nanoparticles with 5 different ligands and unprotected nanoparticles was done through 3 consecutive 24 h tests under 1.5% continuous hydrogen gas flow. The sensors give very stable output, almost no degradation, through 72 h (3 × 24 h) tests for 3 different ligand-linked nanoparticles. The sensor design provides superb stability to the catalyst: Even catalysts of unprotected nanoparticles withstood more than 24 h and the sensor signal degradation is only 20%.

Investigation of the performance of 248 nm excimer laser assisted photoresist removal process in gaseous media by response surface methodology and artificial neural network

Photoresist removal by Excimer laser in different gaseous media viz., hydrogen, helium, argon, nitrogen and air is studied under different parameters viz., laser pulse energy, pulse repetition frequency (PRF) and gas flow rate. Totally 180 experiments (36 experiments for each gaseous medium) were conducted based on the full factorial design. Statistical analysis of data by 3way ANOVA (ANalysis Of VAriance) was carried out to investigate the main effects on photoresist removal process. Photoresist removal rate is observed to be significantly higher in case of hydrogen gas medium compared to other gaseous media studied. Hence, another 48 set of experiments (based on full factorial design) was carried out in hydrogen gas medium. These experimental data were used for modeling the photoresist removal process. Three key operating parameters (i.e. laser energy, pulse repetition rate and hydrogen gas flow rate) were selected as independent variables, and the amount/depth of photoresist removed was considered as the dependent variable (response). Response Surface Methodology (RSM) and Artificial Neural Network (ANN) models were developed based on the experimental design approach to predict etch depth. The predictive capacity of the two models was compared. Analysis of the results showed that the operating parameters can also influence each other’s optimum value. Higher photoresist removal rate observed in hydrogen medium may be attributed to possible Laser Assisted Chemical Reaction (LACR) of hydrogen gas with photoresist polymer. A mechanism has been proposed to explain the interaction of hydrogen molecule with photoresist during the laser irradiance, resulting in generation of hydrogen radicals, which may subsequently undergo additional bond-breaking process of olefinic functional groups (having π bond), along with laser bond breaking process. To the best of the author’s knowledge, this is the first study providing information of LACR of hydrogen gas with photoresist polymer, resulting in higher photoresist removal rate. The LACR of hydrogen gas with photoresist polymer, being a cold process, has potential application in semiconductor industry, where researchers are trying to exploit the process of photoresist removal using hydrogen radical generated at 2000 °C by tungsten hot wire.

Influence of Hydrogen Flow Rates Annealing on the Structural, Optical, and Electrical Properties of Sol-Gel Synthesized Fe doped In2O3 Films

Diluted magnetic semiconductors (DMSs) have always been of great interest to study due to their wide applications in spintronics. This research was carried out to study the influence of different hydrogen gas flow rates annealing on the physical properties of Fe doped indium oxide. In1.92Fe0.08O3 thin films were prepared by a sol-gel method and followed by a spin coating technique. Different flow rates of hydrogen gas were applied during the annealing process. All samples showed high orientation along the (222) direction and exhibit a polycrystalline structure. Grain size increased as the flow rate increased due to the stronger reduction of H2. FTIR studies showed the existence of an O-H bond in the range of 3000 - 4000 cm-1 and it was caused by the flow of H2 gas during the annealing process. The resistivity of In1.92Fe0.08O3 thin films decreased and the carrier concentration increased with increasing hydrogen flow rates. This work has significance on the size-dependent properties and the chemical bonding in Fe doped In2O3 films.

Numerical Study on Characteristics of High-Pressure Hydrogen Gas Flow in a Critical Nozzle

Numerical Study on Characteristics of High-Pressure Hydrogen Gas Flow in a Critical Nozzle

Effect of magnetic field on the synthesis of carbon nanotubes using MPECVD

CNT production is limited by issues regarding CNT growth and morphology. Due to this, further studies on experimental factors regarding CNT production are needed to optimize CNT production in a commercial scale. This study focuses mainly on the determination of the effects of the presence of a magnetic field during CNT synthesis in a Microwave Enhanced Plasma Chemical Vapor Deposition (MPECVD) process using a Whirlpool AVM585 conventional microwave oven. The study also determined the effects of hydrogen catalyst plasma pretreatment on CNT growth. The experiment was based on a Taguchi orthogonal array design. The effects of the experimental factors such as magnetic field strength (0, 5, and 10 mT), catalyst pretreatment time (10, 15, and 20 min), hydrogen gas flow rate (25, 50, and 75 mL/min), and microwave power (451, 570, and 740 W) on the responses such as the catalyst nanoparticle Feret diameter, CNT diameter, tortuosity, weight, and purity were investigated. Among the design factors, application of magnetic field at 10 mT improved all the responses, most notably the CNT diameter and tortuosity being reduced by 60% and 48% compared to runs with no magnetic field, respectively. Under tortuosity, magnetic field was the design factor which had the greatest effect on decreasing the tortuosity of the CNTs at around 100 times the effect measured under other design factors. Catalyst plasma pretreatment was most optimal at the highest hydrogen flow rate and microwave power setting, under the influence of the highest magnetic field strength. The effects of the factors during catalyst plasma pretreatment also resulted to improved characteristics of the CNTs during the CNT synthesis. Overall, the findings suggest that the application of a magnetic field during catalyst plasma pretreatment and the subsequent CNT synthesis results to catalyst nanoparticles and CNTs with improved properties such as lower catalyst nanoparticle Feret diameter, CNT diameter, tortuosity and higher CNT yield and purity.

Chemical vapor deposition growth of sub-centimeter single crystal WSe2 monolayer by NaCl-assistant

Monolayer WSe2 exhibits unique optical and electronic properties, showing great potential applications in functional integrated devices, such as electronic devices and optoelectronics. Understanding the growth behavior and process are the key points for the salt-assisted growth of large domain WSe2 monolayers, it is also very important for its further application in on-chip laser and opto-devices. Here, we report a NaCl-assistant method for controlled growth of single crystal monolayer WSe2 with a domain size up to 0.57 mm on SiO2/Si substrate. Atomic-resolution scanning transmission electron microscopy reveals that the Se1 and Se2 vacancy point defects are the main defect type of those materials. The growth behavior of the salt-assisted method have been systemly investigated. The loading mass of NaCl powder prefers to be less with the controllable vapor process. The flow of hydrogen gas was also preferred to be suitable with a weak etching effect. The morphology of monolayer WSe2 shows a sensitive temperature dependence evolution with the growth temperature increasing. A screw dislocation growth behavior with 15° angle is also observed with the NaCl-assistant method. The results provide a deep understanding of the mechanism for the NaCl-assistant growth of large size monolayer WSe2.

Optical Emission Spectroscopy Study of Ar–H2 Plasma at Atmospheric Pressure

In this paper, Ar–H2 plasma is studied by the nonintrusive optical emission spectroscopy method. The emission spectra of excited species of hydrogen and argon are observed and measured. The effect of an increase in hydrogen gas flow in the Ar–H2 plasma is studied experimentally. The variation in peak intensity and broadening of $\text{H}_{\alpha }$ line with increased hydrogen gas flow rates is examined. It is noticed that the peak intensity of $\text{H}_{\alpha }$ line is very sensitive to hydrogen gas flow rate while the broadening of the line is found to be constant. The broadening of $\text{H}_{\alpha }$ line is observed to be a Lorentzian profile. In addition to this observation, the electron temperature was computed using Boltzmann’s plot method. It is learned that the theoretical and the experimentally evaluated electron densities are not in close agreement with each other. Therefore, the estimation of electron density from the electron temperature will not always be a reliable method in the case of such atmospheric plasma. The saturation effect of electron density and the quenching of Ar I emission lines are also observed and discussed.

Unsupported Pt3ni Aerogels As High Stability Catalysts for PEFC Anodes Under Fuel Starvation Conditions

In polymer electrolyte fuel cells (PEFCs), both anodic and cathodic Pt/C catalysts suffer from significant corrosion of the carbon support during the high potential excursions (> 1 V vs. the reversible hydrogen electrode) concomitant to PEFC operation, which limit the device’s service life. Therefore, further cost reductions could be achieved using catalysts with higher durability, also allowing lower Pt loadings. In this respect, anode catalysts with high stability in cases of gross hydrogen starvation events constitute a pressing need. The latter fuel starvation events are caused by the blockage of the hydrogen gas flow in an anode flow field by water droplets, leading to anode potential increases from ≈ 0 V to ≥ 1.5 V.1 At these potentials, significant corrosion of the carbon support in commercial Pt on carbon black (Pt/CB) catalysts and concomitant performance decreases have been reported.2 Motivated by our previous study, in which an unsupported Pt3Ni aerogel demonstrated remarkable corrosion stability as a PEFC cathode catalyst,3 in this work, the applicability of the former material on the anode side was investigated. Pt3Ni aerogel catalyst was synthesized according to the steps described in reference 4, and commercial Pt/CB (47 wt% Pt, TKK, TEC10E50E) and Pt on graphitized carbon black (Pt/GCB, 30 wt% Pt, TKK, TEC10EA30E) catalysts were used as benchmarks. The hydrogen starvation events were simulated by an accelerated stress test (AST) performed at 80°C, 100% RH, ambient pressure, and H2 / N2 flows of 100 ml/min at cathode and anode, respectively. Under these conditions, 250 potential cycles in a square wave voltammetry pattern between 0 and 1.5 V with a holding time of 10 s at each potential were applied to the anode side (Figure 1). Figure 2 shows polarization curves of membrane electrode assemblies (MEAs) utilizing Pt3Ni aerogel, Pt/CB or Pt/GCB as anode catalysts (with loadings of ≈ 0.05 mgPt/cm2 anode) at beginning and end-of-life (BOL, EOL). The agreement of the BOL data indicates that the performance attained with the aerogel CLs is identical to that obtained with the commercial benchmark catalyst. Interestingly, the AST caused a large performance deterioration for the MEA using Pt/CB or Pt/GCB at the anode, whereas the cell using Pt3Ni was not affected at all. The reasons for the former degradation were investigated using electrochemical impedance spectroscopy and hydrogen pump tests to decouple the overpotential contributions to the materials’ BOL and EOL performance. Figure 2 displays the hydrogen oxidation/evolution polarization curves recorded in these H2-pump experiments, whereby the measured potential was corrected for the cell resistance (R). H2-pump polarization curves in Figure 3A recorded on the Pt3Ni aerogel at BOL and EOL almost completely overlay, indicating minimal kinetic and/or mass transport losses. On the other hand, the overall potential increased for Pt/CB and Pt/GCB (Figures 3B and 3C). The EOL polarization curves for Pt/CB and Pt/GCB deviate from the purely kinetic response derived from the fitting to the Butler-Volmer equation at current densities above 0.5 A/cm2 (see insets in Figures 3B and 3C), pointing at significant mass transport limitations by the end of the AST. To understand the reason for the profound increases in ηtx,anode of Pt3Ni, Pt/CB and Pt/GCB anodes, their catalyst layer structure was investigated by scanning ion microscopy and compared to that of the initial state (Figure 4). For the images of Pt3Ni catalyst surfaces, no change was observed. On the other hand, the Pt/CB and Pt/GCB catalysts at EOL were collapsed and became dense compared to their initial structure, thereby explaining the poor gas transport in the catalyst layers. Ultimately, this approach leads to the conclusion that the majority of the performance losses are related to changes in the anodic CL mass transport properties. It also illustrates the superiority of the Pt3Ni aerogel vs. Pt/CB and Pt/GCB as a PEFC anode catalyst. Acknowledgement This work was carried out in the Electrochemistry Laboratory of Paul Scherrer Institute and funded by the Swiss National Science Foundation (20001E_151122/1), the German Research Foundation (EY 16/18-1) and the European Research Council (ERC AdG 2013 AEROCAT). References 1) P. Rodriguez, T.J. Schmidt, Encyclopedia of Applied Electrochemistry, Springer New York, New York, NY, 1606(2014). 2) J. Speder, A. Zana, I. Spanos, J.J.K. Kirkensgaard, K. Mortensen, M. Hanzlik, M. Arenz, J. Power Sources 261, 14(2014). 3) S. Henning, J. Herranz, H. Ishikawa, B.J. Kim, D. Abbott, L. Kühn, A. Eychmüller, T.J. Schmidt, J. Electrochem. Soc. 164, F1136(2017). 4) S. Henning, L. Kühn, J. Herranz, J. Durst, T. Binninger, M. Nachtegaal, M. Werheid, W. Liu, M. Adam, S. Kaskel, A. Eychmüller, T.J. Schmidt, J. Electrochem. Soc. 163, F998(2016). Figure 1

Surface Modification of Short Carbon Fibers with Carbon Nanotubes to Reinforce Epoxy Matrix Composites.

The homogeneous carbon nanotubes (CNTs) directly grown on short cut carbon fibers (CFs) surface by chemical vapor deposition (CVD) using iron nanoparticles as catalyst. The iron nanoparticles were obtained by the reduction of magnetite particles using mixed nitrogen and hydrogen gas flow at 415 °C. Magnetite particles were prepared through a solvothermal reaction, where iron(III) acetylacetone as catalyst source and polylol as solvent. CNTs grown on CFs were used as reinforcement in epoxy (EP). The effects of density of CNTs grown on CFs (CNTs-CFs) and different mass fractions of CNTs-CFs in EP on the composites flexural strength were investigated. Results indicate that the reaction of iron(III) acetylacetone can synthesize magnetite particles of ca. 10 nm coated on CFs only in triethylene glycol (TREG) or polyethylene glycol 200 (PEG200). When CNTs grown on CFs surfaces at catalyst source concentration of 1.5 mmol/L, the flexural strength of CNTs-CF/EP composites with the addition of 0.8 wt% CNTs-CFs was improved by 28.1% to 102.5 MPa compared to that of pure EP. The homogeneous CNTs grown on CFs enhanced interfacial bonding are responsible for the improvement of composites flexural strength.

On-site SiH4 generator using hydrogen plasma generated in slit-type narrow gap

We have been developing an on-site silane (SiH4) generator based on use of the chemical etching reaction between solid silicon (Si) and the high-density H atoms that are generated in high-pressure H2 plasma. In this study, we have developed a slit-type plasma source for high-efficiency SiH4 generation. High-density H2 plasma was generated in a narrow slit-type discharge gap using a 2.45 GHz microwave power supply. The plasma’s optical emission intensity distribution along the slit was measured and the resulting distribution was reflected by both the electric power distribution and the hydrogen gas flow. Because the Si etching rate strongly affects the SiH4 generation rate, the Si etching behavior was investigated with respect to variations in the experimental parameters. The weight etch rate increased monotonically with increasing input microwave power. However, the weight etch rate decreased with increasing H2 pressure and an increasing plasma gap. This reduction in the etch rate appears to be related to shrinkage of the plasma generation area because increased input power is required to maintain a constant plasma area with increasing H2 pressure and the increasing plasma gap. Additionally, the weight etch rate also increases with increasing H2 flow rate. The SiH4 generation rate of the slit-type plasma source was also evaluated using gas-phase Fourier transform infrared absorption spectroscopy and the material utilization efficiencies of both Si and the H2 gas for SiH4 gas formation were discussed. The main etch product was determined to be SiH4 and the developed plasma source achieved a SiH4 generation rate of 10 sccm (standard cubic centimeters per minute) at an input power of 900 W. In addition, the Si utilization efficiency exceeded 60%.

Efficient and Scalable Photo-Electrochemical Device for Solar Fuel Generation Working Under Concentrated Irradiation

A literature review of demonstrations for photo-electrochemical hydrogen production suggests that interesting solar-to-fuel efficiencies can be obtained by integrating expensive III-V and rare earth elements as photoabsorbing and catalytic materials. Aiming just at high solar-to-fuel efficiency at the expense of low electrochemical current densities is of little use for practical device implementations, particularly for these expensive and high performing materials. The challenge for these photo-electrochemical device demonstrations is to achieve higher operating current densities while maintaining high efficiencies. A close thermal and electronic integration of the photoactive and electrochemical component allows to achieve this goal. Here, we report on the successful experimental demonstration of an integrated photo-electrochemical device employing concentrated solar irradiation and smart thermal management strategies in order to achieve a solar-to-hydrogen efficiency as high as 17.2% along with an electrochemical current density of 900 mA/cmEC 2 and a photovoltaic current density of 6.04 A/cmPV 2. The implemented device (figure 1.a) incorporates a solid ionic conductor as the separator between anode and cathode. The ionic conductor is a nafion 115 membrane which is coated on one side with IrO2 and on the other side with Pt black. The membrane electrode assembly is sandwiched between a Pt coated Ti mesh (a gas diffusion layer) and the custom made Ti bipolar flow plates. The anodic Ti plate is designed with a stage for the direct integration of the photovoltaic (PV) component. The device additionally incorporates a steel plate with a glass window which acts as a channel for the reactant (water), which is guided directly on top of the PV part. This removes any excess heat from the PV, pre-heats the reactant and directly feeds it to the EC part, allowing to benefit the device performance by reducing the PV’s temperature while increasing the electrocatalysis temperature. The device has been tested in our high flux solar simulator facitlity1 (shown in Fig. 1b), which simulates concentrated irradiation homogeneously over an area as large as 20mm by 20 mm. The photoactive area is 4cm2 and the electrocatalytically active area is 25 cm2. The device has been tested in integrated mode for varying concentrations, ranging between 117 and 474 kW/m2. At all these concentrations, a steady state performance was recorded for about 10 minutes and the output hydrogen gas flow was measured, using a combination of water traps (to dry the output stream) and precision flowmeters. The measured, dry hydrogen flow rates correspond to a solar-to-hydrogen efficiency of 17.2%, one of the highest efficiencies ever reported, at an electrochemical current densities up to 900 mA/cmEC 2. Additionally, we have demonstrated one of the highest output power devices (in terms of hydrogen equivalent) for photo-electrochemical production of hydrogen. The dynamic response and stability testing (for ~2 hours) has shown that the implemented device can perform efficiently under varying conditions and for long periods of time. The implemented device opens a new pathway towards scalable and large-scale deployment of photo-electrochemical water splitting. The prototype validates the results of our previously developed 2D multi-physics model 2,3 and demonstrates an efficient and cost effective way of solar hydrogen processing.

Entropy Generation through the Interaction of Laminar Boundary-Layer Flows: Sensitivity to Initial Conditions

A modified form of the Townsend equations for the fluctuating velocity wave vectors is applied to the interaction of a longitudinal vortex with a laminar boundary-layer flow. These three-dimensional equations are cast into a Lorenz-format system of equations for the spectral velocity component solutions. Tsallis-form empirical entropic indices are obtained from the solutions of the modified Lorenz equations. These solutions are sensitive to the initial conditions applied to the time-dependent coupled, non-linear differential equations for the spectral velocity components. Eighteen sets of initial conditions for these solutions are examined. The empirical entropic indices yield corresponding intermittency exponents which then yield the entropy generation rates for each set of initial conditions. The flow environment consists of the flow of hydrogen gas with impurities at a given temperature and pressure in the interaction of a longitudinal vortex with a laminar boundary layer flow. Results are presented that indicate a strong correlation of predicted entropy generation rates and the corresponding applied initial conditions. These initial conditions may be ascribed to the turbulence levels in the boundary layer, thus indicating a source for the subsequent entropy generation rates by the interactive instabilities.

Formation of Poly-Si Films on Glass Substrates by Using Microwave Plasma Heating and Fabrication of TFT’s on the Films

We have developed an apparatus for producing high-density hydrogen plasma. The atomic hydrogen density was 3.0 × 1021 m?3 at a pressure of 30 Pa, a microwave power of 1000 W, and a hydrogen gas flow rate of 5 sccm. We confirmed that the temperatures of tungsten films increased to above 1000?C within 5 s when they were exposed to hydrogen plasma formed using the apparatus. We applied this phenomenon to the selective heat treatment of tungsten films deposited on amorphous silicon films on glass substrates and formed polycrystalline silicon films. To utilize this method, we can perform the crystalline process only on device regions. TFTs were fabricated on the polycrystalline silicon films and the electron mobilities of 60 cm2/Vs were obtained.

Highly self-diffused Sn doping in α-Fe2O3 nanorod photoanodes initiated from β-FeOOH nanorod/FTO by hydrogen treatment for solar water oxidation.

In this study, we present an advanced strategy of low-temperature hydrogen annealing combined with high- temperature quenching in air for activating α-Fe2O3 nanorod photoanodes to boost the photoelectrochemical performance. We report that various low-temperature annealing conditions (340, 360, 380, and 400 °C) under hydrogen gas flow convert β-FeOOH into magnetite (Fe3O4) as well as introduce Sn4+ diffusion from FTO substrates to its surface. Furthermore, high-temperature quenching (800 °C) resulted in the phase change of magnetite (Fe3O4) into hematite (α-Fe2O3) and self Sn4+ doping into the hematite lattice. Thus, the hydrogen-assisted thermally activated hematite photoanode achieved a photocurrent density of 1.35 mA cm-2 at 1.23 V vs. RHE and 1.91 mA cm-2 at 1.4 V vs. RHE, which is 70% and 80% higher than that of directly quenched hematite at 800 °C. These combined two step strategies provide new insight into high Sn-self doping for α-Fe2O3 photoanodes and allow for further development of more efficient solar water oxidation systems.

Cobalt Deposition in Graphene Quantum Dot Bath: Electrochemical and Spectroscopic Features: A Prospective Sensor Material

We have demonstrated here that graphene quantum dots (GQD) bind to cobaltous ion giving it a flowery structure. As a result of this binding the cyclic voltammetric peak potential shows a cathodic shift with reference to unbound cobaltous ion. From the electrochemical data, it is estimated that Co2+ is hexa coordinated with GQD to form the bound species. The electrochemical reduction of cobaltous ion is carried out using four baths. A spectrophotometric examination of aquo cobaltic solution shows a characteristic maximum at 508 nm that is absent when cobaltous ion is in GQD bath. Co composite has been galvanostatically deposited on metal substrates. Fourier transform infrared spectroscopy (FTIR) of Co bound GQD shows distinct peaks at 3246(broad) cm−1, 2089 cm−1, 1639 cm−1, 1392 cm−1, 1274 cm−1, 1099 cm−1, 536 cm−1 that can be attributed to Co-C stretching and C-C stretching. The thermogravimetric analysis (TGA) of the composite shows that it is thermally stable from decomposition up to 600°C. The energy dispersion analysis (EDAX) of the deposited Co shows the presence of carbon and cobalt at 0.25 keV and 7.0 eV respectively. The electrochemically deposited graphene composite responds rapidly to a flowing hydrogen gas stream.

Exergetic performance comparison of air and hydrogen gas flowing through the annular curved duct

The main objective of this study is to parametrically compare the exergetic performance of air and hydrogen gas flow through the curved annular duct. For this purpose, it is assumed that, i) air and hydrogen are considered to be ideal gas, ii) the flow of these gases is steady state and laminar fully developed, ii) these gases have constant physical properties, iii) the channel inner and outer walls are exposed to constant wall boundary condition. Moreover, the following important parameters are taken into consideration: i) aspect ratio (four different values which are 5.50, 3.80, 2.90 and 2.36), ii) environment temperature (ranging from −30 to 30 with 10 °C intervals), iii) Dean number (varying between 24 and 208), and iv) operating pressure (=1 atm). Considering these parameters, exergy destruction and exergy efficiencies are calculated for each aspect ratio. Consequently, exergetic efficiency rises with the increase of Dean number, inner wall temperature, aspect ratio and the decrease of dead state temperature. Also, it is noticed that the gas specie highly affects the volumetric entropy generation rate, exergy destruction rate and exergy efficiency.

Effect of Intrinsic Layer Energy Gap and Thicknesses Optimization on the Efficiency of p-i-n Amorphous Silicon Solar Cell

morphous silicon solar cells with single p-i-n layer were grown on 10 cm 2 ITO coated glass substrates. Fabrication process done by using 13.56 MHz RF-Plasma Enhanced Chemical Vapor Deposition (PECVD). Hydrogen flow on the deposition process is widely known to enable the passivation of the dangling bond on Silicon bonds. The passivation of dangling bond affects the band gap of each layer and cell performance in the absorption of photon. In the deposition process of intrinsic layer, SiH 4 gas flow is set constant at 2.5 sccm, while variation is done in hydrogen gas flow at 0 sccm – 90 sccm. Energy gaps obtained for p-layer and n-layer are 2.0 eV and 2.2 eV at thickness 64 nm and 36 nm respectively. Optimizations have been done for intrinsic layer which band gaps are 1.4 eV, 1.6 eV and 1.9 eV at thickness 400 nm. The solar cell efficiency was increased from 4.8% to 5.64% based on the band gaps variety. In addition, i-layer thicknesses were also varied from 400 nm, 500 nm and 600 nm. Thicknesses variation shows an increase of 5.78% in the solar cell efficiency.

Modulation Effects of Hydrogen on Structure and Photoluminescence of GaN Nanowires Prepared by Plasma-Enhanced Chemical Vapor Deposition

Gallium nitride (GaN) nanowires (NWs) were grown on Si(100) substrates at different hydrogen gas flow rates, using plasma-enhanced chemical vapor deposition. The size and morphology of the GaN NWs could be modulated by controlling the hydrogen atmosphere. The diameters of the GaN NWs ranged from 53 to 221 nm, and their morphology transformed from a hexagonal prism to a triangular pyramid upon changing the hydrogen atmosphere conditions. The modulation effects originated from the competitive equilibrium between surface and interfacial diffusion induced by hydrogen in the vapor–liquid–solid growth mechanism. The photoluminescence spectra of the different GaN NWs may have originated from two metabolic peaks, which were closely related to their nanostructures. These findings provide a simple and convenient method to modulate the structure of GaN NWs and may further the application of GaN in nano-optoelectronic devices.

Experimental and statistical optimization of the hydrogen reduction process of nickel oxide

ABSTRACTReduction of nickel oxide (NiO) by hydrogen gas is an affordable and simple way in comparison with the other chemical methods to produce and retrieve the pure nickel powder. Properties of the reduced Ni powder are dependent on many parameters such as the temperature, holding time, and hydrogen gas flow. The main reported mechanism of hydrogen reduction contains the decomposition of the oxide into gas-state phases and then condensation of the product supersaturated vapor. In the present work, experimental investigation and statistical optimization of these effective parameters on the nickel oxide hydrogen reduction were performed according to Taguchi’s experimental design and related statistical analyses. The produced powder was characterized by oxygen elemental analyses, scanning electron microscopy, and X-ray diffraction. The results showed that the temperature affects the reduction rate of nickel oxide to a significant extent, and the optimized conditions for desirable powder reduction and morphology were determined as 900°C of temperature, 60 min for holding time, and 300 cc/min of gas flow. Finally, a regression equation was derived based on the experimental results, which can predict the reduction rate for each combination of the parameters in the studied range.

Influence of hydrophobic surface treatment toward performance of air filter

This study investigated the performance of hydrophobic surface treatment by using silica aerogel powder via spray coating techniques. Hydrophobic properties were determined by measuring the level of the contact angle. Meanwhile, performance was evaluated in term of the hydrogen gas flow and humidity rejection. The results are shown by contact angle that the microstructure filter, especially in the upper layer and sub-layer has been changed. The results also show an increase of hydrophobicity due to the increased quantity of silica aerogel powder. Results also showed that the absorption and rejection filter performance filter has increased after the addition of silica aerogel powder. The results showed that with the addition of 5 grams of powder of silica aerogel have the highest result of wetting angle 134.11°. The highest humidity rejection found with 5 grams of powder of silica aerogel.