Small Hydrogen Bubbles Research Articles

Effect of a pre-deposited Ni layer on the hydrogen evolution performance of an electroplated Ni–P/CFP composite catalyst in acidic media

In this work, we studied the effect of a pre-deposited Ni layer on the hydrogen evolution performance of Ni–P composite catalysts in acidic media. To elucidate the effect of the pre-deposited Ni layer, pristine Ni–P/carbon fiber paper (CFP) and Ni–P/Ni/CFP composite catalysts were prepared. As a result, the Ni–P/Ni/CFP with a pre-deposited Ni layer had a 21.7% lower overpotential (141 mV) at −10 mA cm−2 than a Ni–P/CFP composite catalyst (180 mV) in 0.5 M H2SO4 solution. This was because the electrochemical surface area and P ratio at the surface of Ni–P/Ni/CFP (2.38 m2 g−1 and 30.26 at%) are 13.2% and 5.4 at% higher than those of the pristine Ni–P/CFP catalyst (1.79 m2 g−1 and 24.87 at%), respectively. Furthermore, the more porous morphology of Ni–P/Ni/CFP could facilitate the effective removal of the produced hydrogen bubbles, leading to the minimized fluctuation of the hydrogen production rate by providing a sufficient surface area for the detachment of small hydrogen bubbles.

Tailoring electrochemical efficiency of hydrogen evolution by fine tuning of TiOx/RuOx composite cathode architecture

Here we report an approach to design composite cathode based on TiOx nanotubes decorated with RuOx nanowhiskers for efficient hydrogen evolution. We tailor catalytic activity of the cathodes by adjustment of morphology of TiOx nanotubular support layer along with variation of RuOx loaded mass and assess its performance using electrochemical methods and wavelet analysis.The highest energy efficiency of hydrogen evolution is observed in 1 M H2SO4 electrolyte to be ca. 64% at −10 mA/cm2 for cathodes of the most developed area, i.e. smaller diameter of tubes, with enhanced RuOx loading. The efficiency is favored by detachment of small hydrogen bubbles what is revealed by wavelet analysis and is expressed in pure noise at wavelet spectrum. At increased current density, −50 or −100 mA/cm2, better efficiency of composite cathodes is supported by titania nanotubes of larger diameter due to an easier release of large hydrogen bubbles manifested in less periodic events appeared in the frequency region of 5–12 s at the spectra.We have shown that efficiency of the catalysts is determined by a pre-dominant type of hydrogen bubble release at different operation regimes depending on specific surface and a loaded mass of ruthenia.

Experimental study and mathematical modeling of two phase flow with a Eulerian approach in a continuous gas evolving electrochlorinator

Electrochlorination systems have become popular. Their hydrodynamic behavior affects the efficiency and power consumption but the reaction environment is complex due to the complex flow arising from gas evolution at the electrodes. Water reduction at the stainless steel cathode generates a large amount of small hydrogen bubbles being then, the only evolving gas at the electrodes that can modify the flow pattern inside the reactor. (Cl2(g) generated at anode is rapidly hydrolyzed into hypochlorous acid or hypochlorite ion). This paper considers the hydrodynamic behavior of the two-phase flow using experimentally and modeled RTD curves, via a weakly coupled Euler-Euler model. Experimental data are in a qualitative agreement with the RTD model.

Modified Surface Activated Bonding Using Si Intermediate Layer for Bonding and Debonding of Glass Substrates

The Liquid Crystal (LC) displays using ultra-thin glass substrates of under 100 µm thick are necessary to realize the next generation display devices including the touch screen of the mobile phone, the tablet electronics and the flexible display. However, the ultra-thin glass substrates are easily deformed and damaged during the display process such as the color filter, LC and Thin Film Transistors (TFTs) at 350-550°C. Therefore the handling of the ultra-thin glass substrates in the process is a key issue for the limitation of the thickness of the display devices. In these days, in order to realize the thin display devices, the glass thinning process by chemical etchant such as HF is widely employed for the fabrication process. In this method, thick and rigid glass substrates are used during the LC display process not to deteriorate the handling quality. After assembling and sealing process, the fabricated displays are immersed in HF and thinned to the target thickness. Although this method has been successfully developed, HF is very toxic and a big environmental load. Therefore, an alternative method to handle the ultra-thin glass substrates without HF process is desirable for the display fabrication. As an alternative method to the glass thinning method, the handling by the carrier glass is has been proposed. The carrier glass is popular way to handle thin and fragile substrates in manufacture and it will enable the handling of the ultra-thin glass substrates in the process and realize the thinner display devices than by the current process without HF. In order to use the carrier glass, the ultra-thin glass should be bonded to the carrier glass and the bonding needs to be endurable for the high temperature process of TFT. Additionally, the ultra-thin glass must be released from the carrier glass after the fabrication process. However, there is no suitable method to bond the glasses and debond after high temperature process. For example, the indirect bonding method such as the adhesive glue cannot keep the bonding during high temperature process and the residue of the adhesive after debonding becomes a problem for the process and the quality of the display. The direct bonding methods like thermal compression bonding and hydrophilic bonding are successfully employed in the manufacturing process of electronics, however, the bond strength is so high that the debonding without mechanical damage to the glass substrates is not possible especially after high temperature process. In this study, we proposed applying Surface Activated Bonding (SAB) method to the bonding and debonding of the glasses for the fabrication of LC display. In the SAB method, the bonding surfaces are activated by Ar ion beam and bonded by atomic force in high vacuum at room temperature. Recently, the SAB method succeeded in bonding of glass using Si intermediate layers of under 20 nm thick which are deposited on the bonding surfaces by ion beam sputtering, nevertheless, the bond strength is too high to debond. In this case, we changed the conventional SAB method using Si layers for glass and controlled the bond strength before after heating. The Si layer was formed on one side of the glass surface in the contrary to the conventional SAB form the Si layers on the both side of the bonding surfaces. After deposition of Si, the bonding surfaces were exposed to nitrogen gas and bonded in vacuum. The bond strength was evaluated by blade insert test and was around 0.9 J/m2. The bonding endured heating at 350-550°C for 90 min and the bond strength after heating was around 0.5 J/m2. The bond strength by this method decreased after heating, whereas generally the glass bonding gets stronger after heating by the other direct bonding method. The decrease of the bond strength enables an easy debonding after the high temperature process in the display fabrication. The small voids can be seen in the bonding interface and this is the reason why the bond strength is controlled. It is indicated that the small voids are derived from water and OH groups on the bonding surfaces that were formed during the exposure to nitrogen gas, and the decomposed OH groups formed the small hydrogen bubbles after heating as a similar process to hydrophilic bonding. In this study, we succeeded in bonding the glass substrates and controlling the bond strength to achieve an easy debonding for the display fabrication. This technique will realize the thinner display devices than by current manufacturing method and reduce the environmental load.

Interaction of Bubbles with Vortex Ring Launched into Bubble Plume

This study is concerned with an experimental exploration for the interactions of bubbles with a vortex ring launched vertically upward into a bubble plume. A vortex ring launcher, composed of a cylinder and a piston, is mounted at the bottom of a water tank. Small hydrogen bubbles are released into still water from a cathode, which is wound around the cylinder outlet, by the electrolysis of water. The bubbles rise by the buoyant force and induce a bubble plume. The water in the cylinder is discharged into the bubble plume by the piston, resulting in a laminar vortex ring convecting along the central axis of the plume. Just after the launch of the vortex ring, the bubbles are spirally entrained into the vortex ring with the roll up of the shear layer. The void fraction within the vortex ring increases with the convection of the vortex ring until a certain displacement of the vortex ring, where the reduction occurs. The vortex ring convects with a constant velocity higher than that in still water. The entrained bubbles reduce the strength of the vortex ring.

Nano Al2O3/phosphate Composite Conversion Coating Formed on Magnesium Alloy for Enhancing Corrosion Resistance

Novel nano Al2O3/phosphate composite conversion coatings with no visible defects were formed on AZ91D magnesium alloy in a phosphate solution containing Al2O3 nanoparticles by applying a magnetic field. The formation of these coatings was investigated using the synchrotron radiation real-time imaging technique. The coatings’ surface morphology, chemical composition and structure were examined by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). Scanning vibrating electrode (SVET) and polarization curves were employed to evaluate their corrosion resistance in NaCl solution. The results show that the superposition of a magnetic field during the coating formation process can promote the generation of small hydrogen bubbles and accelerate their desorption, which favors the embedding of Al2O3 nanoparticles in the amorphous matrix. In the absence of a magnetic field, hydrogen bubble evolution could be one of the main reasons for the development of microdefects in phosphate conversion coatings. This defective phosphate conversion coating is amorphous and contains no Al2O3 nanoparticles, although the phosphate solution contains Al2O3 nanoparticles. The results demonstrate that the nano Al2O3/phosphate composite conversion coating obtained using a magnetic field exhibits better corrosion resistance than defective phosphate conversion coatings obtained without a magnetic field.

Mechanism of gas bubble shoot-off and motion during spark discharge in liquid

The conditions of the excitation of a pulsed plasma discharge on the surface of a processed metal (copper) sample immersed in a conducting aqueous solution have been studied. Cathode polarization of the metal was provided by a high-voltage capacitor bank (4μF) charged to U = 200–1100 V after each discharge. It is established that electric breakdown with a duration not exceeding 0.1 μs is always preceded by the formation of small hydrogen bubbles (with radii r ≈ 37–40 μm) on the polarized metal surface, which takes about 139–159 μs. A mechanism of passivation of the processed metal surface by these hydrogen bubbles, which are synchronously shot off from the electrode surface under the action of the spark discharge, is proposed. Consistent matching of the experimental data and model calculations is used to estimate the main parameters determining the kinetics of bubble detachment from the electrode surface at various voltages U on the capacitor bank.

Three-Dimensional Vortex Method for the Simulation of Bubbly Flow

This study proposes a three-dimensional vortex method for the simulation of bubbly flow. The method discretizes the vorticity field by vortex elements. The behavior of the vortex element and the bubble motion are simultaneously analyzed with the Lagrangian approach to compute the time evolution of the flow. This study also applies the vortex method to the simulation of a bubble plume to demonstrate the validity of the method. In a tank containing water, small hydrogen bubbles are released from the bottom of the tank. The bubbles rise due to the buoyant force and induce the water flow around them. The simulation for the plume at the starting period highlights that the rising bubbles induce large-scale eddies at their top and that the bubbles are entrained into the eddies. The simulation for the developed plume demonstrates that large-scale eddies appear around the rising bubbles and that they cause the meandering behavior of the plume. Such three-dimensional features of the bubble plume are favorably compared with the experimental results, indicating the validity of the proposed vortex method.

Numerical simulation of plane bubble plume by vortex method

This study is dealing with the two-dimensional numerical simulation of a plane bubble plume experimentally investigated by Alam and Arakeri. A vortex method for gas—liquid two-phase flow, proposed by the authors in a prior paper, is applied for the simulation. The method simulates the bubble motion and the induced liquid flow by the two-way coupling approach. In a tank containing water, small hydrogen bubbles are released from an electrode placed on the base of the tank. The bubbles, rising due to the buoyant force, cause the vortical flow of water. The existing numerical methods, such as the finite-difference method and the finite-volume method, compute the bubble plume with regard to the velocity field. But the vortex method calculates directly the vorticity field. Therefore, it promises to simulate successfully the vortical structure predominating the bubble plume. The present simulation makes clear that the meandering behaviour of bubble plume is caused by the large-scale eddies induced by the rising bubbles. The effect of bubble flowrate on the meandering behaviour in the simulation is confirmed to agree well with the experiment. It is also demonstrated that the time-averaged water velocity on the horizontal sections satisfies the similarity distribution when the bubble flowrate is low. These indicate that the authors’ vortex method is indeed applicable to the analysis of plane bubble plume.

Dissolution of hydrogen and the ratio of the dissolved hydrogen content to the produced hydrogen in electrolyzed water using SPE water electrolyzer

Concentration of dissolved hydrogen in electrolyzed water using a solid polymer electrolyte (SPE) water electrolyzer was investigated using a DH-meter. A ratio of the dissolved hydrogen content to an amount of hydrogen concentration calculated from charge passed during electrolysis was estimated. The ratio increased from 10 to 20% with a decrease in current density from 3.0 to 0.3 A dm −2. The effect of the linear velocity of water on the ratio of dissolved hydrogen was studied. The cross-sectional area of the water channel was changed to change the linear velocity of water. The ratio of dissolved hydrogen increased with increasing the velocity. Due to the fast mass transport by high velocity, the small hydrogen bubbles are fast transferred by the diffusion into the bulk water and dissolved. The population density of the small hydrogen bubbles is found to have an effect on the ratio of the dissolving hydrogen.

Conversion of hydrogen bubbles to disk-shaped defects in hydrogen irradiated aluminum

Electron microscopy was carried out on hydrogen bubbles in high purity aluminum. It was found for the first time that small hydrogen bubbles formed by irradiation with 15 keV hydrogen ions at 423 K converted to disk-shaped defects by annealing at higher temperature, depending on the initial concentration of bubbles. The many beam lattice image of the defects suggested that they mostly lay over multiple layers of (111) planes, containing characteristic distortions of the lattice on (111) planes. The formation of the disk-shaped defects is interpreted in terms of small hydrogen bubble coalescence during a random migration and collapse on (111) planes, losing their internal pressure, which may be allowed by the formation of aluminum hydride at high temperature.

Determination of hydrocarbons in sea water using an electrolytic stripping cell.

A stripping cell is described which can be used to analyze and to measure partition coefficients of hydrocarbons in sea water. Small hydrogen bubbles evolved electrolytically from a gold electrode are allowed to rise up a cylindrical cell containing a known amount of sea water. The dissolved hydrocarbons in the sea water are equilibrated with the hydrogen bubbles. The hydrocarbon concentration in the head-space is determined by gas chromatography. The partition coefficient and hydrocarbon concentration in the sea water are determined from the volume of sea water and the hydrocarbon concentration in the headspace after a given volume of hydrogen has bubbled through the cell.

Fluid line growth in grid-generated isotropic turbulence

Fluid material line growth in turbulent flow has been measured by tagging lines with small hydrogen bubbles in the nearly isotropic turbulence behind a regular grid in a water tunnel. The average three-dimensional line lengths were inferred by an intersection-counting method carried out on one-plane photographs. The measurements cover ‘small’ time intervals only.

A Study on the Flow Visualization by the Hydrogen-Bubble Method.

In the investigations of both the steady and unsteady flow in turbomachines, it has been found to be highly successful to visualize the flow in ducts and around the bodies. Recently W. Clutter and O. Smith have presented a suitable technique for flow visualization using small hydrogen-bubbles produced by electrolysis of the working water itself. According to their experiments, unfortunately the method was not applied to the flow with higher velocity than about 0.6m/sec. In order to observe the stream lines flowing at about 5∼8m/sec in an axial-flow type testing water compressor, the authors improved the electric source and the working liquid in the hydrogen-bubble method, and developed several new probes which are inserted into the stream as cathodes for the electrolysis process and which consist of a straight or kinked platinum wire and fork-type brass stem. In a small water tunnel having a test section 60×200 mm and two observation windows on each side, direct current of high tension (2000volts) was charged between the probe and the tunnel duct and thereby the lines of hydrogen-bubbles generated from the probe wire were visible fairly well even in the higher velocity stream of about 7m/sec. Further, using the above mentioned method, some photographs of the rotating stalls occurring in the testing water compressor were taken successfuly as was expected.