Generated Hydrogen Bubbles Research Articles

Hydrogen bubble management in planarly confined aqueous electrolyte: Fundamental factors for scale-up reactor design

Solar photoelectrochemical water-splitting is a potential process for producing renewable hydrogen. Here, the energy transport phenomena associated with hydrogen bubble generation are investigated for the future design of large-scale reactors. Light transfer analysis shows that using a thin aqueous-electrolyte layer is essential for utilizing the full spectrum of solar radiation. The hydrogen bubble flow needs to be redirected to avoid screening the photoelectrode from incident light. Hence, a bubble flow guide for controlling the stream of bubbles in a planarly confined aqueous electrolyte has been proposed. It is found that the surface wettability and inclination angle are important for designing an effective bubble flow guide. The hydrophilic coating on a polymethyl methacrylate surface inhibits bubble adhesion and reduces energy loss. Furthermore, measuring the electrode potential variation during water electrolysis is useful for comparing the performances of bubble flow guides.

Dual-Mode Imaging of Dynamic Interaction between Bubbles and Single Nanoplates during the Electrocatalytic Hydrogen Evolution Process.

Gas bubble formation at electrochemical interfaces can significantly affect the efficiency and durability of electrocatalysts. However, obtaining comprehensive details on bubble evolution dynamics, particularly their dynamic interaction with high-performance structured electrocatalysts, poses a considerable challenge. Herein, dual-mode interference/total internal reflection fluorescence microscopy is introduced, which allows for the simultaneous capture of the evolution pathway of bubbles and the 3D motion of nanoplate electrocatalysts, providing high-resolution and accurate spatiotemporal information. During the hydrogen evolution reaction, the dynamics of hydrogen bubble generation and their interactions with single nanoplate electrocatalysts at the electrochemical interface are observed. The results unveiled that, under constant potential, bubbles initially manifest as fast-moving nanobubbles, transforming into stationary microbubbles subsequently. The morphology of stationary nanoplates regulates the trajectories of these moving nanobubbles while the pinned microbubbles induce the motion of the electrocatalysts. The dual-mode microscopy can be employed to scrutinize numerous multiphase electrochemical interactions with high spatiotemporal resolution, which can facilitate the rational design of high-performance electrocatalysts.

Visualization of Hydrogen Bubbles Using Synchrotron X-Ray CT inside Porous Transport Layer of Direct Toluene Electro-Hydrogenation Electrolyzers

Toluene is a highly versatile solvent commonly used in many industries due to its high energy density and effective hydrogen carrier properties. It can store a considerable amount of hydrogen in a relatively small volume, making it a promising hydrogen carrier for various applications. Toluene's high volumetric energy density also makes it one of the best hydrogen carriers available. Additionally, toluene is easy to handle and transport as it is a liquid at room temperature, and it can be stored and transported like any other liquid fuel. Furthermore, toluene is a safer alternative for hydrogen storage compared to other hydrocarbons due to its low toxicity.Direct toluene-electro hydrogenation electrolyzer is a promising method that enables the simultaneous performance of water electrolysis and toluene hydrogenation in a single system. However, during the toluene direct electrolytic hydrogenation process, the formation of hydrogen bubbles from the electrolysis of water hinders the toluene hydrogenation reaction, leading to a reduced conversion rate of methylcyclohexane (MCH) and Faraday efficiency.In this study, we aimed to understand the conditions for hydrogen bubble generation and transport. We quantitatively evaluated the generation amount and distribution of hydrogen bubbles by visualizing them in an operating electrochemical cell using Synchrotron X-ray CT. Figure 1 displays the distribution of hydrogen bubbles along the porous transport layer (PTL) of the electrochemical cell. These bubbles were visualized using the raw images obtained from Spring-8 and subsequently reconstructed. The cell was operating at a current density of 200 mA/cm2 for a period of 30 minutes with pure water supplied to the anode side. Darker areas in the images indicate regions with hydrogen bubbles, which have a lower density and atomic weight than other substances in the PTL. Therefore, they are more transparent to X-rays and appear darker in the image. Higher current values and longer operation times led to increased hydrogen bubble generation, with a significant increase observed at 30 minutes. By visualizing these hydrogen bubbles, we were able to evaluate the generation distribution, amount, and transport of hydrogen, which can help improve the direct toluene-electro hydrogenation electrolyzer system. Acknowledgement This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References Nagasawa K, Sugita Y, Atienza-Márquez A, Kuroda Y, Mitsushima S. Effect of the cathode catalyst loading on mass transfer in toluene direct electrohydrogenation. Journal of Electroanalytical Chemistry 2023:117431. https://doi.org/10.1016/J.JELECHEM.2023.117431.Shigemasa, A. Atienza-Márquez, K. Inoue, S. Jang, F. Reyna-Peña, T. Araki, “Visualization of dragged water and generated hydrogen bubbles in a direct toluene electro-hydrogenation electrolyzer,” J. Power Sources 2023; 554:232304. https://doi.org/10.1016/j.jpowsour.2022.232304.Nagasawa, A. Kato, Y. Nishiki, Y. Matsumura, M. Atobe, S. Mitsushima, “The effect of flow-field structure in toluene hydrogenation electrolyzer for energy carrier synthesis system. Electrochemical Acta 2017; 246:459-65. https://doi.org/10.1016/j.electacta.2017.06.081. Nagasawa, K. Tanimoto, J. Koike, K. Ikegami, S. Mitushima, “Toluene permeation through solid polymer electrolyte during toluene direct electro-hydrogenation for energy carrier synthesis”, Journal of Power Sources, Vol.439, (2019) 22707. https://doi.org/10.1016/j.jpowsour.2019.227070. Figure 1 SPring-8 CT Visualization Reconstructed image after 30 minutes of operation at 200 mA/cm². Figure 1

Relationship between Bubble Generation Behavior and Hydrogen Evolution Performance at High Current Densities during Alkaline Water Electrolysis

Introduction Alkaline water electrolysis (AWE) has attracted considerable attention as a method to produce hydrogen. However, one of the problems with AWE is the increase in overpotential, which is attributed to bubbles covering the electrode surface at high current densities. Therefore, it is important to understand the bubble generation behavior to develop strategies for reducing the overpotential. In this study, we observed bubble generation behavior on Platinum (Pt) electrodes using a high-speed camera [1] and conducted electrochemical measurements to investigate the relationship between the current density/electrode potential and bubble generation behavior. Experiments Pt wires with diameters of 200 μm were used as the working electrodes. The reference and counter electrodes were a reversible hydrogen electrode (RHE) and Ni rods with a diameter of 3 mm, respectively. All measurements were conducted using a three-electrode electrochemical cell with a 2 M KOH aqueous solution as the electrolyte at 303±1K. To minimize the solution resistance, the working and reference electrodes were positioned as close as possible to each other, with a separation distance of approximately 2 mm. To ensure a uniform current-density distribution, a Ni-rod counter electrode was inserted on both sides of the cell. Observation windows were installed on the sides of the cells. Only a 3-mm parallel section of the working-electrode wire was exposed to the electrolyte to observe the electrolytic reaction, while the rest of the wire was covered with PTFE heat-shrink tube and epoxy resin. After appropriate pretreatment, cyclic voltammetry (CV) measurements were performed at a scan rate of 5 mV s-1 to obtain the polarization curves. Electrochemical impedance spectroscopy (EIS) measurements were conducted at −0.2 to −0.8 V vs. RHE with a potential amplitude of 10 mV, over a frequency range of 3×105 to 1 Hz, where 60 repeated measurements were performed for each frequency. The solution resistance was obtained from Cole–Cole plots and corrected for potential losses. The current density (i geo / A cm-2) was normalized by the geometric surface area of the cylindrically shaped working electrode. Constant current electrolysis was performed under twelve conditions of i geo = −0.05 to −1.5 A cm-2. Under each condition, the formation behavior of hydrogen bubbles was photographed using a high-speed video camera. Results and discussion Figures 1 and 2 show the polarization curves at the cathode and anode, respectively [2]. The overvoltage increased with i geo, as evidenced by the shift of the polarization curves from Tafel slope, in the range of −i geo ＜ 0.9 A cm−2 at the cathode and in the range of i geo > 0.6 A cm−2 at the anode. Figure 3 shows Cole–Cole plots obtained at i geo = −1.0 A cm−2 at the cathode and Figure 4 shows Cole–Cole plots obtained at i geo = 1.0 A cm−2 at the anode [2]. Figure 5 shows the hydrogen bubble generation behavior obtained at i geo = −1.0 A cm−2 at the cathode, and Figure 6 shows oxygen bubble generation behavior obtained at i geo = 1.0 A cm−2 at the anode [2]. The Cole–Cole plots indicate the resistance component on the low-frequency side at high current densities in addition to the charge transfer resistance. Moreover, the arc shapes of the resistance components differ between the anode and cathode, suggesting that different mechanisms are responsible for the increase in the overvoltage at high current densities. We believe that these resistances arise from reactant transfer limitations due to the hydrogen and oxygen bubble layers covering the electrode surfaces. Moreover, it was also confirmed that the charge-transfer resistance is inversely proportional to the current density, indicating that the effective electrode surface area does not change over a wide range of current densities. By comparing Figures 5 and 6, it was observed that oxygen bubbles at the anode where a larger overvoltage increase than cathode was measured had larger diameters and were less likely to detach from the electrode. Furthermore, the bubble layer formed on the electrode surface was thicker on the anode than on the cathode. Acknowledgements Part of this study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in the Advancement of Hydrogen Technologies and Utilization Project (JPNP14021), commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Temperature impacts on the growth of hydrogen bubbles during ultrasonic vibration-enhanced hydrogen generation

To improve the hydrogen precipitation performance on the surface of the catalytic layer of the proton exchange membrane (PEM) hydrogen cathode, ultrasonic vibration was employed to accelerate the detachment of hydrogen bubbles on the surface of the catalytic layer. Based on the energy and mechanical analyses of nano and microbubbles, the hydrogen bubble generation mechanism and the effect of temperature on bubble parameters during the evolution process when the ultrasonic field is coupled with the electric field are investigated. The nucleation frequency of the hydrogen bubbles, the relationship between the pressure and temperature and the operating temperature during the generation and detachment of bubbles as well as the detachment radius of bubbles under the action of the ultrasonic field are obtained. The effects of ultrasound and temperature on hydrogen production were verified by visual experiments. The results show that the operating temperature affects the nucleation, growth, and detachment processes of hydrogen bubbles. The effect of temperature on the nucleation frequency of bubbles mainly comes from the Gibbs free energy required for the electrolysis reaction. The bubble radius and growth rate are both related to the temperature to the power of one-third. Ultrasonic waves enhance the separation of hydrogen bubbles from the catalyst surface by acoustic cavitation and impact effects. An increase in the working temperature reduces the activation energy barriers to be overcome for the electrolysis reaction of water, which together with a decrease in the Gibbs free energy and the surface tension coefficient, leads to an increase in the nucleation frequency of the catalytic layer and a decrease in the radius of bubble detachment, and thus improves the hydrogen precipitation performance. Visualization experiments show that in actual PEM hydrogen production, ultrasonic intensification can promote the formation of nucleation sites. The ultrasonic induced fine bubble flow not only has a drag effect on the bubble, but also intensifies the polymerization growth of the bubble due to the impact of the fine bubble flow, thus speeding up the detachment of the bubble, shortening the covering time of the hydrogen bubble on the surface of the catalytic electrode, reducing the activation voltage loss and improve the hydrogen production efficiency of PEM. The experimental results show that when the electrolyte is 60°C, the maximum hydrogen production efficiency of ultrasound is increased by 7.34%, and the average hydrogen production efficiency is increased by 5.83%.

Morphological control of electrodeposited iron for fluctuating photovoltaic electrical energy

With the Paris Agreement, the installed capacity of green power, such as photovoltaic (PV) and wind power, is growing rapidly at a rate of more than 10 % per year. The practical application of these green electrical energies is limited by the relative lag in the scale of energy storage systems. In response to the pressure on energy storage systems, we explored the feasibility of supplying DC power directly from a PV plant to an industrial electrolyzer by comparing the electrodeposition behavior of Fe2+ in a sulfuric acid system from stabilized DC and fluctuating PV power sources. We found that the factor that damages the stable operation of an iron electrodeposition system the most is the presence of hydrogen evolution reactions, where the generation of hydrogen bubbles reduces the current efficiency of the electrodeposition system and, in severe cases, destroys the surface morphology of the deposited products, causing devastating damage to the system. On this basis, we designed a simple scheme that uses heterogeneous bubble nucleation instead of homogeneous bubble nucleation for rapid bubble expulsion from the cathode surface. Benefiting from the rapid transfer of bubbles, the current efficiency of the electrodeposited iron system increases by 1.25%–10 % at different current densities, and the maximum roughness decreases by 129–2,396 nm, which considerably improves the stability of the electrodeposited iron system for PV power. This work provides useful experimental support for the transformation of the traditional steel smelting industry, which is characterized by high carbon emission and energy consumption, into an environmentally friendly industry.

Chinese herb pollen derived micromotors as active oral drug delivery system for gastric ulcer treatment

Considerable efforts have been devoted to treating gastric ulcers. Attempts in this field tend to develop drug delivery systems with prolonged gastric retention time. Herein, we develop novel Chinese herb pollen-derived micromotors as active oral drug delivery system for treating gastric ulcer. Such Chinese herb pollen-derived micromotors are simply produced by asymmetrically sputtering Mg layer onto one side of pollen grains. When exposed to gastric juice, the Mg layer can react with the hydrogen ions, resulting in intensive generation of hydrogen bubbles to propel the micromotors. Benefiting from the autonomous motion and unique spiny structure, our micromotors can move actively in the stomach and adhere to the surrounding tissues. Besides, their special architecture endows the micromotors with salient capacity of drug loading and releasing. Based on these features, we have demonstrated that our Chinese herb pollen-derived micromotors could effective deliver berberine hydrochloride and show desirable curative effect on the gastric ulcer model of mice. Therefore, these Chinese herb pollen-derived micromotors are anticipated to serve as promising oral drug delivery carriers for clinical applications.

Potentiodynamic Study of The Effects of Nickel on The Electrodeposition of Zinc from Chloride Media

Abstract. The potentiodynamic experiments of the nickel effects on the zinc electrodeposition have been done to understand the impact of Ni impurities on the electrowinning of Zn from spent pickling liquor. The nickel chloride solutions of Ni concentrations 90 and 1 g/dm3 were used as the electrolytes. The latter was also mixed with 90 g/dm3 Zn in the experiments. All the runs were carried out at room temperature with 40 mV/s continuous polarization speed and with 1/s sampling rate. It was observed that nickel electrodeposition from chloride media containing 90 g/dm3 Ni started with the generation of hydrogen bubbles, entirely blocking the cathode surface. Only a slight current development was observed until the polarization potential ~ -0,8 V. The visual observation showed bubbles also formed at the anode, which may represent chlorine and/or oxygen evolution. While, in the electrodeposition of nickel with only 1 g/dm3 Ni concentration in the electrolyte, metal deposition was hardly observed, but visible hydrogen bubbles constantly blocked the cathode surface. A similar tendency was observed in the mixed-solution electrolysis cell; the initial tiny bubbles accumulated at the cathode surface more than in the pure Zn solution. The enhancement of H2 evolution indicates how nickel deposition may contribute to the loss of useful current in the process of Zn electrodeposition. The mass of nickel deposited from the mixed solutions significantly decreases as the Ni concentration decreases in the electrolyte, while the mass of deposited zinc is relatively constant. It means that the purity of the produced Zn is appreciably higher – with respect to Ni – if nickel is efficiently eliminated from the solution before electrowinning.

The “tornado” effect induced by magnetohydrodynamic convection in an electrolytic cell with a wire-electrode

High energy consumption is the key problem to be solved in water electrolysis for hydrogen production. Imposing magnetic field during electrolysis is proved to be a research-worthy method to reduce the required electrical energy, since the magnetohydrodynamic convection can be induced without additional energy input. Considering the structure of commercial electrolyzers, the magnetic field perpendicular to the electrode surface is most likely to be applied in practical engineering. But there is still a lack of research on the gas-liquid two-phase flow in the electrolytic cell under this condition. To avoid mutual blocking between a large number of bubbles and obtain clear two-phase flow images of the electrolysis process, a wire electrode is used as cathode to generate hydrogen bubbles in this work. The cell voltage is obviously reduced by external magnetic field, and an interesting “bubble tornado” is formed under the action of induced magnetohydrodynamic convection. The numerical simulation results and theoretical analysis indicate that: (1) the formation of the bubble chain is caused by low-pressure region along the vertical axis; (2) the unstable low-pressure region is the key factor leading to the formation of continuously deformed bubble chain; (3) the bubble dispersion may be related to Kelvin-Helmholtz flow instability. We anticipate our work being a starting point for the application of magnetic field in practical engineering.

Visualization of dragged water and generated hydrogen bubbles in a direct toluene electro-hydrogenation electrolyzer

Methylcyclohexane is an appealing liquid organic hydrogen carrier produced from toluene hydrogenation. The direct toluene electro-hydrogenation technique in proton exchange membrane electrolyzers avoids heat losses and reduces the electricity consumption concerning the conventional methods. However, this technology faces a critical issue. The water dragged by electro-osmosis from the anode side blocks the toluene supply to the cathode reaction site. This paper presents the experimental visualization, for the first time, of water droplets and generated hydrogen bubbles inside the cathode porous transport layer of a direct toluene electro-hydrogenation cell. Experiments were conducted under different current densities and using not only pure water but also dilute sulfuric acid as anode reactant. The visualizations revealed that the bubbling grew sharply as the electric current increased between 20 and 100 mA/cm2. It was also observed that water droplets got stuck inside the cell. As for hydrogen, small bubbles left the cell rapidly while larger ones stayed inside for longer. Finally, the experimental visualizations confirmed that the water dragging phenomenon was mitigated by using dilute sulfuric acid as anode reactant instead of pure water. Indeed, the hydrogen generation was halved at 200 mA/cm2 and the methylcyclohexane Faraday efficiency was boosted by 15%–22% points.

Visualization of Hydrogen Bubbles in Porous Transport Layer in Toluene Direct Electro-Hydrogenation Electrolyzer Using X-Ray CT System

Introduction Currently, the use of renewable energy is being promoted as an approach to decarbonization. However, renewable energy requires stable energy storage and supply because the amount of electricity is affected by time and climate. One of the solutions is use of hydrogen as an energy source. As the demand for hydrogen increases in the future, a large amount of hydrogen will be needed, and the storage and transportation of large amounts of hydrogen will also be necessary. However, the methods for storing and transporting large amounts of hydrogen have not yet been established, and this is one of the challenges in the current hydrogen utilization. One of the methods for storing and transporting large amounts of hydrogen is the organic hydride method. The organic hydride method is a method of storing and transporting hydrogen using hydrogenation and dehydrogenation of organic compounds. Among these, the use of toluene and methylcyclohexane (MCH) has attracted attention. The advantages of using toluene and MCH include the following: because toluene and MCH are liquids at normal temperature and pressure, they can be transported at about 1/500th the volume of direct hydrogen gas transport; toluene and MCH can be reused; hydrogenation and dehydrogenation are the only reactions, so no byproducts are generated; and they can be transported in the same way as petroleum. Hydrogen can be transported in the same way as petroleum. Therefore, it is expected to be used as a storage and transport medium for hydrogen.A toluene direct electro hydrogenation electrolyzer is available as a means of hydrogenating toluene. In the toluene direct electro hydrogenation electrolyzer, hydrogen and toluene are supplied to the electrolyzer, and electricity is applied to protonate the hydrogen and supply it to toluene to produce MCH. The advantages are that cost and time losses can be reduced because water electrolysis and toluene hydrogenation can be performed simultaneously, there is no heat loss in the reaction, and the theoretical decomposition voltage can be reduced compared to electrolysis of water and hydrogenation of toluene separately. However, during hydrogenation of toluene, a part of the water being electrolyzed is transferred to the toluene reaction surface, reducing the reaction efficiency to MCH. In addition, part of the protonated hydrogen becomes hydrogen bubbles, which inhibit the fuel supply and reduce the reaction area. Furthermore, the phenomena of water movement and hydrogen bubbles in toluene hydrogenation have not yet been studied.In this study , we aim to understand the generation of hydrogen bubbles by visualizing the phenomena in toluene hydrogenation using a toluene direct electro hydrogenation electrolyzer with an X-ray CT system, and to provide a guideline for future research on the suppression of hydrogen bubble generation and water movement. Fig. 1 shows a schematic diagram of the toluene direct electro- hydrogenation electrolyzer used in this experiment. The electrolyzer consists of a catalyst layer, a gas diffusion layer (GDL), and a separator, in that order. The electrolyzer is operated by supplying toluene to the anode side and hydrogen to the cathode side, and electricity is supplied. Visualization of the interface between the GDL and catalyst layer on the cathode side of the electrolyzer during operation using an X-ray CT system allows the phenomena on the reaction surface to be visualized. Figure 2 Visualization of the inside of the electrolyzer during operation. Fig. 2 (a) shows the electrolyzer filled with MCH and (b) shows the electrolyzer filled with toluene. The toluene electrolyzer generates fewer hydrogen bubbles, which confirms that the reaction is normal, and the correlation between the current density and the generation of hydrogen bubbles is examined. Figure 1

Ceramic nanofiltration membranes for efficient fouling mitigation through periodic electrolysis

Ceramic membranes are gaining importance in several mainstream membrane applications. Their high chemical and thermal resistance stability make them ideal candidates for oil/water separation, dye rejections, in dairy production, catalyst recovery and in treating a variety of wastewater effluents. Although ceramic microfiltration and ultrafiltration membranes are a predominant research area, there is still limited research on ceramic nanofiltration membranes, especially on controlling its fouling propensity. High flux values in such membranes can cause rapid fouling which lead to a compromise in membrane performance. In this work, we have modified commercial ceramic TiO2 NF membrane by coating it with titanium through an e-beam deposition process. Coating with titanium did not bring about any change in the inherent membrane properties such as its thermal resistance, structure and hydrophilicity. The superhydrophilic membrane showed good electrical conductivity, which enabled us to test the membrane for its self-cleaning ability through periodic electrolysis. Sodium alginate, yeast, humic acid and their mixtures were used as model foulants. A cross-flow filtration setup was used where the membrane acted as a cathode and a potential of 2–4.5 V was applied periodically depending upon the type of foulant. Without membrane cleaning, a sharp decline in flux to even till 10 % of its original value was noticed during some filtration tests. However, a high flux recovery from 88 to 98 % was achieved when the membrane was subjected to intermittent cleaning. The Ti-coated NF ceramic membrane showed efficient surface cleaning. The generation of hydrogen bubbles helped in sweeping away the cake layer formed as a result of concentration polarization. These electro-ceramic NF membranes allow us to address critical problems associated with such pressure driven processes where biofouling is a major problem.

Co-Mo microcolumns decorated with trace Pt for large current density hydrogen generation in alkaline seawater

Electrolysis in seawater is cost-saving but challenging approach for hydrogen production. In this study, self-supported anticaustic three dimensional (3D) microcolumns anchored with trace Pt clusters on nickel foam (NF) is prepared through solvothermal followed by thermal reduction procedures (Pt-Co-Mo). The as-synthesized electrode owns superhydrophilic and aerophilic surface which favors close contact between the electrode and electrolyte and release of the generated hydrogen bubbles. Besides, the strong synergistic effect between Pt and matrix lead to a significantly improved HER intrinsic activity. Thanks to the above merits, the self-supported Pt-Co-Mo electrode presents outstanding HER activity, which only requires an extremely low overpotentials of 179.2 mV and 194.1 mV to reach a large current density of 2000 mA cm−2 in 1 M KOH and 1 M KOH seawater, respectively. For overall water splitting, cell voltages down to 1.50 V and 1.51 V are necessary to drive 10 mA cm−2 in 1 M KOH and alkaline seawater, respectively.

Titanium coating on ultrafiltration inorganic membranes for fouling control

• Electrically conductive UF ceramic membrane. • Fouling control and prevention through periodic electrolysis. • Ti-coating on Al 2 O 3 through e-beam deposition process. • High water flux of about 700 LMH. • High flux recovery; reaching ˃90% of original value after the 1st cycle. Inorganic membranes hold great potential for various mainstream applications such as in wastewater treatment, drug manufacturing, food and beverage production, and dairy purification. There are numerous commercially available ceramic membranes which possess high corrosion resistance, high strength, and good heat resistance. However, these membranes are still prone to fouling causing a considerable decline in membrane performance and hence shorter life-times. Conventional methods for flux recovery include rigorous chemical backwashing, producing large amounts of sludge leading to disposal problems. In this work, commercial α-Alumina (Al 2 O 3 ) ultrafiltration (UF) membranes were coated with titanium through an e-beam deposition process. The titanium coating rendered the membrane conductive, without changing the superhydrophilicity and average pore size of the membrane. Thermal degradation profiles suggested good thermal characteristics of the membrane. Good electrocatalytic activity for hydrogen evolution reaction was observed for the membrane, with an over-potential of 450 mV and 400 mV vs. Reference Hydrogen Electrode in acid and base solutions. The conductive membrane allowed for periodic electrolysis which is a fast and simple technique for fouling control and prevention. The membrane was used as a cathode during a cross-flow filtration setup, where 2.0 V was applied for 5 min during intervals. Without electrolysis, a considerable decline in flux was observed reaching almost 10% and 40% of its original value during yeast and sodium alginate (SA) filtration respectively. However, substantial flux recovery to 87% and 97.5% was achieved after the first cleaning cycle during yeast and sodium alginate (SA) filtration respectively. Thereafter, considerable flux recovery was achieved during each subsequent electrolysis cycle. Membrane’s good electrocatalytic properties led to the generation of hydrogen bubbles which helped in sweeping away the foulants from the membrane’s surface.

Visualization of Dragged Water and Generated Hydrogen Bubbles in a Direct Toluene Electro-Hydrogenation Electrolyzer

Visualization of Dragged Water and Generated Hydrogen Bubbles in a Direct Toluene Electro-Hydrogenation Electrolyzer

Estimation of critical number of hydrogen bubbles for critical current density using the dry spot model

The hydrogen evolving system has an upper operation limit called critical current density (CCD), where electrochemically generated hydrogen bubbles form hydrogen film on the surface just like the critical heat flux (CHF) in the boiling system. With aim of proposing a model envisaging the hydrogen bubble configuration, ‘insulated spot model’ is proposed by applying the dry spot model for the CHF using 1.5 M of sulfuric acid electrolysis system. Critical number of bubbles at the CCD is estimated by the insulated spot model. Nucleation characteristics of the present electrolysis system are applied and then the critical number of bubbles is calculated as 6, which predicts measured CCD with error of 7.4%. Accordingly, a hexagonal packing structure is envisaged for the hydrogen bubble configuration. It is concluded that the CCD phenomenon is dominated by the hydrodynamic behavior, similar to the CHF and it can be regarded as a miniature CHF.

Suction-Cup-Inspired Adhesive Micromotors for Drug Delivery.

Micromotors have opened novel avenues for drug delivery due to their capacity for self‐propelling. Attempts in this field trend towards ameliorating their functions to promote their clinical applications. In this paper, an ingenious suction‐cup‐inspired micromotor is presented with adhesive properties for drug delivery in the stomach. The micromotors are fabricated by using hydrogel replicating the structure of suction‐cup‐like microparticles, which derive from self‐assembly of colloidal crystals under rapid solvent extraction, followed by loading magnesium (Mg) in the bottom spherical surface. The Mg‐loaded micromotors can realize spontaneous movement due to the continual generation of hydrogen bubbles in gastric juice. The combination of unique suction‐cup‐like structure with excellent motion performance makes the micromotor an ideal carrier for drug delivery as they can efficiently adhere to the tissue. Moreover, benefiting from the porous structure, the hydrogel micromotors exhibit a high volume‐surface ratio, which enables efficient drug loading. It is demonstrated that the suction‐cup‐inspired micromotors can adhere efficiently to the ulcer‐region in the stomach and release drugs due to their distinctive architecture and spontaneous motion, exhibiting desirable curative effect of gastric ulcer. Thus, the suction‐cup‐inspired micromotors with adhesive properties are expected to advance the development of micromotor in clinical applications.

Integrated Bundle Electrode with Wettability-Gradient Copper Cones Inducing Continuous Generation, Directional Transport, and Efficient Collection of H2 Bubbles.

The hydrogen evolution reaction (HER), as an efficient process of converting various energies into high-purity hydrogen, has attracted much attention from both scientific research studies and industrial productions. However, its wide applications still confront considerable difficulties, for example, bubble coverage on the electrode and bubble dispersion in the electrolyte, which will disturb current distribution and isolate active sites from reaction ions resulting in a high reaction overpotential and large Ohmic voltage drop. Consequently, timely removing the generated gas bubbles from the electrode as well as avoiding their direct release into the electrolyte can be an effective approach to address these issues. In this work, we have developed an elegant electrode, that is, the integrated bundle electrode with wettability-gradient copper cones, which is endowed with the multifunctions of continuous generation, direct transport, and efficient collection of hydrogen bubbles. All processes are proceeding on the electrode, which not only remove the generated hydrogen bubbles efficiently but also prevent the hydrogen bubbles from releasing into the electrolyte, which should greatly advance the development of water electrolysis and offer inspirations for people to fabricate more efficient HER devices.

Hydrogen bubble-assisted growth of Pt3Te4 for electrochemical catalysts

Novel materials and structures with abundant active sites have been in continuous demand for electrochemical catalytic applications. In this study, we synthesized platinum telluride (Pt3Te4) nanocrystals on two-dimensional metallic molybdenum ditelluride (MoTe2) using a dynamic hydrogen bubble template method in the hydrogen evolution reaction (HER). The local crystal structure and chemical state of the Pt3Te4 nanocrystals were investigated using X-ray nano-diffraction and X-ray nano-absorption spectroscopy. In our electrochemical deposition method, the morphology, and HER performance of the Pt3Te4 nanocrystals could be manipulated through the hydrogen bubble generation rate. Thus, the nanorod-shaped Pt3Te4 nanocrystals, fabricated by a high rate of hydrogen bubble generation, exhibited outstanding HER performance, which is in contrast with the HER performance of hemisphere-shaped Pt3Te4. Our study provides a facile and systematic way of synthesizing high-performance electrochemical catalysts using the hydrogen bubble-assisted growth method.

Interfacial Design to Enhance Photocatalytic Hydrogen Evolution via Optimizing Energy and Mass Flows

Energy and mass transfer in photocatalytic systems plays a significant role in photocatalytic water splitting, but relevant research has long been ignored. Here, an interfacial photocatalytic mode for photocatalytic hydrogen production is exploited to optimize the energy and mass flows and mainly includes a heat-insulating layer, a water-channel layer, and a photothermal photocatalytic layer. In this mode, the energy flow is optimized for efficient spreading, conversion, and utilization. A low-loss path (ultrathin water film) and an efficient heat localized zone are constructed, where light energy, especially infrared-light energy, can transfer to the target functional membrane surface with low loss and the thermal energy converted from light can be localized for further use. Meanwhile, the optimization of the mass flow is achieved by improving the desorption capacity of the products. The generated hydrogen bubbles can rapidly leave from the surface of the photocatalyst, along with the active sites being released timely. Consequently, the photocatalytic hydrogen production rate can be increased up to about 6.6 times that in a conventional photocatalytic mode. From the system design aspect, this work provides an efficient strategy to improve the performance of photocatalytic water splitting by optimizing the energy and mass flows.