Electrolytic Bubbles Research Articles

Ultrafast Quasi-Solid-State Microwave Construction of Spongy Cobalt-Molybdenum Phosphide for Hydrogen Production Over Wide pH Range.

The developed strategies for synthesizing metal phosphides are usually cumbersome and pollute the environment. In this work, an ultrafast (30s) quasi-solid-state microwave approach is developed to construct cobalt-molybdenum phosphide decorated with Ru (Ru/CoxP-MoP) featured porous morphology with interconnected channels. The specific nanostructure favors mass transport, such as electrolyte bubbles transfer and exposing rich active sites. Moreover, the coupling effects between metallic elements, especially the decorated Ru, also act as a pivotal role on enhancing the electrocatalytic performance. Benefiting from the effects of composition and specific nanostructure, the prepared Ru/CoxP-MoP exhibits efficient HER performance with a current density of 10mAcm-2 achieved in 1m KOH, 0.5mH2SO4, seawater containing 1mKOH and 1mPBS, with overpotentials of 52, 59, 55, 90mV, and coupling with good stability. This work opens a novel and fast avenue to design metal-phosphide-based nanomaterials in energy-conversion and storage fields.

Experimental study of ECDM using a porous electrode containing internal micropores

ABSTRACT In electrochemical discharge machining (ECDM), continuous renewal of electrolyte between the tool electrode and the workpiece guarantees stable discharge machining. Proposed in this paper is Porous-electrode ECDM (p-ECDM) using a tool electrode made of porous material containing micrometer pores. The rough surface of the porous electrode promotes electrolyte regeneration between the electrodes to produce a stable and relatively thin gas film. At the same time, the internal connected micropores are used to provide controlled gas flow to the processing area, reduce the energy consumption of electrolytic bubbles, and improve the discharge energy to achieve efficient ECDM processing. Experimental results indicate that compared with a solid electrode, the porous electrode has faster electrolyte renewal, smaller bubble volume, more-stable voltage characteristics, 22.55% less overcut, a 4.7% smaller heat-affected zone, and better deep hole processing ability. Experimental results for p-ECDM assisted by controlled airflow demonstrate a 54.23% increase in the material removal rate.

Modeling electrolysis in reduced gravity: producing oxygen from in-situ resources at the moon and beyond

Molten Regolith Electrolysis, as an in situ resource utilization (ISRU) technology, has the potential to enable the production of oxygen and metallic alloys on the Lunar surface; opening new doors in Cis-Lunar, and eventually Martian space exploration. This research studies the fundamental physics which govern the formation, growth, detachment, and rise of electrolytic bubbles. To this end, computational fluid dynamic (CFD) models were developed and run, to simulate water electrolysis, molten salt electrolysis (MSE), and molten Lunar regolith (MRE) electrolysis across multiple reduced gravity levels. The results demonstrate that reduced gravity, electrode surface roughness (possibly due to surface degradation), fluid properties, and electrode orientation can all affect electrolytic efficiency and possibly even stall electrolysis by delaying bubble detachment. The findings of this research must be considered when designing and operating electrolysis systems at reduced gravity levels.

Synergistic heterointerface engineering of Co9S8/Ni(OH)2 hierarchical nanosheets for remarkable overall water splitting

Sustainable production of hydrogen from electrochemical water spitting by cost-effective and non-precious bifunctional electrocatalyst is of remarkable interest and extremely desirable. Here, a novel hierarchical Co9S8/Ni(OH)2 heterostructure with porous nanosheets was fabricated as the heterogeneous bifunctional electrodes to achieve remarkable water electrolysis. Synergistic coexistence of Co9S8 and Ni(OH)2 nanostructure with crystalline-amorphous feature can induce a large number of chemically coupled heterointerfaces as catalytically accessible active sites to accelerate electron transfer kinetics and enable a super-hydrophilic feature to contact electrolyte and release gas bubbles. Thus, such Co9S8/Ni(OH)2 heterostructure electrode verifies a remarkable electrocatalytic activity with low overpotentials of 274 mV at 100 mA cm−2 for OER and 109 mV at 10 mA cm−2 for HER. As assembled in a lab-made electrolyzer, the Co9S8/Ni(OH)2 heterostructures as bifunctional electrodes enable 1.51 V to achieve an overall water splitting at 10 mA cm−2, along with the outstanding stability at about 100 mA cm−2 up to 55 h. This work paves a bright way to design and construct non-precious materials as effective and advanced electrocatalysts for electrolysis in water.

Electroflotation Treatment of Industrial Wastewater in a Specially Designed Electroflotator Powered by a Solar Panel

Currently, the anode in existing electroflotators is a dense mesh with small cells, which causes salt deposits to form on its surface during the electrolysis of waste water. In another case, the salt deposits completely cover the cells, which stops the electroflotation process by preventing the passage of electrolytic hydrogen bubbles through them. The use of an anode in the form of a dense mesh with small cells in electroflotators, on the one hand, increases the density of direct current flowing in industrial wastewater during electroflotation of industrial wastewater, and therefore increases the formation of microdispersed electrolytic hydrogen bubbles, which contribute to the successful electroflotation of industrial wastewater. On the other hand, the use of an anode in the form of a dense mesh with small cells in electroflotators sharply reduces the passage through this mesh of electrolytic hydrogen bubbles, formed during electroflotation of industrial wastewater, which sharply slows down electroflotation process. When the author devised electroflotation treatment for industrial wastewater in a specially built electroflotator, powered by a solar panel, this issue was resolved. The article presents a developed method of electroflotation treatment of industrial wastewater in a specially designed electroflotator, powered by a solar panel (solar cell), which includes an electrolysis base and uses negatively charged electrolytic hydrogen bubbles with a calculated dispersion, which release microscopic particles from wastewater in the process of wastewater treatment by floating up in the wastewater of the created by them strong complexes: negatively charged microdispersed electrolytic hydrogen bubbles + microscopic particles of wastewater from industrial wastewater in the process of an elementary act of flotation.

Electroflotation Treatment of Industrial Wastewater in a Specially Designed Electroflotator Powered by a Solar Panel

Currently, the anode in existing electroflotators is a dense mesh with small cells, which causes salt deposits to form on its surface during the electrolysis of waste water. In another case, the salt deposits completely cover the cells, which stops the electroflotation process by preventing the passage of electrolytic hydrogen bubbles through them. The use of an anode in the form of a dense mesh with small cells in electroflotators, on the one hand, increases the density of direct current flowing in industrial wastewater during electroflotation of industrial wastewater, and therefore increases the formation of microdispersed electrolytic hydrogen bubbles, which contribute to the successful electroflotation of industrial wastewater. On the other hand, the use of an anode in the form of a dense mesh with small cells in electroflotators sharply reduces the passage through this mesh of electrolytic hydrogen bubbles, formed during electroflotation of industrial wastewater, which sharply slows down electroflotation process. When the author devised electroflotation treatment for industrial wastewater in a specially built electroflotator, powered by a solar panel, this issue was resolved. The article presents a developed method of electroflotation treatment of industrial wastewater in a specially designed electroflotator, powered by a solar panel (solar cell), which includes an electrolysis base and uses negatively charged electrolytic hydrogen bubbles with a calculated dispersion, which release microscopic particles from wastewater in the process of wastewater treatment by floating up in the wastewater of the created by them strong complexes: negatively charged microdispersed electrolytic hydrogen bubbles + microscopic particles of wastewater from industrial wastewater in the process of an elementary act of flotation.

A novel electrolytic gas lift reactor for efficient microbial electrosynthesis of acetate from carbon dioxide

The low current density impedes the practical application of microbial electrosynthesis for CO2 fixation. Engineering the reactor design is an effective way to increase the current density, especially for H2-mediated microbial electrosynthesis reactors. The electrolytic bubble column microbial electrosynthesis reactor has shown great potential for scaling up, but the mixing and gas mass transfer still need to be enhanced to further increase the current density. Here, we introduced an inner draft tube to the bubble column to tackle the problem. The addition of draft tube resulted in a 76.6% increase in the volumetric mass transfer coefficient (kLa) of H2, a 40% increase in the maximum current density (337 A/m2) and a 72% increase in average acetate production rate (3.1 g/L/d). The computational fluid dynamics simulations showed that the addition of draft tube enhanced mixing efficiency by enabling a more ordered cyclic flow pattern and a more uniform gas/liquid distribution. These results indicate that the electro-bubble column reactor with draft tube holds great potential for industrial implementation.

Minimum current for detachment of electrolytic bubbles

The efficiency of water electrolysis is significantly impacted by the generation of micro- and nanobubbles on the electrodes. Here molecular dynamics simulations are used to investigate the dynamics of single electrolytic nanobubbles on nanoelectrodes. The simulations reveal that, depending on the value of current, nucleated nanobubbles either grow to an equilibrium state or grow unlimitedly and then detach. To account for these findings, the stability theory for surface nanobubbles is generalized by incorporating the electrolytic gas influx at the nanobubble's contact line and adopting a real gas law, leading to accurate predictions for the numerically observed transient growth and stationary states of the nanobubbles. With this theory, the minimum current for bubble detachment can also be derived analytically. In the detachment regime, the radius of the nanobubble first increases with time (t) as $R\propto t^{1/2}$ and then as $R\propto t^{1/3}$ , up to bubble detachment.

Investigating mass transfer around spatially-decoupled electrolytic bubbles

Electrolytic bubbles have a profound impact on mass transport in the vicinity of electrodes and greatly influence the electrolyzer efficiency and cell overpotential. However, experimental measurements of concentration fields around electrolytic bubbles with high spatio-temporal resolution is challenging. In this study, a succession of spatially-decoupled electrolytic bubbles growing in an initially quiescent electrolyte is simulated. The bubbles grow and depart from a hydrophobic cavity at the center of a ring microelectrode. The gas-liquid interface is modeled using a moving mesh topology. A geometric cutting protocol is developed to handle topology changes during bubble departure. The simulated bubbles show good agreement with the bubble growth dynamics observed in experiments. The bubbles in this spatially-decoupled system outgrow the region of electrolyte that is saturated with dissolved hydrogen. This leaves the apex of the bubble interface exposed to an undersaturated region of the electrolyte which leads to an outward flux of hydrogen gas. This is shown to limit the gas evolution efficiency of bubbles even though that they grow at a constant volumetric rate. By analyzing the distribution of the flux of dissolved hydrogen along the bubble interface along with the development of dissolve hydrogen concentration profiles around the bubble, we show that the magnitude of the outward diffusive flux at the apex of the bubble decreases with increasing electrolysis current.

An Electrolytic Bubble Column with Gas Recirculation for High-Rate Microbial Electrosynthesis of Acetate from CO2

An Electrolytic Bubble Column with Gas Recirculation for High-Rate Microbial Electrosynthesis of Acetate from CO₂

Comparison of in-situ and ex-situ electrolytic H2 supply for microbial methane production from CO2

Both in-situ and ex-situ electrolytic H2 supply have been used for biomethane production from CO2. However, the pros and cons of them have not been systematically compared. The present study makes this comparison using a 20 L continuous stirred-tank reactor equipped with external and internal electrolyzers. Compared to the ex-situ H2 supply, the in-situ electrolytic H2 bubbles were one order of magnitude smaller, which resulted in improved H2 mass transfer and biomass growth. Consequently, the methane production rate and the coulombic efficiency of the in-situ H2 supply (0.51 L·L-1·d-1, 96%) were higher than those of the ex-situ H2 supply (0.30 L·L-1·d-1, 56%). However, due to high internal resistance, the energy consumption for the in-situ electrolysis was 2.54 times higher than the ex-situ electrolysis. Therefore, the in-situ electrolytic H2 supply appears to be more promising, but reducing energy consumption is the key to the success of this technology.

Experimental and numerical analysis on electrolytic bubble group dynamics in the aluminum electrolysis process using the slotted anode

The CuSO4 aqueous solution electrolysis experiment is conducted to investigate the electrical bubble dynamics using the slotted anode to reveal the gas removal mechanism. A three-dimensional transient mathematical model coupled discrete phase model (DPM) − discrete-continuum transition model (DCTM) − volume of fluid (VOF) method is developed to track the dispersed bubble trajectory, bridge the dispersed bubble to continuous gas, and resolve the deformed bubble surface, respectively. The slotted anode decreases the bubble diameter compared with the traditional anode because the slot shortens the bubble motion distance to decrease the bubble residence time. The slot width smaller than the detached bubble diameter can limit the bubble deformation. Increasing current plays a dual role in bubble motion in the experiment: it accelerates the bubble coalescence process but decreases the bubble collision probability. The longitudinal slot is more conducive to reducing the maximum bubble coverage and increasing the bubble release frequency than the transverse slot.

An electrolytic bubble column with an external hollow fiber membrane gas–liquid contactor for effective microbial electrosynthesis of acetate from CO2

Currently, almost all microbial electrosynthesis (MES) reactors were biofilm-driven whether the cathode electron transfer was direct or indirect. It has been proven that cathode biofilm formation is time-consuming, and the current density achieved on these biofilms was relatively low. However, the main challenge for the non-biofilm-driven MES is how to maintain a good Columbic efficiency (CE) at high current densities. Here, we report a novel electro-H2 bubble column reactor with an external hollow fiber membrane gas–liquid contactor to tackle the challenge. The electrolyzer was placed at the bottom of the reactor to produce H2 micro-bubbles (mean diameter 169 ± 7 µm) at a current density of 156 A/m2. The bubble column was put on the top of the cathodic chamber of the electrolyzer to extend the H2 retention time, while the hollow fiber membrane gas–liquid contactor in the external loop was used to recover the unused gas. Consequently, the homoacetogens in reactor could efficiently convert the electrolytically-produced H2 and the externally-supplied CO2 into acetate. The volume of the catholyte (5.5 L) in this reactor is one order of magnitude higher than all reported MES reactors. Batch tests with enriched homoacetogens demonstrated a maximum acetate production rate (1.15 g/Lcatholyte/d, 898 g/m2cathode/d), acetate titer (34.5 g/L) could be achieved in this setup, and the average (maximum) CE of the electron to acetate efficiency was 64% (92%). Besides, dissolved H2 measurement and bacteria community analysis indicated the high acetate titers were likely caused by the H2 oversaturation situation and good substrate/product mass transfer rather than the selection of certain types of homoacetogens. The electro-H2 bubble reactor seems to be a promising MES setup for scale-up and practical application.

Electroflotation Treatment of Industrial Wastewater in a Specially Designed Electroflotator Powered by a Solar Panel

Currently, the anode in existing electroflotators is a dense mesh with small cells, which causes salt deposits to form on its surface during the electrolysis of waste water. In another case, the salt deposits completely cover the cells, which stops the electroflotation process by preventing the passage of electrolytic hydrogen bubbles through them. The use of an anode in the form of a dense mesh with small cells in electroflotators, on the one hand, increases the density of direct current flowing in industrial wastewater during electroflotation of industrial wastewater, and therefore increases the formation of microdispersed electrolytic hydrogen bubbles, which contribute to the successful electroflotation of industrial wastewater. On the other hand, the use of an anode in the form of a dense mesh with small cells in electroflotators sharply reduces the passage through this mesh of electrolytic hydrogen bubbles, formed during electroflotation of industrial wastewater, which sharply slows down electroflotation process. When the author devised electroflotation treatment for industrial wastewater in a specially built electroflotator, powered by a solar panel, this issue was resolved. The article presents a developed method of electroflotation treatment of industrial wastewater in a specially designed electroflotator, powered by a solar panel (solar cell), which includes an electrolysis base and uses negatively charged electrolytic hydrogen bubbles with a calculated dispersion, which release microscopic particles from wastewater in the process of wastewater treatment by floating up in the wastewater of the created by them strong complexes: negatively charged microdispersed electrolytic hydrogen bubbles + microscopic particles of wastewater from industrial wastewater in the process of an elementary act of flotation.

Boosting high-current water electrolysis: Superhydrophilic/superaerophobic nanosheet arrays of NiFe LDH with oxygen vacancies in situ grown on iron foam

Developing cost-effective and superior bifunctional electrocatalysts for alkaline water splitting is crucial to realizing hydrogen economy. However, in industrial applications, especially at high current densities, the sluggish kinetic process and the dissatisfactory prolonged stability of electrocatalysts astrict their applications. Herein, the superhydrophilic/superhydrophobic NiFe layered double hydroxide (LDH) with oxygen vacancies was designed in situ grown on iron foam (NiFe/IF) as a high-performance bifunctional electrocatalyst. The unique feature of the superhydrophilic/superaerophobic surface makes for electrolyte penetration and bubbles release, and the existence of oxygen vacancies grants the catalyst with enhanced inherent catalytic activity. Moreover, in situ Raman analysis reveals NiFe LDH could undergo surface reconstruction into active NiOOH species in the electrooxidation environment. Profiting from the above superiorities, the prepared NiFe/IF displays superior OER activity in 1 M KOH with low overpotentials of 245.2, and 480.2 mV to supply 100 and 1000 mA cm−2, respectively. And the NiFe/IF exhibits prominent stability at 1000 mA cm−2 under a simulated industrial condition (6 M KOH and 85 °C). Moreover, the water electrolysis device based on NiFe/IF as anode and cathode was assembled with a commercial solar cell to simulate a photovoltaic-driven water splitting system, which revealed a superior efficiency of 15.13% for solar hydrogen production.

Heterostructured Mo2N–Mo2C Nanoparticles Coupled with N‐Doped Carbonized Wood to Accelerate the Hydrogen Evolution Reaction

Mo2C is a promising non‐precious hydrogen evolution reaction (HER) electrocatalyst. However, regulating the strong hydrogen adsorption characteristics of Mo2C and finding suitable support electrodes are essential processes before Mo2C can replace Pt to realize a sustainable hydrogen economy. Herein, the facile synthesis of heterostructured Mo2N–Mo2C nanoparticles on N‐doped carbonized wood (Mo2N–Mo2C/N‐CW) as a self‐supported electrode through carbonization and NH3 plasma treatment is demonstrated. The synergistic effects of heterostructured Mo2N–Mo2C and N‐CW with aligned microchannels provide enhanced catalytic activity, fast charge transfer kinetics, additional active site exposure, and rapid transport of the electrolyte and H2 bubbles, which improves the HER performance. Consequently, the Mo2N–Mo2C/N‐CW electrode exhibits superior HER performance with low overpotentials of only 79 and 311 mV to reach 10 and 500 mA cm−2 in an acidic solution, respectively. It also exhibits long‐term stability for 20 h in the high‐current‐density region (110 mA cm−2). The density functional theory (DFT) calculations at various sites reveal that the heterointerface of Mo2N and Mo2C promoted the catalytic activity by optimizing the adsorption/desorption of hydrogen.

Juice concentration using juice electrolysis generated by solar cells of solar panel

Juice concentrates are made by extracting water from freshly squeezed juice. Extracting water from fresh juice today is done by evaporation, freezing of the water, or using diaphragms. During evaporating, freshly squeezed juice is heated in a vacuum below the boiling point to preserve all its beneficial substances. When water freezes, it is removed by cold. When using diaphragms, freshly squeezed juice is passed through a membrane with tiny cells, as a result of which water penetrates through the membrane, and large molecules of freshly squeezed juice concentrate are deposited on the membrane. All these methods of concentrating freshly squeezed juice require large economic costs. The article presents the concentration of fresh juice, using electrolysis of the aqueous component of fresh juice, generated by direct electric current from a solar cell of a solar panel, leading to the formation of negatively charged microdispersed electrolytic hydrogen bubbles and the production of high-quality fresh juice concentrate by flotation of microsolid components of fresh juice with these bubbles. In the process of freshly squeezed juice concentration, water is not removed from the juice, but itself ensures that a high-quality foamy juice concentrate is obtained in an electroflotator-concentrator simply, quickly, and economically (without the cost of electricity).

Automated Process Control System for the Production of Advanced Foam Materials Using a Programmable Logic Controller

Obtaining foam materials with high physical and mechanical properties is one of the most important tasks, associated with the needs of the chemical industry, medicine, mechanical engineering and space technology. Known methods for producing foam materials create foam materials by foaming aqueous dispersions of high polymers, using thermal decomposition of organic and inorganic substances, by using radiation degradation of a thermoplastic polymer; by foaming polyurethane compositions by injection of condensed hydrogen under high pressure and others. All these methods, on the one hand, are uneconomical and harmful. The toxicity of thermal decomposition products and the unfavorable influence of the chemical nature of gas-forming agents worsen the properties of the resulting material. On the other hand, these processes only produce certain foams, which greatly limit their applicability to a wide range of foams. This article presents the developed automated process control system of production of advanced foam materials using a programmable logic controller, in the RAM of which a computer program is embedded, which allows the use of vibroturbulization intensive mixing with optimal parameters for the formation of electrolytic hydrogen bubbles from the hydrogen gas entering to the chamber with a thermoplastic, obtained separately in the electrolysis chamber by electrolysis of water, and uniform saturation by them of the thermoplastic at its melting temperature in automatic mode.

Observation of H2 Evolution and Electrolyte Diffusion on MoS2 Monolayer by In Situ Liquid-Phase Transmission Electron Microscopy.

Unit-cell-thick MoS2 is a promising electrocatalyst for the hydrogen evolution reaction (HER) owing to its tunable catalytic activity, which is determined based on the energetics and molecular interactions of different types of HER active sites. Kinetic responses of MoS2 active sites, including the reaction onset, diffusion of the electrolyte and H2 bubbles, and continuation of these processes, are important factors affecting the catalytic activity of MoS2 . Investigating these factors requires a direct real-time analysis of the HER occurring on spatially independent active sites. Herein, the H2 evolution and electrolyte diffusion on the surface of MoS2 are observed in real time by in situ electrochemical liquid-phase transmission electron microscopy (LPTEM). Time-dependent LPTEM observations reveal that different types of active sites are sequentially activated under the same conditions. Furthermore, the electrolyte flow to these sites is influenced by the reduction potential and site geometry, which affects the bubble detachment and overall HER activity of MoS2 .

Potential response of single successive constant-current-driven electrolytic hydrogen bubbles spatially separated from the electrode

The presence of bubbles in gas-evolving electrolytic processes can heavily alter the mass transport of gaseous products and can induce severe overpotential penalties at the electrode through the action of bubble coverage (hyperpolarization) and electrolyte constriction (Ohmic shielding). However, bubble formation can also alleviate the overpotential by lowering the concentration of dissolved gas in the vicinity of the electrode. In this study, we investigate the latter by considering the growth of successive hydrogen bubbles driven by a constant current in alkaline-water electrolysis and their impact on the half-cell potential in the absence of hyperpolarization. The bubbles nucleate on a hydrophobic cavity surrounded by a ring microelectrode which remains free of bubble coverage. The dynamics of bubble growth does not adhere to one particular scaling law in time, but undergoes a smooth transition from pressure-driven towards supply-limited growth. The contributions of the different bubble-induced phenomena leading to the rich behaviour of the periodic fluctuations of the overpotential are identified throughout the different stages of the bubble lifetime, and the influence of bubble size and applied current on the concentration and Ohmic overpotential components is quantified. We find that the efficiency of gas absorption, and hence the concentration-lowering effect, increases with increasing bubble size and also with increasing current. However, the concentration-lowering effect is always eventually countered and overcome by the effect of Ohmic shielding as the bubble size outgrows and eclipses the electrode ring beneath.