Release Of Hydrogen Bubbles Research Articles

Defect Passivation of Mn2+-Doped CsPbX3(X=Cl,Br) Perovskite Nanocrystals as Electrocatalyst for Overall Water Splitting.

Mn doping has been used to improve the physical chemistry of lead halide perovskite nanocrystals such as CsPbX3, where X is a halogen ion. In this paper, a two-phase method for Mn-doped CsPbX3 nanosheets (where X=Br, Cl), namely water-hexane system, is reported. Compared to conventional catalyst arrays, the band gap of CsPbBr3 nanocrystalline is easily tuned, the carrier diffusion distance is remote, the band edge position of the band structure is favorable for a wide range of electrocatalytic redox reactions, and the catalytic active site is maximally exposed, providing a larger electrolyte contact area. The porous hierarchical structure also accelerates the release of hydrogen bubbles. The results showed that the optimized Mn : CsPbBr3 catalyst exhibited excellent electrolytic performance of aquatic hydrogen in alkaline electrolyte (1 mol/L KOH). The overpotentials of the oxygen evolution reaction (OER) at the current densities of 10 and 100 mA cm-2 are only 114.4 and 505.4 mV, respectively, with a Tafel slope of 43 mV dec-1. At a current density of 10 mA cm-2, the excess potential required for the hydrogen evolution reaction (HER) is 158.6 mV and it exhibits excellent electrochemical stability. The Mn : CsPbBr3 nanocrystalline consists of two electrodes for hydrolysis of water, requiring only a voltage of 1.45 V. This provides implications for the optimization of electrocatalysts in alkaline electrolytes with the aim of developing next generation 2D electrocatalysts for overall water splitting.

Enhancing hydrogen bubble release from a microelectrode through precise tuning of Marangoni forces with nonionic surfactant

Understanding and controlling hydrogen bubble growth and detachment during water electrolysis is crucial for improving its efficiency. This study investigates bubble dynamics for hydrogen evolution on a platinum microelectrode in an acidic electrolyte with different gas/electrolyte surface tensions by adding varying surfactant concentrations. Three hydrogen bubble evolution patterns were observed: periodic detachment of individual bubbles at low surfactant concentrations of 0 and 1 × 10−7 M, respectively; one or two small bubbles are formed at the foot of the bubble during the evolution of single main bubble at intermediate surfactant concentrations of 1 × 10−6 and 1 × 10−5 M; and periodic detachment of large bubbles with aperiodic release of tiny bubbles at higher surfactant concentrations of 1 × 10−4 M. The concentration Marangoni force on individual H2 bubbles decreases significantly with surfactant concentration. This results in shorter evolution cycles from 138.12 to 6.98 s at −0.6 V vs the saturated calomel electrode, reduced detachment radii from 765.95 to 359.54 μm at −0.6 VSCE, and accelerated hydrogen bubble growth. This finding offers a new way to control bubble dynamics during electrochemical bubble formation.

Enhancement of micro hole wetting and hydrogen bubble release in the process of Ni micro electroforming under megasonic field

Micro hole wetting and hydrogen bubble release are two technical issues in the process of micro hole electroforming. A novel method of megasonic (1.7 MHz) field was introduced in order to solve the two problems and fabricate 20 μm micro column array in this paper. Micro electroforming experiments, capillary tube experiments, electrochemical experiments and testing of contact angle and surface tension coefficient were conducted without and with megasonic field. Experimental results indicated that megasonic field can promote micro hole wetting and bubbles release in the process of micro electroforming. 20 μm micro column array can be fabricated successfully under 2 W/cm2 megasonic field. Because megasonic can decrease the contact angle between photoresist and electroforming solution, reduce the surface tension coefficient of electroforming solution and increase equilibrium potential of nickel. New mechanisms on enhancement of micro hole wetting and bubble release under megasonic field were revealed. The research provides a new comprehension of micro hole wetting and bubble release, which may be good for develop a new method to fabricate micro column array.

Boosting Nitrate to Ammonia Electroconversion through Hydrogen Gas Evolution over Cu-foam@mesh Catalysts.

The hydrogen evolution reaction (HER) is often considered parasitic to numerous cathodic electro-transformations of high technological interest, including but not limited to metal plating (e.g., for semiconductor processing), the CO2 reduction reaction (CO2RR), the dinitrogen → ammonia conversion (N2RR), and the nitrate reduction reaction (NO3-RR). Herein, we introduce a porous Cu foam material electrodeposited onto a mesh support through the dynamic hydrogen bubble template method as an efficient catalyst for electrochemical nitrate → ammonia conversion. To take advantage of the intrinsically high surface area of this spongy foam material, effective mass transport of the nitrate reactants from the bulk electrolyte solution into its three-dimensional porous structure is critical. At high reaction rates, NO3-RR becomes, however, readily mass transport limited because of the slow nitrate diffusion into the three-dimensional porous catalyst. Herein, we demonstrate that the gas-evolving HER can mitigate the depletion of reactants inside the 3D foam catalyst through opening an additional convective nitrate mass transport pathway provided the NO3-RR becomes already mass transport limited prior to the HER onset. This pathway is achieved through the formation and release of hydrogen bubbles facilitating electrolyte replenishment inside the foam during water/nitrate co-electrolysis. This HER-mediated transport effect "boosts" the effective limiting current of nitrate reduction, as evidenced by potentiostatic electrolyses combined with an operando video inspection of the Cu-foam@mesh catalysts under operating NO3-RR conditions. Depending on the solution pH and the nitrate concentration, NO3-RR partial current densities beyond 1 A cm-2 were achieved.

Electrodeposition of composite coatings based on copper matrix included titanium dioxide in sulfuric acid solutions

The process of reduction of Cu2+ from sulfuric acid solutions containing titanium dioxide as a dispersed phase (DP) was studied by electrolysis method. Composite electrochemical coatings (CEC) with a copper matrix with the inclusion of titanium dioxide were obtained. It has been established that with a change in the current density in the range of 50–300 A/m2, the content of titanium dioxide in the CEC noticeably decreases. It is shown that an increase in the concentration of DP in the range of 5-20 g/l and the concentration of sulfuric acid from 50 to 250 g/l leads to an increase in the content of titanium dioxide in the coatings. It was also found that with an increase in the stirring rate (100–600 rpm) and the concentration of Cu2+ (5–50 g/l), the content of titanium dioxide in the coating increases. It is noted that at low concentrations of Cu2+ in the electrolyte, a loose powdery precipitate formed, which is associated with the occurance of cathodic processes at current densities above the limiting current and with the co-release of hydrogen. The release of hydrogen bubbles additionally contributes to the loosening of the precipitate, and also prevents co-deposition of titanium dioxide. It is found that a dense uniform coating is obtained upon polarization by a cathode pulsed current. The proportion of inclusion of titanium dioxide in the composition of the composite coating with a change in current density in the range of 50-400 A/m2 reaches 2.1%. However, at current density above 400 A/m2, copper is deposited in the form of a powder, and no coating is formed.The obtained CEC were identified by electron scanning microscopy, and their elemental composition was determined, confirming the presence of titanium dioxide. The micrographs show a uniform distribution of TiO2 particles on the cathode surface.

Scalable Synthesis of Pt Nanoflowers on Solution‐Processed MoS2 Thin Film for Efficient Hydrogen Evolution Reaction

Nanostructuring of Pt nanocatalysts increases the surface‐to‐volume ratio, thus enabling efficient usage of Pt for hydrogen evolution reaction (HER). Direct electrochemical reduction of Pt on the electrode can produce nanostructured Pt catalysts, which has been time‐consuming for the conventional colloidal synthesis. However, carbon‐based growth templates commonly used to create Pt nanoparticles offer limited control over morphologies and HER performance. Herein, a facile electrochemical synthesis of Pt nanoflowers (NFs) with well‐defined petals is presented. Semiconducting MoS2 nanosheets are solution processed into a film on a carbon paper (CP) to synthesize Pt NFs upon reduction of Pt precursor. The Pt NFs show higher HER activities than spherical or spiky Pt nanoparticles because of their larger active surface area and enable faster release of hydrogen bubbles during HER. By generating sulfur vacancies and MoOx on the MoS2 template using a reactive ion etching, the areal density and spatial uniformity of Pt NFs can be greatly enhanced and a mass activity can be achieved more than 10 times as high as that of the conventional Pt/C electrode. Multiple electrodes with nearly similar electrochemical properties can be repeatedly produced by using a single precursor solution, which highlights the cost‐efficiency and scalability of our synthesis strategy.

Achieving highly efficient pH-universal hydrogen evolution by superhydrophilic amorphous/crystalline Rh(OH)3/NiTe coaxial nanorod array electrode

Design of high-performance pH-universal electrocatalysts is critical to practical large-scale hydrogen generation as a carbon-neutral fuel, yet challenging. Herein, we report an unique motif with crystalline nickel tellurium nanorods enclosed by amorphous rhodium hydroxide (a-Rh(OH)3/NiTe), formed through a hydrothermal synthesis and a subsequent chemical etching process, to address this challenge. The as-prepared a-Rh(OH)3/NiTe cathode enables a current density of 100 mA cm−2 with low overpotentials of 51, 109, and 64 mV for HER in alkaline, neutral and acidic media, respectively. As revealed by density functional theory (DFT) calculations, the electronic interactions between a-Rh(OH)3 and NiTe enhance the performance of Rh active sites. More importantly, the motif possesses superhydrophilicity and aerophobicity features, which not only facilitates the access to electrolytes but also ensures the fast release of hydrogen bubbles, endowing the electrocatalyst with advanced pH-universal HER activity. This work provides insights for the design of highly efficient electrocatalysts for hydrogen evolution at both molecular and mesoscopic levels.

Short-Term In Vivo Response to Anodized Magnesium Alloy as a Biodegradable Material for Bone Fracture Fixation Devices.

Biodegradable materials based on magnesium alloys have a huge potential for bone fracture fixation devices due to their adequate mechanical properties and biocompatibility. However, their fast degradation and the consequent liberation of hydrogen gas at the initial stages of implantation is the major limitation for their use. In this study, the AZ91D magnesium alloy was surface treated by an environment-friendly, nontoxic, and low-cost anodizing process and the early in vivo response was studied in a rat transcortical model. Adequate maturation of woven bone around implants-detected at day 7 post implantation-to lamellar bone was observed from day 15. Lamellar bone after 15 and 30 days of implantation presented similar volume, mineralization pattern, mineral to protein content, and estimated bone maturity between anodized AZ91D and polylactic acid (control) implants. Histology observation showed neither release of hydrogen bubbles in the region closed to the anodized AZ91D implant nor systemic effects on liver, kidney, and spleen. Thus, anodizing of AZ91D in the conditions stated here induced an adequate short-term in vivo response, which postulates their use as potential biodegradable fracture fixation devices for bone healing.

Production of silumins with highly dispersed inverted microstructure

Thermodynamic calculations of the structure of metal melts, processes of their crystallization and degassing in the eutectic reaction have been made. It is shown. That the main structural elements are nanocrystals, and hydrogen bubbles have a direct effect on the morphology of eutectic crystals and the phase structuring process. Physical and chemical principles and mechanisms for modifying the microstructure of silumins have been developed. It has been found that the main processes affecting the modification of phase crystals are the intensity of coagulation of nanocrystals, refining from adsorbed oxygen and hydrogen atoms, and preventing the release of hydrogen bubbles on eutectic crystals. Environmentally safe methods of casting silumins with highly dispersed inverted microstructure are developed, based on mixing of liquid metal and liquid-hard alloy, accelerated hardening and structural-hereditary modification. Antifriction silumin has been developed, which in terms of friction wear resistance exceeds and replaces industrial aluminium and tin bronzes, but is cheaper and lighter in 2–3 times. Universal silumin modifiers for steel, bronze, cast iron, brass have been developed. Devices and crystallizers with a flood-jet cooling system have been developed, which are 2–3 times more effective than normal ones. Experimental-industrial casting section for production of solid and hollow billets from silumins with highly dispersed inverted microstructure has been created. These pieces are supplied to more than 100 industrial enterprises of Belarus, Russia, Korea and Ukraine.

In-situ synthesis of hollow Co–MoS2 nanocomposites on the carbon nanowire arrays/carbon cloth as high-performance catalyst for hydrogen evolution reaction

The design and synthesis of non-precious metal catalysts that effectively convert water into molecular hydrogen in an acidic environment is essential to reduce the energy loss in the water splitting process. Among them, molybdenum disulfide (MoS2) is considered as an effective alternative to Pt-based materials due to its excellent structure properties. Here, by using metal-organic framework (MOF) as the precursor, sodium molybdate as molybdenum sources and thiourea as sulfur sources, a hollow structure of Co–MoS2 electrocatalyst was prepared on highly conductive carbon nanowire arrays/carbon cloth (CA/CC) by hydrothermal reaction. The combination of carbon nanowire arrays and carbon cloth ensures the high conductivity, while the hollow Co–MoS2 structure promotes the penetration of electrolytes and the release of hydrogen bubbles. The overpotential is only 296 mV when the current density was ~1500 mA/cm2, which shows excellent catalytic hydrogen evolution activity of the material. In addition, the three-dimensional hollow structure avoids the use of adhesives between the active material and the self-supporting material, which can improve the stability of the material and provides a new idea to design commercial electrocatalysts.

Copper-nickel oxide nanofilm modified electrode for non-enzymatic determination of glucose

CuxO-NiO nanocomposite film for the non-enzymatic determination of glucose was prepared by the novel modifying method. At first, anodized Cu electrode was kept in a mixture solution of CuSO4, NiSO4 and H2SO4 for 15 minutes. Then, a cathodization process with a step potential of -6 V in a mixture solution of CuSO4 and NiSO4 was initiated, generating formation of porous Cu-Ni film on the bare Cu electrode by electrodeposition assisted by the release of hydrogen bubbles acting as soft templates. Optimized conditions were determined by the experimental design software for electrodeposition process. Afterward, Cu-Ni modified electrode was scanned by cyclic voltammetry (CV) method in NaOH solution to convert Cu and Ni nanoparticles to the nano-scaled CuxO-NiO film. The electrocatalytic behavior of the novel CuxO-NiO film toward glucose oxidation was studied by CV and chronoamperometry (CHA) techniques. The calibration curve of glucose was found linear in a wide range of 0.04–5.76 mM, with a low limit of detection (LOD) of 7.3 µM (S/N = 3) and high sensitivity (1.38 mA mM-1 cm-2). The sensor showed high selectivity against some usual interfering species and high stability (loss of only 6.3 % of its performance over one month). The prepared CuxO-NiO nanofilm based sensor was successfully applied for monitoring glucose in human blood serum and urine samples.

Biodegradable Magnesium Bone Implants Coated with a Novel Bioceramic Nanocomposite.

Magnesium (Mg) alloys are being investigated as a biodegradable metallic biomaterial because of their mechanical property profile, which is similar to the human bone. However, implants based on Mg alloys are corroded quickly in the body before the bone fracture is fully healed. Therefore, we aimed to reduce the corrosion rate of Mg using a double protective layer. We used a magnesium-aluminum-zinc alloy (AZ91) and treated its surface with micro-arc oxidation (MAO) technique to first form an intermediate layer. Next, a bioceramic nanocomposite composed of diopside, bredigite, and fluoridated hydroxyapatite (FHA) was coated on the surface of MAO treated AZ91 using the electrophoretic deposition (EPD) technique. Our in vivo results showed a significant enhancement in the bioactivity of the nanocomposite coated AZ91 implant compared to the uncoated control implant. Implantation of the uncoated AZ91 caused a significant release of hydrogen bubbles around the implant, which was reduced when the nanocomposite coated implants were used. Using histology, this reduction in the corrosion rate of the coated implants resulted in an improved new bone formation and reduced inflammation in the interface of the implants and the surrounding tissue. Hence, our strategy using a MAO/EPD of a bioceramic nanocomposite coating (i.e., diopside-bredigite-FHA) can significantly reduce the corrosion rate and improve the bioactivity of the biodegradable AZ91 Mg implant.

Hydrogen bubble evolution from magnetized nickel wire electrode

How to reduce the bubble coverage of the electrode is one of the key issues in water electrolysis which is related to the reduction of energy consumption. In this work, the magnetized nickel electrode with 100 μm diameter is used as working electrode in hydrogen evolution reaction (HER) during alkaline water electrolysis (1 mol/L, KOH). According to the experimental observation, both of the bubble's diameter and number have decreased at the magnetized surface compared with the unmagnetized one. The B–H loop measurement shows that the residual magnetic field intensity (Br) of the magnetized nickel electrode is up to 0.03 T. It can be found from the numerical simulation result that the residual magnetic field exactly right brings the Lorentz force and magnetohydrodynamic (MHD) convection near the electrode surface, which play the role of helping hydrogen bubble release from the electrode, even if the external magnetic field is absent in experiment. The new finding may develop a new way of utilizing magnetic field in water electrolysis for gas product elimination and energy conservation.

A Magnesium-based Nanobiocomposite Processed by a Novel Technique Combining High Shear Solidification and Hot Extrusion.

Most of the currently available Mg-based biomaterials corrode too fast in the physiological environment, causing many problems including hydrogen bubble release and premature mechanical failure. It is commonly recognized that high biodegradation rate is the major factor limiting their clinical applications. The present research aims to develop a new magnesium (Mg)-based biomaterial with a controlled biodegradation rate. A magnesium-hydroxyapatite (Mg-1.61Zn-0.18Mn-0.5Ca/1HA) nanocomposite was developed by a novel technique which combines high shear solidification and hot extrusion, followed by heat treatment. The microstructure and biodegradation rate of the nanocomposite in HBSS Hanks' Balanced Salt Solution were assessed. Biodegradation behaviour was studied using electrochemical corrosion and immersion test. Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were used to characterize the surface microstructure, biodegradation morphology and to analyse the biodegradation products. Few patents were also cited in the article. Under the optimized procedure of high shear solidification, extrusion and heat treatment at 400°C, the Mg-1.61Zn-0.18Mn-0.5Ca/1HA exhibited a satisfactory biodegradation rate of 0.12±0.04 mm/year. This technology shows a potential of breakthrough innovation in the manufacturing of Mg-based biomaterials with a decreased biodegradation rate.

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.

Electrode-normal magnetic field facilitating neighbouring electrochemical bubble release from hydrophobic islets

This paper gives an experimental study on electrochemical hydrogen bubble evolution at electrode surface partially covered with hydrophobic materials under electrode-normal magnetic field. Base on the method of photoetching and electrochemical co-deposition (PECD), the electrode partially covered with nickel–polytetrafluoroethylene (Ni-PTFE) materials is prepared to generate the controlled hydrogen bubble at specified islet. The anchored bubble evolution at hydrophobic islet is observed under magnetic field. Experimental results show that the hydrogen bubble release from the hydrophobic site is relatively random. Although it is not found that the obvious influence of micro-magnetohydrodynamic convection (MMHDC) on the single bubble release from isolated hydrophobic islet, MMHDC exactly plays the role of facilitating pair of bubbles releases from neighbouring hydrophobic islands. The new developed explanation of the mechanism of MMHDC influence on electrochemical bubble release has been given based on the method of numerical simulation.

High hydrogen evolution performance of Al doped CoP3 nanowires arrays with high stability in acid solution superior to Pt/C

To promote hydrogen production through water splitting, novel porous 3D Al doped CoP3 nanowire arrays on carbon fiber paper are successfully fabricated as an effective self-supported electrode for hydrogen evolution reaction. The results indicate that the electrocatalytic performance of CoP3 can be dramatically enhanced via Al doping. It only needs an overpotential of only 40 mV to achieve the current density of 10 mA cm−2 with a small Tafel slop of 43 mV dec−1 for the Al (10%)-CoP3 nanowire arrays. Moreover, the Al (10%)-CoP3 NAs/CFP exhibit superior HER efficiency to Pt/C film at high overpotentials due to prompt release of hydrogen bubbles on the special nanowire arrays surfaces. This study demonstrates an avenue for further improving the electrocatalytic activity via tuning the electronic structures and adjusting the surface morphologies through heteroatoms doping.

Controlled electrodeposition of CoMoSx on carbon cloth: A 3D cathode for highly-efficient electrocatalytic hydrogen evolution

Three-dimensional (3D) hydrogen evolution reaction (HER) catalysts are admirable for their advantages of enhanced electrolyte diffusion, more efficient utilization of active sites and easy release of hydrogen bubbles. In this work, the binder-free 3D cathode CoMoSx/CC has been successfully fabricated with the employment of 3D electrode, carbon cloth (CC). CoMoSx film was successfully deposited on CC with controllable morphology and thickness by the convenient co-electrodeposition process. Moreover, the deposition conditions have been optimized systematically. CoMoSx/CC fabricated under optimum conditions has achieved excellent HER performance with a small onset overpotential of 100 mV. It needed only 100, 125 and 180 mV overpotential (vs. RHE) to reach the current density of 10, 20 and 100 mA/cm2 respectively, which performed the highest electrocatalytic activity among binary metal sulfide HER catalysts ever reported.

In vivo biocompatibility of Mg implants surface modified by nanostructured merwinite/PEO.

Magnesium (Mg) alloys have been suggested as biodegradable bone implant materials due to their good intrinsic biocompatibility and great mechanical properties. Although magnesium has attractive properties as an orthopedic implant material, its quick degradation and low bioactivity may lead to the loss of mechanical integrity of the implant during the bone healing process. In this paper, we endeavor to surmount the abovementioned defects using the surface coating technique. We have recently coated AZ91 magnesium implants with merwinite (Ca3MgSi2O8) through the coupling of plasma electrolytic oxidation (PEO) and electrophoretic deposition method. In this work, we are specifically focused on the in vivo examinations of the coated implants in comparison with the uncoated one. For the in vivo experiment, the rod samples, including the uncoated and merwinite/PEO coated implants, were imbedded into the greater trochanter of rabbits. The results of the in vivo animal test indicated an improvement in biodegradability including slower implant weight loss, reduction in Mg ion released from the coated implants in the blood plasma, lesser release of hydrogen bubbles and an improvement in biocompatibility including an increase in the amount of bone formation and ultimately a mild bone inflammation after the surgery according to the histological images. In summary, proper surface treatment of magnesium implants such as silicate bioactive ceramics may improve their biocompatibility under physiological conditions to making them suitable and applicable for future clinical applications.

In vivo study of nanostructured akermanite/PEO coating on biodegradable magnesium alloy for biomedical applications.

The major issue for biodegradable magnesium alloys is the fast degradation and release of hydrogen gas. In this article, we aim to overcome these disadvantages by using a surface modified magnesium implant. We have recently coated AZ91 magnesium implants by akermanite (Ca2 MgSi2 O7 ) through the combined electrophoretic deposition (EPD) and plasma electrolytic oxidation (PEO) methods. In this work, we performed the in vitro and in vivo examinations of these coated implants using L-929 cell line and rabbit animal model. The in vitro study confirmed the higher cytocompatibility of the coated implants compare to the uncoated ones. For the in vivo experiment, the rod samples were implanted into the greater trochanter of rabbits and monitored for two months. The results indicated a noticeable biocompatibility improvement of the coated implants which includes slower implant weight loss, reduction in Mg ion released from the coated samples in the blood plasma, lower release of hydrogen bubbles, increase in the amount of bone formation and ultimately lower bone inflammation after the surgery according to the histological images. Our data exemplifies that the proper surface treatment of the magnesium implants can improve their biocompatibility under physiological conditions to make them applicable in clinical uses. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 1798-1808, 2015.