Bubble growth kinetics has been attracting vast attention in water electrolysis and other gas evolution reactions,but mostly investigated under ambient pressure.For practical scenarios,bubble evolution is usually carr...Bubble growth kinetics has been attracting vast attention in water electrolysis and other gas evolution reactions,but mostly investigated under ambient pressure.For practical scenarios,bubble evolution is usually carried out under high pressure.To better understand the bubble growth kinetics,we monitored the hydrogen bubble evolution process at increased pressures during electrochemical hydrogen production.Unlike the common sense that high pressures could result in smaller bubble size,our results revealed that the increased pressure would increase the aerophilicity of electrode surface,with decreased bubble contact angle from 111°to 89°for 0.1‒2.0MPa,increased detachment size from 233 to 1207μm,and reduced growth coefficient from 230 to 10.9 for the high pressures from 0.1 to 3.0 MPa.The steady high-pressure bubble growth kinetics are basically governed by the as-formed supersaturation in bulk solution,which is the balance between the driving force(current density)and the enlarged solubility of bulk solution under high pressure.Insufficient driving force would induce the depletion of bulk supersaturation and stagnate the bubble growth.Further investigation on high-pressure bubble evolution behaviors should shed light on practical industrial electrode design with extended usage life.展开更多
Understanding bubbles evolution kinetics on electrodes with varied geometries is of fundamental importance for advanced electrodes design in gas evolution reaction.In this work,the evolution kinetics of electro-genera...Understanding bubbles evolution kinetics on electrodes with varied geometries is of fundamental importance for advanced electrodes design in gas evolution reaction.In this work,the evolution kinetics of electro-generated hydrogen bubbles are recorded in situ on three(i.e.smooth,nanoporous,and nanoarray)Pt electrodes to identify the geometry dependence.The bubble radius shows a time-dependent growth kinetic,which is tightly-connected to the electrode geometry.Among the three electrodes,the smooth one shows a typical time coefficient of 0.5,in consistence with reported values;the nanoporous one shows a time coefficient of 0.47,less than the classic one(0.5);while the nanoarray one exhibits fastest bubble growth kinetics with a time coefficient higher than 0.5(0.54).Moreover,the nanoarray electrode has the smallest bubble detachment size and the largest growth coefficient(23.3)of all three electrodes.Based on the experimental results,a growth model combined direct bottom-injection with micro-convection is proposed to illustrate the surface geometry dependent coefficients,i.e.,the relationship between geometry and bubble evolution kinetics.The direct injection of generated gas molecules from the bottom of bubbles at the three phase boundaries are believed the key to tailor the bubble wetting states and thus determine the bubble evolution kinetics.展开更多
In this paper,dendritic Bi film electrodes with porous structure had successfully been prepared on glassy carbon electrode using a constant current electrolysis method based on hydrogen bubble dynamic templates.The el...In this paper,dendritic Bi film electrodes with porous structure had successfully been prepared on glassy carbon electrode using a constant current electrolysis method based on hydrogen bubble dynamic templates.The electrode prepared using a large applied current density showed an increased internal electroactive area and a significantly improved electrochemical performance.The analytical utility of the prepared dendritic Bi film electrodes for the determination of Pb(Ⅱ)and Cd(Ⅱ)in the range of 5–50 μg·L^(-1)were presented in combination with square wave stripping voltammetry in model solution.Compared with non-porous Bi film electrode,the dendritic Bi film electrode exhibited higher sensitivity and lower detection limit.The prepared Bi film electrode with dendritic structure was also successfully applied to real water sample analysis.展开更多
The effects of streaks on boundary layer transition depend on the initial amplitude of T-S waves introduced to excite the transition. This problem was studied in a flat-plate boundary layer in water tunnel by using hy...The effects of streaks on boundary layer transition depend on the initial amplitude of T-S waves introduced to excite the transition. This problem was studied in a flat-plate boundary layer in water tunnel by using hydrogen bubble method. Three T-S wave initial amplitudes were tested. The results show that both narrow and wide-spacing streaks depress the transition excited by T-S waves with lower initial amplitude. However, when transition is excited by T-S waves of higher initial amplitude, the narrow-spacing streaks depress the transition, while the wide-spacing streaks promote the transition. Futrther the underlying mechanisms were also analyzed.展开更多
In this paper, an experimental investigation on the flow structures in a turbulent bounda- ry layer employing a special laser light sheet-Hydrogen bubble flow visualization technique is described. It is observed that ...In this paper, an experimental investigation on the flow structures in a turbulent bounda- ry layer employing a special laser light sheet-Hydrogen bubble flow visualization technique is described. It is observed that the high/low speed streaks are directly related to the hairpin or horseshoe-like vortices. This observation can give a better understanding of the physical mechanism in the turbulent boundary layer.展开更多
The work investigates influence of the electrolyte conductivity on the onset of partial contact glow discharge electrolysis(CGDE)in a water electrolysis.Critical current density(CCD)and breakdown voltage were measured...The work investigates influence of the electrolyte conductivity on the onset of partial contact glow discharge electrolysis(CGDE)in a water electrolysis.Critical current density(CCD)and breakdown voltage were measured together with in situ observation of hydrogen bubble behavior,whose influence has not been focused on.For a fixed current during normal electrolysis,hydrogen coalescence adjacent to cathode surface was invigorated at a lower conductivity.Photographic analyses elucidated the hydrogen coalescence characteristics by quantifying size and population of detached hydrogen bubbles.The CCD increased about 104% within given range of conductivity(11.50-127.48 mS·cm^(-1))due to impaired bubble coalescence,which delays hydrogen film formation on the cathode.Meanwhile,decreasing trend of breakdown voltage was measured with increased conductivity showing maximum drop of 74%.It is concluded that onset of partial CGDE is directly affected by hydrodynamic bubble behaviors,whereas the electrolyte conductivity affects the bubble formation characteristics adjacent to cathode electrode.展开更多
Studies on the high-lift mechanisms of butterfly gliding flights shed light on the design of the micro air vehicles.The flow field around a simplified Danaus plexippus model is investigated using the hydrogen bubble v...Studies on the high-lift mechanisms of butterfly gliding flights shed light on the design of the micro air vehicles.The flow field around a simplified Danaus plexippus model is investigated using the hydrogen bubble visualization and the Particle Image Velocimetry(PIV)techniques.There are three near-wall topological patterns with different Angles of Attack(AoAs):the separation bubble,the Leading-Edge Vortex(LEV)and the high Ao As flow.For the separation bubble pattern,two saddles and two foci form in the middle of the model.The features of the LEV pattern are the leading-edge separation lines.The topological characteristics of the separation lines are changed by the interaction between the LEV and the Wing-Tip Vortex(WTV).For the high Ao As flow pattern,four unstable foci are found at the forewing and the hindwing respectively.The angle between the trajectory of the WTV and the model increases with increasing Ao A even though the slope of the WTV angle versus Ao A curve declines at the moderate AoAs.展开更多
This paper describes the discharge control technique on boundary used in two models, one is the model of hot water drainning in Dayawan Nyclear Power Plant, Guangdong, and the other is the model for trainhing the sand...This paper describes the discharge control technique on boundary used in two models, one is the model of hot water drainning in Dayawan Nyclear Power Plant, Guangdong, and the other is the model for trainhing the sand bar at the Guanhe Estuary, Jiangsu. Many years of application shows that this technique has the advantages of good reliability, repeatability and validity. The speedometer of hydrogen bubble is also introduced in this paper. The device can display and store tracing lines in a computer, and help operators to obtain the value and direction of transient velocity of a nonsteady current, thus, the problem of measurment of low current velocity in tidal model tests is solved and the automation of the measurement of current velocity is realized.展开更多
In this work,a novel stearic acid modified nickel-based(NiSA)superhydrophobic composite coating with good anti-corrosion properties was prepared on magnesium alloy AZ31 surface through electroless nickel-phosphorus pl...In this work,a novel stearic acid modified nickel-based(NiSA)superhydrophobic composite coating with good anti-corrosion properties was prepared on magnesium alloy AZ31 surface through electroless nickel-phosphorus plating,electrodeposition of porous nickel,and decoration with stearic acid.Surface topography,chemical groups,and structural compositions of the Ni SA coating were characterized through scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),and X-ray diffraction(XRD),respectively.Adhesion of the Ni SA coating was evaluated by a tape test method,and corresponding water contact angle(WCA)and water sliding angle(WSA)were tested by a contact angle meter.Results indicate that WCA value of the Ni SA coating was154.6°±3.7°,and WSA value was 5.9°±1.7°,indicating a high superhydrophobicity.Electrochemical impedance spectroscopy(EIS)and Tafel fitting reveal that the corrosion current density of the coating(j_(corr)=1.41×10^(-8)A cm^(-2))was three orders of magnitude lower than that of the bare magnesium alloy,and the corresponding lowfrequency impedance modulus(|Z|_(f=0.01 Hz)=554.65 kΩcm^(2))increased by three orders of magnitude,verifying high corrosion resistance.Moreover,all contact angles(CA)of common liquid stains in life were higher than150°,indicating the good anti-fouling capability of the NiSA coating.展开更多
基金National Key Research and Development Project,Grant/Award Number:2022YFA1504000National Natural Science Foundation of China,Grant/Award Numbers:21935001,22379005+1 种基金Fundamental Research Funds for the Central UniversitiesMinistry of Finance and theMinistry of Education of PRC。
文摘Bubble growth kinetics has been attracting vast attention in water electrolysis and other gas evolution reactions,but mostly investigated under ambient pressure.For practical scenarios,bubble evolution is usually carried out under high pressure.To better understand the bubble growth kinetics,we monitored the hydrogen bubble evolution process at increased pressures during electrochemical hydrogen production.Unlike the common sense that high pressures could result in smaller bubble size,our results revealed that the increased pressure would increase the aerophilicity of electrode surface,with decreased bubble contact angle from 111°to 89°for 0.1‒2.0MPa,increased detachment size from 233 to 1207μm,and reduced growth coefficient from 230 to 10.9 for the high pressures from 0.1 to 3.0 MPa.The steady high-pressure bubble growth kinetics are basically governed by the as-formed supersaturation in bulk solution,which is the balance between the driving force(current density)and the enlarged solubility of bulk solution under high pressure.Insufficient driving force would induce the depletion of bulk supersaturation and stagnate the bubble growth.Further investigation on high-pressure bubble evolution behaviors should shed light on practical industrial electrode design with extended usage life.
基金This work was supported by the National Natural Science Foundation of China(NSFC)the National Key Research and Development Project(Nos.2018YFB1502401 and 2018YFA0702002)+3 种基金the Royal Society and the Newton Fund through the Newton Advanced Fellowship award(NAF\R1\191294)the Program for Changjiang Scholars and Innovation Research Team in the University(No.IRT1205)the Fundamental Research Funds for the Central Universitiesthe long-term subsidy mechanism from the Ministry of Finance and the Ministry of Education of China.
文摘Understanding bubbles evolution kinetics on electrodes with varied geometries is of fundamental importance for advanced electrodes design in gas evolution reaction.In this work,the evolution kinetics of electro-generated hydrogen bubbles are recorded in situ on three(i.e.smooth,nanoporous,and nanoarray)Pt electrodes to identify the geometry dependence.The bubble radius shows a time-dependent growth kinetic,which is tightly-connected to the electrode geometry.Among the three electrodes,the smooth one shows a typical time coefficient of 0.5,in consistence with reported values;the nanoporous one shows a time coefficient of 0.47,less than the classic one(0.5);while the nanoarray one exhibits fastest bubble growth kinetics with a time coefficient higher than 0.5(0.54).Moreover,the nanoarray electrode has the smallest bubble detachment size and the largest growth coefficient(23.3)of all three electrodes.Based on the experimental results,a growth model combined direct bottom-injection with micro-convection is proposed to illustrate the surface geometry dependent coefficients,i.e.,the relationship between geometry and bubble evolution kinetics.The direct injection of generated gas molecules from the bottom of bubbles at the three phase boundaries are believed the key to tailor the bubble wetting states and thus determine the bubble evolution kinetics.
基金Supported by the National Natural Science Foundation of China(51472073,51201058)
文摘In this paper,dendritic Bi film electrodes with porous structure had successfully been prepared on glassy carbon electrode using a constant current electrolysis method based on hydrogen bubble dynamic templates.The electrode prepared using a large applied current density showed an increased internal electroactive area and a significantly improved electrochemical performance.The analytical utility of the prepared dendritic Bi film electrodes for the determination of Pb(Ⅱ)and Cd(Ⅱ)in the range of 5–50 μg·L^(-1)were presented in combination with square wave stripping voltammetry in model solution.Compared with non-porous Bi film electrode,the dendritic Bi film electrode exhibited higher sensitivity and lower detection limit.The prepared Bi film electrode with dendritic structure was also successfully applied to real water sample analysis.
基金supported by the National Natural Science Foundation of China (11072017)
文摘The effects of streaks on boundary layer transition depend on the initial amplitude of T-S waves introduced to excite the transition. This problem was studied in a flat-plate boundary layer in water tunnel by using hydrogen bubble method. Three T-S wave initial amplitudes were tested. The results show that both narrow and wide-spacing streaks depress the transition excited by T-S waves with lower initial amplitude. However, when transition is excited by T-S waves of higher initial amplitude, the narrow-spacing streaks depress the transition, while the wide-spacing streaks promote the transition. Futrther the underlying mechanisms were also analyzed.
文摘In this paper, an experimental investigation on the flow structures in a turbulent bounda- ry layer employing a special laser light sheet-Hydrogen bubble flow visualization technique is described. It is observed that the high/low speed streaks are directly related to the hairpin or horseshoe-like vortices. This observation can give a better understanding of the physical mechanism in the turbulent boundary layer.
基金sponsored by the Korean Ministry of Science and ICT(MSIT)supported by nuclear Research&Development program grant funded by the National Research Foundation(NRF)(2021M2D1A1084838)。
文摘The work investigates influence of the electrolyte conductivity on the onset of partial contact glow discharge electrolysis(CGDE)in a water electrolysis.Critical current density(CCD)and breakdown voltage were measured together with in situ observation of hydrogen bubble behavior,whose influence has not been focused on.For a fixed current during normal electrolysis,hydrogen coalescence adjacent to cathode surface was invigorated at a lower conductivity.Photographic analyses elucidated the hydrogen coalescence characteristics by quantifying size and population of detached hydrogen bubbles.The CCD increased about 104% within given range of conductivity(11.50-127.48 mS·cm^(-1))due to impaired bubble coalescence,which delays hydrogen film formation on the cathode.Meanwhile,decreasing trend of breakdown voltage was measured with increased conductivity showing maximum drop of 74%.It is concluded that onset of partial CGDE is directly affected by hydrodynamic bubble behaviors,whereas the electrolyte conductivity affects the bubble formation characteristics adjacent to cathode electrode.
基金funded by the National Natural Science Foundation of China (No. 11721202)。
文摘Studies on the high-lift mechanisms of butterfly gliding flights shed light on the design of the micro air vehicles.The flow field around a simplified Danaus plexippus model is investigated using the hydrogen bubble visualization and the Particle Image Velocimetry(PIV)techniques.There are three near-wall topological patterns with different Angles of Attack(AoAs):the separation bubble,the Leading-Edge Vortex(LEV)and the high Ao As flow.For the separation bubble pattern,two saddles and two foci form in the middle of the model.The features of the LEV pattern are the leading-edge separation lines.The topological characteristics of the separation lines are changed by the interaction between the LEV and the Wing-Tip Vortex(WTV).For the high Ao As flow pattern,four unstable foci are found at the forewing and the hindwing respectively.The angle between the trajectory of the WTV and the model increases with increasing Ao A even though the slope of the WTV angle versus Ao A curve declines at the moderate AoAs.
文摘This paper describes the discharge control technique on boundary used in two models, one is the model of hot water drainning in Dayawan Nyclear Power Plant, Guangdong, and the other is the model for trainhing the sand bar at the Guanhe Estuary, Jiangsu. Many years of application shows that this technique has the advantages of good reliability, repeatability and validity. The speedometer of hydrogen bubble is also introduced in this paper. The device can display and store tracing lines in a computer, and help operators to obtain the value and direction of transient velocity of a nonsteady current, thus, the problem of measurment of low current velocity in tidal model tests is solved and the automation of the measurement of current velocity is realized.
基金financially supported by the National Natural Science Foundation of China(No.52271073)the Central Government Guided Special Program(No.2021ZYD0049)+1 种基金the Young Elite Scientists Sponsorship Program by CAST(No.2018QNRC001)the Opening Project of Material Corrosion and Protection Key Laboratory of Sichuan Province(No.2022CL17)
文摘In this work,a novel stearic acid modified nickel-based(NiSA)superhydrophobic composite coating with good anti-corrosion properties was prepared on magnesium alloy AZ31 surface through electroless nickel-phosphorus plating,electrodeposition of porous nickel,and decoration with stearic acid.Surface topography,chemical groups,and structural compositions of the Ni SA coating were characterized through scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),and X-ray diffraction(XRD),respectively.Adhesion of the Ni SA coating was evaluated by a tape test method,and corresponding water contact angle(WCA)and water sliding angle(WSA)were tested by a contact angle meter.Results indicate that WCA value of the Ni SA coating was154.6°±3.7°,and WSA value was 5.9°±1.7°,indicating a high superhydrophobicity.Electrochemical impedance spectroscopy(EIS)and Tafel fitting reveal that the corrosion current density of the coating(j_(corr)=1.41×10^(-8)A cm^(-2))was three orders of magnitude lower than that of the bare magnesium alloy,and the corresponding lowfrequency impedance modulus(|Z|_(f=0.01 Hz)=554.65 kΩcm^(2))increased by three orders of magnitude,verifying high corrosion resistance.Moreover,all contact angles(CA)of common liquid stains in life were higher than150°,indicating the good anti-fouling capability of the NiSA coating.
