scholarly journals A model of the growth of hydrogen bubbles in the electrolysis of water

2021 ◽  
Vol 927 ◽  
Author(s):  
F.J. Higuera
Keyword(s):  
Current Density ◽  
Electrode Surface ◽  
Reaction Model ◽  
Supersaturated Solution ◽  
Average Current Density ◽  
Hydrogen Bubbles ◽  
Diffusion Controlled ◽  
Dilute Aqueous Solution ◽  
Average Current ◽  
And Migration

The growth of attached bubbles during the electrochemical evolution of hydrogen at a horizontal cathode at the base of a quiescent, dilute aqueous solution is analysed using a simple model of the process that includes the Butler–Volmer reaction model, the diffusion and migration of electroactive species and a symmetry condition that approximately accounts for the presence of periodically spaced bubbles on the electrode surface. The diffusion controlled growth of a bubble approximately follows a $t^{1/2}$ law when the spacing of the bubbles on the electrode is large, departing slightly from it due to the non-uniformity of the concentration of dissolved hydrogen in the supersaturated solution into which the bubble grows, and approaches a $t^{1/3}$ law when the spacing decreases. The space- and time-averaged current density increases exponentially with the applied voltage for an alkaline solution when the consumption of water in the reaction is not taken into account. For an acidic solution, the average current density saturates to a transport limited value that depends on bubble spacing. For a given voltage, the presence of attached bubbles increases the average current density due to the decrease of the concentration overpotential caused by the bubbles. The spacing of the bubbles on the electrode surface decreases when the voltage increases if the maximum supersaturation at the electrode is imposed to be constant. The result suggests that coalescence of attached bubbles will occur above a certain voltage.

The efficient use of stabilizing materials in superconducting solenoids

1969 ◽  
Vol 47 (13) ◽  
pp. 1401-1407 ◽  
Author(s):  
Richard Stevenson
Keyword(s):  
Current Density ◽  
Transient Heat Conduction ◽  
Point Of View ◽  
Average Current Density ◽  
Initial Current ◽  
Current Sharing ◽  
Purity Aluminium ◽  
High Purity Aluminium ◽  
Average Current ◽  
Composite Conductor

The problem of stability of superconducting solenoids is considered from a thermal point of view. The transient heat conduction equation for a superconducting tape clad with normal material and operated in a current sharing mode is studied, and a solution for the temperature distribution is obtained. The composite conductor is considered stable if its final temperature in the current sharing mode corresponds to the critical temperature for the initial current density in the superconductor. Using this criterion, the operating point of the superconductor and its stabilizing cladding thickness can be chosen to give a maximum average current density in the composite conductor at any field. Calculations are given for Nb3Sn tape clad with OFHC copper and with high purity aluminium.

scholarly journals The study of Zn–Co alloy coatings electrochemically deposited by pulse current

2012 ◽  
Vol 66 (5) ◽  
pp. 749-757 ◽  
Author(s):  
Jelena Bajat ◽  
Miodrag Maksimovic ◽  
Milorad Tomic ◽  
Miomir Pavlovic
Keyword(s):  
Surface Roughness ◽  
Current Efficiency ◽  
Direct Current ◽  
Current Density ◽  
Pulse Current ◽  
Pulse Plating ◽  
Cathodic Current ◽  
Average Current Density ◽  
Corrosion Stability ◽  
Average Current

The electrochemical deposition by pulse current of Zn-Co alloy coatings on steel was examined, with the aim to find out whether pulse plating could produce alloys that could offer a better corrosion protection. The influence of on-time and the average current density on the cathodic current efficiency, coating morphology, surface roughness and corrosion stability in 3% NaCl was examined. At the same Ton/Toff ratio the current efficiency was insignificantly smaller for deposition at higher average current density. It was shown that, depending on the on-time, pulse plating could produce more homogenous alloy coatings with finer morphology, as compared to deposits obtained by direct current. The surface roughness was the greatest for Zn-Co alloy coatings deposited with direct current, as compared with alloy coatings deposited with pulse current, for both examined average current densities. It was also shown that Zn-Co alloy coatings deposited by pulse current could increase the corrosion stability of Zn-Co alloy coatings on steel. Namely, alloy coatings deposited with pulse current showed higher corrosion stability, as compared with alloy coatings deposited with direct current, for almost all examined cathodic times, Ton. Alloy coatings deposited at higher average current density showed greater corrosion stability as compared with coatings deposited by pulse current at smaller average current density. It was shown that deposits obtained with pulse current and cathodic time of 10 ms had the poorest corrosion stability, for both investigated average deposition current density. Among all investigated alloy coatings the highest corrosion stability was obtained for Zn-Co alloy coatings deposited with pulsed current at higher average current density (jav = 4 A dm-2).

Study on the Influence of Electrode Collocation to Electric Field Characteristic of ESP

2014 ◽  
Vol 875-877 ◽  
pp. 1683-1686
Author(s):  
Cheng Liang Jia ◽  
You Shan Sun ◽  
Chao Huang ◽  
Wan Peng Zhang ◽  
Fang Chen
Keyword(s):  
Electric Field ◽  
Current Density ◽  
Surface Current ◽  
Electrode Configuration ◽  
Electrode Gap ◽  
Average Current Density ◽  
Surface Current Density ◽  
Discharge Electrode ◽  
Field Characteristic ◽  
Average Current

A laboratory-scale ESP with new electrode configuration was established to investigate the electric field characteristic. Eight teeth prick line and prick plate with the length of 20mm were employed as discharge electrodes, respectively. The effects of discharge electrode type and electrode gap on V-I characteristic and surface current density were studied. The results showed that the optimum electrode gaps were 350-400mm for eight teeth line and 300-350mm for prick plate, which could obtained higher average current density and lower variance.

Current Distribution in a Polymer Electrolyte Membrane Fuel Cell Under Flooding Conditions

2009 ◽  
Author(s):  
A. Jamekhorshid ◽  
G. Karimi ◽  
X. Li
Keyword(s):  
Fuel Cell ◽  
Polymer Electrolyte ◽  
Current Distribution ◽  
Current Density ◽  
Polymer Electrolyte Membrane ◽  
Operating Conditions ◽  
Average Current Density ◽  
Electrolyte Membrane ◽  
Wide Range ◽  
Average Current

Non-uniform current distribution in polymer electrolyte membrane fuel cells results in local over-heating, accelerated ageing, and lower power output than expected. This issue is very critical when fuel cell experiences water flooding. In this work, the performance of a PEM fuel cell is investigated under cathode flooding conditions. A partially flooded GDL model is proposed to study local current density distributions along flow fields over a wide range of cell operating conditions. The model results show as cathode inlet humidity and/or cell pressure increase the average current density for the unflooded portions of the cell increases but the system becomes more sensitive to flooding. Operating the cell at higher temperatures would lead to higher average current densities and the chance of system being flooded is reduced. In addition, higher cathode stoichiometries prevent system flooding but the average current density remains almost constant.

Modeling, parametric analysis and optimization of an anode-supported planar solid oxide fuel cell

2015 ◽  
Vol 229 (17) ◽  
pp. 3125-3140 ◽  
Author(s):  
Mehdi Borji ◽  
Kazem Atashkari ◽  
Nader Nariman-zadeh ◽  
Mehdi Masoumpour
Keyword(s):  
Fuel Cell ◽  
Solid Oxide Fuel Cell ◽  
Temperature Difference ◽  
Current Density ◽  
Solid Oxide ◽  
Oxide Fuel ◽  
Multi Objective Optimization ◽  
Average Current Density ◽  
Multi Objective ◽  
Average Current

Solid oxide fuel cell is a promising tool for distributed power generation systems. This type of power system will experience different conditions during its operating life. The present study aims to simulate mathematically a direct internal reforming planar type anode supported solid oxide fuel cell considering mass and energy conservation equations along with a complete electrochemical model. Two main reactions, namely water–gas shift reaction and methane steam reforming reaction, are considered as two dominant reactions occurring in a fuel cell. Such a model may be employed to examine the effect of different operating conditions on main solid oxide fuel cell parameters, such as temperature gradients, power, and efficiency. Furthermore, using such mathematical model, a multi-objective optimization procedure can be applied to determine maximum cell efficiency and output power under constraints such as the allowable temperature difference and limited operating potential. The selected design variables are air ratio, fuel utilization, average current density, steam to carbon ratio, and pre-reforming rate of methane. It has been revealed that any increase in pre-reforming rate of methane and steam to carbon ratio of the entering fuel will lead to efficiency penalty and more uniform temperature distribution along the cell. In addition, the more average current density increases, the less electric efficiency is achieved, and on the other hand, the more temperature difference along the cell is seen. Besides, it is shown that some interesting and important relationships as useful optimal design principles involved in the performance of solid oxide fuel cells can be discovered by Pareto based multi-objective optimization of the mathematically obtained model representing their electric performance. Such important optimal principles would not have been obtained without the use of both mathematical modeling and the Pareto optimization approach.

Preparation of Ni-ZrO2-CeO2 Nanocomposite Coatings by Pulse Electrodeposition

2013 ◽  
Vol 395-396 ◽  
pp. 174-178 ◽  
Author(s):  
Yang Yang Xu ◽  
Yu Jun Xue ◽  
Fang Yang ◽  
Chun Yang Liu ◽  
Ji Shun Li
Keyword(s):  
Current Density ◽  
Smooth Surface ◽  
Pulse Current ◽  
Nanocomposite Coating ◽  
Pulse Electrodeposition ◽  
Nanocomposite Coatings ◽  
Duty Ratio ◽  
Average Current Density ◽  
Average Current ◽  
Surface Morphologies

Ni-ZrO2-CeO2nanocomposite coatings were prepared by pulse electrodeposition. The effect additions of ZrO2and CeO2nanoparticles, average current density, duty ratio and frequency of pulse current on nanoparticle contents of Ni-ZrO2-CeO2nanocomposites were studied. The surface morphologies and microhardness of different nanocomposite coatings (Ni-ZrO2, Ni-CeO2, Ni-ZrO2-CeO2) were analyzed. The results show that, with the average current density, duty ratio and frequency increased, the nanoparticle contents increased at first and then decreased. Compared with Ni-ZrO2and Ni-CeO2, the surface morphology of Ni-ZrO2-CeO2nanocomposite coating showed better smooth surface and more compact microstructure, the microhardness was also higher.

Effect of Pulse Electrodeposition Parameters on Microhardness of Ni-ZrO2-CeO2 Nanocomposite Coating

2014 ◽  
Vol 1049-1050 ◽  
pp. 31-34
Author(s):  
Shuang Shuang Liu ◽  
Yu Jun Xue ◽  
Yang Yang Xu ◽  
Ji Shun Li
Keyword(s):  
Composite Coating ◽  
Current Density ◽  
Pulse Current ◽  
Pulse Frequency ◽  
Nanocomposite Coating ◽  
Pulse Electrodeposition ◽  
Duty Ratio ◽  
Positive Duty ◽  
Average Current Density ◽  
Average Current

Ni-ZrO2-CeO2 nanocomposite coating was prepared by pulse electrodeposition. The effect of addition of ZrO2 and CeO2 nanoparticles, average current density, duty cycle and pulse current on microhardness of Ni-ZrO2-CeO2 nanocomposites were studied. The results show that microhardness of nanocomposite is increased at first and then decreased with the increasing additive amounts of two kinds of nanoparticles. With increasing reverse the average current density, the microhardness of the composite coating increases. Also, the microhardness of nanocomposite fall with the increasing of pulse frequency. With the positive duty ratio increasing, the microhardness of the composite coating increase at first and then decreased, but with the increasing of the reverse duty ratio, the microhardness of nanocomposite coating is gradually decreased.

Experimental Study of Mechanical Properties of Electroformed Nanocrystalline Ni-Mn Alloys

2008 ◽  
Vol 375-376 ◽  
pp. 148-152
Author(s):  
Jian Ming Yang ◽  
Di Zhu
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Tensile Properties ◽  
Current Density ◽  
Average Current Density ◽  
Mean Grain Size ◽  
Average Current ◽  
Mn Content ◽  
The Mean ◽  
Deposition Current Density

In this paper, the measurements of microhardness and tensile properties are performed to the electroformed Ni-Mn alloys which the mean grain size is near to or less than 100nm. It is studied that the effect of average deposition current density on microhardness and tensile properties of the alloys and the effect of post-electroforming annealing on microhardness of the alloys. The results show that with the increment of average current density, microhardness and strength of the alloys increase and elongation decreases because of the increment of Mn content and the decrement of grain size of the alloys. Microhardness of the alloys are slightly improved after annealing.

Electromigration Reliability With Respect to Cu Weight Contents of Sn–Ag–Cu Flip-Chip Solder Joints Under Comparatively Low Current Stressing

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Yi-Shao Lai ◽  
Ying-Ta Chiu
Keyword(s):  
Intermetallic Compound ◽  
Ambient Temperature ◽  
Current Density ◽  
Flip Chip ◽  
Solder Joints ◽  
Average Current Density ◽  
Current Stressing ◽  
Weight Content ◽  
Average Current ◽  
Better Than

This work presents electromigration reliability and patterns of Sn–3Ag–0.5Cu and Sn–3Ag–1.5Cu∕Sn–3Ag–0.5Cu composite flip-chip solder joints with Ti∕Ni(V)∕Cu under bump metallurgy (UBM), bonded on Au∕Ni∕Cu substrate pads. The solder joints were subjected to an average current density of 5kA∕cm2 under an ambient temperature of 150°C. Under the situation when electron charges flow from the UBM toward the substrate, Sn diffuses from the Cu–Ni–Sn intermetallic compound developed around the UBM toward the UBM and eventually causes the Ni(V) layer to deform. Electromigration reliability of Sn–3Ag–1.5Cu∕Sn–3Ag–0.5Cu composite flip-chip solder joints was found to be better than that of Sn–3Ag–0.5Cu solder joints. According to the morphological observations on cross-sectioned solder joints, a failure mechanism is proposed as follows. Since the deformation of the Ni(V) layer as a result of Sn diffusion toward the UBM is considered as the dominant failure, a greater Cu weight content in the solder joints would trap more Sn in the Sn–Cu interfacial reaction and would therefore retard the diffusion of Sn toward the UBM and hence enhance the electromigration reliability.

Influences of Pulse Current Density on the Characteristics of Ni-W-P-CeO2-SiO2 Composite Coatings

2011 ◽  
Vol 418-420 ◽  
pp. 856-860 ◽  
Author(s):  
Rui Dong Xu ◽  
Da Cheng Zhai ◽  
Shuang Li Hu
Keyword(s):  
Chemical Composition ◽  
Current Density ◽  
Pulse Current ◽  
Composite Coatings ◽  
Average Current Density ◽  
Fine Grained ◽  
Fine Grained Structure ◽  
Average Current ◽  
S Deposition ◽  
Microhardness Tester

Square-wave double pulse current was used to electrodeposit Ni-W-P-CeO2-SiO2composite coatings in fine-grained structure on the surface of carbon steel, influences of forward pulse average current density, +Jm, in the range of 5~25A/dm2on characteristics of the composite coatings were researched, and the chemical compositionSubscript texts, deposition rate, microhardness and microstructures were evaluated by EDX, SEM and Microhardness tester. The results show that the uniform composite coatings can be obtained at +Jmof 20A/dm2, which possess higher microhardness of 735Hv. The grains sizes of the composite coatings decrease when +Jmis increased from 5A/dm2to 20A/dm2, while the reappearance of large grains structure at 25A/dm2.

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