Research Article Preparation of Al-Mg Alloy Electrodes by

Research ArticlePreparation of Al-Mg Alloy Electrodes by Using PowderMetallurgy and Their Application for Hydrogen Production

Wen-Nong Hsu12 Teng-Shih Shih1 and Ming-Yuan Lin2

1 Department of Mechanical Engineering National Central University Chung-Li 32054 Taiwan2Department of Mechanical and Vehicle Engineering Army Academy Chung-Li 32092 Taiwan

Correspondence should be addressed to Wen-Nong Hsu nong88yamcom

Received 4 August 2014 Accepted 26 August 2014 Published 23 November 2014

Academic Editor Chin-Chia Wu

Copyright copy 2014 Wen-Nong Hsu et alThis is an open access article distributed under the Creative CommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The choice of an electrode is the most critical parameter for water electrolysis In this study powder metallurgy is used to preparealuminum-magnesium (Al-Mg) alloy electrodes In addition to pure Mg and Al electrodes five Al-Mg alloy electrodes composedof Al-Mg (10wt) Al-Mg (25wt) Al-Mg (50wt) and Al-Mg (75wt) were prepared In water electrolysis experiments thepure Al electrode exhibited optimal electrolytic efficiency However the Al-Mg (25wt) alloy was the most efficient when theanticorrosion effect and materials costs were considered In this study an ultrasonic field was applied to the electrolysis cell toimprove its efficiencyThe results revealed that the current increased by approximately 231when placed in a 30wtKOH solutionunder the ultrasonic field Electrochemical polarization impedance spectroscopy (EIS) was employed to evaluate the effect of theultrasonic field on the reduction of polarization resistance The results showed that the concentration impedance in the 30wtKOH electrolyte decreased markedly by 44ndash51Ω

1 Introduction

Hydrogen is a clean pollution-free and economical energycarrier which indicates that it has the greatest potentialfor use as an alternative energy source Hydrogen releasesenergy without producing greenhouse gases such as CO

2

and it has the highest power density among all fuels Ithas high development potential and it is a clean powersource with an indefinite supply In the 1800s scientistsgenerated high-purity hydrogen and oxygen by conductingwater electrolysisWater contains a large amount of hydrogenand it is the ideal material to obtain it from Hydrogen poweris superior to other energy sources because it is renewableand can be used to generate electric power or heat Througha chemical reaction hydrogen can form water which can bedecomposed into hydrogen and oxygen through electrolysisTherefore performingwater electrolysis to produce hydrogenis a crucial method for generating energy Improving theefficiency of water electrolysis for hydrogen production is avaluable research topic

The voltage required to perform water electrolysis con-sists of largely reversible potential (123V 1 atm 25∘C)However the actual decomposition potential is higher than123V Low reaction overpotential is crucial to improvingthe efficiency and economic viability of water hydrolysisbecause high energy consumption and a low hydrogen outputare two issues affecting the applicability of water electrolysis[1] To reduce the overpotential and increase the hydrogenoutput several previous studies have discussed the effects ofworking parameters such as alkaline (KOH NaOH) or acid(HCl H

2SO4) electrolytes relative electrode distance flow-

field effect and electrolyte temperature on the electrolytichydrogen production efficiency For example Nagai et al[2] de Souza et al [3 4] and Licht et al [5] have shownthat the flow field generated from electrolyte stirring resultedin a higher ion concentration on the electrode surfacethereby increasing the electrolytic efficiency Dubey et al [6]employed carbon nanotubes to replace graphite electrodesto increase the efficiency of hydrogen production Nikolicet al [7] added cobalt and tungsten ions to an alkaline

Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2014 Article ID 594984 7 pageshttpdxdoiorg1011552014594984

2 Advances in Materials Science and Engineering

electrolyte reduced the power consumption by 15 andproduced the same amount of hydrogen In addition certainstudies have used additional externalmechanisms to improvethe efficiency of water electrolysis For example Lin et al[8] applied a magnetic field to an electrolyte solution todiscuss the magnetic phenomenon of electrolytes underthe Lorentz force and demonstrated improvements in thepolarization potential and hydrogen production efficiencyMatsushima et al [9 10] applied a magnetic field duringelectrolysis to examine the polarization overpotential curvein oversaturated electrolytes

In water electrolysis one of the most critical factors isthe choice of an electrode material The characteristics ofan ideal electrode include low operating potential favorableelectrocatalytic properties time stability and low cost Plat-inum is widely used as an electrode material although it isrelatively expensive Considering the cost iron cobalt nickelstainless steel and graphite are also widely used electrodematerials [11 12] Regarding the methods for manufacturingelectrodes powder metallurgy is a convenient and efficienttechnique that has numerous advantages such as low energyconsumption efficient material usage and simple procedureFurthermore its products can be designedwith porosity uni-form chemical composition refractorymaterials and incom-patible composite materials For this study Al-Mg electrodesof various compositions were sintered and their electrolyticperformance was subsequently evaluated in distinct alkalineelectrolytes to identify electrodes suitable for water electrol-ysis Finally we applied an ultrasonic field to accelerate thereduction of the accumulated impedance caused by the for-mation of numerous bubbles on the electrode surface High-frequency longitudinal ultrasonic waves cause continuouschanges in positive and negative pressure in fluid mediaand generate tens of thousands of microvacuum bubbles aphenomenon known as ldquocavitation bubblesrdquo [13ndash16] Cavita-tion bubbles continuously form extrude and break resultingin the disturbance and rapid degasification of the fluidEarly in the nineteenth century metallurgists understoodthat applying ultrasonic energy to a molten medium woulduniformly disperse impurities and have a degassing effectThis could improve the quality of cast products substantially[16 17] This study examined the effect of applying ultrasonicenergy to various electrolyte concentrations during waterelectrolysis and evaluated the effect of various electrodes onthe performance of hydrogen production Electrochemicalpolarization impedance spectroscopy (EIS) was employed tomeasure the related polarization phenomena and a camerawas used to capture images of the bubble flow field

2 Experimental

The electrodes used in the study were prepared using apowder metallurgy method Pure Al and Mg powders wereused as raw materials The mean particle size of bothpowders was approximately 100 mesh In addition five alloyelectrodes composed ofAl-Mg (10wt) Al-Mg (25wt) Al-Mg (50wt) Al-Mg (75wt) andAl-Mg (90wt)were alsoprepared After thoroughly mixing the various compositions

d

f g

b a

h

c

e

G

+minus

Figure 1 The experiment devices (a) Electrodes (b) electrolysiscell (c) outer cell (d) potentiostat (e) ultrasonic generator (f)computer (g) thermometer and (h) camera

of powder the mixture was placed in a metal mold andpressed at 200MPa for 30 s To prevent oxidation at elevatedtemperatures a quartz tube furnace was filled with protectivegas (hydrogen) during the sintering process The electrodespecimens were sintered to 500∘C held at that temperaturefor 3 h and then left to cool to room temperature in thefurnace The sintered electrode specimens were fabricatedwith a dimension of 12times 12times 5mm (119871times119882times119867) for subsequentanalysis

Because Ni electrodes are corrosion-proof as well as acid-and alkali-resistant in electrolytes a pure Ni anode was usedin this study Seven types of electrodes were prepared ascathodes (working electrodes) with a total geometric area ofapproximately 144mm2The distance between electrodes wasfixed at 30mmThree electrolyte concentrations (ie 10 wt20wt and 30wt) of KOH were used The electrobathused in this experiment was composed of an acid- and alkali-resistant acrylic material (30 times 15 times 100mm 119871 times 119882 times 119867)Figure 1 shows the experimental apparatus The AUTOLABPGSTAT302N potentiostat of the Netherlands ECO wasused for the I-V curve measurement of water electrolysisin each electrode to analyze the electrolytic performanceA 225-W ultrasonic field was introduced to the outer cellduring water electrolysis A camera was used to record theeffect of the ultrasonic field on the bubble beams In thisexperiment the frequency response analyzer (FRA) moduleof the potentiostat was used to measure the EIS curves ofthe electrochemical reactionThe EIS curve was transformedinto the impedance spectrum by using the Nyquist curveof the equivalent circuit Curve fitting was performed usingsoftware to analyze the impedance distribution in the set-equivalent circuit and to obtain the impedance values Basedon these data the following section discusses the effects of

Advances in Materials Science and Engineering 3

Table 1 The electrolytic performance of the experimental electrodes

Property ElectrodesMg Al-Mg (90wt) Al-Mg (75wt) Al-Mg (50wt) Al-Mg (25wt) Al-Mg (10wt) Al

(a) Conductivity (IACS) 38 11 7 4 8 14 62(b) Corrosion rate () 0 0 0 0 0 45 99(c) Decomposition voltage (V) 365 350 340 315 285 255 235

0 10 20 30 40 50 60 70 80 90 100

0 10 20 30 40 50 60 70 80 90 100

700

600

500

400

300

200

100

Weight percent magnesium

Mg

Mg

Al

Al

Atomic percent magnesium

Al3Mg2

Al12Mg17

R

660452∘C

450∘C 437

∘C

650∘C

Tem

pera

ture

(∘C)

Figure 2 The phase diagram of Al-Mg alloy

the various parameters on the impedance values during theelectrochemical experimental process

3 Results and Discussion

31 Electrolytic Performance of the Al-Mg Electrodes Thephase diagram in Figure 2 shows the microstructures of thematerials used in this study Selecting an electrode materialfirst involves considering its electrical conductivity becausea high electrical conductivity facilitates efficient electrolysisIn this study conductivity is expressed in accordance withthe International Annealed Copper Standard (IACS) Table 1(line A) shows the conductivity results of the electrodes Thepure Al and Mg electrodes were more conductive than thealloy composites (62 IACS and 38 IACS resp) However theconductivity of the Al-Mg (50wt) alloy electrodes yieldedsubstantially lower values (4 IACS) exhibiting the lowestconductivity

Electrode materials should exhibit corrosion resistanceto basic electrolytes Table 1 (line B) shows the relationshipbetween the electrolysis time and corrosion weight percent-age for each electrode at a fixed voltage of 5V in the 30wtKOH electrolyte for 8 h The pure Al and Al-Mg (10wt)electrodes were subject to corrosion Formula (1) shows thereaction of the pure Al sample in the KOH electrolyte TheKOHelectrolyte inwaterwas dissociated to yieldK+ andOHminusions and then the combination of Al and OHminus ions resultedin Al(OH)

4

minus which led to corrosion The byproduct of this

20 25 30 35 40 45 50 55 60 65

000204060810121416182022

Mg Al

Voltage (V)

Curr

ent d

ensit

y (A

cm

2)

minus02

Al-Mg (90wt)Al-Mg (75 wt)

Al-Mg (50 wt)Al-Mg (25 wt)Al-Mg (10 wt)

Figure 3 The I-V curve of seven electrodes in 30wt KOHelectrolyte

chemical reaction produced hydrogen and the product inwater electrolysis was also hydrogen If electrode consump-tion was not considered the pure Al electrode produced anadequate amount of hydrogen However the Al-Mg (25wt)electrode electrolyzed in the 30wt KOH electrolyte for8 h exhibited good corrosion resistance If the corrosionresistance of the electrodes is considered theAl content of theAl-Mg alloy electrode should be equal to or less than 75wt

2Al (s) + 2KOH (s) + 6H2O (aq)

997888rarr 2K+ (aq) + 2Al(OH)4

minus(aq) + 3H

2(g)

(1)

32The I-VCurve of Al-Mg Electrodes Figure 3 shows the I-Vcurves of the seven electrodes in the 30wtKOH electrolyteThe decomposition voltages (Table 1 line C) were obtainedby plotting a tangent on the I-V curve and intersecting the119909-axis The decomposition voltage of the pure Al and Mgelectrodes was approximately 235V and 365V respectivelyIn summary an electrode with a low decomposition voltageis more efficient As shown in Figure 3 the magnitude ofthe current density of the electrodes is in the order of Al gtAl-Mg (10wt) gt Al-Mg (25wt) gt Al-Mg (50wt) gt Al-Mg (75wt) gt Al-Mg (90wt) gtMgThe pure Al electrodeyielded the most favorable I-V curve and the current densitydecreases with the weight percentage of Al By contrast theI-V curve of the pure Mg electrode indicated that it was


1 2 3 4 5 6

00

01

02

03

04

05

06

07

Voltage (V)

10 wt10 wt with ultra

Curr

ent d

ensit

y (A

cm

2)

(a)

1 2 3 4 5 6

00

02

04

06

08

10

Voltage (V)


Curr

ent d

ensit

y (A

cm

2)

(b)

1 2 3 4 5 6

00

02

04

06

08

10

12

14

Voltage (V)


minus02

Curr

ent d

ensit

y (A

cm

2)

(c) (d) (e)

Figure 4 The effect of applying ultrasound on the water electrolysis for Al-Mg (25wt) electrode (a) 10 wt (b) 20wt (c) 30wt KOHelectrolyte (d) bubbles (without ultra) and (e) bubbles (with ultra)

the least efficient for electrolysis In summary the pure Alelectrode exhibited a low decomposition voltage and optimalelectrolytic efficiency although it was susceptible to corrosionbecause of its high activity Therefore it is suitable for use asa consumable electrode If both the corrosion property andelectrolytic efficiency are considered the preferred Al-Mgalloy electrode would be the Al-Mg (25wt) specimen Inother words the increase in phase content of the intermetalliccompound (Al

12Mg17) in the Al-Mg electrodes facilitates

corrosion resistance

33 The Effect of Ultrasound Application on the Efficiency ofWater Electrolysis for theAl-Mg (25wt) Electrode atDifferentElectrolyte Concentrations An ultrasonic wave refers to asound pressure wave at frequencies higher than 20 kHz

Ultrasonic waves generate cyclic alternating acoustic pres-sures of compression and tensionWhen the acoustic pressureis sufficiently strong the liquid is subjected to tensile forcesduring the negative cycle of the wave and the moleculesof the liquid can be pulled away from one another to formcavitation bubbles which are transient bubbles During thefollowing compression cycle the cavitation bubbles collapseviolently forming microjets and shock waves Some of thesecavitation bubbles grow rapidly under the influence of thealternating acoustic pressure and the directed diffusion ofdissolved gas from the liquid thereby forming steady bubblesThe numerous bubbles coagulate and rise to the surface of theliquid which is called ldquoultrasonic degassingrdquo

The electrolytic performance of the Al-Mg (25wt)electrode was examined in three electrolyte concentrations


25 30 35 40 45 50 55 60 65000102030405060708091011


Z998400998400

(Ω)

Z998400 (Ω)

(a)

15 20 25 30 35 40 4500

02

04

06

08

10


Z998400998400

(Ω)

Z998400 (Ω)

(b)

16 18 20 22 24 26 28 30 32 34 36 38

00

01

02

03

04

05

06


Z998400998400

(Ω)

Z998400 (Ω)

(c)

00

05

10

15

20

25

30

With ultra

30 wt20 wt

OhmicActiveConcentration

10 wt

No With ultraNo With ultraNo

RΩ

(d)

Figure 5 The Nyquist curves and polarization impedance chart at different electrolytes (a) 10 wt (b) 20wt (c) 30wt and (d)polarization impedances

with and without ultrasound Figures 4(a)ndash4(c) show the I-Vcurves of water electrolysis at 5 V The results revealed thatthe current increased by 53 185 and 231 when theultrasound was applied to the 10wt 20wt and 30wtKOH electrolyte concentrations respectively Moreover thecamera which was used to record the bubble behaviors in theelectrolytic process revealed bubble clusters that were createdthrough ultrasonic forced oscillation These phenomena areeasy to understand Introducing an ultrasound to the elec-trolytic cell resulted in acoustic cavitation The creation ofgas bubbles (both hydrogen and oxygen) on the electrodesaccelerated and steady bubbles were formed through directdiffusion The bubble clusters grew rapidly and detachedfrom the electrode surface in the sound field effectivelyreducing the polarization resistance in the electrolytic cell andenhancing electrolytic efficiency

In addition to using an I-V curve to calculate the powerefficiency a Nyquist potential impedance equivalent diagramwas used to examine the relationship between the change inthe polarization impedances and ultrasonic action Figure 5shows the EIS curves measured using the constant electricdisplacement FRAmodule with an electrode spacing of 3mmand external potential of 28 V For the 10wt electrolytecondition without ultrasound the EIS curve in Figure 5(a)shows two clearly defined semicircles The results indicatedthat both the activation and concentration polarizationincreased because of the low electrical conductivity andpoor hydration effect Under a low-frequency condition theelectrochemical reaction time increased and the activationand concentration polarization curves could be measuredUnder the 20wt and 30wt electrolyte conditions thelow-frequency semicircles (Figures 5(b) and 5(c)) were not


clearly defined because of the improved hydration effect Theelectron and ion exchange rate between the electrodes and theelectrolyte solution was high and the overall reaction timedecreased Although the low frequencies produced longerreaction times the polarization phenomena wereminimizedIn summary applying the ultrasound to the electrolytic cellreduced polarization impedance in all cases

Figure 5(d) shows the activation and concentrationimpedance at three electrolyte concentrations which wereobtained from the regression curves of the EIS curvesin Figures 5(a)ndash5(c) Overall the results revealed thatapplying ultrasonic waves to various electrolytes can effec-tively improve impedance The ohm impedance activationimpedance and concentration impedance values decreasedby approximately 1ndash30Ω 15ndash76Ω and 44ndash51Ωrespectively The concentration impedance values exhibitedthe greatest reduction because the ultrasonic field removedthe hydrogen and oxygen bubbles from the electrodes whichdestroyed the diffusion layer reduced electrode foulingand altered the absorption and surface conditions Conse-quently the ion transmission improved the limiting currentincreased and the overpotential decreased Furthermore anincrease in ohmic impedance was obvious for the 30wtelectrolyte concentration Under these conditions the hydra-tion effect of the electrolyte improved the electron and ionexchange rate between the electrode and electrolyte washigh and the electrochemical reactionwas violentThereforenumerous bubbles formed between the electrodes leading toan increase in ohmic impedance When the ultrasound wasapplied to the electrolysis system the bubbles on the electrodesurface were removed rapidly and the ohmic impedancedecreased from 18 to 12 Ω

4 Conclusion

In this study seven electrodes were prepared using a powdermetallurgy method The current density of the obtainedelectrodes exhibited the following characteristic Al gt Al-Mg (10wt) gt Al-Mg (25wt) gt Al-Mg (50wt) gt Al-Mg(75wt) gt Al-Mg (90wt) gt Mg The experimental resultsrevealed that the electrolytic efficiency increased with the Alcontent in the electrode However Al is easily oxidized toform Al(OH)

4

minus in a KOH electrolyte Based on the anticor-rosion and electrolytic efficiency of the electrodes the Al-Mg (25wt) electrode would be the ideal candidate in otherwords the Al content of the Al-Mg alloy electrodes shouldbe equal to or less than 75wt This electrode exhibitedhigh corrosion resistance and it is easy to obtain as well aseconomical Furthermore the ultrasonic wave was applied tothe cells to reduce the polarization resistance The increasein current observed for various electrolyte concentrationsrevealed the following tendency 30wt KOH gt 20wtKOH gt 10 wt KOH In the 30wt KOH the optimalcurrent increased by 231 The EIS curves measured usingthe FRA module and the regression curves indicated aneffective improvement in polarization impedance betweenthe electrodes under ultrasonic vibration The concentration

polarization in the 30wt KOH under ultrasonic conditionsdecreased to 44ndash51Ω during electrolysis

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors are grateful to the three anonymous referees fortheir helpful comments on an earlier version of this paper

References

[1] K Mazloomi N B Sulaiman and H Moayedi ldquoElectricalefficiency of electrolytic hydrogen productionrdquo InternationalJournal of Electrochemical Science vol 7 no 4 pp 3314ndash33262012

[2] N Nagai M Takeuchi T Kimura and T Oka ldquoExistence ofoptimum space between electrodes on hydrogen production bywater electrolysisrdquo International Journal of Hydrogen Energyvol 28 no 1 pp 35ndash41 2003

[3] R F de Souza J C Padilha R S GoncalvesMO de Souza andJ Rault-Berthelot ldquoElectrochemical hydrogen production fromwater electrolysis using ionic liquid as electrolytes towards thebest devicerdquo Journal of Power Sources vol 164 no 2 pp 792ndash798 2007

[4] R F de Souza J C Padilha R S Goncalves and J Rault-Berthelot ldquoDialkylimidazolium ionic liquids as electrolytes forhydrogen production from water electrolysisrdquo ElectrochemistryCommunications vol 8 no 2 pp 211ndash216 2006

[5] S Licht B Wang S Mukerji T Soga M Umeno and HTributsch ldquoOver 18 solar energy conversion to generation ofhydrogen fuel theory and experiment for efficient solar watersplittingrdquo International Journal of Hydrogen Energy vol 26 no7 pp 653ndash659 2001

[6] P K Dubey A S K Sinha S Talapatra N Koratkar P MAjayan and O N Srivastava ldquoHydrogen generation by waterelectrolysis using carbon nanotube anoderdquo International Jour-nal of Hydrogen Energy vol 35 no 9 pp 3945ndash3950 2010

[7] V M Nikolic G S Tasic A D Maksic D P Saponjic S MMiulovic and M P Marceta Kaninski ldquoRaising efficiency ofhydrogen generation from alkaline water electrolysismdashenergysavingrdquo International Journal of Hydrogen Energy vol 35 no22 pp 12369ndash12373 2010

[8] M-Y Lin L-WHourng andC-WKuo ldquoThe effect ofmagneticforce on hydrogen production efficiency in water electrolysisrdquoInternational Journal of Hydrogen Energy vol 37 no 2 pp 1311ndash1320 2012

[9] H Matsushima A Bund W Plieth S Kikuchi and Y Fuku-naka ldquoCopper electrodeposition in a magnetic fieldrdquo Elec-trochimica Acta vol 53 no 1 pp 161ndash166 2007

[10] C-Y Hung S-D Li C-C Wang and C-Y Chen ldquoInfluencesof a bipolar membrane and an ultrasonic field on alkaline waterelectrolysisrdquo Journal of Membrane Science vol 389 pp 197ndash2042012

[11] L de Silva Munoz A Bergel D Feron and R BasseguyldquoHydrogen production by electrolysis of a phosphate solutionon a stainless steel cathoderdquo International Journal of HydrogenEnergy vol 35 no 16 pp 8561ndash8568 2010


[12] A Bai and C-C Hu ldquoComposition controlling of Co-Ni andFe-Co alloys using pulse-reverse electroplating through meansof experimental strategiesrdquo Electrochimica Acta vol 50 no 6pp 1335ndash1345 2005

[13] E A Neppiras ldquoAcoustic cavitation an introductionrdquoUltrason-ics vol 22 no 1 pp 25ndash28 1984

[14] R E Apfel ldquoAcoustic cavitation inceptionrdquo Ultrasonics vol 22no 4 pp 167ndash173 1984

[15] E A Neppiras ldquoAcoustic cavitation thresholds and cyclicprocessesrdquo Ultrasonics vol 18 no 5 pp 201ndash209 1980

[16] K S Suslick ldquoThe chemical effects of ultrasoundrdquo ScientificAmerican vol 80 pp 80ndash86 1989

[17] G I Eskin ldquoCavitation mechanism of ultrasonic melt degas-singrdquo Ultrasonics Sonochemistry vol 2 no 2 pp S137ndashS1411995

Submit your manuscripts athttpwwwhindawicom

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Smart Materials Research



MetallurgyJournal of


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MaterialsJournal of


Nano

materials


Journal ofNanomaterials


electrolyte reduced the power consumption by 15 andproduced the same amount of hydrogen In addition certainstudies have used additional externalmechanisms to improvethe efficiency of water electrolysis For example Lin et al[8] applied a magnetic field to an electrolyte solution todiscuss the magnetic phenomenon of electrolytes underthe Lorentz force and demonstrated improvements in thepolarization potential and hydrogen production efficiencyMatsushima et al [9 10] applied a magnetic field duringelectrolysis to examine the polarization overpotential curvein oversaturated electrolytes

In water electrolysis one of the most critical factors isthe choice of an electrode material The characteristics ofan ideal electrode include low operating potential favorableelectrocatalytic properties time stability and low cost Plat-inum is widely used as an electrode material although it isrelatively expensive Considering the cost iron cobalt nickelstainless steel and graphite are also widely used electrodematerials [11 12] Regarding the methods for manufacturingelectrodes powder metallurgy is a convenient and efficienttechnique that has numerous advantages such as low energyconsumption efficient material usage and simple procedureFurthermore its products can be designedwith porosity uni-form chemical composition refractorymaterials and incom-patible composite materials For this study Al-Mg electrodesof various compositions were sintered and their electrolyticperformance was subsequently evaluated in distinct alkalineelectrolytes to identify electrodes suitable for water electrol-ysis Finally we applied an ultrasonic field to accelerate thereduction of the accumulated impedance caused by the for-mation of numerous bubbles on the electrode surface High-frequency longitudinal ultrasonic waves cause continuouschanges in positive and negative pressure in fluid mediaand generate tens of thousands of microvacuum bubbles aphenomenon known as ldquocavitation bubblesrdquo [13ndash16] Cavita-tion bubbles continuously form extrude and break resultingin the disturbance and rapid degasification of the fluidEarly in the nineteenth century metallurgists understoodthat applying ultrasonic energy to a molten medium woulduniformly disperse impurities and have a degassing effectThis could improve the quality of cast products substantially[16 17] This study examined the effect of applying ultrasonicenergy to various electrolyte concentrations during waterelectrolysis and evaluated the effect of various electrodes onthe performance of hydrogen production Electrochemicalpolarization impedance spectroscopy (EIS) was employed tomeasure the related polarization phenomena and a camerawas used to capture images of the bubble flow field

2 Experimental

The electrodes used in the study were prepared using apowder metallurgy method Pure Al and Mg powders wereused as raw materials The mean particle size of bothpowders was approximately 100 mesh In addition five alloyelectrodes composed ofAl-Mg (10wt) Al-Mg (25wt) Al-Mg (50wt) Al-Mg (75wt) andAl-Mg (90wt)were alsoprepared After thoroughly mixing the various compositions

d

f g

b a

h

c

e

G

+minus

Figure 1 The experiment devices (a) Electrodes (b) electrolysiscell (c) outer cell (d) potentiostat (e) ultrasonic generator (f)computer (g) thermometer and (h) camera

of powder the mixture was placed in a metal mold andpressed at 200MPa for 30 s To prevent oxidation at elevatedtemperatures a quartz tube furnace was filled with protectivegas (hydrogen) during the sintering process The electrodespecimens were sintered to 500∘C held at that temperaturefor 3 h and then left to cool to room temperature in thefurnace The sintered electrode specimens were fabricatedwith a dimension of 12times 12times 5mm (119871times119882times119867) for subsequentanalysis

Because Ni electrodes are corrosion-proof as well as acid-and alkali-resistant in electrolytes a pure Ni anode was usedin this study Seven types of electrodes were prepared ascathodes (working electrodes) with a total geometric area ofapproximately 144mm2The distance between electrodes wasfixed at 30mmThree electrolyte concentrations (ie 10 wt20wt and 30wt) of KOH were used The electrobathused in this experiment was composed of an acid- and alkali-resistant acrylic material (30 times 15 times 100mm 119871 times 119882 times 119867)Figure 1 shows the experimental apparatus The AUTOLABPGSTAT302N potentiostat of the Netherlands ECO wasused for the I-V curve measurement of water electrolysisin each electrode to analyze the electrolytic performanceA 225-W ultrasonic field was introduced to the outer cellduring water electrolysis A camera was used to record theeffect of the ultrasonic field on the bubble beams In thisexperiment the frequency response analyzer (FRA) moduleof the potentiostat was used to measure the EIS curves ofthe electrochemical reactionThe EIS curve was transformedinto the impedance spectrum by using the Nyquist curveof the equivalent circuit Curve fitting was performed usingsoftware to analyze the impedance distribution in the set-equivalent circuit and to obtain the impedance values Basedon these data the following section discusses the effects of





0 10 20 30 40 50 60 70 80 90 100

0 10 20 30 40 50 60 70 80 90 100

700

600

500

400

300

200

100


Mg

Mg

Al

Al


Al3Mg2

Al12Mg17

R

660452∘C

450∘C 437

∘C

650∘C

Tem

pera

ture

(∘C)






4


20 25 30 35 40 45 50 55 60 65

000204060810121416182022

Mg Al

Voltage (V)

Curr

ent d

ensit

y (A

cm

2)

minus02





2Al (s) + 2KOH (s) + 6H2O (aq)

997888rarr 2K+ (aq) + 2Al(OH)4

minus(aq) + 3H

2(g)

(1)



1 2 3 4 5 6

00

01

02

03

04

05

06

07

Voltage (V)


Curr

ent d

ensit

y (A

cm

2)

(a)

1 2 3 4 5 6

00

02

04

06

08

10

Voltage (V)


Curr

ent d

ensit

y (A

cm

2)

(b)

1 2 3 4 5 6

00

02

04

06

08

10

12

14

Voltage (V)


minus02

Curr

ent d

ensit

y (A

cm

2)

(c) (d) (e)









25 30 35 40 45 50 55 60 65000102030405060708091011


Z998400998400

(Ω)

Z998400 (Ω)

(a)

15 20 25 30 35 40 4500

02

04

06

08

10


Z998400998400

(Ω)

Z998400 (Ω)

(b)

16 18 20 22 24 26 28 30 32 34 36 38

00

01

02

03

04

05

06


Z998400998400

(Ω)

Z998400 (Ω)

(c)

00

05

10

15

20

25

30

With ultra

30 wt20 wt


10 wt


RΩ

(d)







4 Conclusion


4





Acknowledgments


References


























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







0 10 20 30 40 50 60 70 80 90 100

0 10 20 30 40 50 60 70 80 90 100

700

600

500

400

300

200

100


Mg

Mg

Al

Al


Al3Mg2

Al12Mg17

R

660452∘C

450∘C 437

∘C

650∘C

Tem

pera

ture

(∘C)






4


20 25 30 35 40 45 50 55 60 65

000204060810121416182022

Mg Al

Voltage (V)

Curr

ent d

ensit

y (A

cm

2)

minus02





2Al (s) + 2KOH (s) + 6H2O (aq)

997888rarr 2K+ (aq) + 2Al(OH)4

minus(aq) + 3H

2(g)

(1)



1 2 3 4 5 6

00

01

02

03

04

05

06

07

Voltage (V)


Curr

ent d

ensit

y (A

cm

2)

(a)

1 2 3 4 5 6

00

02

04

06

08

10

Voltage (V)


Curr

ent d

ensit

y (A

cm

2)

(b)

1 2 3 4 5 6

00

02

04

06

08

10

12

14

Voltage (V)


minus02

Curr

ent d

ensit

y (A

cm

2)

(c) (d) (e)









25 30 35 40 45 50 55 60 65000102030405060708091011


Z998400998400

(Ω)

Z998400 (Ω)

(a)

15 20 25 30 35 40 4500

02

04

06

08

10


Z998400998400

(Ω)

Z998400 (Ω)

(b)

16 18 20 22 24 26 28 30 32 34 36 38

00

01

02

03

04

05

06


Z998400998400

(Ω)

Z998400 (Ω)

(c)

00

05

10

15

20

25

30

With ultra

30 wt20 wt


10 wt


RΩ

(d)







4 Conclusion


4





Acknowledgments


References


























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




1 2 3 4 5 6

00

01

02

03

04

05

06

07

Voltage (V)


Curr

ent d

ensit

y (A

cm

2)

(a)

1 2 3 4 5 6

00

02

04

06

08

10

Voltage (V)


Curr

ent d

ensit

y (A

cm

2)

(b)

1 2 3 4 5 6

00

02

04

06

08

10

12

14

Voltage (V)


minus02

Curr

ent d

ensit

y (A

cm

2)

(c) (d) (e)









25 30 35 40 45 50 55 60 65000102030405060708091011


Z998400998400

(Ω)

Z998400 (Ω)

(a)

15 20 25 30 35 40 4500

02

04

06

08

10


Z998400998400

(Ω)

Z998400 (Ω)

(b)

16 18 20 22 24 26 28 30 32 34 36 38

00

01

02

03

04

05

06


Z998400998400

(Ω)

Z998400 (Ω)

(c)

00

05

10

15

20

25

30

With ultra

30 wt20 wt


10 wt


RΩ

(d)







4 Conclusion


4





Acknowledgments


References


























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




25 30 35 40 45 50 55 60 65000102030405060708091011


Z998400998400

(Ω)

Z998400 (Ω)

(a)

15 20 25 30 35 40 4500

02

04

06

08

10


Z998400998400

(Ω)

Z998400 (Ω)

(b)

16 18 20 22 24 26 28 30 32 34 36 38

00

01

02

03

04

05

06


Z998400998400

(Ω)

Z998400 (Ω)

(c)

00

05

10

15

20

25

30

With ultra

30 wt20 wt


10 wt


RΩ

(d)







4 Conclusion


4





Acknowledgments


References


























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






4 Conclusion


4





Acknowledgments


References


























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials

















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Documents

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