hydrogen production using reduced-iron nanoparticles by laser...

Hindawi Publishing CorporationISRN Renewable EnergyVolume 2013 Article ID 827681 7 pageshttpdxdoiorg1011552013827681

Research ArticleHydrogen Production Using Reduced-Iron Nanoparticles byLaser Ablation in Liquids

Takehiro Okada1 Taku Saiki1 Seiji Taniguchi2 Tsuyoshi Ueda1 Kazuhiro Nakamura1

Yusuke Nishikawa1 and Yukio Iida1

1 Department of Electrical and Electronic Engineering Faculty of Engineering Science Kansai University 3-3-35 Yamate-choSuita Osaka 564-8680 Japan

2 Institute for Laser Technology 1-8-4 Utsubo-honmachi Nishi-ku Osaka 550-0004 Japan

Correspondence should be addressed to Takehiro Okada gd50022livejp

Received 28 December 2012 Accepted 3 February 2013

Academic Editors S S Kalligeros and Z Oktay

Copyright copy 2013 Takehiro Okada et alThis is an open access article distributed under theCreative CommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

A recyclable energy cycle using a pulsed laser and base-metal nanoparticles is proposed In this energy cycle iron nanoparticlesreduced from iron oxides by laser ablation in liquid are used for hydrogen generation The laser energy can be stored in the base-metal nanoparticles as the difference between the chemical energies of iron oxide and iron According to the results of an experimenton hydrogen production using the reduced iron nanoparticles the reaction efficiency of the hydrogen generation at a temperatureof 673K was more than 94 for the ideal amount of generated hydrogen

1 Introduction

It has been expected that the application of hydrogen pro-duced by using clean renewable energy such as solar powerwill solve the problem of global warming and depletion offossil fuels Many researches on hydrogen production havebeen conducted around the world [1ndash6] Among them theresearches on generating hydrogen on the basis of the reac-tion of a metal with water are particularly interesting for thefollowing reason the method used to produce the hydrogenis very simple and low cost Magnesium [2 3] aluminum [4]and iron [5 6] have already been used to generate hydrogenIron has the advantage of high safety in regard to handlingbecause it hardly reacts with water at low temperature whencompared to magnesium and aluminum In some researchesmetal nanoparticles were used to generate hydrogen [6] It isimportant to increase the surface area of themetal particles byldquomicronizingrdquo the particles to improve the reaction efficiencyof metals with water Moreover the generated metal oxidesshould return tometals by reducing to realize an energy cycle

The metal oxides can be reduced to the metal and brokeninto nanoparticles by using pulsed-laser ablation in liquid [7ndash13] This process consists of three steps first the metal oxide

is heated to a high temperature in a short time by irradiatinglaser pulses onto a metal-oxide powder in the liquid Secondafter the laser pulse is irradiated metal oxides are evaporatedand metals are atomized the separated oxygen is rearrangedas the outer shell of themetal particlesThird after themetalsare separated from their oxides near the irradiation point ofthe laser pulse themetal atoms are aggregated by cooling andnanoparticles are produced rapidly As physical mechanismsnamely the ablation mechanism of the metal oxide in theliquid coulomb explosions [14 15] and thermal ablation havebeen proposedWith this pulsed-laser ablation in liquid highreduction efficiency is obtained because the liquid also worksas a coolant Recombination between oxygen and metalparticles is prevented because liquid cools the generatedmetal particles rapidly Furthermore it has the advantage thatit can create nanoparticles with low cost easily because theproduced particles can be collected easily

As shown in Figure 1 an energy cycle produced by using apulsed laser and base-metal nanoparticles has been proposed[16] In general the metal nanoparticles generated by pulsed-laser ablation in liquid have been applied only to thin-filmcoatings owing to the high cost of the laser oscillator Asshown in Figure 2 many kinds of solar-pumped lasers have

2 ISRN Renewable Energy

Solar energy

Pulse laser

Metal oxideXO

MetalX

Reactedwith water

Hydrogenproduction

Reduction Oxidation

Nanoparticle

Solar-pumpedlaser

lt5000 K

Figure 1 Proposed energy cycle using solar energy

Figure 2 Small-scale solar-pumped laser

been developed [16ndash18]They can directly convert from inco-herent solar light to laser light And they have an advantage interms of consuming almost only solar powerwhen generatinga laser beam Now optical-optical conversion efficiency ofsolar-pumped lasers has been improved to almost 60 (iefrom solar light to laser light) by improvements in opticaltechnology [18] Moreover these lasers can generate laserpulses with high energy and high peak intensity Accordinglythey can be used for reducing metal oxide and fabricatingmetal nanoparticles in our proposed energy cycle The pro-duction of hydrogen by using reduced metal powder withnanometer-order diameters by continuous wave (CW) orpulsed laser has not been reported until now except for ourreport In this study iron nanoparticles were synthesizedby reduction by pulsed laser in liquids and the reactionefficiency of producing hydrogen by reacting the fabricatedmetal nanoparticles with vaporized water was experimentallyinvestigated

2 Experimental Setup

21 Laser Ablation in Liquids The required energy for reduc-ing iron metal oxides is determined as follows Fe

2O3 Fe3O4

and FeO are generally known as ldquoiron oxidesrdquo According tocrystal structure there are many typesThe chemical formulafor the reduction of Fe

2O3is given as

1

2Fe2O3(s) 997888rarr Fe (s) + 3

4O2(g) Δ119867 = 412 kJmol (1)

The chemical formula for the reduction of Fe3O4is given as

1

3Fe3O4(s) 997888rarr Fe (s) + 2

3O2(g) Δ119867 = 373 kJmol

(2)

Here Δ119867 is the enthalpy energy required for reducing unitmol Fe The basic enthalpy energy required for reducingFe2O3to Fe3O4is 392 kJ per unit mol of Fe

3O4 These

chemical reactions are all endothermic reactions It is clearfrom (1) and (2) that the required chemical energy toseparate the iron and oxygen atoms is large As for thetemperature required to change the Fe

2O3to Fe3O4 2100K

is required once the temperature is reduced to 1700K AfterFe2O3is changed to Fe

3O4 the Fe

3O4must be heated to

1900K to reduce it to FeO Iron can then be obtained afterheating the FeO to a higher temperature still It is generallyconsidered that FeO did not exist to change Fe

3O4and iron

by disproportionate ambient temperature After FeOparticlesare generated they will change to iron and Fe

3O4particles

due to the disproportionate reaction below 850KThe following metal-oxide powders were used to reduce

and produce metal nanoparticles Fe2O3powder 98 purity

mean size 45 120583m (325mesh) Fe3O4powder (Kojyundo

Chemical Laboratory Japan) mean size 1 120583m and ironpowder (Kojyundo Chemical Laboratory Japan) mean sizebelow 5 120583m Since the metal oxides are small it is supposedthat the size of the powder 119899 in the case of laser ablation inliquids is submicron

Experimental setups based on laser ablation in liquidto reduce metal-oxide powders are shown in Figure 3 Theexperimental setup based on the laser ablation in liquid toreduce Fe

2O3powders using a low-repetitionNdYAGpulsed

laser (Surelite II SLI-10 Continuum wavelength 1064 nmpulse duration 8 ns repetition frequency 10Hz) is shownin Figure 3(a) The diameter of the output laser beam was6mm (eminus2) A pear-shaped silicon-glass bottle was used toreduce the Fe

2O3powders Laser pulses are entered to a

mirror in the horizontal direction and they change directionto the vertical direction under the glass bottleThe laser pulseswere irradiated on the bottom of the glass bottle About 4of the irradiated laser energy was reflected on the surfaceof the bottle by the Fresnel reflection The laser pulses werefocused in the acetone liquid at a distance of 15mm fromthe bottom of the glass bottle The quantity of acetone in thebottle was 30mL Oxygen in the acetone was removed by

ISRN Renewable Energy 3

Laser

Mirror

Acetone

Fe2O3 powder

80 mm

(a)

in water

Magnetic stirrer

Laser

119891 = 50mm 20 mm

Fe3O4 powder

(b)

Figure 3 Experimental setup for laser ablation in liquid (a) Reducing Fe2O3powder with 10-Hz NdYAG pulsed laser and (b) reducing

Fe3O4powder with high-repetition-rate NdYAG pulsed laser

using argon for eight minutes Here the irradiation fluencewas evaluated to be more than 20 Jcm2 Free convection wasthus generated in the glass bottleThe effect is the same as thatcaused by the mixing The irradiation time was 20 minutesTo obtain reduced 50mg of iron nanoparticles the reductionexperiment was repeated 14 times The total weight of theFe2O3powder used was 70mg

The experimental setup based on laser ablation in liquidto reduce Fe

3O4powders by using a high-repetition NdYAG

pulsed laser is shown in Figure 3(b) In this study we usedhigh-repetition microchip NdYAG pulsed laser Maximumoutput-averaged laser power was 250mW laser wavelengthwas 1064 nm repetition rate of the laser pulses was 18 kHzand pulse duration was 8 ns A beam with a diameter of6mm (1e2) was focused by using a lens with a focal lengthof 50mm The diameter of the focused beam was thus20120583m at the front of each glass bottle Glass bottles with adiameter of 20mmΦ and length of 38mmL were used in theexperiment 100mg of Fe

3O4was confined in the glass bottles

with 5mL of pure water and stirred The water was mixedby magnetic stirrer (rotation velocity 1200 rpm) during laserpulses irradiation Laser pulses were irradiated to the waterwith the metal oxides in glass bottle for 10 minutes Herethe fluence of the irradiated laser pulse was estimated to be45 Jcm2 After laser irradiation thewater was removed fromthe glass bottle and the powder was dried This process wasrepeated five times The reduced powder was collected anda part of all the reduced iron nanoparticles with the weightof 100mg was picked up and measured The reduced ironnanoparticles were used for the hydrogen production

Fluence (Jcm2) and the intensity (Wcm2) of the irra-diating laser pulses are important for reducing metal oxidesby laser ablation in liquids The fluence must be adequatelymore than 01 Jcm2 to heat the metal-oxide particles to ahigh temperature over their melting point and the intensity

must be over sub 01 GWcm2 due to induction of avalancheionization and extraction of electrons from the metal oxides

The conditions for the irradiation intensity of the laserpulses and the high absorption coefficient are adequate forreducing Fe

3O4powders However for reducing Fe

2O3by

using the high-repetition NdYAG pulsed laser the absorp-tion coefficient at 1064 nm wavelength is low the irradiationintensity and fluence are low and it has been found thatthe reduction of Fe

2O3using a high-repetition NdYAG

pulsed laser is hard Accordingly in this study a low-repetition NdYAG pulsed laser was used for reducing theFe2O3powder Additionally it has already been found in our

experiments that the Fe3O4powders can be reduced by using

this low-repetition NdYAG pulsed laserAnalysis of crystal structure by X-ray Diffraction (XRD)

(MAXima XXRD-7000 Shimadzu Japan) was performed tocheck the quantities of iron in the Fe

3O4powders irradiated

by the high-repetition NdYAG pulsed laser K-120572 X-rayradiation of copper was irradiated onto the samples

22 Hydrogen Production The method used for hydrogenproduction is described in the following The chemicalformula for reacting Fe

3O4powders with vaporized water is

given as

Fe3O4(s) + 12H2O (g) 997888rarr 3

2Fe2O3(s) + 12H2(g)

Δ119867 = 3648 kJmol(3)

And the chemical formula for reacting iron powders withvaporized water is given as

Fe (s) + 43H2O (g) 997888rarr 1

3Fe3O4(s) + 43H2(g)

Δ119867 = minus506 kJmol(4)


Fe powder H2H2O

(a)

Hot plate with controlling temperature

WaterVaporized water

hydrogen

Steel wool after combustion

Fe

Hydrogen

Downward displacementof water

(b)

Figure 4 Hydrogen production (a) photo of instrument for hydrogen production and (b) experimental setup

In (3) the enthalpy energy is for per unit mol Fe to reactwith vaporized water In the reaction of Fe

3O4with water

the water must be at high temperature and vaporized Thereaction of Fe

3O4withwater is endothermic and the reaction

of iron with water is exothermic It is clear that a certainamount of energy which is required for reducing metaloxide is needed for reacting Fe

3O4with water Thus the

reaction for hydrogen production using Fe3O4powder is

difficult at 673K Equation (4) shows that 12 of the storedpotential energy when the metal oxide was reduced is wastedas heat The experimental setup for generating hydrogenis shown in Figure 4 A photo of the reaction container isshown in Figure 4(a) and experimental setup for generatinghydrogen is shown in Figure 4(b) The outer size of thealuminum container was 20 times 20mm2 times 9mmt and thecontainer is solid and does not react with pure water at upto 973K The inner size of the aluminum container was 5times 8mm2 times 3mmt The center of the device was placed onthe reduced iron nanoparticles placed on an aluminum-foilsheet and steel wool was set between the container andthe right aluminum tube to prevent outflow of the powderThe aluminum container was heated in the range of 523 to673K by hot plate (CHP-170AN Asone Japan) Pure waterat a temperature of 295K was injected into the containerfrom the left aluminum tube Once the water was absorbedthe steel wool combusted and the water was vaporized andreacted with the iron powder After the reaction hydrogenwas extracted from the right aluminum tube The generatedhydrogen was collected by the water-replacement methodThe generated hydrogen was gathered in a silicon glass bottle

When iron nanoparticles were used for hydrogen pro-duction it was necessary to heat them Compared with theseresults using reduced Fe nanoparticles micron-diameter ironpowder with a weight of 100mg irradiated laser pulses wasused for the hydrogen productionThe reduction process wasrepeated 10 times The synthesized iron nanoparticles werealso used for the hydrogen production

3 Results

31 Reduced Iron Nanoparticles from Iron Oxides The XRDanalysis shows that the iron nanoparticles have a lot of 120574FeThe results of analyzing iron powders by XRD are shownin Figure 5 In common cases determining the quantity ofiron was difficult because the peak spectrum of Fe

3O4is

20 30 40 50 60 70 80

Inte

nsity

(1)

(2)

2120579

Fe3O4120574Fe

Figure 5 Results of analyzed Fe3O4powder and reduced iron

nanoparticles byXRD (1) Fe3O4powder and (2) Fe

3O4powder after

irradiating laser pulses

larger than that of 120572Fe or 120574Fe at the same quantity Twocomponents of 120574Fe at angles of 428 and 75 degrees can beseen in Figure 5 The 120574Fe component was clearly recognizedThe spectrum peak of iron at 428 degrees was evaluatedby extracting the Fe

3O4component and is nearly as high

as that of Fe3O4at 431 degrees Thus the reduced iron

nanoparticles contain a large quantity of 120574Fe but a negligiblequantity of Fe

3O4 In the common case the 120572Fe and Fe

3O4

components are recognized at angles of 447 and 431 degreesThe 120572Fe component is normally observed However it hasbeen already reported that when a CW laser or a pulsed laserwas used to heat the surface of a stainless plate120572Fe is changedto 120574Fe by a high temperature generated by laser [19]

As for Fe2O3reduction it is easy to judge the state of iron

oxides by their color when laser irradiation was conductedThe color of the Fe

2O3in the glass bottle changed from

red to black And some reduced iron nanoparticles becameglossy The color of the iron was silvery-white As for Fe

3O4

reductions when the reduced iron was observed the colorof a few iron particles was gray and most of the remainingpowder was black However inside the reduced iron waspure iron and only the outside of the reduced iron wasoxidized The mean size of the produced iron nanoparticles


0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30Water (mL)

Ideal volume 261 (mL)

Volu

me o

f gen

erat

ed h

ydro

gen

(mL)

673K

Fe2O3 70mg

5mg times14 times

Figure 6 Hydrogen generated by using Fe2O3after laser-pulse

irradiation

0

10

20

30

40

50

60

0 5 10 15 20 25 30Water (mL)


Fe powder

523K

573K

673K

623K

Fe3O4 powder 673KVolu

me o

f gen

erat

ed h

ydro

gen

(mL)

Figure 7 Hydrogen production using pure iron powder

was measured by a particle-size analyzer to be a mean size inthe order of 20 nm

32 Hydrogen Production Density of generated hydrogenwas measured by a hydrogen meter (Finch-Mono II Japan)The obtained hydrogen was diluted once with 500mL air andthe density was measured The density of the hydrogen wascompared with that of the hydrogen produced by electrolysisIt was thereby confirmed that the hydrogen concentrationwas near 99 and almost the same as that produced byelectrolysis

Hydrogen production was conducted using reduced ironnanoparticles from Fe

2O3powder The experimental results

are shown in Figure 6 The instrument for producing hydro-gen was heated by the hot plate at up to 673K About 25mLof hydrogenwas obtained when the instrument was heated at673K The theoretical volume needed for generating hydro-gen using 50mg of iron nanoparticles was 261mL whenall of the Fe

2O3particles (with the weight of 70mg) were

reduced The maximum reaction efficiency using reduced

0

10

20

30

40

50

60

0 5 10 15 20 25 30Water (mL)


Volu

me o

f gen

erat

ed h

ydro

gen

(mL)

Fe powder after laser irradiationFe3O4 powder after laser irradiationFe3O4 powder

673K

573K

523K

623K

673K

673K

Figure 8 Hydrogen production using pure iron and Fe3O4powder

after laser-pulse irradiation

iron nanoparticles from Fe2O3powder was evaluated to be

96 from the experimental resultHydrogen production was produced by using 100mg of

pure iron powder in the reactor The experimental results areshown in Figure 7 The reactor was heated at 523 573 623and 673K and 25mL of water was used Most of hydrogen(35mL) was obtained when the temperature of the heatedreactor was at 673K The theoretical volume to generatehydrogen using iron powder with a weight of 100mg is533mL The maximum volume of hydrogen was generatedat 673K and the reaction efficiency for hydrogen generationwas evaluated to be 66 while less than 03mL of hydrogenwas obtained using Fe

3O4particles with the mean size of

1 120583m when the instrument was heated at 673KHydrogen production was conducted using iron

nanoparticles (with a weight of 100mg) made from pureiron powder irradiated by a high-repetition-rate microchipNdYAG pulsed laser in water The experimental resultsare shown in Figure 8 The reactor was also heated at 523573 and 673K The amount of water used was 20mL Themaximum volume of generated hydrogen was 50mL atreactor temperature of 673K The reaction efficiency forhydrogen generation was evaluated as about 94 Thetheoretical volume of hydrogen that can be generated is533mL It has been found that the reaction speed andefficiency using iron powder irradiated by laser pulseswere improved because the mean size of the iron powderbecame 10 nm order and the surface area of reacting ironparticles increased A maximum amount of hydrogen wasalso observed at 673K

Finally hydrogen production was conducted usingreduced iron nanoparticles (with a weight of 100mg)from Fe

3O4powder irradiated by the high-repetition-rate

microchip NdYAG pulsed laser in liquid The reactor washeated at 523 573 623 and 673K and 25mL of pure water


was used The experimental results are shown in Figure 8The maximum amount of hydrogen obtained was 50mLwhen the temperature of the reactor was 673K The reactionefficiency of the hydrogen generationwas evaluated to be 94for a theoretical volume of generated hydrogen of 533mL

4 Discussion

Fe2O3 Fe3O4 and iron powders were reduced by using laser

ablation in liquid Iron oxide was chosen as a metal oxide forthe energy cycle because the Clarke number was the thirdand the iron amount in recoverable reserves which could bemined economically and technically is about 10 times that ofaluminum oxide Iron is easy to obtain and use

We discuss the absorption of laser pulses to metal oxidesThe absorption process of a laser pulse by metal oxides hastwo possibilities normal linear absorption and multiphotonabsorption In this experiment in laser ablation in liquidsthe latter mainly occurs Smaller particles make electronsin the metal oxides more active and electron emission willthus occur actively The absorption coefficients of Fe

2O3and

Fe3O4are markedly different Fe

3O4powder should be used

for the energy recycle because its absorption coefficient at1064 nm wavelength is high and after producing hydrogenFe3O4powders are mainly produced

If a CW laser is used for reduction of the metal oxidesthe reduction efficiency will be low because the generatedtemperature of the metal oxides is low The CW laser hasa low peak power and it cannot heat the metal oxides upto a melting temperature in a short time Moreover the lowintensity results in no avalanche ionization and less electronejection

The coulomb explosion and thermal ablation had beenproposed as the ablation mechanism of the metal oxide inthe liquid The coulomb explosion was mainly considered inthis study It has been suggested that metal-oxide particlesare broken into pieces in the Coulomb explosion Firstly themetal oxide is heated to over itsmelting temperature at whichit changes to form a gel Electrons in the atoms of the metaloxide are ejected by the intense electric field of the irradiatedlaser pulses After the particles becomepositively charged themetal oxides repel each other by the same positive chargeFinally a plasma is produced and atomized In the case ofusing water for laser ablation a subreaction occurs In thecoulomb explosion the ejected electrons and oxide atomreact with the water and OHminus ions are generated As a resultthe water becomes alkaline This phenomenon had alreadybeen observed in some experiments

Two lasers high- and low-repetition-rate NdYAG pulsedlasers were used to reduce Fe

2O3and Fe

3O4by laser

ablation in liquid It was found that the high-repetition-rate laser attained higher reduction efficiency than the low-repetition-rate laser The reduction efficiency of the metaloxides generated by using the high-repetition laser pulseswas higher than that for the low-repetition pulsed laser forthe same averaged laser power The reduction efficiency willdepend on the interaction time between the metal oxidesand laser pulses The emission time of electrons should be

determined by a single factor namely multiplication of pulseduration and repetitive rateThus it will be possible to reduce100mg of metal oxides in less than 10 minutes by using ahigh-repetition-pulse laser Moreover metal with more than200mg of oxides can be reduced in 10 minutes Reduction ofmetal oxide will occur in single laser pulse

We conducted hydrogen production by using smallinstrument for hydrogen production and the reduced ironHydrogen was produced by using a small instrument andthe reduced iron As a consequence the obtained reactionefficiency of hydrogen generation using iron nanoparticlesreduced by laser pulses was 94 which is high enough inthe case that the particles have oxide shells It means that thereduction of the metal particles by laser ablation in liquidswas almost complete Moreover power generation in thehydrogen fuel cell was confirmed

If the particle sizes of the iron nanoparticles were lessthan 10 nm it is predicted that iron nanoparticles will reactwith water completely by heating the temperature of theinstrument for hydrogen production to be close to 373K

For producing hydrogen using iron nanoparticlesreduced from Fe

3O4 a dispersing agent for protecting the

condensed nanoparticles is commonly used An agent wasnot used in the present study because the condensationshould not affect the reaction efficiency In the case of usingwater for producing hydrogen the surfaces of the producediron nanoparticles are oxidized However the oxide surfacedid not affect the reaction efficiency of hydrogen production

An energy loss occurs in the process of producing hydro-gen for the produced iron nanoparticles The energy loss isone eighth of the stored energy in the iron nanoparticles asthe difference of the potential energy between iron oxidesand iron in the reducing process It is small and convertsto heat However only 43mg of water is needed to reactwith 100mg of pure iron In this experiment the weight ofthe water used was 25 g Thus a lot of water was wastedwithout reacting with the iron nanoparticles To eliminatethis waste first the water should be confined in the reactorto improve the reaction efficiency with iron nanoparticlesSecond the reaction efficiency of the iron nanoparticlesshould be suppressed to 90 because the production rateof hydrogen degrades remarkably It introduces to save therequiredwater and electricity to heat and to recycle efficiently

Solar energy or other natural energies are considered assources of laser power for laser ablation in liquid Howeverthe most suitable lasers for energy cycles are considered tobe solar-pumped lasers because common lasers have lowelectro-optical conversion efficiency

In the future we will establish a clean-energy hydrogen-production cycle that is simple low-cost no-carbon andrecyclable by combining a solar-pumped laser and laserablation

5 Conclusion

Fe2O3and Fe

3O4powders were reduced with high efficiency

by NdYAG pulsed lasers based on laser ablation in liquidsIt was experimentally demonstrated that the produced iron


nanoparticles can be used for hydrogen generation in anenergy cycle For hydrogen production using the reducediron nanoparticles the reaction efficiency of the hydrogengeneration at a temperature of 673K was more than 94 forthe theoretically ideal amount of generated hydrogen Fe

3O4

powders remain after the hydrogen is produced and theyshould be reduced by pulsed laser Iron nanoparticles arereproduced and used for producing hydrogen again

The laser pulses should be generated using a naturalenergy source such as solar power or wind power Further-more the laser pulses can be generated directly from solarlight by using solar-pumped lasers It has been expectedthat our proposed energy cycle by using pulsed laser andthe Fe nanoparticles will be realized The proposed energycycle using a pulsed laser and iron nanoparticles is expectedto provide simple low-cost and no-carbon production ofrecyclable hydrogen

References

[1] P Charvin S Abanades F Lemort and G Flamant ldquoHydrogenproduction by three-step solar thermochemical cycles usinghydroxides and metal oxide systemsrdquo Energy and Fuels vol 21no 5 pp 2919ndash2928 2007

[2] M S Mohamed T Yabe C Baasandash et al ldquoLaser-inducedmagnesium production from magnesium oxide using reducingagentsrdquo Journal of Applied Physics vol 104 no 11 Article ID113110 2008

[3] M Uda H Okuyama T Suzuki and Y Yamada ldquoHydrogengeneration from water using Mg nanopowder produced by arcplasmamethodrdquo Science and Technology of AdvancedMaterialsvol 13 Article ID 025009 2012

[4] X Jiang M Watanabe H Onishi and R Saito ldquoApplicationsof recycled materials to fuel cell and related technologiesrdquoTransactions of the Materials Research Society of Japan vol 29no 5 pp 2507ndash2510 2004 (Japanese)

[5] P B Tarman and D V Punwani ldquoHydrogen production bythe steam-iron processrdquo in Proceedings of the 14th IntersocietyEnergy Conversion Engineering Conference vol 11 pp 286ndash2931976

[6] K Otsuka T Kaburagi C Yamada and S Takenaka ldquoChemicalstorage of hydrogen by modified iron oxidesrdquo Journal of PowerSources vol 122 no 2 pp 111ndash121 2003

[7] A Henglein ldquoPhysicochemical properties of small metal par-ticles in solution ldquomicroelectroderdquo reactions chemisorptioncomposite metal particles and the atom-to-metal transitionrdquoThe Journal of Physical Chemistry B vol 97 pp 5457ndash5471 1993

[8] M S Sibbald G humanov and T M Cotton ldquoReduction ofcytochrome c by halide-modified laser-ablated silver colloidsrdquoThe Journal of Physical Chemistry B vol 100 pp 4672ndash46781996

[9] M Kawasaki and N Nishimura ldquoLaser-induced fragmentativedecomposition of ketone-suspended Ag 2O micropowdersto novel self-stabilized Ag nanoparticlesrdquo Journal of PhysicalChemistry C vol 112 no 40 pp 15647ndash15655 2008

[10] H Wang A Pyatenko K Kawaguchi X Li Z Swiatkowska-Warkocka and N Koshizaki ldquoSelective pulsed heating for thesynthesis of semiconductor and metal submicrometer spheresrdquoAngewandte Chemie vol 49 no 36 pp 6361ndash6364 2010

[11] S Taniguchi T Saiki T Okada and T Furu ldquoSynthesis ofreactive metal nanoparticles by laser ablation in liquids and its

applicationsrdquo in Proceedings of the 421th Topical Meeting of TheLaser Society of Japan Laser Technology for 21st Century RTM-11-56 pp 25ndash30 2011

[12] V Amendola P Riello andMMeneghetti ldquoMagnetic nanopar-ticles of iron carbide iron oxide ironiron oxide and metaliron synthesized by laser ablation in organic solventsrdquo Journalof Physical Chemistry C vol 115 no 12 pp 5140ndash5146 2011

[13] T Okada S Taniguchi T Saiki T Furu K Y Iida and MNakatsuka ldquoSynthesis of Fe and FeO nanoparticles by laserablation in liquids and its applicationsrdquo in Proceedings of the the1st Advanced Lasers and Photon Sources pp 81ndash82 2012

[14] J Purnell E M Snyder S Wei and A W Castleman JrldquoUltrafast laser induced coulomb explosion of clusterswith highcharge statesrdquo Chemical Physics Letters vol 229 pp 333ndash3391994

[15] K Yamada K Miyajima and F Mafune ldquoIonization of goldnanoparticles in solution by pulse laser excitation as studied bymass spectrometric detection of gold cluster ionsrdquo The Journalof Physical Chemistry C vol 111 Article ID 033401 2007

[16] T Saiki T Okada K Nakamura T Karita Y Nishikawa andY Iida ldquoAir cells using negative metal electrodes fabricatedby sintering pastes with base metal nanoparticles for efficientutilization of solar energyrdquo International Journal of EnergyScience vol 2 no 6 pp 228ndash234 2012

[17] M Weksler and J Shwartz ldquoSolar-pumped solid-state lasersrdquoIEEE Journal of Quantum Electronics vol 24 no 6 pp 1222ndash1228 1988

[18] T Saiki M Nakatsuka and K Imasaki ldquoHighly efficient lasingaction of Nd3+- and Cr3+-doped yttrium aluminum garnetceramics based on phonon-assisted cross-relaxation using solarlight sourcerdquo Japanese Journal of Applied Physics vol 49 no 8Article ID 082702 2010

[19] C Cui J Hu Y Liu K Gao and Z Guo ldquoMorphologicaland structural characterizations of different oxides formed onthe stainless steel by NdYAG pulsed laser irradiationrdquo AppliedSurface Science vol 254 no 20 pp 6537ndash6542 2008

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Solar energy

Pulse laser

Metal oxideXO

MetalX

Reactedwith water

Hydrogenproduction

Reduction Oxidation

Nanoparticle

Solar-pumpedlaser

lt5000 K

Figure 1 Proposed energy cycle using solar energy

Figure 2 Small-scale solar-pumped laser

been developed [16ndash18]They can directly convert from inco-herent solar light to laser light And they have an advantage interms of consuming almost only solar powerwhen generatinga laser beam Now optical-optical conversion efficiency ofsolar-pumped lasers has been improved to almost 60 (iefrom solar light to laser light) by improvements in opticaltechnology [18] Moreover these lasers can generate laserpulses with high energy and high peak intensity Accordinglythey can be used for reducing metal oxide and fabricatingmetal nanoparticles in our proposed energy cycle The pro-duction of hydrogen by using reduced metal powder withnanometer-order diameters by continuous wave (CW) orpulsed laser has not been reported until now except for ourreport In this study iron nanoparticles were synthesizedby reduction by pulsed laser in liquids and the reactionefficiency of producing hydrogen by reacting the fabricatedmetal nanoparticles with vaporized water was experimentallyinvestigated

2 Experimental Setup

21 Laser Ablation in Liquids The required energy for reduc-ing iron metal oxides is determined as follows Fe

2O3 Fe3O4

and FeO are generally known as ldquoiron oxidesrdquo According tocrystal structure there are many typesThe chemical formulafor the reduction of Fe

2O3is given as

1

2Fe2O3(s) 997888rarr Fe (s) + 3

4O2(g) Δ119867 = 412 kJmol (1)

The chemical formula for the reduction of Fe3O4is given as

1

3Fe3O4(s) 997888rarr Fe (s) + 2

3O2(g) Δ119867 = 373 kJmol

(2)

Here Δ119867 is the enthalpy energy required for reducing unitmol Fe The basic enthalpy energy required for reducingFe2O3to Fe3O4is 392 kJ per unit mol of Fe

3O4 These

chemical reactions are all endothermic reactions It is clearfrom (1) and (2) that the required chemical energy toseparate the iron and oxygen atoms is large As for thetemperature required to change the Fe

2O3to Fe3O4 2100K

is required once the temperature is reduced to 1700K AfterFe2O3is changed to Fe

3O4 the Fe

3O4must be heated to

1900K to reduce it to FeO Iron can then be obtained afterheating the FeO to a higher temperature still It is generallyconsidered that FeO did not exist to change Fe

3O4and iron

by disproportionate ambient temperature After FeOparticlesare generated they will change to iron and Fe

3O4particles

due to the disproportionate reaction below 850KThe following metal-oxide powders were used to reduce

and produce metal nanoparticles Fe2O3powder 98 purity

mean size 45 120583m (325mesh) Fe3O4powder (Kojyundo

Chemical Laboratory Japan) mean size 1 120583m and ironpowder (Kojyundo Chemical Laboratory Japan) mean sizebelow 5 120583m Since the metal oxides are small it is supposedthat the size of the powder 119899 in the case of laser ablation inliquids is submicron

Experimental setups based on laser ablation in liquidto reduce metal-oxide powders are shown in Figure 3 Theexperimental setup based on the laser ablation in liquid toreduce Fe

2O3powders using a low-repetitionNdYAGpulsed

laser (Surelite II SLI-10 Continuum wavelength 1064 nmpulse duration 8 ns repetition frequency 10Hz) is shownin Figure 3(a) The diameter of the output laser beam was6mm (eminus2) A pear-shaped silicon-glass bottle was used toreduce the Fe

2O3powders Laser pulses are entered to a

mirror in the horizontal direction and they change directionto the vertical direction under the glass bottleThe laser pulseswere irradiated on the bottom of the glass bottle About 4of the irradiated laser energy was reflected on the surfaceof the bottle by the Fresnel reflection The laser pulses werefocused in the acetone liquid at a distance of 15mm fromthe bottom of the glass bottle The quantity of acetone in thebottle was 30mL Oxygen in the acetone was removed by


Laser

Mirror

Acetone

Fe2O3 powder

80 mm

(a)

in water

Magnetic stirrer

Laser

119891 = 50mm 20 mm

Fe3O4 powder

(b)













2O3by











given as

Fe3O4(s) + 12H2O (g) 997888rarr 3

2Fe2O3(s) + 12H2(g)

Δ119867 = 3648 kJmol(3)


Fe (s) + 43H2O (g) 997888rarr 1

3Fe3O4(s) + 43H2(g)



Fe powder H2H2O

(a)



hydrogen


Fe

Hydrogen


(b)



3O4with water








3 Results


3O4is

20 30 40 50 60 70 80

Inte

nsity

(1)

(2)

2120579

Fe3O4120574Fe



3O4powder after







3O4






3O4



0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30Water (mL)


Volu

me o

f gen

erat

ed h

ydro

gen

(mL)

673K

Fe2O3 70mg

5mg times14 times


irradiation

0

10

20

30

40

50

60

0 5 10 15 20 25 30Water (mL)


Fe powder

523K

573K

673K

623K


me o

f gen

erat

ed h

ydro

gen

(mL)









0

10

20

30

40

50

60

0 5 10 15 20 25 30Water (mL)


Volu

me o

f gen

erat

ed h

ydro

gen

(mL)


673K

573K

523K

623K

673K

673K














4 Discussion




2O3and







2O3and Fe

3O4by laser











5 Conclusion

Fe2O3and Fe





3O4



References

























RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy




Laser

Mirror

Acetone

Fe2O3 powder

80 mm

(a)

in water

Magnetic stirrer

Laser

119891 = 50mm 20 mm

Fe3O4 powder

(b)













2O3by











given as

Fe3O4(s) + 12H2O (g) 997888rarr 3

2Fe2O3(s) + 12H2(g)

Δ119867 = 3648 kJmol(3)


Fe (s) + 43H2O (g) 997888rarr 1

3Fe3O4(s) + 43H2(g)



Fe powder H2H2O

(a)



hydrogen


Fe

Hydrogen


(b)



3O4with water








3 Results


3O4is

20 30 40 50 60 70 80

Inte

nsity

(1)

(2)

2120579

Fe3O4120574Fe



3O4powder after







3O4






3O4



0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30Water (mL)


Volu

me o

f gen

erat

ed h

ydro

gen

(mL)

673K

Fe2O3 70mg

5mg times14 times


irradiation

0

10

20

30

40

50

60

0 5 10 15 20 25 30Water (mL)


Fe powder

523K

573K

673K

623K


me o

f gen

erat

ed h

ydro

gen

(mL)









0

10

20

30

40

50

60

0 5 10 15 20 25 30Water (mL)


Volu

me o

f gen

erat

ed h

ydro

gen

(mL)


673K

573K

523K

623K

673K

673K














4 Discussion




2O3and







2O3and Fe

3O4by laser











5 Conclusion

Fe2O3and Fe





3O4



References

























RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy




Fe powder H2H2O

(a)



hydrogen


Fe

Hydrogen


(b)



3O4with water








3 Results


3O4is

20 30 40 50 60 70 80

Inte

nsity

(1)

(2)

2120579

Fe3O4120574Fe



3O4powder after







3O4






3O4



0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30Water (mL)


Volu

me o

f gen

erat

ed h

ydro

gen

(mL)

673K

Fe2O3 70mg

5mg times14 times


irradiation

0

10

20

30

40

50

60

0 5 10 15 20 25 30Water (mL)


Fe powder

523K

573K

673K

623K


me o

f gen

erat

ed h

ydro

gen

(mL)









0

10

20

30

40

50

60

0 5 10 15 20 25 30Water (mL)


Volu

me o

f gen

erat

ed h

ydro

gen

(mL)


673K

573K

523K

623K

673K

673K














4 Discussion




2O3and







2O3and Fe

3O4by laser











5 Conclusion

Fe2O3and Fe





3O4



References

























RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy




0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30Water (mL)


Volu

me o

f gen

erat

ed h

ydro

gen

(mL)

673K

Fe2O3 70mg

5mg times14 times


irradiation

0

10

20

30

40

50

60

0 5 10 15 20 25 30Water (mL)


Fe powder

523K

573K

673K

623K


me o

f gen

erat

ed h

ydro

gen

(mL)









0

10

20

30

40

50

60

0 5 10 15 20 25 30Water (mL)


Volu

me o

f gen

erat

ed h

ydro

gen

(mL)


673K

573K

523K

623K

673K

673K














4 Discussion




2O3and







2O3and Fe

3O4by laser











5 Conclusion

Fe2O3and Fe





3O4



References

























RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy





4 Discussion




2O3and







2O3and Fe

3O4by laser











5 Conclusion

Fe2O3and Fe





3O4



References

























RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy





3O4



References

























RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy







RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy



hydrogen production using reduced-iron nanoparticles by laser...

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