The pellet making-ready followed the chaste course of the scatter metallurgy assiduity (NTUA): hematite (Fe2O3) or magnetite (Fe3O4) scatters were homogenized in a plasticizer and greasing environment, among a rotating pan (Figure 7). Conclusionantly, disks were instigateed in a 150 hinder hydraulic instigate (Figure 8). NTUA reasond the experiment of CERTH (coordinators of the HYDROSOL designs to profits in the equittalented making-ready of the pellets).
Figure 7. Rotating panFigure 8. The 150 hinder hydraulic instigate
Succeeding the edictobjurgate pelletization by the hydraulic instigate, the pellets were lowergindividual sintering and contraction in a inferior weather (oxygen-subdued weather) oven as pompn in Figure 9, in adjust to earn the magnetite sight informed by XRD, as pompn in Figure 10.
Figure 9. The sintering oven.Figure 10. XRD defense of the sinteblushing pellet, certifying the magnetite sight
The porosity of the pellet and the neck harvest, oblation stextinguished habitual equitableties, bear been monitoblushing by SEM, as pompn in Figure 11, as polite as by the chaste instigateurizing ordainments.
This fashion, the magnetite pellets bear been stabilized in habitual, electric and magnetic equitableties, oblation habitual robustness and electric resistivity lowerneath 10 Ohm or <103 ïOhm.m (non-used pellet).
Furthermore, an late manufacturing ordain has been contemplated by the SUN Unit to the preceding industrial technique. During sintering and contraction ordain, magnetic opportunity can be borrowed extraneously to the sintering and blushingucing ovens to magnetically orient the magnetite dipoles in the desiblushing course, totalowing restraint late Lorentz restraintce repress.
2.2. A unsubstantial-film catalyst
We bear conceived and familiar a unsubstantial film artifice restraint the hydrogen restraintmation which can be integrated in an automated scheme. The artifice can besides be reasond restraint the contraction and oxidation ordain in oxide semiconducting films cherished by metal substrates-wafers, equal if they do refertalented unfold adequate magnetic adjust. The ordainment is established on the Lorentz restraintces strikeed on the blushingucing – oxidizing conducting electrons in the said oxide semiconducting films. Hence, this artifice can snare oxygen and hydroxyl from infectious insinuate, thus unresisting hydrogen. This such contraction and oxidation ordain in public life, as polite as inferior weather stipulations.
A point collision, conducive restraint the HELENIC REF design refers to the three-flake depicted in Figure 15. The reform flake consists of a magnetite film refertalented thicker than 500 nm, an insulating unsubstantial film sustaining the magnetite film, refertalented thicker than 500 nm and finally a resounding wafer made of Al or other metal, sustaining the insulating and the magnetite unsubstantial film.
Figure 15. Schematic of the catalyst
Likely manufacturing ordainments include electrodeposition, material mist manifestation, chemical mist manifestation as polite as lithography and masking ordainments restraint the breed of electric contacts on the reform unsubstantial film.
Concerning Fe3O4 (magnetite) film, a prefertalented yet refertalented inappropriate plight is to be talented to arcollocate magnetic adjust in total atoms of the ferrimagnetic cells of the oxide. This is achieved by magnetic opportunity during manifestation or by post-processing magnetic opportunity annealing with succeeding opportunity cooling.
The desiblushing equitableties of the Fe3O4 (magnetite) film are tellingly as follows:
- Structure of the magnetite sight, which can be informed by X-ray scatter diffraction
- Multi-grained microstructure with smtotal necks among atoms, monitoblushing by Electron Microscopy
- Resistivity lowerneath 10 kOhm, telling of semiconducting sight
- Magnetic adjust, perceive-keepd by monitoring the magnetic hysteresis loop
- Habitual robustness perceive-keepd by self-denial and groove measurement
Applying electric floating through the resounding stay of the film consequences in magnetic opportunity correspondent to the exterior of the film and perpendicular to the applied electric floating. The repletion of this opportunity is:
Where I is the applied electric floating and a the besottedness of the film. If the besottedness a (combine of the magnetite film and the insulating unsubstantial film) are near than 1 ïm and the floating I is C Amperes, then the applied opportunity is:
Thus, the applied opportunity is repressltalented by the applied electric floating through the resounding stay. This floating can abundantly be in the adjust of individual Amperes in dc edict or distinct tens of Amperes in pulsed edict, if the besottedness of the resounding stay is in the adjust of 100 ïm, thus totalowing the transmission of magnetic opportunity larger than 1 T in the neighborhood of the oxide semiconducting film.
Therefore, perishing electric floating through resounding stay, individual can againstfeit the magnetic opportunity perpendicular to the course of electric floating perishing through the magnetite unsubstantial film. The courses of these brace electric floatings characterizes the course of the Lorentz restraintce on the conducting electrons of the magnetite film. Correspondent floatings consequence in restraintcing the electrons towards the insulating unsubstantial film, conjuncture anti-correspondent floatings restraintce them towards the exterior of the magnetite film. These brace irrelative courses of Lorentz restraintces bear a irrelative issue on the evolution of the magnetite unsubstantial film, strikeing as catalyst restraint the restraintmation of hydrogen.
Perishing electric floating correlative the magnetite film, rebellious on the electric floating perishing through the resounding substobjurgate of the magnetite film, (i.e. from another beginning), correlative the selfselfsimilar course of the floating infectious to the resounding substrate, consequences in a Lorentz restraintce strikeing on the commit carriers (electrons) tender them from the exterior towards the insulating unsubstantial film. Thus, the exterior of the magnetite film becomes strikeivated, in other vote is subdued ascribtalented to the opposition of the referableiceed Lorentz electrons.
Activation is the breed of electron vacancies, oblation the breed of innovating oxygen vacancies (advance of oxygen vacancies). Thus, the resistivity drops, and the applied voltage consequences in palliable floating, which extensions the topical sphere to 280 – 320C. Such sphere extension is observtalented by any bark of pyrometer. The sphere extension is relying on the coalition of the electric floating perishing through the oxide semiconducting film and the magnetic opportunity infectious to it ascribtalented to the electric floating perishing through the resounding stay.
The issue is revoctalented and un-hysteretic: extension or wane of the repletion of I x H fruit, where I is the applied floating on the oxide film and H the opportunity consequenceing from the floating on the resounding substrate, consequences in un-hysteretic and revoctalented extension or wane of the sphere and contraction of the oxide film deferenceively.
Such strikeivation can be deeptained equal in public life: the couple-of-a-trade among the Lorentz electrons established contraction and the generous life oxidation finally consequences in oxidation which can besides be macroscopically perceive-keepd by the wane of the strikeivated (reduced) area on the generous exterior of the film. Having scant the floating perishing through the resounding stay may consequence in strikeivation (reduction) shrinkage. In this truth, increasing the floating infectious to the resounding substobjurgate precedently the radiation disappears, or precedently oxygen re signation advance disappears, the oxygen re signation advance is rejuvenated. Such rejuvenation is altogether revoctalented by using the magnetic opportunity effected by the floating perishing through the resounding stay (in the adjust of 1 T).
Succeeding adequate oxidation (sight alteration of total the Fe3O4 film to Fe2O3) such oxygen re signation advance and conclusionant contraction of the combination is impractictalented with magnetic opportunitys of this adjust.
The contraction and oxidation ordain can be monitoblushing by measuring the exterior resistivity of the magnetite film. Such resistivity depicts the extension or wane of oxygen vacancies on the exterior and conclusionantly the majority of the oxide pellet. Extension and wane of this resistivity is equiponderant to the oxidation and contraction of the resistivity of the exterior deferenceively.
This issue is observtalented in total kinds of oxide semiconducting films equal in the deficiency of adequate magnetic adjust in them. To be talented to perceive-keep this issue in oxide semiconducting films, they should be in a consecutive firm propound restraintm, unfolding equal a smtotal electric conductivity, and arranged that magnetic opportunity and electric floating of equittalented waveframe and repletion are conjointly applied on the semiconducting oxide film and the conducting (metallic) stay.
Such contraction ordainment can be reasond in the contraction of combinations perishing on or through the film exterior. Our nucleus is the contraction of unadulterated mist insinuate to H2, by media of snareping the oxygen or the hydroxyl of the insinuate atom to the subdued (or strikeivated) magnetite. Such oxidation with conclusionant hydrogen restraintmation can be reversed tail to oxide contraction (activation) by media of pareason the insinuate mist transmission. This fashion, the brace electric floatings accomplish imbrace (activate) again the exterior of the oxide film, arranged that no insinuate mists are infectious to the pellet exterior or substantiality.
A incontrovertible collision of such issue is the reason of the said plife of Fe3O4 (magnetite) film with its resounding stay restraint the restraintmation of hydrogen and oxygen from insinuate mists, using the succeedingcited algorithm:
- Rebellious electric floatings by through the resounding stay and the oxide semiconducting film in the selfselfsimilar course. Thus, the exterior of the oxide semiconducting film is subdued (activated).
- Then, insinuate mist is infectious on the exterior of the oxide semiconducting film, consequenceing in oxygen snareping, hydrogen restraintmation and oxidation of the exterior of the oxide semiconducting film.
- As quickly as the opposition of the exterior of the oxide semiconducting film abounds a incontrovertible prelude, indicating attain to a nice flatten of oxide film exterior contraction, the insinuate mist transmission is stopped.
- Thus, the oxide film exterior is re-activated, followed by conclusionant oxygen acquit, until the opposition of the oxide film exterior attaines a poverty prelude, indicating equittalented contraction (activation), which is equittalented restraint oxygen snareping.
- Then, insinuate mist is re-infectious to the re-activated oxide film exterior restraint hydrogen restraintmation.
The restraintmation of hydrogen and oxygen is followed by an unreflective storage of these brace gases in irrelative chambers to be reasond restraint any room, love eager incendiarism or fuel cell evolution or other meaning.
Harvest of the unsubstantial film catalysts
The Dynamic Hydrogen Bubble Template (DHBT) is an palliable ordainment restraint the faithless of macrostructures with nanopercolable aspect walls. The ordainment has been named from the phenomena when a train of hydrogen-bubbles generated on the exterior of the substrae strike love a dynamic indirect template. Figure 1 demonstrates the presumptive arrival of the technique. Figure 1(a) represents the hydrogen-evolution commencement attribute on the exterior there is no metal/metal-oxide manifestation. The dimension of the bubbles increasing correlative the length from the substobjurgate exterior. Fig 1(b) pomps the SEM-image of copper nanofoams dexterous by DHBT.
Figure 1. (a) Simplified patronymic of DHBT generated metal/metal-established foams; (b) Honeycomb-love Cu-warranty structure made by DHBT.
The electrochemical manifestation jurisprudence of the harvest of the catalyst is disjoined in brace deep talents. At primitive precursive experiments on manifestation of magnetite film were carried extinguished in adjust to determine the adjusts of repletion of the irrelative compromised parameters (floating dullness, geometry absence of wonder.). , the electrochemical manifestation of lusty-oxide films was carried extinguished as a precursive arrival. Established on the consequences of the characterization, the parameters of the manifestation were sundry in a haughty collocate in adjust to earn 3D-structublushing percolable nanofoams.
The films were electrodeposited onto copper substrates (purity: 99.5%). The substrates were habitually reserved with 800 and 2000 emery papers, deferenceively. Henceforward, the reserved substrates were ultrasonically cleaned in deionized insinuate, ethanol and acetone, deferenceively. The 2 cm2 strikeive exterior area of the substobjurgate was ensublushing by wholesale nail-polish and insulating tape. The galvanostatic manifestation was carried extinguished in a brace-electrode cell using a DC Power Supply. Platinum-mesh was reasond as against electrode.
Brace irrelative ordainment of the established electrode bear been tested as pompn in Figure 2. The electrolytic bath was a strongly alkaline discontinuance with pH 12.5 made of 0.037 M Fe2(SO4)3.x H2O, 0.1 M triethanolamine (TEA) and 2 M NaOH. Succeeding mixing the components at T = 80 ï‚°C the discontinuance had greyish-unseasoned hue and no foulness was perceive-keepd.
The parameters of the manifestation ordain were sundry in the stipulations of floating dullness, bath sphere and manifestation interval. The collocate of cathodic floating dullness was chosen j = 5-15 mA.cm-2, the depostion interval was ardent from 5 min to 6 hours and the bath sphere was adjusted T = 60-90 ï‚°C. The trifling besottednesses of the dexterous structures were fitted by using the Faraday-law.
The exterior morphology of the warrantyed film-layers were elaboobjurgate by scanning electron microroom (Nova NanoSEM 230) and the crystallographic characterization was strong by X-ray diffraction (Bruker D8 Advance, Cu radiation-40kV, 35mA).
Figure 16. a) copper tripredilection reasond as established electrode (W) by turning the strikeive exterior towards the exterior of the electrolyte b) copper-plate (W) reasond as established electrode by immersing it altogether and by turning the strikeive exterior towards the against electrode (C).
Concerning the harvest of 3D-structublushing percolable films, the substobjurgate manifestation was refertalented progressive (Cu-foil, guiltlessness: 99.5%). SiC polishing papers were reasond in trice of 800, 1500, 2500 and 4000, deferenceively as a exterior pre-treatment. Total the pre-treated illustrations were ultrasonically cleaned in deionized insinuate, ethanol and acetone, deferenceively. In that truth, the strikeive exterior area of the substrates was subdued to 0.5 cm-2 and agricultural with nail-polish and insulating tape. The galvanostatic manifestation was carried extinguished in a brace electrode cell using a BioLogic SP 300 potentiostat. Platinum-wire was reasond as against electrode.
Concerning the consequence of the film-manifestation the ordainment of the established electrode was stable in perpendicular position. The electrolytic bath, concentrations and its equitableties were the selfselfsimilar as descriptive over. The cathodic floating dullness was sundry in the collocate ofj = 0.075-1 A.cm-2, the depostion interval was progressive among 30 sec to 180 s and the bath sphere was adjusted T = 90 ï‚°C. Similar films bear besides been familiar by using sputtering manifestation and electron-gun aided manifestation (Figure 17).
Apart from the electrolytic ordainment, unsubstantial magnetite films were besides warrantyed onto insulating films by usign spuutering and electron gun material evaporation at the NTUA. However, the earned consequences on the porosity of the magnetite films are refertalented compartalented with the DHBT ordainment and consequently they are refertalented demonstrattalented at their floating objurgate. Nevertheless, experiments are lower fashion to earn PVD films of the capacity perceive-keepd in the electrodeposited films.
- Characterization of catalysts
- Structural dissection
The catalyst pellets were dexterous by a proprietary ordain from Fe3O4 scatters. IP SAS reasond Fe3O4 scatter with visible guiltlessness reform than 99% and trifling atom dimension of 2-4um gifted by chemicalstore.com, fruit enactment FE3O4M1. The sight compound strong by XRD (X-Ray Diffraction) is pompn in Figure 38. Minor traces of Hematite can be perceive-keepd at 32.8Â° 2Theta restraint the illustration effected at IP SAS.
Figure 38. XRD jurisprudencels from pellets dexterous by SUN (red) and IP SAS (blue). Marked patron sights are Magnetite (cerulean lines) and Hematite (ebon lines)
A natural XRD defense in the majority SUN pellets and in majority CERTH pellets is artistic in Figure 1, demonstrating scientific magnetite intercourse.
Figure 1. XRD defense of majority pellets from SUN (left) and CERTH (right) illustrating scientific intercourse of magnetite
Sight alterations were elaboobjurgate by the media of in-situ XRD bestowed in Figure 41. Illustrations were mortar milled to earn a slender scatter that could be unfurl on the illustration holder of the furnace. Milling restraintce was kept minimal to guard the structure of the pellet talents. Linear heating with implied objurgate was reasond to earn polite-defined diffraction maxima with deference to the important to clamor ratio. Diffractometer was configublushing restraint correspondent radiate publicity with a induced LiF monochromator to suinstigate fluorescence from the Fe containing pellets.
Formerly unadulteratedly magnetite pellets are transforming to hematite in the neighborhood of 300Â°C. Succeeding the alteration no other sight exexchange was perceive-keepd. Pellets gifted by SUN exibit the alteration at palliable temparature than the pellets dexterous at IP SAS. This can be atributed to the feebleer dimension of the Fe3O4 crystallites in the SUN pellets.
Detailed jurisprudencel criterion is pompn in Figure 42. The elaboobjurgate scatteblushing pellets unfold merely intercourse of magnetite and hematite deferenceively. Diffraction maxima at 26Â° 2Theta corresponds to SiO2 bestow as a unsubstantial flake grown on the non-reflective Si illustration holder.
Figure 41. In-situ XRD jurisprudencels of catalysts in life weather with implied heating objurgate
Figure 42. In-situ XRD jurisprudencels of annealed catalyst pellets at implied spheres.
Marked patron sights Magnetite (cerulean lines) and Hematite (ebon lines).
Catalyst dexterous at SUN left, IP SAS correct.
Crystallographic consider of the lusty-oxide unsubstantial films illustrations was besides realized. Figure 4 represents the identification of the perceive-keepd peaks. Figure 4(a) pomps the consequences of illustration dexterous in 3300 s in 70 ï‚°C bath with -5 mA.cm-2 floating dullness. Grazing stroke XRD jurisprudencels of this illustration pomp the intercourse of magnetite (cerulean lines) and copper substobjurgate (unseasoned lines). Grazing predilection was 2 (blushing flexion) and 6 degrees (cerulean flexion), deferenceively.
In Figure 4(b) the consequences of illustration with selfselfsimilar stipulations as in Figure 4(a) can be conceiven, yet in this fstrike the floating dullness was -9 mA.cm-2. Here, grazing stroke XRD jurisprudencels pomp lusty (grey lines) and copper (unseasoned lines). Grazing predilection was 2 (blushing flexion) and 6 degrees (cerulean flexion), deferenceively. Figure 4(c/1) and (c/2) pomp the consequences of XRD enslaved from the selfselfsimilar illustration with manifestation stipulations of 2 hours manifestation interval in 85 ï‚°C bath and -12.5 mA.cm-2 floating dullness.
Figure 4. X-ray diffractograms of the lusty-oxide electrodeposited illustrations dexterous lower irrelative stipulations. a, Î”t=3300 s,T = 70 Â°C, j= -5 mA cm-2; b, Î”t=3300 s, T= 70Â°C, j= -9 mA cm-2; c/1, Î”t=7200 s, T= 85Â°C, j = -12.5 mA cm-2; c/2, scatter scratched from the exterior of illustration c/1
In Figure 4(c/1) the grazing stroke XRD jurisprudencels were dindividual on the illustration with the substrate. Free attraction of magnetite (cerulean lines), lusty (grey lines) and copper as substobjurgate (unseasoned lines). Grazing predilection was 2 (blushing flexion) and 6 degrees (cerulean flexion), deferenceively. Figure 4(c/2) demonstrates grazing stroke XRD jurisprudencel of unbound scatter from the selfselfsimilar illustration as (c/1). Merely magnetite sight (cerulean lines) is detected. Grazing predilection was 2 degrees. The XRD consequences pomp free attraction of magnetite if the floating dullness does refertalented abound 8 mA.cm-2 cathodic floating dullness (conceive Figures 4(a) and (b).
Apart from that, XPS studies bear besides been executed succeeding the inhibit convocation. Restraint integration reasons, they are demonstrated merely in the Milestindividual 1 instrument.
- Microstructural dissection
Morphology of pellets succeeding making-ready was elaboobjurgate by the media of SEM (scanning electron microscopy) pompn in Fig. 39. The atom dimension is larger restraint the catalyst dexterous by SUN. The atom dimension of illustration dexterous at IP SAS is in good-natured-natured bargain with the creator referableice and is rather homogenous in dimension disposal. Illustration dexterous at SUN is unfolding a irrelative dimension disposal ranging from very slender sub-micron atoms up to atoms with dimension increasing 50um pompn in Fig. 39 and 40. As can be conceiven the porosity of the dexterous pellets is palliable restraint the pellet dexterous at IP SAS.
The grid pompn in Fig. 40 is indemnifying the illustration from entity destroyed by the magnetic opportunity in the microroom and thus contaminating the microroom scheme by slender magnetic clay in the pole-piece, lens and guide scheme. It is value to referableice that the atom dimension is refertalented at-once explaining the diffraction maxima broadening pompn in instable in Fig. 38. This is ascribtalented to the fstrike that the diffraction dodeep dimension is rather irrelative than the atom dimension of a atom. We can positively propound that the diffraction dodeep dimension is feebleer in the pellet dexterous at SUN rather than at IP SAS opposing the perceive-keepd atom-dimension disposal.
Figure 39. SEM micrographs of catalysts dexterous by SUN (left) and IP SAS (right)
Figure 40. Low magnification micrographs of catalyst dexterous by SUN (left) and IP SAS (right)
Micrographs from the CERTH pellets (Figure 41) illustobjurgate a free attraction of necks, binding restraint the speaking contraction of sphere.
Figure 41. Micrographs of the CERTH pellets, illustrating the intercourse of micro-necks, binding restraint the correction of the electric and habitual equitableties
Concerning the unsubstantial film catalysts, SEM dissection was executed. Figure 3 demonstrates 4 irrelative SEM-images of the dexterous illustrations. Fig 3(a) was enslaved on a illustration dexterous in 300 s manifestation bound in 60Â°C bath with -7.5 mA cm-2 floating dullness, and the trifling besottedness was 2.24 Î¼m. In Fig 3(b) can be conceiven the morphology of the illustration dexterous in 300 s at 70Â°C with-5 mA cm-2 floating dullnesswith trifling besottedness of 23.55 Î¼m. Fig 3(c) pomps the SEM-consequence of the illustration warrantyed with the selfselfsimilar bath sphere and floating dullness as 3(b) yet adequate manifestation interval: Î”t = 900 s (dn = 30.28 Î¼m). Fig 3(d) represents the SEM-image of the illustration dexterous in the haughtyest bath sphere 90Â°C with 5 min manifestation interval, -7.5 mA cm-2 floating dullness (dn = 4.42 Î¼m).
The SEM-images freely pomp the structural exchanges by increasing the bath-temperature. Filamentous warranty structure has been perceive-keepd at 90 ï‚°C. Ascribtalented to the galvanostatic manifestation edict the undeveloped values bear been refertalented chronicled. Restraint reform lowerstanding of the structural restraintmations potentiostatic manifestation edict should be effected.
Figure 3. SEM-images of the electrodeposited lusty-oxide illustrations with irrelative manifestation parameters (a) Î”t=300 s,T= 60Â°C, j= -7.5 mA cm-2 at 30000X magnification (b) Î”t=300 s, T= 70Â°C, j = -5 mA cm-2 at 15 000X magnification(c) Î”t=900 s, T= 70Â°C, j= -5 mA cm-2at 10000X magnification (d) Î”t=300 s, T= 90Â°C, j= -7.5 mA cm-2 at 10000X magnification.
Concerning nano-foam, ascribtalented to the fstrike that the experiments were dindividual in the suppress late the characterization of the dexterous nanostructures was dindividual merely by scanning electron microscope. Figure 5 demonstrates the primitive calm consequences of the electrochemical manifestation of lusty-established 3D structures by using hydrogen breed on the exterior as a indirect template.
Such a structure was a consequence of applying -0.375 A.cm-2 and further indirect floating dullness, namely -1 A.cm-2 with irrelative warrantying intervals. Fig 5(a) to Fig 5 (c) represents a affectly structure ordain of the 3D networks with pore dimension collocate in 2-6 Î¼m. Other kind of warranty can be perceive-keepd at Fig 5(d) to Fig 5(e) with compact dendrites correlative the pore-sides by using floating dullness -0.375 A.cm-2 with irrelative manifestation intervals. The restraintmation of percolable flake is refertalented so open love in the antecedent truth, yet the dimension of pores are suppress in the selfselfsimilar collocate than the pores restraintmed at -1 A.cm-2.