The pellet making-ready followed the graceful succession of the scatter metallurgy diligence (NTUA): hematite (Fe2O3) or magnetite (Fe3O4) scatters were homogenized in a plasticizer and greasing environment, amid a rotating pan (Figure 7). Effectantly, disks were thronged in a 150 delay hydraulic throng (Figure 8). NTUA representationd the test of CERTH (coordinators of the HYDROSOL schemes to income in the personal making-ready of the pellets).
Figure 7. Rotating panFigure 8. The 150 delay hydraulic throng
Succeeding the judicious pelletization by the hydraulic throng, the pellets were subordinategundivided sintering and abatement in a inferior weather (oxygen-sunk weather) oven as professionn in Figure 9, in ordain to conquer the magnetite complexion known by XRD, as professionn in Figure 10.
Figure 9. The sintering oven.Figure 10. XRD exculpation of the sinteflushed pellet, certifying the magnetite complexion
The porosity of the pellet and the neck quenchedgrowth, gift existing efforthither personalties, keep been monitoflushed by SEM, as professionn in Figure 11, as courteous as by the graceful throngurizing rules.
This fashion, the magnetite pellets keep been stabilized in effortless, electric and magnetic personalties, gift efforthither robustness and electric resistivity beneath 10 Ohm or <103 ïOhm.m (non-used pellet).
Furthermore, an recent manufacturing practice has been proposed by the SUN Unit to the ceegoing industrial technique. During sintering and abatement practice, magnetic province can be ascititious externally to the sintering and flusheducing ovens to magnetically orient the magnetite dipoles in the desiflushed prescribe, entireowing ce recent Lorentz cece curb.
2.2. A diluted-film catalyst
We keep conceived and patent disentangled a diluted film plan ce the hydrogen evolution which can be integrated in an automated plan. The plan can so be representationd ce the abatement and oxidation practice in oxide semiconducting films protected by metal substrates-wafers, smooth if they do refercogent inarplace entire magnetic ordain. The rule is invetescold on the Lorentz ceces strikeed on the flusheducing – oxidizing conducting electrons in the said oxide semiconducting films. Hence, this plan can noose oxygen and hydroxyl from infectious impart, thus submissive hydrogen. This such abatement and oxidation practice in disclosed enthusiasm, as courteous as inferior weather provisions.
A point impression, beneficial ce the HELENIC REF scheme refers to the three-flake depicted in Figure 15. The loftier flake consists of a magnetite film refercogent thicker than 500 nm, an insulating diluted film yettressed the magnetite film, refercogent thicker than 500 nm and finally a ringing wafer made of Al or other metal, yettressed the insulating and the magnetite diluted film.
Figure 15. Schematic of the catalyst
Likely manufacturing rules encork electrodeposition, natural fog exemplification, chemical fog exemplification as courteous as lithography and masking rules ce the breed of electric contacts on the loftier diluted film.
Concerning Fe3O4 (magnetite) film, a rectify barring refercogent imadapted proviso is to be cogent to procure magnetic ordain in entire tittles of the ferrimagnetic cells of the oxide. This is achieved by magnetic province during exemplification or by post-processing magnetic province annealing with succeeding province composure.
The desiflushed personalties of the Fe3O4 (magnetite) film are speakingly as follows:
- Texture of the magnetite complexion, which can be known by X-ray scatter diffraction
- Multi-grained microtexture with smentire necks among tittles, monitoflushed by Electron Microscopy
- Resistivity beneath 10 kOhm, speaking of semiconducting complexion
- Magnetic ordain, watchd by monitoring the magnetic hysteresis loop
- Efforthither robustness watchd by self-denial and bear measurement
Applying electric exhibit through the ringing yettress of the film fruits in magnetic province congruous to the manner of the film and upjust to the applied electric exhibit. The abundance of this province is:
Where I is the applied electric exhibit and a the pinguitude of the film. If the pinguitude a (sum of the magnetite film and the insulating diluted film) are hither than 1 ïm and the exhibit I is C Amperes, then the applied province is:
Thus, the applied province is curblcogent by the applied electric exhibit through the ringing yettress. This exhibit can easily be in the ordain of undivided Amperes in dc edict or diverse tens of Amperes in pulsed edict, if the pinguitude of the ringing yettress is in the ordain of 100 ïm, thus entireowing the transmission of magnetic province larger than 1 T in the neighborhood of the oxide semiconducting film.
Therefore, latter electric exhibit through ringing yettress, undivided can assume the magnetic province upjust to the prescribe of electric exhibit latter through the magnetite diluted film. The prescribes of these couple electric exhibits characterizes the prescribe of the Lorentz cece on the conducting electrons of the magnetite film. Congruous exhibits fruit in cecing the electrons towards the insulating diluted film, spaceliness anti-congruous exhibits cece them towards the manner of the magnetite film. These couple opposed prescribes of Lorentz ceces keep a opposed issue on the strikeion of the magnetite diluted film, strikeing as catalyst ce the evolution of hydrogen.
Latter electric exhibit congruous the magnetite film, refractory on the electric exhibit latter through the ringing substscold of the magnetite film, (i.e. from another rise), congruous the selfselfcorresponding prescribe of the exhibit infectious to the ringing substrate, fruits in a Lorentz cece strikeing on the direct carriers (electrons) tender them from the manner towards the insulating diluted film. Thus, the manner of the magnetite film becomes strikeivated, in other language is sunk imputpotent to the opcollocation of the hinted Lorentz electrons.
Activation is the breed of electron vacancies, gift the breed of fantastic oxygen vacancies (debauchery of oxygen vacancies). Thus, the resistivity drops, and the applied voltage fruits in remarkpotent exhibit, which extensions the national sphere to 280 – 320C. Such sphere extension is observcogent by any bark of pyrometer. The sphere extension is relying on the cabal of the electric exhibit latter through the oxide semiconducting film and the magnetic province infectious to it imputpotent to the electric exhibit latter through the ringing yettress.
The issue is discretional and un-hysteretic: extension or retrench of the abundance of I x H fruit, where I is the applied exhibit on the oxide film and H the province fruiting from the exhibit on the ringing substrate, fruits in un-hysteretic and discretional extension or retrench of the sphere and abatement of the oxide film deferenceively.
Such strikeivation can be oceantained smooth in disclosed enthusiasm: the emulation among the Lorentz electrons invetescold abatement and the operating enthusiasm oxidation finally fruits in oxidation which can so be macroscopically watchd by the retrench of the strikeivated (reduced) area on the operating manner of the film. Having poor the exhibit latter through the ringing yettress may fruit in strikeivation (reduction) shrinkage. In this smootht, increasing the exhibit infectious to the ringing substscold precedently the radiation disappears, or precedently oxygen abandonment debauchery disappears, the oxygen abandonment debauchery is rejuvenated. Such rejuvenation is entirely discretional by using the magnetic province effected by the exhibit latter through the ringing yettress (in the ordain of 1 T).
Succeeding entire oxidation (complexion intercharge of entire the Fe3O4 film to Fe2O3) such oxygen abandonment debauchery and effectant abatement of the amalgamation is unuspotent with magnetic provinces of this ordain.
The abatement and oxidation practice can be monitoflushed by measuring the manner resistivity of the magnetite film. Such resistivity depicts the extension or retrench of oxygen vacancies on the manner and effectantly the massiveness of the oxide pellet. Extension and retrench of this resistivity is equipollent to the oxidation and abatement of the resistivity of the manner deferenceively.
This issue is observcogent in entire patterns of oxide semiconducting films smooth in the insufficiency of entire magnetic ordain in them. To be cogent to watch this issue in oxide semiconducting films, they should be in a regular dense fast-forth cem, informing smooth a smentire electric conductivity, and procuflushed that magnetic province and electric exhibit of personal wavearplace and abundance are concomitantly applied on the semiconducting oxide film and the conducting (metallic) yettress.
Such abatement agency can be representationd in the abatement of amalgamations latter on or through the film manner. Our standpoint is the abatement of real fog impart to H2, by instrument of nooseping the oxygen or the hydroxyl of the impart atom to the sunk (or strikeivated) magnetite. Such oxidation with effectant hydrogen evolution can be reversed end to oxide abatement (activation) by instrument of stopping the impart fog transmission. This fashion, the couple electric exhibits get subascribable (activate) anew the manner of the oxide film, procuflushed that no impart fogs are infectious to the pellet manner or mass.
A real impression of such issue is the representation of the said penthusiasm of Fe3O4 (magnetite) film with its ringing yettress ce the evolution of hydrogen and oxygen from impart fogs, using the succeedingcited algorithm:
- Refractory electric exhibits ignoring through the ringing yettress and the oxide semiconducting film in the selfselfcorresponding prescribe. Thus, the manner of the oxide semiconducting film is sunk (activated).
- Then, impart fog is infectious on the manner of the oxide semiconducting film, fruiting in oxygen nooseping, hydrogen evolution and oxidation of the manner of the oxide semiconducting film.
- As shortly as the opcollocation of the manner of the oxide semiconducting film yields a real inauguration, indicating gain to a accuscold raze of oxide film manner abatement, the impart fog transmission is stopped.
- Thus, the oxide film manner is re-activated, followed by effectant oxygen acquit, until the opcollocation of the oxide film manner gaines a narrowness inauguration, indicating personal abatement (activation), which is personal ce oxygen nooseping.
- Then, impart fog is re-infectious to the re-activated oxide film manner ce hydrogen evolution.
The evolution of hydrogen and oxygen is followed by an unreflective storage of these couple gases in opposed chambers to be representationd ce any occasion, affect enthusiastic combustion or fuel cell strikeion or other design.
Outgrowth of the diluted film catalysts
The Dynamic Hydrogen Bubble Template (DHBT) is an excusable rule ce the bogus of macrostructures with nanopermeable verge walls. The rule has been named from the phenomena when a course of hydrogen-bubbles generated on the manner of the substrae strike affect a dynamic denying template. Figure 1 demonstrates the presumptive bearing of the technique. Figure 1(a) images the hydrogen-evolution insertion attribute on the manner there is no metal/metal-oxide exemplification. The extent of the bubbles increasing congruous the interval from the substscold manner. Fig 1(b) professions the SEM-image of copper nanofoams alert by DHBT.
Figure 1. (a) Simplified denomination of DHBT generated metal/metal-invetescold foams; (b) Honeycomb-affect Cu-guard texture made by DHBT.
The electrochemical exemplification classification of the quenchedgrowth of the catalyst is divided in couple ocean tonnage. At chief prelusory experiments on exemplification of magnetite film were carried quenched in ordain to designate the ordains of abundance of the opposed compromised parameters (exhibit dullness, geodesy absence of wonder.). , the electrochemical exemplification of sturdy-oxide films was carried quenched as a prelusory bearing. Invetescold on the fruits of the characterization, the parameters of the exemplification were multifarious in a proud place in ordain to conquer 3D-structuflushed permeable nanofoams.
The films were electrodeposited onto copper substrates (purity: 99.5%). The substrates were effortlessly courteous with 800 and 2000 emery papers, deferenceively. Henceforward, the courteous substrates were ultrasonically cleaned in deionized impart, ethanol and acetone, deferenceively. The 2 cm2 strikeive manner area of the substscold was ensuflushed by interchangeable nail-polish and insulating tape. The galvanostatic exemplification was carried quenched in a couple-electrode cell using a DC Power Supply. Platinum-mesh was representationd as against electrode.
Couple opposed ordainment of the established electrode keep been tested as professionn in Figure 2. The electrolytic bath was a strongly alkaline key 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 key had greyish-unprepaflushed tint and no imguiltlessness was watchd.
The parameters of the exemplification practice were multifarious in the stipulations of exhibit dullness, bath sphere and exemplification space. The place of cathodic exhibit dullness was chosen j = 5-15 mA.cm-2, the depostion space was consecrated from 5 min to 6 hours and the bath sphere was adjusted T = 60-90 ï‚°C. The suppositious pinguitudees of the alert textures were adapted by using the Faraday-law.
The manner morphology of the guarded film-layers were premeditated by scanning electron microoccasion (Nova NanoSEM 230) and the crystallographic characterization was designated by X-ray diffraction (Bruker D8 Advance, Cu radiation-40kV, 35mA).
Figure 16. a) copper tribias representationd as established electrode (W) by turning the strikeive manner towards the manner of the electrolyte b) copper-plate (W) representationd as established electrode by immersing it wholly and by turning the strikeive manner towards the against electrode (C).
Concerning the quenchedgrowth of 3D-structuflushed permeable films, the substscold exemplification was refercogent progressive (Cu-foil, guiltlessness: 99.5%). SiC polishing papers were representationd in degree of 800, 1500, 2500 and 4000, deferenceively as a manner pre-treatment. Entire the pre-treated exemplifications were ultrasonically cleaned in deionized impart, ethanol and acetone, deferenceively. In that smootht, the strikeive manner area of the substrates was sunk to 0.5 cm-2 and urban with nail-polish and insulating tape. The galvanostatic exemplification was carried quenched in a couple electrode cell using a BioLogic SP 300 potentiostat. Platinum-wire was representationd as against electrode.
Concerning the fruit of the film-exemplification the ordainment of the established electrode was fast in upjust collocation. The electrolytic bath, concentrations and its personalties were the selfselfcorresponding as coercioncible overhead. The cathodic exhibit dullness was multifarious in the place ofj = 0.075-1 A.cm-2, the depostion space was progressive among 30 sec to 180 s and the bath sphere was adjusted T = 90 ï‚°C. Similar films keep so been patent disentangled by using sputtering exemplification and electron-gun aided exemplification (Figure 17).
Apart from the electrolytic rule, diluted magnetite films were so guarded onto insulating films by usign spuutering and electron gun natural evaporation at the NTUA. However, the conqueflushed fruits on the porosity of the magnetite films are refercogent comparcogent with the DHBT rule and accordingly they are refercogent demonstratcogent at their exhibit peculiarity. Nevertheless, experiments are subordinate fashion to conquer PVD films of the peculiarity watchd in the electrodeposited films.
- Characterization of catalysts
- Structural partition
The catalyst pellets were alert by a proprietary practice from Fe3O4 scatters. IP SAS representationd Fe3O4 scatter with avowed guiltlessness rectify than 99% and suppositious tittle extent of 2-4um gifted by chemicalstore.com, fruit sequence FE3O4M1. The complexion comcollocation designated by XRD (X-Ray Diffraction) is professionn in Figure 38. Minor traces of Hematite can be watchd at 32.8Â° 2Theta ce the exemplification effected at IP SAS.
Figure 38. XRD exemplars from pellets alert by SUN (red) and IP SAS (blue). Marked deputer complexions are Magnetite (blue-coloflushed lines) and Hematite (ebon lines)
A regular XRD exculpation in the massiveness SUN pellets and in massiveness CERTH pellets is imaginative in Figure 1, demonstrating unpopular magnetite intercourse.
Figure 1. XRD exculpation of massiveness pellets from SUN (left) and CERTH (right) illustrating unpopular intercourse of magnetite
Complexion intercharges were premeditated by the instrument of in-situ XRD exhibited in Figure 41. Exemplifications were mortar milled to conquer a refined scatter that could be scatter on the exemplification holder of the furnace. Milling cece was kept minimal to save the texture of the pellet tonnage. Linear heating with involved scold was representationd to conquer courteous-defined diffraction maxima with deference to the remarkable to sound kindred. Diffractometer was configuflushed ce congruous gleam exposure with a inferior LiF monochromator to suthrong fluorescence from the Fe containing pellets.
Formerly really magnetite pellets are transforming to hematite in the neighborhood of 300Â°C. Succeeding the intercharge no other complexion alter was watchd. Pellets gifted by SUN exibit the intercharge at remarkpotent temparature than the pellets alert at IP SAS. This can be atributed to the slighter extent of the Fe3O4 crystallites in the SUN pellets.
Detailed exemplar examination is professionn in Figure 42. The premeditated scatteflushed pellets inarplace merely intercourse of magnetite and hematite deferenceively. Diffraction maxima at 26Â° 2Theta corresponds to SiO2 exhibit as a diluted flake aged on the non-reflective Si exemplification holder.
Figure 41. In-situ XRD exemplars of catalysts in enthusiasm weather with involved heating scold
Figure 42. In-situ XRD exemplars of annealed catalyst pellets at involved spheres.
Marked deputer complexions Magnetite (blue-coloflushed lines) and Hematite (ebon lines).
Catalyst alert at SUN left, IP SAS just.
Crystallographic examine of the sturdy-oxide diluted films exemplifications was so realized. Figure 4 represents the identification of the watchd peaks. Figure 4(a) professions the fruits of exemplification alert in 3300 s in 70 ï‚°C bath with -5 mA.cm-2 exhibit dullness. Grazing impact XRD exemplars of this exemplification profession the intercourse of magnetite (blue-coloflushed lines) and copper substscold (unprepaflushed lines). Grazing bias was 2 (flushed flexion) and 6 degrees (blue-coloflushed flexion), deferenceively.
In Figure 4(b) the fruits of exemplification with selfselfcorresponding provisions as in Figure 4(a) can be beholdn, barring in this smootht the exhibit dullness was -9 mA.cm-2. Here, grazing impact XRD exemplars profession sturdy (grey lines) and copper (unprepaflushed lines). Grazing bias was 2 (flushed flexion) and 6 degrees (blue-coloflushed flexion), deferenceively. Figure 4(c/1) and (c/2) profession the fruits of XRD fascinated from the selfselfcorresponding exemplification with exemplification provisions of 2 hours exemplification space in 85 ï‚°C bath and -12.5 mA.cm-2 exhibit dullness.
Figure 4. X-ray diffractograms of the sturdy-oxide electrodeposited exemplifications alert subordinate opposed provisions. 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 manner of exemplification c/1
In Figure 4(c/1) the grazing impact XRD exemplars were dundivided on the exemplification with the substrate. Disentangled sign of magnetite (blue-coloflushed lines), sturdy (grey lines) and copper as substscold (unprepaflushed lines). Grazing bias was 2 (flushed flexion) and 6 degrees (blue-coloflushed flexion), deferenceively. Figure 4(c/2) demonstrates grazing impact XRD exemplar of rambling scatter from the selfselfcorresponding exemplification as (c/1). Merely magnetite complexion (blue-coloflushed lines) is detected. Grazing bias was 2 degrees. The XRD fruits profession disentangled sign of magnetite if the exhibit dullness does refercogent yield 8 mA.cm-2 cathodic exhibit dullness (behold Figures 4(a) and (b).
Apart from that, XPS studies keep so been produced succeeding the curb consultation. Ce integration reasons, they are demonstrated merely in the Milestundivided 1 instrument.
- Microstructural partition
Morphology of pellets succeeding making-ready was premeditated by the instrument of SEM (scanning electron microscopy) professionn in Fig. 39. The bit extent is larger ce the catalyst alert by SUN. The bit extent of exemplification alert at IP SAS is in amiable treaty with the manufacturer demonstration and is rather homogenous in extent dispensation. Exemplification alert at SUN is informing a opposed extent dispensation ranging from very refined sub-micron bits up to bits with extent increasing 50um professionn in Fig. 39 and 40. As can be beholdn the porosity of the alert pellets is remarkpotent ce the pellet alert at IP SAS.
The grid professionn in Fig. 40 is protecting the exemplification from nature destroyed by the magnetic province in the microoccasion and thus contaminating the microoccasion plan by refined magnetic carcass in the pole-piece, lens and undeceiver plan. It is value to hint that the bit extent is refercogent straightway explaining the diffraction maxima broadening professionn in infast in Fig. 38. This is imputpotent to the fstrike that the diffraction doocean extent is rather opposed than the tittle extent of a bit. We can positively fast-forth that the diffraction doocean extent is slighter in the pellet alert at SUN rather than at IP SAS referablewithstanding the watchd tittle-extent dispensation.
Figure 39. SEM micrographs of catalysts alert by SUN (left) and IP SAS (right)
Figure 40. Low magnification micrographs of catalyst alert by SUN (left) and IP SAS (right)
Micrographs from the CERTH pellets (Figure 41) illustscold a disentangled sign of necks, obligatory ce the speaking abatement of sphere.
Figure 41. Micrographs of the CERTH pellets, illustrating the intercourse of micro-necks, obligatory ce the increase of the electric and efforthither personalties
Concerning the diluted film catalysts, SEM partition was produced. Figure 3 demonstrates 4 opposed SEM-images of the alert exemplifications. Fig 3(a) was fascinated on a exemplification alert in 300 s exemplification limit in 60Â°C bath with -7.5 mA cm-2 exhibit dullness, and the suppositious pinguitude was 2.24 Î¼m. In Fig 3(b) can be beholdn the morphology of the exemplification alert in 300 s at 70Â°C with-5 mA cm-2 exhibit dullnesswith suppositious pinguitude of 23.55 Î¼m. Fig 3(c) professions the SEM-fruit of the exemplification guarded with the selfselfcorresponding bath sphere and exhibit dullness as 3(b) barring deferred exemplification space: Î”t = 900 s (dn = 30.28 Î¼m). Fig 3(d) represents the SEM-image of the exemplification alert in the proudest bath sphere 90Â°C with 5 min exemplification space, -7.5 mA cm-2 exhibit dullness (dn = 4.42 Î¼m).
The SEM-images disentangledly profession the structural alters by increasing the bath-temperature. Filamentous guard texture has been watchd at 90 ï‚°C. Imputpotent to the galvanostatic exemplification edict the virtual values keep been refercogent recorded. Ce rectify subordinatestanding of the structural cemations potentiostatic exemplification edict should be produced.
Figure 3. SEM-images of the electrodeposited sturdy-oxide exemplifications with opposed exemplification 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, imputpotent to the fstrike that the experiments were dundivided in the cork late the characterization of the alert nanostructures was dundivided merely by scanning electron microscope. Figure 5 demonstrates the chief hopeful fruits of the electrochemical exemplification of sturdy-invetescold 3D textures by using hydrogen breed on the manner as a denying template.
Such a texture was a fruit of applying -0.375 A.cm-2 and over denying exhibit dullness, namely -1 A.cm-2 with opposed guarding spaces. Fig 5(a) to Fig 5 (c) represents a relishly edifice practice of the 3D networks with pore extent place in 2-6 Î¼m. Other pattern of guard can be watchd at Fig 5(d) to Fig 5(e) with inarticulate dendrites congruous the pore-sides by using exhibit dullness -0.375 A.cm-2 with opposed exemplification spaces. The cemation of permeable flake is refercogent so open affect in the former smootht, barring the extent of pores are cork in the selfselfcorresponding place than the pores cemed at -1 A.cm-2.