ELECTROLYTIC CELL FOR H2 GENERATION

Abstract

The invention provides an electrolytic cell (200) for temporally shifted electrolytic production of H.sub.2 and O.sub.2, the electrolytic cell comprising a cell compartment (210), wherein the cell compartment comprises a gas evolution electrode (220) and an electron storage electrode (230), wherein the gas evolution electrode comprises a nickel-based electrode, wherein the electron storage electrode comprises an iron-based electrode, and wherein an electrochemical storage capacity C.sub.gee of the gas evolution electrode is≤5% of an electrochemical storage capacity C.sub.esc of the electron storage electrode.

Claims

1. An electrolytic cell (200) for temporally shifted electrolytic production of H.sub.2 and O.sub.2, the electrolytic cell (200) comprising a cell compartment (210), wherein the cell compartment (210) comprises a gas evolution electrode (220) and an electron storage electrode (230), wherein the gas evolution electrode (220) comprises an electrode selected from the group consisting of a nickel-based electrode, a stainless steel-based electrode, a titanium-based electrode and a platinum-based electrode, wherein the electron storage electrode (230) comprises an iron-based electrode, and wherein an electrochemical storage capacity C.sub.gee of the gas evolution electrode (220) is≤5% of an electrochemical storage capacity C.sub.ese of the electron storage electrode (230).

2. The electrolytic cell (200) according to claim 1, wherein a surface area of the gas evolution electrode (220)≥10% of a surface area of the electron storage electrode (230), and wherein the surface area of the gas evolution electrode is≤125% of the surface area of the electron storage electrode, and wherein the electrochemical storage capacity C.sub.gee of the gas evolution electrode (220) is≤0.1% of the electrochemical storage capacity C.sub.ese of the electron storage electrode (230), and wherein the gas evolution electrode (220) comprises an electrode selected from the group comprising a porous electrode, a mesh electrode, a wire electrode, and a plate electrode.

3. The electrolytic cell (200) according to claim 1, wherein the cell compartment (210) comprises a cell compartment opening (219) configured for adding a fluid to the cell compartment (210) and/or for removing a fluid from the cell compartment (210) and wherein the electrolytic cell (200) comprises an airtight housing (201) comprising the cell compartment (210).

4. The electrolytic cell (200) according to claim 1, wherein the cell compartment (210) further comprises a separator (216) arranged between the gas evolution electrode (220) and the electron storage electrode (230), wherein the separator (216) defines a gas evolution subcompartment (212) and an electron storage subcompartment (213), wherein the separator (216) is configured to block transport of one or more of O.sub.2 and H.sub.2 between the gas evolution subcompartment (212) and the electron storage subcompartment (213).

5. The electrolytic cell (200) according to claim 4, wherein the separator (216) is a membrane (211).

6. The electrolytic cell (200) according to claim 1, wherein the cell compartment (210) is a membrane-free compartment (214).

7. The electrolytic cell (200) according to claim 1, wherein the electrolytic cell (200) comprises a recombination catalyst configured to catalyze a recombination of H.sub.2 and O.sub.2 to H.sub.2O, and/or wherein the electron storage electrode (230) comprises an additive selected from the group comprising bismuth sulfide, bismuth oxide, Sn, and Pb.

8. The electrolytic cell (200) according to claim 1, wherein the cell compartment (210) comprises an electrolyte (240), wherein the electrolyte is a liquid electrolyte, wherein the concentration of hydroxide (OH.sup.−) in water is selected from the range of 0.1-8 mol/L.

9. The electrolytic cell (200) according to claim 1, wherein the electrolytic cell (200) comprises a vertical bipolar arrangement (270, 270b) or a horizontal bipolar arrangement (270, 270a).

10. The electrolytic cell (200) according to claim 1, wherein the electrolytic cell (200) comprises or is functionally coupled to a charge control unit, wherein during a charging operation, the charge control unit is configured to impose a potential difference between the gas evolution electrode (220) and the electron storage electrode (230)≥1.37 V, and during a discharging operation, the charge control unit is configured to impose a potential difference between the electron storage electrode (230) and the gas evolution electrode (220) selected from the range of 0.01-1.0 V.

11. The electrolytic cell (200) according to claim 1, wherein the electron storage electrode is a solid electrode.

12. The electrolytic cell (200) according to claim 1, wherein during operation, the iron-based electron storage electrode goes through Fe.fwdarw.Fe(OH).sub.2.fwdarw.Fe cycles.

13. A method (300) for controlling the electrolytic cell (200) according to claim 1, the method comprising controlling a potential difference and/or a current flow between the gas evolution electrode (220) and the electron storage electrode (230).

14. The method (300) according to claim 13, wherein the method (300) further comprises controlling the potential difference and/or the current flow in dependence of one or more of H.sub.2 demand and charging level of the electrolytic cell (200).

15. The method (300) according to claim 13, wherein the method (300) further comprises controlling the volume of an electrolyte (240) in the cell compartment (210), wherein the method (300) further comprises: (i) replacing at least 50% of the cell compartment volume of electrolyte (240) in the cell compartment (210) with a storage gas after charging, and subsequently (ii) replacing at least 50% of the cell compartment volume of the storage gas in the cell compartment (210) with a second electrolyte prior to discharging, wherein the storage gas comprises H.sub.2 and/or an inert gas.

16. The method (300) according to claim 13, the method (300) further comprising controlling a temperature of the cell compartment (210) below a maximum temperature T.sub.max during a charging time, wherein the maximum temperature T.sub.max≤40° C., and the method (300) further comprising controlling a gas pressure within the cell compartment (210), wherein the method comprises charging the electrolytic cell (200) at a gas pressure selected from the range of 0.1-10 bar, and wherein the method (300) comprises discharging the electrolytic cell (200) at a gas pressure selected from the range of 1-800 bar.

17. The method (300) according to claim 13, wherein the method comprises discharging the electrolytic cell according to the reactions:
2H.sub.2O+2e.sup.−.fwdarw.H.sub.2+2O.sup.− at the gas evolution electrode, and
Fe+2OH.sup.−.fwdarw.Fe(OH).sub.2+2e.sup.− at the electron storage electrode; and wherein the method comprises charging the electrolytic cell according to the reactions:
Fe(OH).sub.2+2e.sup.−.fwdarw.Fe+2OH.sup.− at the electron storage electrode and
4OH.sup.−.fwdarw.2H.sub.2O+O.sub.2+4e.sup.− at the gas evolution electrode.

18. An electrolytic system (100) comprising the electrolytic cell (200) according to claim 1, and a control system (140) configured to control the electrolytic system (100).

19. The electrolytic system (100) according to claim 17, wherein the electrolytic system (100) comprises a plurality of electrolytic cells (200), and wherein the electrolytic system (100) comprises a parallel arrangement and/or a serial arrangement of the plurality of electrolytic cells (200).

20. The electrolytic system (100) according to claim 18, wherein the control system is configured to control a potential difference and/or a current flow between the gas evolution electrode (220) and the electron storage electrode.

21. A use of the electrolytic cell (200) according to claim 1, wherein the cell compartment (210) comprises an electrolyte (240) in fluid contact with the gas evolution electrode (220) and the electron storage electrode (230), wherein during at least part of a charging time the electrolytic cell (200) is charged at a potential difference between the gas evolution electrode (220) and the electron storage electrode (230) of more than 1.2 V, and wherein during at least part of a discharging time the electrolytic cell (200) is discharged at a potential difference between the electron storage electrode (230) and the gas evolution electrode (220) selected from the range of 0.0-1.0 V.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0141] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0142] FIG. 1A-B schematically depict embodiments of the electrolytic cell.

[0143] FIG. 2A-C schematically depict an embodiment of the electrolytic cell.

[0144] FIG. 3A-B schematically depicts further embodiments of the electrolytic cell.

[0145] FIG. 4 schematically depicts an embodiment of the method.

[0146] The schematic drawings are not necessarily on scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0147] FIG. 1A schematically depicts an embodiment of the electrolytic cell 200 for temporally shifted electrolytic production of H.sub.2 and O.sub.2. The electrolytic cell 200 comprises a cell compartment 210, wherein the cell compartment 210 comprises a gas evolution electrode 220 and an electron storage electrode 230. In the depicted embodiment, the gas evolution electrode 220 comprises a nickel-based electrode, and the electron storage electrode 230 comprises an iron-based electrode. In embodiments, an electrochemical storage capacity C.sub.gee of the gas evolution electrode 220 may be≤1% of an electrochemical storage capacity C.sub.ese of the electron storage electrode 230.

[0148] In the depicted embodiment, an electrolytic system 100 comprises the electrolytic cell 200 and a control system 140 configured to control the electrolytic system 100. The electrolytic system 100, especially the electrolytic cell 200, comprises a first electrical connection 120 functionally coupled to the gas evolution electrode 220, and a second electrical connection 130 functionally coupled to the electron storage electrode 230. In further embodiments, the control system 140 is configured to carry out the method 300 according to the invention.

[0149] In embodiments, the electrochemical storage capacity C.sub.gee of the gas evolution electrode 220 may be≤5%, such as ≤1%, especially ≤0.1%, of the electrochemical storage capacity C.sub.ese of the electron storage electrode 230. In further embodiments, a (total) surface area of the gas evolution electrode 220≥50% of a (total) surface area of the electron storage electrode 230, especially the geometric surface area of the side of the gas evolution electrode facing the electron storage electrode≥50% of the geometric surface area of the side of the electron storage electrode facing the gas evolution electrode. In the depicted embodiment wherein the volume of the electrodes appears roughly equal, the gas evolution electrode 220 may comprise a (Ni-)mesh electrode. In further embodiments, the bulk volume of the gas evolution electrode 220 may be smaller (or larger) than the electron storage electrode.

[0150] In the depicted embodiment, the cell compartment 210 is a membrane-free compartment 214.

[0151] FIG. 1B schematically depicts a further embodiment of the electrolytic cell 200. In the depicted embodiment, the cell compartment 210 comprises the gas evolution electrode 220, the electron storage electrode 230, the electrolyte 240, a gas 245, and a membrane 211. The gas 245 may, in embodiments, be one or more of be a charging gas comprising O.sub.2, a discharging gas comprising H.sub.2, or an inert gas, such as N.sub.2.

[0152] In embodiments, the electrolytic cell 200 may comprise an airtight housing 201 comprising the cell compartment 210, wherein the airtight housing 201 is substantially closed. In further embodiments, the cell compartment 210 may comprise a cell compartment opening 219 configured for adding a fluid, such as electrolyte 240, to the cell compartment 210 and/or for removing a fluid, such as the gas 245, from the cell compartment 210. In further embodiments, the cell compartment 210 may comprise two or more cell compartment openings 219. A cell compartment 210 comprising two or more cell compartment openings 219 may be beneficial for, for example, purging of the cell compartment with a gas, such as inert gas, especially N.sub.2. Hence, the airtight housing 201 may be substantially closed, except for the cell compartment opening(s) 219.

[0153] The membrane 211 may be arranged between the gas evolution electrode 220 and the electron storage electrode 230. The membrane may be configured to block transport of one or more of O.sub.2 and H.sub.2 between the gas evolution subcompartment 212 and the electron storage subcompartment 213, especially H.sub.2. The membrane may further be configured to allow transport of one or more of H.sub.2O and OH.sup.− between the gas evolution subcompartment 212 and the electron storage subcompartment 213. Hence, the membrane may be impermeable to one or more of O.sub.2 and H.sub.2, and the membrane may be permeable to one or more of H.sub.2O and OH.sup.−.

[0154] In further embodiments, the gas evolution subcompartment 212 and the electron storage subcompartment 213 may each comprise or be functionally coupled to a respective cell compartment opening 219.

[0155] In the depicted embodiment, the membrane 211 separates the cell compartment 210 in two subcompartments, i.e., the membrane 211 defines a gas evolution subcompartment 212 (comprising the gas evolution electrode) and an electron storage subcompartment 213 (comprising the electron storage electrode).

[0156] In further embodiments, the membrane 211 may be arranged along part of a dimension of the cell compartment 210. For example, the membrane may be arranged to separate (or: facilitate separating) the electrolyte 240 in two regions, or the membrane may be arranged to separate (or: facilitate separating) the gas 245 in two regions. It will be clear to the person skilled in the art that, in such embodiments, the separation of the membrane 211 will depend on the respective amounts of electrolyte 240 and gas 245 in the cell compartment 210.

[0157] In embodiments, the electrolytic cell 200 may comprise an electrolyte 240 during use, especially during (dis-)charging, of the electrolytic cell. If the electrolytic cell 200 is not being actively charged or discharged, the electrolytic cell 200 may be devoid of electrolyte 240, i.e., in embodiments, the electrolytic cell 200 may be devoid of electrolyte 240. In the depicted embodiment, the electrolytic cell 200 comprises an electrolyte 240 at an electrolyte level approximately equal to the top of the electrodes, i.e., in the depicted embodiment the electrolyte 240 may essentially surround the electrodes. In embodiments, the electrolyte level may be varied during operation.

[0158] The electrolytic cell 200 is schematically depicted in operation in FIG. 1A-B.

[0159] FIG. 2A schematically depicts a cross-sectional side view of an embodiment of the electrolytic cell 200. Especially, an embodiment of the electrolytic cell 200 comprises a bipolar arrangement (of electrodes) 270, especially a horizontal bipolar arrangement (of electrodes) 270, 270a. The electrolytic cell 200 comprises a bipolar plate 271, especially a bipolar plate comprising a vat (also “container”). The electrolytic cell comprises an electron storage electrode 230 arranged on a first side, especially a top side, of the bipolar plate 271. The electrolytic cell comprises a gas evolution electrode 220 arranged on a second side (especially a bottom side) of the bipolar plate 271. Two bipolar plates 271 may be stacked on each other to provide an interdigitation of the gas evolution electrode 220 and the electron storage electrode 230. In the depicted embodiment, four stacked bipolar plates 271 are drawn (no electron storage electrode 230 drawn on the top bipolar plate 271, no gas evolution electrode 220 drawn below the bottom bipolar plate 271). For visualization purposes only, the top two bipolar plates 271 are drawn in close proximity (interdigitated), whereas the middle two and bottom two bipolar plates 271 are drawn further apart. During operation, the (electrodes of the) bipolar plates 271 may be preferably interdigitated (such as the depicted top two bipolar plates 271). Two stacked bipolar plates 271 may be connected via a plate sealing 272.

[0160] In embodiments, in a stack of bipolar plates 271, the bottom bipolar plate and the top bipolar plate may comprise or be functionally coupled with an electrical connection, especially a first electrical connection 120 functionally coupled to the gas evolution electrode 220, and a second electrical connection 130 functionally coupled to the electron storage electrode 230.

[0161] In embodiments, the bipolar plate 271 may comprise a top opening and/or a bottom opening, especially wherein the top opening is configured for adding and/or removing a gas 245, and wherein the bottom opening is configured for adding and/or removing electrolyte 240. In the depicted embodiment, the electrolytic cell 200 is devoid of electrolyte 240 (which may be added prior to charging and/or discharging of the electrolytic cell 200).

[0162] FIG. 2B schematically depicts a top view of the embodiment of FIG. 2A. Reference sign C indicates a possible location of the cross-sectional view depicted in FIG. 2A. Hence, in embodiments, the electron storage electrode 230 may comprise a single continuous electrode, whereas the gas evolution electrode 220 comprises a plurality of spatially separated gas evolution electrodes 220 in functional contact with different parts of the electron storage electrode 230. In the depicted embodiment, each of the gas evolution electrodes 220 is surrounded by a separation space 260 configured to prevent short-circuiting between the gas evolution electrodes 220 and the electron storage electrode 230. Hence, in embodiments, the volume of the electrolytic cell 200 may essentially comprise electron storage electrode except for the space for gas evolution electrodes 220 and corresponding space 260.

[0163] In further embodiments, (each of) the gas evolution electrode(s) 220 may have an (approximately) cylindrical shape and the electron storage electrode 230 may comprise (approximately) a cylindrical hole to host the gas evolution electrode 220 (and the electrolyte 240) and to provide the separation space 260. In such embodiments, the outer (cylindrical) (non-base) surface area of the gas evolution electrode 220 may be≥10% of the inner (cylindrical) surface area of the (cylindrical hole of the) electron storage electrode (230), especially ≥20%, such as ≥35%, especially ≥50% such as ≥75%, especially ≥90%, including 100%. Similarly, in further embodiments, the inner (cylindrical) (non-base) surface area of the gas evolution electrode may be≤125%, especially ≤100%, such as ≤90%, especially ≤80%.

[0164] FIG. 2C schematically depicts a close-up of the embodiment depicted in FIG. 2A. In the depicted embodiment, the electrolyte 240 may be configured between the electron storage electrode 230 and the gas evolution electrode 220 (essentially in the separation space 260). The gas evolution electrode 220 may comprise a hollow electrode. The gas evolution electrode 220 may be surrounded by a separator 216 configured to block transport of one or more of O.sub.2 and H.sub.2. The gas evolution electrode 220 may comprise a hydrophobic coating, especially a hydrophobic coating configured to guide a gas 245 evolved at the gas evolution electrode. Hence, in embodiments, a hydrophobic coating may be applied to the inside of the (hollow) gas evolution electrode 220. In further embodiments, the gas evolution electrode 220 may comprise a porous electrode comprising a hydrophobic coating, especially the gas evolution electrode 220 may comprise a porous electrode internally comprising a hydrophobic coating, i.e., a hydrophobic coating arranged at the inside of the porous electrode.

[0165] In embodiments, the bipolar plate 271 may comprise or be functionally coupled to an isolator configured to separate the bipolar plate 271 from the electrolyte 240, i.e. configured to reduce, especially prevent, direct contact between the bipolar plate 271 and the electrolyte 240. In further embodiments, the electrolytic cell 200 may comprise an isolator arranged between the bipolar plate 271 and the electrolyte 240. In further embodiments, the isolator may comprise a plastic cover.

[0166] Hence, during charging, the gas evolution electrode 220 may provide a first gas 245a that can leave the electrolytic cell 100 through a first headspace, especially through a hollow section in the bipolar plate 271, especially a hollow section comprising a hydrophobic coating, and the electron storage electrode 230 may provide a second gas 245b (essentially the self-discharge gas) that becomes trapped in a second headspace arranged between one or more of separators 216, bipolar plate 271, electrolyte 240, and electron storage electrode 230.

[0167] FIG. 3A-B schematically depict top views of an embodiment of the electrolytic cell 200 comprising a vertical bipolar arrangement (of electrodes) 270, 270b. For visualization purposes only the two rightmost bipolar plates 271 are drawn in close proximity, whereas the middle two and the two leftmost bipolar plates 271 are drawn spaced apart for visualization purposes.

[0168] In embodiments wherein the electrolytic cell 200 comprises the vertical bipolar arrangement 270, 270b, the gas evolution electrode 220 and the electron storage electrode 230 may especially comprise flat and/or sheet-like electrodes. The embodiment comprising interdigitation of the gas evolution electrode 220 and the electron storage electrode 230 as depicted in FIG. 3B may provide a higher storage density and/or reduced gas evolution electrode volume (including separation space 260) relative to the embodiment as depicted in FIG. 3A.

[0169] In embodiments, the horizontal bipolar arrangement 270, 270a and/or the vertical bipolar arrangement 270, 270b may provide scalability as arrangement with a plurality of bipolar plates 271 can be provided.

[0170] FIG. 4 schematically depicts experimental observations obtained using the method 300 for controlling the electrolytic cell 200. The method comprises controlling the potential difference and/or the current flow, in the depicted embodiment especially controlling the current flow, between the gas evolution electrode 220 and the electron storage electrode 230. Line L.sub.1 indicates the measured voltage between the gas evolution electrode 220 and the electron storage electrode 230 (V.sub.gee−V.sub.ese) while charging/discharging with a controlled current flow. In this tested embodiment, the gas evolution electrode 220 comprises a SST mesh and the electron storage electrode 230 comprises an iron-based electrode. During a first time period τ.sub.1 and a third time period τ.sub.3, a current flow was imposed between the gas evolution electrode 220 and the electron storage electrode 230 for charging of the electrolytic cell 200, resulting in O.sub.2 evolution at the gas evolution electrode 220, a Fe(OH).sub.2.fwdarw.Fe transition at the electron storage electrode 230, and some H.sub.2 evolution at the electron storage electrode 230 (due to self-discharge). During a second time period τ.sub.2 and a fourth time period τ.sub.4 a current flow was imposed between the gas evolution electrode 220 and the electron storage electrode 230 for discharging of the electrolytic cell 200, resulting in H.sub.2 evolution at the gas evolution electrode 220 and a Fe.fwdarw.Fe(OH).sub.2 transition at the electron storage electrode 230. During the first time period τ.sub.1 and the third time period τ.sub.3 O.sub.2 and H.sub.2 were produced in a ratio of approximately 7.5:1. During the second time period τ.sub.2 and the fourth time period τ.sub.4 approximately no O.sub.2 was produced. The ratio of H.sub.2 produced in τ.sub.1 and τ.sub.3 versus τ.sub.2 and τ.sub.4 was approximately 6.5:1.

[0171] In embodiments, the method 300 may further comprise controlling the potential difference and/or the current flow in dependence of one or more of H.sub.2 demand and charging level of the electrolytic cell 200.

[0172] In embodiments, the method may further comprise controlling the volume of an electrolyte 240 in the cell compartment 210. For example, with respect to the embodiment of the electrolytic cell 200 depicted in FIG. 1B, the method may comprise controlling the volume (or “level”) of the electrolyte 240 and gas 245 in the cell compartment 210. In further embodiments, the method 300 may comprise replacing at least 50% of the cell compartment volume of electrolyte 240 in the cell compartment 210 with an inert gas after charging and subsequently replacing at least 50% of the cell compartment volume of the inert gas in the cell compartment 210 with a second electrolyte prior to discharging. In further embodiments, the electrolyte 240 and the second electrolyte may be different, especially the electrolyte 240 and the second electrolyte may be the same.

[0173] FIG. 4 also schematically depicts a use of the electrolytic system 100, especially the electrolytic cell 200, according to the invention. During the use, the cell compartment 210 comprises an electrolyte 240 in fluid contact with the gas evolution electrode 220 and the electron storage electrode 230. During at least part of a charging time the electrolytic cell 200 is charged at a potential difference between the gas evolution electrode 220 and the electron storage electrode 230 of more than 1.2 V, especially a potential difference≥1.37 V, such as ≥1.6 V, especially ≥1.8 V (here: 1.6 V). During at least part of a discharging time the electrolytic cell 200 is discharged at a potential difference between the electron storage electrode 230 and the gas evolution electrode 220 selected from the range of 0.0-1.0 V (here: 0.25V). In embodiments, the cell compartment 210 may comprise an electrolyte 240 during the charging time and may comprise a second electrolyte during the discharging time, wherein the electrolyte and the second electrolyte are different.

[0174] The term “substantially” herein, such as in “substantially all light” or in “substantially consists”, will be understood by the person skilled in the art. The term “substantially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term “substantially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term “comprise” includes also embodiments wherein the term “comprises” means “consists of”. The term “and/or” especially relates to one or more of the items mentioned before and after “and/or”.

[0175] For instance, a phrase “item 1 and/or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term “comprising” may in an embodiment refer to “consisting of” but may in another embodiment also refer to “containing at least the defined species and optionally one or more other species”.

[0176] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0177] The term “further embodiment” may refer to an embodiment comprising the features of the previously discussed embodiment, but may also refer to an alternative embodiment.

[0178] The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

[0179] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “to comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0180] The invention further applies to a device comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings.

[0181] The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.