PH-GRADIENT-ENABLED MICROSCALE BIPOLAR INTERFACES FOR DIRECT LIQUID-FUEL/OXIDANT FUEL CELLS

Abstract

Described herein are direct liquid fuel cells with an alkaline anodic fuel stream including a solution of liquid fuel such as alcohols, ethers, glycols or compounds of hydrazine, and an acidic cathode oxidant stream including a solution of a suitable oxidant such as hydrogen peroxide or a gas steam with 1% to 100% O.sub.2. These cells are used as primary stationary and/or mobile power sources and also function in a secondary role as range extenders when coupled with a primary power source.

Claims

1. A method of electrochemical conversion from combining an oxidant and a fuel source comprising a liquid fuel, the method comprising: introducing either an oxidant or a fuel source comprising a liquid fuel to a first electrode comprising a first catalyst coated by a first ion exchange ionomer; or introducing either an oxidant or a fuel source comprising a liquid fuel to a second electrode comprising a second catalyst coated by a second ion exchange ionomer.

2. The method of claim 1, wherein the first ion exchange ionomer and the second ion exchange ionomer are each independently selected from the group consisting of anion exchange ionomers and cation exchange ionomers.

3. The method of claim 1, wherein the first electrode and the second electrode are separated by an ion exchange membrane.

4. The method of claim 3, wherein the ion exchange membrane is selected from the group consisting of cation membranes, anion exchange membranes, microscale bipolar interfaces, and combinations thereof.

5. The method of claim 3, wherein a reaction with a reduced or oxidized species from the first electrode and an oxidized or reduced species from the second electrode occurs at the ion exchange membrane.

6. The method of claim 5, wherein the reaction results in splitting water, forming water, forming a compound produced by a half-cell reaction occurring at the first electrode and the second electrode, or forming a compound produced by an overall full cell reaction.

7. The method of claim 1, wherein the first catalyst is a metallic or a non-metallic particle or a metallic or a non-metallic film comprising a material selected from the group consisting of Ni, Pt, Pd, Ir, Au, Ag, CoO, a noble metal, a metal alloy thereof, a metal mixture thereof, and a combination thereof; or the second catalyst is a metallic or a non-metallic particle or a metallic or a non-metallic film comprising a material selected from the group consisting of Ni, Pt, Pd, Ir, Au, Ag, CoO, a noble metal, a metal alloy thereof, a metal mixture thereof, and a combination thereof.

8. The method of claim 1, wherein the first ion exchange ionomer or the second ion exchange ionomer comprises a material selected from the group consisting of Nafion®212, Nafion®115, Nafion®117, sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene tri-block copolymer, sulfonated poly (phenylene oxide), BAM (Ballard), poly(ethylene-co-tetrafluoroethylene)-graft-poly(styrene sulfonic acid), poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid), sulfonated poly(arylene ether ether ketone), sulfonated poly(4-phenoxybenzoyl-1,4-phenylene), sulfonated polysulfone, and combinations thereof.

9. The method of claim 4, wherein the anion exchange membrane or anion exchange ionomer comprises a material selected from the group consisting of a polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene tri-block copolymer-based backbone, poly (phenylene oxide)-based backbone, polysulfone-based backbone, poly(N,N-diallylazacycloalkane)-based backbone, bromoalkyl-tethered poly(biphenyl alkylene)-based backbone, multiblock copoly(arylene ether)-based backbone, poly (vinylbenzyl chloride)-based backbone, cardo-polyetherketone-based backbone, and combinations thereof.

10. The method of claim 4, wherein the anion exchange membrane or anion exchange ionomer comprises a functional group selected from the group consisting of benzyl-trimethylammonium, benzyl-imidazolium, guanidium, benzyl-tris (2, 4, 6-trimethoxyphenyl) phosphonium, permethyl cobaltocenium, 1,4-dimethylpiperazinium, benzyl-trimethylphosphonium, and combinations thereof.

11. The method of claim 2, wherein the cation exchange ionomer comprises a material selected from the group consisting of sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene tri-block copolymer, perfluorinated Nafion® solution, sulfonated poly (phenylene oxide), sulfonated polysulfone, sulfonated poly (arylene ether ether ketone), sulfonated poly(4-phenoxybenzoyl-1,4-phenylene), and combinations thereof.

12. The method of claim 1, wherein the oxidant or the fuel source is fed contacted with the electrodes in a single-pass mode or in a recycle mode.

13. The method of claim 1, wherein the first ion exchange ionomer coating or the second ion exchange ionomer coating is of a thickness and coverage sufficient to increase a pH gradient across the interface compared to a pH gradient without the first ion exchange ionomer coating or without the second ion exchange ionomer coating.

14. The method of claim 1, wherein the first ion exchange ionomer coating or the second ion exchange ionomer coating is of a thickness and a coverage sufficient to provide a pH gradient of about 1 pH unit per nm of the interface.

15. The method of claim 1, wherein the first ion exchange ionomer coating or the second ion exchange ionomer coating is of a thickness and a coverage sufficient to prevent catholyte contact with an anode active site.

16. The method of claim 1, wherein the oxidant is selected from the group consisting of hydrogen peroxide, oxygen, and perchlorate.

17. The method of claim 1, wherein the liquid fuel is selected from the group consisting of an alcohol, an ether, glycol, and hydrazine hydrate.

18. The method of claim 17, wherein the alcohol is selected from the group consisting of methanol and ethanol.

19. The method of claim 1, wherein the concentration of the fuel source is in the range of from about 0.01 M to about 25 M.

20. The method of claim 1, wherein the concentration of the fuel source is in the range of from about 0.1 M to about 10 M.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1A is a depiction of an exemplary embodiment of half-cell and overall reactions in a direct methanol/hydrogen peroxide fuel cell (DMFC) with an anodic bipolar interface in accordance with the present disclosure.

[0011] FIG. 1B is a graphical depiction of an exemplary embodiment of the impact of anode catalyst loading on the performance of a DMFC with an anodic bipolar interface in accordance with the present disclosure. Closed symbols represent cell voltage and open symbols represent power density.

[0012] FIG. 2 is a graphical depiction of an exemplary embodiment of the impact of methanol fuel stream concentration on the performance of a DMFC in accordance with the present disclosure. Closed symbols represent cell voltage and open symbols represent power density.

[0013] FIG. 3 is a graphical depiction of an exemplary embodiment of the impact of increased oxidant flow on the performance of a DMFC in accordance with the present disclosure. Closed symbols represent cell voltage and open symbols represent power density.

[0014] FIG. 4 is a graphical depiction of an exemplary embodiment of the impact of increased fuel flow on the performance of a DMFC in accordance with the present disclosure. Closed symbols represent cell voltage and open symbols represent power density.

[0015] FIG. 5 is a depiction of an exemplary embodiment of half-cell and overall reactions in a direct ethanol/hydrogen peroxide fuel cell (DEFC) with an anodic bipolar interface in accordance with the present disclosure.

[0016] FIG. 6 is a graphical depiction of an exemplary embodiment of the impact of operating temperature on the performance of a DEFC in accordance with the present disclosure. Closed symbols represent cell voltage and open symbols represent power density.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0017] In some embodiments of the present disclosure, a method of electrochemical conversion from combining an oxidant and a fuel source comprising a liquid fuel is disclosed. The method comprises introducing either an oxidant or a fuel source comprising a liquid fuel to a first electrode comprising a first catalyst coated by a first ion exchange ionomer; or introducing either an oxidant or a fuel source comprising a liquid fuel to a second electrode comprising a second catalyst coated by a second ion exchange ionomer.

[0018] In some embodiments, the first ion exchange ionomer and the second ion exchange ionomer are each independently selected from an anion exchange ionomer and a cation exchange ionomer.

[0019] In some embodiments, the first electrode and the second electrode are separated by an ion exchange membrane.

[0020] In some embodiments, a reaction with a reduced or oxidized species from the first electrode and an oxidized or reduced species from the second electrode occurs at an interface between the ion exchange ionomer coating and the ion exchange membrane. In some embodiments, the reaction results in splitting water, forming water, forming a compound produced by a half-cell reaction occurring at the first electrode and the second electrode, or forming a compound produced by an overall full cell reaction.

[0021] In some embodiments, the ion exchange membrane is a cation membrane or an anion exchange membrane.

[0022] In some embodiments, the first catalyst is a metallic or a non-metallic particle or a metallic or a non-metallic film comprising a material selected from the group consisting of Ni, Pt, Pd, Ir, Au, Ag, CoO, a noble metal, a metal alloy thereof, a metal mixture thereof, and combinations thereof.

[0023] In some embodiments, the second catalyst is a metallic or a non-metallic particle or a metallic or a non-metallic film comprising a material selected from the group consisting of Ni, Pt, Pd, Ir, Au, Ag, CoO, a noble metal, a metal alloy thereof, a metal mixture thereof, and combinations thereof.

[0024] In some embodiments, the cation exchange membrane or cation exchange ionomer comprises a material selected from one or more of the group consisting of Nafion®212, Nafion®115, Nafion®117, polymers having a chemical formula of (C.sub.7HF.sub.13O.sub.5S. C.sub.2F.sub.4).sub.x, sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene tri-block copolymer, sulfonated poly (phenylene oxide), BAM (Ballard), poly(ethylene-co-tetrafluoroethylene)-graft-poly(styrene sulfonic acid), poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid), sulfonated poly(arylene ether ether ketone), sulfonated poly(4-phenoxybenzoyl-1,4-phenylene), sulfonated polysulfone, and combinations thereof.

[0025] Nafion® is a perfluorinated ion exchange membrane.

[0026] Nafion®212 is a perfluorinated membrane having a thickness of 0.002 inches and a chemical formula of (C.sub.7F.sub.13O.sub.5S.C.sub.2F.sub.4).sub.x in the following structural orientation, where the value of m/(m+n) is in the range of from about 0.001 to about 1:

##STR00001##

[0027] Nafion®115 is a perfluorinated membrane having a thickness of 0.005 inches and a chemical formula of (C.sub.7F.sub.13O.sub.5S.C.sub.2F.sub.4).sub.x in the following structural orientation, where the value of m/(m+n) is in the range of from about 0.001 to about 1:

##STR00002##

[0028] Nafion®117 is a perfluorinated membrane having a thickness of 0.007 inches and a chemical formula of (C.sub.7F.sub.13O.sub.5S.C.sub.2F.sub.4).sub.x in the following structural orientation, where the value of m/(m+n) is in the range of from about 0.001 to about 1:

##STR00003##

[0029] In some embodiments, the anion exchange membrane or anion exchange ionomer comprises a material selected from one or more of the group consisting of a polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene tri-block copolymer-based backbone, poly (phenylene oxide)-based backbone, polysulfone-based backbone, poly(N,N-diallylazacycloalkane)-based backbone, bromoalkyl-tethered poly(biphenyl alkylene)-based backbone, multiblock copoly(arylene ether)-based backbone, poly (vinylbenzyl chloride)-based backbone, cardo-polyetherketone-based backbone, and combinations thereof.

[0030] In some embodiments, the backbone comprises a functional group selected from one or more of the group consisting of benzyl-trimethylammonium, benzyl-imidazolium, guanidium, benzyl-tris (2, 4, 6-trimethoxyphenyl) phosphonium, permethyl cobaltocenium, 1,4-dimethylpiperazinium, benzyl-trimethylphosphonium, and combinations thereof.

[0031] In some embodiments, the cation exchange ionomer comprises a material selected from one or more of the group consisting of sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene tri-block copolymer, perfluorinated Nafion® solution, a solution comprising a polymer having a chemical formula of (C.sub.7HF.sub.13O.sub.5S.C.sub.2F.sub.4).sub.x, sulfonated poly (phenylene oxide), sulfonated polysulfone, sulfonated poly (arylene ether ether ketone), sulfonated poly(4-phenoxybenzoyl-1,4-phenylene), and combinations thereof.

[0032] In some embodiments, the reducing agent or the oxidizing agent is fed contacted with the electrodes in a single-pass mode or in a recycle mode.

[0033] In some embodiments, the first ion exchange ionomer coating or the second ion exchange ionomer coating is of a thickness and coverage sufficient to increase a pH gradient across the interface compared to a pH gradient without the ionomer coating; to provide a pH gradient of about 1 pH unit per nm of the interface; or prevent catholyte contact with an anode active site.

[0034] In some embodiments, the oxidant is selected from hydrogen peroxide, oxygen, and perchlorate.

[0035] In some embodiments, the liquid fuel is selected from an alcohol, an ether, glycol, and hydrazine hydrate.

[0036] In some embodiments, the alcohol is selected from methanol and ethanol.

[0037] In some embodiments, the concentration of the fuel source is in the range of from about 0.01 M to about 25 M, from about 0.05 M to about 20 M, from about 0.1 M to about 10 M, from about 0.5 M to about 5 M, or from about 1 M to about 3 M.

[0038] As disclosed herein, the microscale-bipolar interface has been demonstrated to be able to maintain large pH gradients between acidic and alkaline phases in ex-situ tests. Further, such interfaces have been used in DMFC/DEFC devices. As further detailed herein, a high voltage DMFC device was obtained with an open circuit voltage of 1.9 V. The DMFC yielded a promising peak power density of 280 mW/cm.sup.2. A high voltage DEFC device was also obtained with an open circuit voltage of 1.5 V. The DEFC yielded a promising peak power density of 150 mW/cm.sup.2. Bipolar interface configuration allows for the use of non-platinum group catalysts for an anode and minimizes the crossover of fuels and oxidants. The high performance of the DMFC/DEFC enables a potential usage in transportation such as fuel cell automobile stacks and range extenders as well as in stationary power and portable power applications.

[0039] There is interest in the field of electrochemical energy generation for the present disclosure. DMFC and DEFC have been considered as suitable power suppliers for portable and mobile devices. The liquid fuels of DMFC and DEMC are easier to be stored and transported compared with compressed H.sub.2 fuel widely used for proton exchange membrane fuel cells. However, the high fuel cross-over rate observed when using perfluorosulfonic-based membrane, such as Nafion®, has resulted in fuel loss and reduced fuel cell voltage. In some embodiments, the first ion exchange ionomer or the second ion exchange ionomer comprise a chemically stabilized perfluorosulfonic acid/PTFE copolymer in the acid (H+) form. Also, DMFC and DEFC have been operated most commonly with O.sub.2 as the oxidant, which results in low cell voltage. Herein, a pH-gradient-enabled microscale bipolar interface configuration is incorporated in electrochemical cells operated with liquid fuels and H.sub.2O.sub.2 as an oxidant. This setup enables operation of high voltage fuel cell devices with minimized fuels crossover and provides an acceptable current density (150-250 mA/cm.sup.2) at 1.0 V.

Examples

[0040] Preparation and Characterization of pH-Gradient-Enabled Microscale Bipolar Interface (PMBI)

[0041] The structure and formation of the bipolar interface in accordance with this example is disclosed in U.S. patent application Ser. No. 16/379,212, filed on Apr. 9, 2019, which claims priority from U.S. Provisional Application Ser. No. 62/654,870 filed on Apr. 9, 2018, both of which are incorporated herein by reference in their entirety.

[0042] Direct Methanol/Hydrogen Peroxide Fuel Cell

[0043] Half-Cell and Overall Reactions in a DMFC with Bipolar Interface

Anode:CH.sub.3OH+6OH.sup.−.Math.5H.sub.2O+6e.sup.−+CO.sub.2 E.sup.0,a=−0.78V vs. SHE  (1)

Cathode:3H.sub.2O.sub.2+6H.sup.++6e.sup.−.fwdarw.6H.sub.2O E.sup.0,c=1.77V vs. SHE  (2)

Overall reaction:CH.sub.3OH+3H.sub.2O.sub.2+6H.sup.++6OH.sup.−.Math.CO.sub.2+11H.sub.2O E.sup.0=2.55V  (3)

[0044] The junction potential correction has been evaluated to be:

3M KOH∥1.5M H.sub.2SO.sub.4E.sub.j=0.83V  (4)

[0045] This value was estimated based on the detailed derivation provided by Ünlü, M.; Zhou, J.; Kohl, P. A., “Hybrid Anion and Proton Exchange Membrane Fuel Cells”, The Journal of Physical Chemistry C 2009, 113, (26), 11416-11423, and together with equation (3) to yield the net cell voltage.

Net cell voltage:E.sup.0−E.sub.j=1.72V  (5)

[0046] The theoretical open circuit voltage (OCV) of a DMFC with a bipolar interface is 1.72 V. A peak power density of 306 mW/cm.sup.2 with an OCV of 1.64 V was obtained upon initial optimization of the device. This setup enabled high voltage fuel cell device operation with minimized fuel/oxidant crossover and provided an acceptable current density (250 mA/cm.sup.2) at 1.0 V. PtRu/C on Ni-foam was utilized as the catalyst at the anode and Pt/C was utilized as the catalyst at the cathode. A loading of 3 mg.sub.Pt-Ru/C/cm.sup.2 at the anode achieved the best DMFC performance. Results are shown in FIG. 1B.

[0047] Half-Cell and Overall Reactions in a DMFC without the Bipolar Interface.

Anode:CH.sub.3OH+6OH.sup.−.Math.5H.sub.2O+6e.sup.−+CO.sub.2 E.sup.0,a=−0.78V vs. SHE  (7)

Cathode:3H.sub.2O.sub.2+6H.sup.++6e.sup.−.fwdarw.6H.sub.2O E.sup.0,c=1.77V vs. SHE  (8)

Overall reaction:CH.sub.3OH+3H.sub.2O.sub.2+6H.sup.30+6OH.sup.−.Math.CO.sub.2+11H.sub.2O E.sup.0=2.55V  (9)

[0048] Though the theoretical OCV of a DMFC without a bipolar interface is higher (2.55 V) than a DMFC with a bipolar interface (1.72 V), most DMFCs were operated below 1 V. The uniform pH environment at anode and cathode in a DMFC resulted in low cell voltage due to the crossover of fuels and oxidant.

[0049] Impact of Methanol Concentration on Performance.

[0050] The current produced by an ideal electrochemical device is directly proportional to the amount of reactant supplied. In a DMFC, this anticipated improvement in performance has to be balanced against the cross-over of methanol from the anode to the cathode side and the subsequent side-reaction at the cathode. Increasing the fuel concentration results in a larger methanol concentration gradient across the device and drives methanol cross-over. Examining the performance of a DMFC with 0.5 M, 1.5 M, 5 M and 10 M methanol feeds, the cell with a 5M methanol feed was found to yield the best performance. Results are shown in FIG. 2.

[0051] Impact of Asymmetric Fuel and Oxidant Flow Rates on Performance.

[0052] As detailed above, 5 M methanol was identified as the optimal fuel concentration. The stoichiometric ratio of methanol and hydrogen peroxide is in the ratio of 1:3 as seen from Eq. (3). Unfortunately, given the relative instability of hydrogen peroxide, solutions above 30 wt % of hydrogen peroxide (about 10 M) in water are not readily available. Further, the acid stabilized oxidant feed of hydrogen peroxide is further diluted to accommodate the acid and hence has a hydrogen peroxide molarity of about 5 M. Given that the methanol feed is 5 M, stoichiometry indicates that a minimum oxidant molarity of 15 M is required. Thus, the effect of increasing the oxidant flow rate on DMFC performance with fuel to oxidant flow rate ratios of 1:1, 1:3 and 1:6 was examined. Results are shown in FIG. 3. Surprisingly, the DMFC with 1:1 flow ratio exhibited the best performance. Oxidant residence time contributed to this unexpected effect.

[0053] Methanol cross-over is a significant issue in DMFCs. One solution to reducing methanol cross-over is to lower the fuel feed concentration. This creates the opposite problem of excess (non-stoichiometric) oxidant concentration. Thus, the impact of increasing the oxidant flow rate on DMFC performance was examined. Starting off with a fuel concentration of 0.5 M and an oxidant concentration of about 5 M (with a stoichiometrically required oxidant concentration being 1.5 M), fuel to oxidant flow rate ratios of 1:1, 3:1, and 6:1 were examined. Once again, surprisingly, the DMFC with 1:1 flow ratio exhibited the best performance. The results are shown in FIG. 4. Oxidant residence time and methanol cross-over contributed to this unexpected effect.

[0054] Direct Ethanol/Hydrogen Peroxide Fuel Cell

[0055] Half-Cell and Overall Reactions in a DEFC with Bipolar Interface.

Anode:C.sub.2H.sub.5OH+3H.sub.2O .Math.12H.sup.++12e.sup.−+2CO.sub.2 E.sup.0,a=−0.74V vs. SHE  (10)

Cathode:6H.sub.2O.sub.2+12H.sup.++12e.sup.−.fwdarw.12H.sub.2O E.sup.0,c=1.77V vs. SHE  (11)

Overall reaction:C.sub.2H.sub.5OH+6H.sub.2O.sub.2.Math.2CO.sub.2+9H.sub.2O E.sup.0=2.51V  (12)

[0056] The junction potential correction has been evaluated to be:

3M KOH∥1.5M H.sub.2SO.sub.4E.sub.j=0.83V  (13)

[0057] This value was estimated based on the detailed derivation provided by Ünlü, M.; Zhou, J.; Kohl, P. A., “Hybrid Anion and Proton Exchange Membrane Fuel Cells”, The Journal of Physical Chemistry C 2009, 113, (26), 11416-11423, and together with equation (12) to yield the net cell voltage.

Net cell voltage:E.sup.0−E.sub.j=1.68V  (14)

[0058] A peak power density of 150 mW/cm.sup.2 was obtained for DEFC with cell voltage of 1.5 V. PtRu/C on Ni-foam was utilized as the catalyst at the anode and Pt/C was utilized as the catalyst at the cathode. The optimum concentration of ethanol was 1.5 M and optimum operating temperature was 60° C.

[0059] Half-Cell and Overall Reactions in a DMFC without Bipolar Interface.

Anode:C.sub.2H.sub.5OH+3H.sub.2O .Math.12H.sup.++12e.sup.−+2CO.sub.2 E.sup.0,a=−0.74V vs. SHE  (15)

Cathode:6H.sub.2O.sub.2+12H.sup.+12e.sup.−.fwdarw.12H.sub.2O E.sup.0,c=1.77V vs. SHE  (16)

Overall reaction:C.sub.2H.sub.5OH+6H.sub.2O.sub.2.Math.2CO.sub.2+9H.sub.2O E.sup.0=2.51V  (17)

[0060] This written description uses examples to illustrate the present disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any compositions or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have elements that do not differ from the literal language of the claims, or if they include equivalent elements with insubstantial differences from the literal language of the claims.

[0061] As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” “contains”, “containing,” “characterized by” or any other variation thereof, are intended to cover a non-exclusive inclusion, subject to any limitation explicitly indicated. For example, a composition, mixture, process or method that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process or method.

[0062] The transitional phrase “consisting of” excludes any element, step, or ingredient not specified. If in the claim, such would close the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith. When the phrase “consisting of” appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.

[0063] The transitional phrase “consisting essentially of” is used to define a composition or method that includes materials, steps, features, components, or elements, in addition to those literally disclosed, provided that these additional materials, steps, features, components, or elements do not materially affect the basic and novel characteristic(s) of the claimed disclosure. The term “consisting essentially of” occupies a middle ground between “comprising” and “consisting of”.

[0064] Where a disclosure or a portion thereof is defined with an open-ended term such as “comprising,” it should be readily understood that (unless otherwise stated) the description should be interpreted to also describe such a disclosure using the terms “consisting essentially of” or “consisting of.”

[0065] Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

[0066] Also, the indefinite articles “a” and “an” preceding an element or component of the disclosure are intended to be nonrestrictive regarding the number of instances (i.e. occurrences) of the element or component. Therefore “a” or “an” should be read to include one or at least one, and the singular word form of the element or component also includes the plural unless the number is obviously meant to be singular.