System and method for storing hydrogen

A system includes a canister and a fuel cell. The canister defines an internal volume configured to have a hydride bed positioned therein. The canister includes at least 1.0 kWH/kg of energy based on a heating value of 120 kJ/g of hydrogen present. The hydride bed includes lithium aluminum hydride, aluminum hydride, or a combination thereof. The hydride bed is configured to release hydrogen gas when heated to a predetermined temperature. The fuel cell is configured to receive the hydrogen gas from the canister and to use the hydrogen gas as fuel to produce power for a load.

FIELD OF THE DISCLOSURE

The present disclosure is directed to systems and methods for storing hydrogen. More particularly, the present disclosure is directed to systems and methods for powering a load using stored hydrogen.

BACKGROUND

Hydrogen fuel cell systems offer the possibility of high specific energies (e.g., >800 Wh/kg), but hydrogen storage remains a challenge and limits scalability. The most common hydrogen storage method employed today uses high-pressure (e.g., typically carbon fiber) hydrogen tanks. Although this storage method has a reasonable specific energy and energy density at large scale (e.g., >50 kWh), it is often too heavy and too spacious at medium and small scales (e.g., <10 kWh). In addition, the high pressure requirement limits the design flexibility of the storage system.

SUMMARY

A canister is disclosed. The canister includes a body defining a single, contiguous internal volume configured to have a hydride bed positioned therein. The hydride bed includes lithium aluminum hydride, aluminum hydride, or a combination thereof. A scaling factor of the canister is greater than about 0.5 and less than about 1.0. The scaling factor refers to a mass of the hydride bed divided by a mass of the canister with the hydride bed therein. The canister includes at least 1.0 kWH/kg of energy. A first heater element is positioned at least partially in the internal volume and embedded at least partially within the hydride bed. The first heater element is configured to heat the hydride bed substantially uniformly, thereby causing the hydride bed to release hydrogen. A first temperature sensor is positioned at least partially in the internal volume. The first temperature sensor is configured to measure a temperature in the internal volume.

A system is also disclosed. The system includes a canister and a fuel cell. The canister defines an internal volume configured to have a hydride bed positioned therein. The canister includes at least 1.0 kWH/kg of energy based on a heating value of 120 kJ/g of hydrogen present. The hydride bed includes lithium aluminum hydride, aluminum hydride, or a combination thereof. The hydride bed is configured to release hydrogen gas when heated to a predetermined temperature. The fuel cell is configured to receive the hydrogen gas from the canister and to use the hydrogen gas as fuel to produce power for a load.

A method is also disclosed. The method includes storing a hydride bed in a canister. The method also includes heating the hydride bed with a first heater element in the canister, which causes the hydride bed to release hydrogen gas. The method also includes transferring the hydrogen gas from the canister to a fuel cell. The method also includes generating power with the fuel cell using the hydrogen gas as fuel. The method also includes providing the power from the fuel cell to a load to power the load.

It should be noted that some details of the figures have been simplified and are drawn to facilitate understanding rather than to maintain strict structural accuracy, detail, and scale.

DESCRIPTION

Reference will now be made in detail to the present teachings, examples of which are illustrated in the accompanying drawings. In the drawings, like reference numerals have been used throughout to designate identical elements. In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific examples of practicing the present teachings. The following description is, therefore, merely exemplary.

The present disclosure is directed a system for storing hydrogen. As described in greater detail below, the system may include a canister (also referred to as a hydride canister)100, which is shown inFIG. 1. The canister100may serve as a hydrogen carrier for proton-exchange membrane (PEM) fuel cells. When coupled with such a fuel cell, the canister100may be capable of delivering 1000 Wh/kg of energy or more. The canister100and fuel cells may be used in, for example, electric and hybrid-electric passenger aircrafts, unmanned aerial and/or underwater vehicles, auxiliary power units, and emergency power units.

The phrase “single, contiguous” refers to one item (e.g., volume) that is undivided. The phrase “internal volume” refers to the space or volume inside the canister100. The phrase “hydride bed” refers to a collection of hydride within the internal volume. The hydride refers to an anion of hydrogen. It may also be known as a compound in which one or more hydrogen centers have nucleophilic, reducing, or basic properties. The hydride bed may be in a solid state, a liquid state, a gas state, or a combination thereof.

The canister100may include a body110that is made from metal such as aluminum, stainless steel, or other like metals, or non-metal such as a resin or the like. The body110may be in the shape of a cylinder, a sphere, etc. The body110defines an internal volume112. The internal volume112may be a single, contiguous internal volume, or a plurality of internal volume portions that are separated by dividers. Hydrogen may be stored in the internal volume112in a liquid or solid state. For example, the hydrogen may be stored as a metastable hydride bed in the internal volume112. The hydride bed may be made from or include, for example, lithium aluminum hydride (LiAlH4) and/or aluminum hydride (AlH3). The hydride bed may have a mass from about 0.3 kg to about 20 kg.

The hydride bed may have a gravimetric density from about 1 to about 15 wt % H, or from about 3 to about 10 wt % H. The hydride bed may have a volumetric density from about 10 to about 120 kg/m3, or from about 50 to about 100 kg/m3, or from about 70 to about 100 kg/m3, or greater than 70 kg/m3on a material basis. The hydride bed may have a desorption temperature from about 80° C. to about 200° C., or from about 10 to about 150° C. As described in greater detail below, the hydride bed may be thermally decomposed to release hydrogen gas from the canister100. The hydrogen gas may have a pressure from about 1 bar to about 1000 bar when released from the canister100.

The body110may include a first (e.g., upper) end120and a second (e.g., lower) end130. The first and second ends120,130may be integral with the body110. In another implementation, the first and second ends120,130may be or include end caps that are coupled (e.g., screwed or adhered) to the body110.

The first end120of the body110may include or define one or more fluid openings (one is shown:122) through which the hydrogen and/or hydride may flow. For example, hydrogen and/or hydride may be introduced into the internal volume112through the fluid opening122. Similarly, hydrogen and/or hydride may flow out of the internal volume112through the fluid opening122. The fluid opening122is described in greater detail below with respect toFIG. 2.

The second end130of the body110may include or define one or more cable openings (four are shown:132A,132B,132C,132D). One or more of the cable openings132A-132D may include a cable interconnect (four are shown:134A,134B,134C,134D) proximate thereto and/or extending at least partially therethrough (e.g., from an exterior of the body110to the internal volume112). The cable interconnects134A-134D may provide a hermetic seal. The cable openings132A-D and cable interconnects134A-134D are discussed in greater detail below with respect toFIG. 3.

The canister100may also include one or more heater elements (two are shown:140A,140B). In one implementation the heater elements140A,140B may be two portions of a single heater. The heater elements140A,140B may be or include resistive wires that may be oriented as coils, a zig-zag pattern, etc. The heater elements140A,140B may extend from an exterior of the body110, through the cable openings132A,132B and/or the cable interconnects134A,134B, to the internal volume112. The heater elements140A,140B may be positioned or embedded at least partially within the hydrogen and/or the hydrogen bed in the internal volume112. The heater elements140A,140B may be configured to heat the hydrogen and/or the hydride bed in the internal volume112substantially uniformly to a temperature between about 120° and about 200° C. Substantially uniform heating enables the rate of hydrogen evolution to be determined from the temperature of the hydride bed and the composition (determined from previous measurements of the rate) by using a previously-determined rate equation or look-up table. In the example shown inFIG. 1, the heater elements140A,140B include electrically-insulated heater wires that are wrapped in helical coils inside the internal volume112. The heater elements140A,140B may be powered by a single source. The heater element140A may be positioned (e.g., radially) inward from an inner surface of the body110, and the heater element140B may be positioned (e.g., radially) outward from the heater element140A and/or in contact with the inner surface of the body110. In an alternative implementation, the heater elements140A,140B may be or include internal plates, fins, or the like.

The canister100may also include one or more temperature sensors (three are shown:150A,150B,150C). The temperatures sensors may be or include, for example, thermocouples. The temperature sensors150A,150B may extend from an exterior of the body110, through the cable openings132C,132D and/or the cable interconnects134C,134D, to the internal volume112. The temperature sensors150A,150B may be configured to measure the temperature of the hydrogen and/or the hydride bed in the internal volume112. In the example shown inFIG. 1, the first temperature sensor150A may be coupled to the first heater element140A and positioned (e.g., radially) inward from the inner surface of the body110. The second temperature sensor150B may be coupled to the second heater element140B and/or the inner surface of the body110. The third temperature sensor150C may be coupled to an outer surface of the body110.

The canister100may also include insulation160positioned inside and/or outside of the body110. The insulation160may reduce the amount of heat that is transmitted through the body110to the environment. The insulation160may be or include a blanket (e.g., fiberglass or aerogel), a foam mold, or an external spray-on or paint-on foam. In another implementation, the insulation160may be in the form of thermos or dewar where the insulating effect is achieved through an evacuated wall.

As described in greater detail below, the heater elements140A,140B may heat the hydride bed in the internal volume112, which may cause the hydride bed to release hydrogen gas. The rate of conversion to hydrogen gas may be (e.g., directly) proportional to the temperature of the hydride bed. The temperature sensors150A,150B may measure the temperature (e.g., of the hydride bed) in the internal volume112, and the amount of heat generated by the heater elements140A,140B may be controlled (e.g., increased, decreased, or maintained) to control the rate of conversion to hydrogen gas. For example, the rate may be increased by increasing the temperature, and the rate may be decreased by decreasing the temperature.

FIG. 2illustrates a schematic view of a portion of the canister100showing the first end120of the body110including the fluid opening122, according to an implementation. A hollow tube210may extend at least partially through the fluid opening122. The tube210may be made of, for example, silicone.

A flange adapter220may be coupled to the first end120of the body110and/or the tube210. The flange adapter220may be made from, for example, aluminum. The flange adapter220may include an inner (e.g., flange) portion222, an outer (e.g., nut) portion224, and a connector226. The inner portion222may be positioned in the internal volume112. The inner portion222may be conical or frustoconical to funnel the hydrogen into the tube210. The outer portion224may be positioned outside of the body110. The connector226may extend at least partially through the fluid opening122. As shown, the connector226may be positioned at least partially around the tube210. The inner portion222and the outer portion224may be coupled (e.g., screwed) to the connector226.

A filter230may be coupled to the flange adapter220. As shown, the filter230may be positioned in the internal volume112and coupled to the inner portion222of the flange adapter220. In another implementation, the filter230may be positioned outside the body110and coupled to the outer portion224of the flange adapter220. The filter230may be configured to prevent particles that are greater than or equal to a predetermined size from flowing through the fluid opening122and to an exterior of the body110. The predetermined size may be from about 0 μm to about 10 μm (e.g., about 2 μm). The filter230may be or include a gasket made of fritted nickel. An inner end of the tube210may be positioned in the internal volume112between the fluid opening122and the filter230.

In at least one implementation, a scrubber may also be coupled to and/or positioned proximate to the flange adapter220. The scrubber may remove gaseous and/or molecular impurities from the gas stream. More particularly, the filter230may remove particles, and the scrubber may remove gaseous species (e.g., water vapor, hydrocarbons, etc.).

An adhesive240may be applied to surfaces of the body110, the tube210, the flange adapter220(e.g., the inner portion222, the outer portion224, and/or the connector226), the filter230, or a combination thereof to create a hermetic seal around the fluid opening122at temperatures from about 0° C. to about 250° C. or from about 25° C. to about 200° C. For example, the adhesive240may be applied between the inner portion222of the flange adapter220and an inner surface of the body110, between the inner portion222of the flange adapter220and the filter230, between the outer portion224of the flange adapter220and an outer surface of the body110, between the tube210and the connector226, or the like.

FIG. 3illustrates a schematic view of a portion of the canister100showing the second end130of the body110including the cable openings132A-132D and the cable interconnects134A-134D, according to an implementation. For the sake of simplicity, a single cable opening132A and a single cable interconnect134A are described below. It will be appreciated that one or more of the other cable openings132B-132D may be the same as or different from the cable opening132A, and one or more of the other cable interconnects134B-134D may be the same as or different from the cable interconnect134A. In at least one implementation, the cable interconnects134C,134D may be omitted. In embodiments, there may be from 2 to about 10 cable openings and corresponding interconnectors, or from about 3 to about 6 cable openings and corresponding interconnectors, or from about 4 to about 5 cable openings and corresponding interconnectors.

The cable interconnect134A may include one or more washers. For example, a first (e.g., inner) washer310A may be positioned in the internal volume112, and a second (e.g., outer) washer310B may be positioned outside of the first end130of the body110. The washers310A,310B may be or include insulating washers made of, for example, silicone.

The cable interconnect134A may also include one or more electrical connections, such as crimp connections. For example, the inner washer310A may be positioned at least partially between a first (e.g., inner) electrical connection320A and the inner surface of the body110, and the outer washer310B may be positioned at least partially between a second (e.g., outer) electrical connection320B and the outer surface of the body110.

The cable interconnect134A may also include an adhesive330. The adhesive330may be applied to surfaces of the body110; the heater element140A; the washers310A,310B; the electrical connections320A,320B, or a combination thereof. The adhesive330may create a hermetic seal around the cable opening132A at temperatures from about 0° C. to about 250° C. or from about 25° C. to about 200° C.

As shown, the heater element140A may extend through the cable opening132A and the cable interconnect134A (e.g., through the washers310A,310B and the electrical connections320A,320B). The heater element140A may include a metallic wire340. At least a portion of the wire340may be wrapped with a thermal insulator342. The insulator342may be made from, for example, silicone. The thermal insulator342may be wrapped around a portion of the wire340that is outside the body110. In addition, the insulator342may be wrapped around a portion of the wire340that is in the internal volume112and positioned within the wire interconnect134A. As shown, a portion of the wire340that is in the internal volume112and not positioned within the wire interconnect134A may not be wrapped with the thermal insulator342, but may be coated with an electrical insulator. This unwrapped portion may heat the hydride bed in the internal volume112.

FIG. 4illustrates a schematic view of a (e.g., power) system400including the canister100, according to an implementation. The system400may also include a fuel cell410, which may receive hydrogen gas from the canister100. The fuel cell410may use the hydrogen gas as fuel to generate power for the canister100and/or a (e.g., DC) load420. In an alternative implementation, the canister100may also or instead receive power from an external DC power supply (e.g., a battery).

The system400may also include a temperature control circuit430that controls the amount of power provided (e.g., from the fuel cell410) to the heater elements140A,140B. As discussed above, this controls the amount of heat generated in the internal volume112by the heater elements140A,140B, which controls the amount of hydrogen released from the canister100to the fuel cell410. The temperature control circuit430may receive temperature measurements from the first temperature sensor150A, the second temperature sensor150B, and/or the third temperature sensor150C as shown inFIG. 1.

The temperature control circuit430may be pre-programmed with a specific temperature profile, so that hydrogen from the canister100may be released at a predefined rate (e.g., 1 wt %/hr for 7 hours). In another implementation, the temperature control circuit430may be configured to adjust the amount of power provided to the heater elements140A,140B, and thus the temperature in the internal volume112, and thus the amount of hydrogen released from the canister100. The adjustment may be in response to a (e.g., varying) demand from the load420. The adjustment may also or instead be in response to an integrated current of the power provided to the canister100and/or the load420. The adjustment may also or instead be in response to an integrated flow of the hydrogen provided to the fuel cell410. The adjustment may also or instead be in response to a pressure of the hydrogen in the canister100and/or a pressure of the hydrogen gas provided to the fuel cell410. The pressure may be measured using, for example, a pressure gauge440.

A canister was assembled using a body made from aluminum in the shape of a cylinder, similar to that shown inFIG. 1. The body110included two end caps. The properties of the canister are provided in Tables 1-5 below. The heater coils each included a wire (e.g., Kanthal A-1, 20 gauge) that was insulated with Kapton. The heater coils were wrapped into a first (e.g., inner) coil and a second (e.g., outer) coil that extended the full length of the body. The heater coils were responsive to a temperature control circuit and uniformly heated the hydride bed.

The canister was filled with 160 g (317 mL) of LiAlH4catalyzed with TiF3 (3 mol %). Three thermocouples were used to monitor and/or control the temperature. More particularly, a first thermocouple was mounted on the inner heater coil, with the thermocouple end positioned substantially in the center of the hydride bed. A second thermocouple wire was mounted on the outer heater coil, just inside the inner insulation, with the thermocouple end fixed in close proximity to the insulated heater coil, functioning both as a monitor and control thermocouple. A third thermocouple was mounted on the outer surface of the body of the canister, to monitor the outside temperature of the canister.

The heater coil was controlled by the temperature control circuit, guided by the second (e.g., outer coil) thermocouple. All wires (e.g., two heater coils and two thermocouple wires) were fed into the canister through sealed wire interconnects to maintain a hermetic seal within the canister. Hydrogen gas was released through a fluid opening at one end of the canister. A filter gasket was used to prevent entrained particles from entering the hydrogen gas stream. The canister was designed with an aerogel insulation (details listed in Table 4) on the inside of the canister and end caps to prevent heat transfer to the outer wall and the environment. The total mass and volume of the canister with the hydride was 261 g and 330 mL, respectively. The total amount of hydrogen stored within the canister was 11.5 g, resulting in a system with 4.4 wt % H. The theoretical specific energy of the system was 1.59 kWh/kg based on the lower heating value of hydrogen.

Results from a thermal desorption test of the canister in Example 1 are shown inFIGS. 5A-5C. The Kanthal heater coil was powered using a 40 W power source (20 V, 2 A).FIG. 5Aillustrates a graph500showing temperatures in the center of the canister (measured by the first thermocouple), on the inner wall of the canister (measured by the second thermocouple), and on an outer wall of the canister (measured by the third thermocouple), according to an implementation. No temperature difference between the outer and inner coils was observed once the set temperature was reached. The effect of the internal insulation was measured by the third thermocouple (e.g., outside the canister), which was about 50° C. to about 60° C. lower than the internal temperature.

FIG. 5Billustrates a graph510showing a hydrogen evolution rate (e.g., in L H2/min) from the canister, according to an implementation. The flow rate reached a maximum of 1.9 L/min at about 140° C. and then decreased. Faster discharge rates may be achieved by supplying a higher power (e.g., >40 W) to the heater coils.

FIG. 5Cillustrates a graph520showing a total amount of hydrogen released from the canister (i.e., the integrated flow), according to an implementation. The total amount was about 130 L. The calculated amount of hydrogen in the canister (based on the data provided in Tables 1-5) was about 129 L (at room/ambient temperature), confirming that all of the hydrogen was evolved from the hydride during this test.

A power system was demonstrated using a canister similar to the one described in Example 1. The hydrogen gas output (i.e., H2) from the canister was connected to the input of a 150 W proton-exchange membrane (PEM) fuel cell. The electrical output from the fuel cell was connected in parallel to the heater coils (through a temperature control circuit) and to an external DC load, as shown inFIG. 4. The amount of power provided to the heater coils was determined by a temperature profile programmed into the temperature control circuit.

Results from a test of the power system are shown inFIGS. 6A-6CandFIG. 7. More particularly,FIG. 6Aillustrates a graph600showing temperatures in the center of the canister (measured by the first thermocouple), on the inner wall of the canister (measured by the second thermocouple), and the pre-programed temperature profile (e.g., the set point).FIG. 6Billustrates a graph610showing a hydrogen evolution rate (e.g., in L H2/min) from the canister with a dashed line showing a target rate of 0.5 L/min.FIG. 6Cillustrates a graph620showing a total amount of hydrogen released from the canister (i.e., the integrated flow).

FIG. 7illustrates a graph700showing fuel cell power/performance and hydrogen pressure with respect to time, according to an implementation. The fuel cell was supplied with hydrogen gas exclusively from the canister. At about 34 minutes, the total output of the fuel cell was about 40 W, which was the sum of the power going to the heater coils and the applied load (19 V). Over the next few minutes, the applied load was increased by decreasing the DC voltage set point on the applied load progressively down to 16 V. As the load voltage was decreased, the fuel cell output increased up to about 80 W.

The canister described in Example 1 may be modified (e.g., to achieve higher specific energy) in a variety of ways, such as by using a thinner filter gasket, a higher heater wire gauge, commercial heater wire insulation, and/or a thinner aluminum wall thickness (of the body). The properties of an alternative LiAlH4canister design are shown in Tables 6-10 below. In this design, the specific energy of the canister is 1.96 kWh/kg, and the energy density is 1.34 kWh/L.

The canisters described in the Examples 1-3 may be further modified by replacing the LiAlH4with an alternative hydrogen carrier, such as aluminum hydride (AlH3). AlH3has a higher crystalline density (e.g., about 1.5 g/cm3), a lower desorption enthalpy (e.g., about 10 kJ/mol), and a higher gravimetric hydrogen content (e.g., about 10 wt % H) compared to LiAlH4. The properties of a canister constructed using AlH3, rather than LiAlH4, are shown in Tables 11-15 below. Although the canister properties are similar, the use of AlH3, rather than LiAlH4, may result in a higher specific energy (e.g., 2.77 kWh/g) and a higher energy density (e.g., 2.73 Wh/cm3).

As illustrated above, the canister100may scale well from about 0.1 kWh to about 50 kWh and above. For example, the canister100may be part of a 200 W system running for 30 minutes at 0.1 kWh. In another example, the canister100may be part of a 5 kW system running for 10 hours at 50 kWh. If these energies are converted into a mass of the hydride bed, this may yield about 0.4 kg to about 20 kg for LiAlH4and about 0.03 kg to about 15 kg for AlH3.

The scaling factor (e.g., the mass of the hydride bed divided by the sum of the mass of the canister100with the hydride bed therein) may be greater than about 0.5, greater than about 0.6, greater than about 0.7, greater than about 0.8, greater than about 0.9, greater than about 0.95, and/or less than about 1.0. In addition, the specific energy of/in the canister100may be from about 1.0 kWh/kg to about 3 kWh/kg based on a heating value of 120 kJ/g of hydrogen (e.g., the hydride bed) present. For example, the specific energy may be from about 1.9 kWh/kg to about 2.7 kWh/kg. Furthermore, the energy density of/in the canister100may be from about 1.3 kWh/L to about 3 kWh/L. For example, the energy density may be from about 2 kWh/L to about 2.7 kWh/L. The canister100may include a total amount of hydride from about 0.03 kg to about 20 kg. The canister100may include a total amount of energy stored of about 0.1 KWh to about 50 KWh.

FIG. 8illustrates a flowchart of a method800for powering a load using stored hydrogen, according to an implementation. The method800is from the perspective of the system400and the components therein. It will be appreciated that the order of the steps provided below may vary and/or two or more of the steps may occur at least partially simultaneously.

The method800may include receiving and/or storing hydrogen in the canister100, as at802. The hydrogen may be stored as a solid hydride bed in the canister100.

The method800may also include heating the hydride bed in the canister100using the heater elements140A,140B, as at804. As discussed, above, the hydride bed may release hydrogen gas in response to being heated, and the hydrogen gas may flow out of the canister100via the fluid outlet122.

The method800may also include directing or transferring the hydrogen gas from the canister100to the fuel cell410, as at806. The method800may also include generating power with the fuel cell410using the hydrogen gas as fuel, as at808.

The method800may also include providing the power from the fuel cell410to a load420to power the load, as at810. The method800may also include providing the power from the fuel cell410to the heater elements140A,140B to power the heater elements140A,140B, as at812. The power may be used by the heater elements140A,140B to generate the heat discussed in step804. In some implementations, step812may be omitted, and the heater elements140A,140B may be powered by a battery.

The method800may also include measuring a temperature inside and/or outside of the canister100using the temperature sensors150A-150C, as at814. The method800may also or instead include measuring a pressure of the hydrogen using the pressure gauge440, as at816. The pressure of the hydrogen may be measured inside the internal volume112of the canister100. Alternatively, the pressure of the hydrogen may be measured after it flows out of the canister100on the way to the fuel cell410. The method800may also or instead include measuring an amount of the load420, as at818. For example, the amount of the load420may vary over time.

The method800may also include controlling820(e.g., increasing, decreasing, or maintaining) an amount of the power provided to the heater elements140A,140B, as at820. The amount of power provided to the heater elements140A,140B may be controlled with the temperature control circuit430. As discussed above, the amount of power provided to the heater elements140A,140B may be directly proportional to the amount of heat generated by the heater elements140A,140B in the internal volume112. The amount of power may be controlled in response to the temperature (measured at814), the pressure (measured at816), the amount of the load420(measured at818), or a combination thereof.

While the present teachings have been illustrated with respect to one or more implementations, alterations and/or modifications can be made to the illustrated examples without departing from the spirit and scope of the appended claims. In addition, while a particular feature of the present teachings may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular function. As used herein, the terms “a”, “an”, and “the” may refer to one or more elements or parts of elements. As used herein, the terms “first” and “second” may refer to two different elements or parts of elements. As used herein, the term “at least one of A and B” with respect to a listing of items such as, for example, A and B, means A alone, B alone, or A and B. Those skilled in the art will recognize that these and other variations are possible. Furthermore, to the extent that the terms “including,” “includes,” “having,” “has,” “with,” or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” Further, in the discussion and claims herein, the term “about” indicates that the value listed may be somewhat altered, as long as the alteration does not result in nonconformance of the process or structure to the intended purpose described herein. Finally, “exemplary” indicates the description is used as an example, rather than implying that it is an ideal.