Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J45/00—Discharge tubes functioning as thermionic generators

Definitions

• the present embodiments relate to electric power generation, conversion, and transfer. More specifically, the embodiments disclosed herein are related to nano-scale energy conversion devices that generate electric power through thermionic energy conversion and thermoelectric energy conversion, and methods of making and using the same.
• Portable electric power generating devices are often used to power devices where access to electric power from the electric power grid is not practical (e.g., mobile phones and tablets in a shopping complex and satellites in orbit about the Earth). Such devices are also used when access to the grid is not possible (e.g., remote installations with intermittent or no grid availability). In addition, such devices are used as a backup power supply to support continued operation of critical equipment during a grid event (e.g., a blackout or a brownout).
• a grid event e.g., a blackout or a brownout
• Standard, portable electric power generation devices include gasoline engines and diesel engines. However, when in operation, these devices require frequent monitoring to ensure that necessary refueling is performed to maintain the devices in operation.
• Photoelectric devices e.g., solar cells are effective only when sufficient light is available.
• Commercially available electric power storage devices include, for example, electrochemical batteries and solid state batteries.
• electrochemical batteries and solid state batteries due to limited charges on electrochemical and solid state batteries, frequent replacement and/or recharging are required.
• electrochemical batteries and solid state batteries have a relatively large footprint when used for emergency and backup power supplies in industrial facilities.
• microelectronic devices are not always compatible with the employment of electrochemical batteries and solid state batteries.
• One example of a microelectronic device possibly requiring a compact, long-life, low-current, electric power device is a low power electronic sensor which is installed for long-term unattended operation in an inaccessible location.
• Another example of a microelectronic device possibly requiring a compact, long-life, minimal power draw is a nonvolatile memory circuit of a compact computing device.
• Other portable power generation devices include fuel cells and nuclear batteries. Fuels cells require hydrogen replacement after a period of time and, similar to electrochemical and solid state batteries, fuel cells have a relatively large footprint when used as emergency and backup power supplies in industrial facilities. Nuclear batteries rely on processes that include fission, fusion, or radioactive decay of the nuclei of atoms. These processes are relatively inefficient and require shielding to reduce the emissions of ionizing radiation that are a natural by-product of the nuclear processes.
• An apparatus and a method are provided to generate electric power.
• the apparatus is provided with first and second electrodes.
• the first electrode includes a first substrate including at least one first material having a first work function value, with the first material including tungsten (W).
• the first electrode also includes at least one second material, different from the first material, with the second material deposited over at least a portion of the first material such that the first electrode has a second work function value less than the first work function value.
• the second material includes cesium oxide (CS 2 O).
• the second electrode is separated from the first electrode by a distance.
• the second electrode includes a second substrate with at least one third material, with the third material different from the first and second materials.
• the third material which includes gold (Au), has a third work function value.
• the second electrode also includes at least one fourth material, different from the first and third materials.
• the fourth material which includes cesium oxide (CS 2 O), is deposited over at least a portion of the third material such that the second electrode has a fourth work function value less than the third work function value.
• a method of manufacturing an apparatus comprises fabricating a first electrode and a second electrode.
• a first electrode substrate including at least a first material is provided, wherein the first material has a first work function value, the first material including tungsten (W).
• At least one second material, different from the first material is deposited over at least a portion of the first material, the deposit of the at least one second material creating a second work function value for the first electrode, the second work function value being less than the first work function value, and the second material including cesium oxide (CS 2 O).
• a second electrode substrate including at least one third material different from the first and second materials is provided, wherein the third material has a third work function value, the third material including gold (Au).
• At least one fourth material is deposited over at least a portion of the at least one third material, the deposit of the at least one fourth material creating a fourth work function value for the second electrode, the fourth work function value being less than the third work function value, and the fourth material including CS2O.
• FIG. 1 depicts a cutaway view of an embodiment of a nano-scale energy conversion device.
• FIGS. 2A and 2B depict a flow chart illustrating a process for manufacturing a nano-scale energy conversion device.
• FIG. 3 depicts a cutaway view of AN embodiment of a partially constructed nano scale energy conversion device.
• FIG. 4 depicts a table of work function values of elemental bulk materials.
• FIG. 5 depicts a perspective view of a process for depositing a thermionic electron emissive material on an electrode substrate.
• FIG. 6 depicts a graphical representation of work function values as a function of particle size.
• FIG. 7 depicts an overhead view of a covalently-bonded dipole deposited on the surface of an electrode through an electrospray deposition of a thermionic electron emissive material on the electrode substrate.
• FIG. 8 depicts a cutaway view of an embodiment of a nanofluid including a plurality of nanoparticle clusters suspended in a dielectric medium.
• FIG. 9 depicts a flow chart illustrating a process for generating electric power with the nano-scale energy conversion device.
• FIG. 10 depicts a cutaway view of an embodiment of the nano-scale energy conversion device showing a relationship between the work functions of the electrodes and nanofluid therein.
• FIG. 11 depicts a graphical representation of the effect of the emitter work function value being larger than the collector work function value.
• FIG. 12 depicts a schematic view of electron transfer through collisions of the nanoparticle clusters.
• FIG. 13 depicts a schematic view of an embodiment of employment of the nano scale energy conversion device.
• FIG. 14 depicts a schematic view of a system of stacked or grouped nano-scale energy conversion devices to that generates electric power from waste heat.
• FIG. 15 depicts a cutaway view of waste heat harvesting system that includes a nano-scale energy conversion device coupled to an electronic chip that harvests electrical energy from waste heat from the electronic chip.
• FIG. 16 depicts an exploded view of an electric power generation system that includes an array of nano-scale energy conversion devices coupled to an array of solar cells that harvests electrical energy from waste heat from the solar cell array.
• Thermionic power conversion provides a method to convert heat into electrical energy.
• Thermionic electric power conversion generators convert heat energy to electrical energy by an emission of electrons from a heated emitter electrode (i.e ., a cathode). Electrons flow from an emitter electrode, across an inter-electrode gap, to a collector electrode ⁇ i.e., an anode), through an external load, and return back to the emitter electrode, thereby converting heat to electrical energy.
• Recent improvements in thermionic power converters include selecting materials with lower work functions for the electrodes and using a fluid to fill the inter-electrode gap. The electron transfer density is limited by the materials of the electrodes and the materials of the fluid in the inter-electrode gap ⁇ i.e., the associated work functions).
• FIG. 1 illustrating a cutaway view of an embodiment of a nano- scale energy conversion device (100) that is configured to generate electrical power.
• the nano-scale energy conversion device (100) is sometimes referred to as a cell or a layer.
• a plurality of devices (100) may be organized as a plurality of cells or a plurality of layers in series or parallel, or a combination of both to generate electrical power at the desired voltage, current, and power output.
• the nano-scale energy conversion device (100) includes an emitter electrode (cathode) (102) and a collector electrode (anode) (104).
• the emitter electrode (102) and collector electrode (104) are collectively referred to as the electrodes (106) of the nano-scale energy conversion device (100).
• a plurality of insulator posts, also referred to herein as columns, standoffs, or micro pillars, (108) (only one shown) maintain separation between the electrodes (106) such that the electrodes (106) and the insulator posts (108) define a cavity (110).
• the insulator posts (108) are fabricated with a dielectric material, such as, and without limitation, alkanethiol, sol-gel with aerogel-like properties, corona dope, super corona dope, silicon, silicon-oxide, polymer, any dielectric material, or a combination including one or more of the foregoing.
• nano- scale energy conversion device (100) includes two opposing electrodes (106) separated by insulator posts (108) with a cavity (110) filled with a nanofluid (112) between the electrodes (106).
• the emitter electrode (102) and the collector electrode (104) are each fabricated with different materials, with the different materials having separate and different work function values.
• the work function of a material is the minimum thermodynamic work (i.e ., minimum energy) needed to remove an electron from a solid to a point in a vacuum immediately outside a solid surface of the material.
• the work function is a material-dependent characteristic. Work function values are typically expressed in units of electron volts (eV). Accordingly, the work function of a material determines the minimum energy required for electrons to escape the surface, with lower work functions generally facilitating electron emission.
• the emitter electrode (102) has a higher work function value than the collector electrode (104).
• the difference in work function values between the electrodes (106) due to the different electrode materials induces a contact potential difference between the electrodes (106) that has to be overcome to transmit electrons through the nanofluid (112) within the cavity (110) from the emitter electrode (102) to the collector electrode (104).
• Both electrodes (106) emit electrons; however, as explained in more detail elsewhere herein, once the contact potential difference is overcome, the emitter electrode (102) will emit significantly more electrons than the collector electrode (104). A net flow of electrons will be transferred from the emitter electrode (102) to the collector electrode (104), and a net electric current will flow from the emitter electrode (102) to the collector electrode (104). This net current causes the emitter electrode (102) to become positively charged and the collector electrode (104) to become negatively charged. Accordingly, the nano-scale energy conversion device (100) generates an electron current that is transmitted from the emitter electrode (102) to the collector electrode (104).
• the nanofluid (112) includes a dielectric medium (114) and a plurality of nanoparticle clusters (116) suspended in the dielectric medium (114).
• the nanofluid (112) minimizes ohmic heating and eliminates formation of space charges in the cavity (110) such that arcing in the medium (114) is prevented.
• the dielectric medium (114) is one of water, silicone oil, or alcohol.
• the dielectric medium (114) is a sol-gel with aerogel-like properties and low thermal conductivity values that reduce heat transfer therethrough, e.g., thermal conductivity values less than 1.0 watts per meter-degrees Kelvin (W/(m-K)).
• the thermal conductivity of the dielectric medium (114) is as low as 0.013 watts per meter- degrees Kelvin (W/(m-K)), as compared to the thermal conductivity of water at 20 degrees Celsius (°C) of 0.6 W/(m-K). Accordingly, the nanofluid (112) minimizes heat transfer through the cavity (110) with low thermal conductivity values.
• the heat transport in the thermal conductivity nanofluid (112) is proportional to the temperature difference between the electrodes (102) and (104). For example, if the heat transport in a low thermal conductivity nanofluid is small, a high temperature difference between the two electrodes (102 and 104) can be maintained during operation.
• the electrical conductivity of the nanofluid (112) changes with operation of the corresponding device.
• the nanoparticle clusters (116) may be fabricated from metal and metal alloys, ceramics, cermet, composites, and other materials. Some of the nanoparticle clusters (116) may include materials dissimilar from other nanoparticle clusters (116).
• the nanofluid (112) includes nanoparticle clusters (116) of gold (Au) (118) and silver (Ag) (120).
• nanoparticle clusters refers to a grouping of 6 to 8 atoms of the associated materials, e.g., Au and Ag, where the number of atoms is non limiting,
• the nanoparticle clusters (116) have work function values that are greater than the work function values for the electrodes (106).
• the work function values of the Au nanoparticle clusters (118) and the Ag nanoparticle clusters (120) are 4.1 eV and 3.8 eV, respectively.
• charge transport through electron hopping and Brownian motion is facilitated by the greater work function values of the nanoparticle clusters (116) and use of at least two types of nanoparticle clusters (116), each type with a different work function value.
• the Brownian motion of the nanoparticle clusters (116) includes collisions between the nanoparticle clusters (116) among themselves and collisions between the nanoparticle clusters (116) and the two electrodes (102) and (104).
• the nanoparticle clusters (116) are coated with alkanethiol to form a dielectric barrier thereon, where the selection of alkanethiol is non-limiting. In at least one
• dodecanethiols are used.
• at least one other alkane shorter than dodecanethiol and decanethiol is used.
• the length of the alkane chain is limited by the need for the nanoparticle conductive cores to be within 1 nm to transfer electrons from one conductive surface to another.
• the alkanethiol coating reduces coalescence of the nanoparticle clusters (116).
• the nanoparticle clusters (116) have a diameter in the range of 0.5 nm to 5 nm.
• the nanoparticle clusters (116) have a diameter in the range of 1-3 nm.
• the nanoparticle clusters (116) have a diameter of 2 nm.
• the nanoparticle clusters (116) of Au (118) and Ag (120) are tailored to be electrically conductive with charge storage features. Accordingly, the nanofluid (112), including the suspended nanoparticle clusters (116), provides a conductive pathway for electrons to travel across the cavity (110) from the emitter electrode (102) to the collector electrode (104) through charge transfer.
• a plurality of emitter electrons (122) and a plurality of collector electrons (124) are shown proximate to the cavity (110) within the respective emitter electrode (102) and collector electrode (104).
• An electron (126) is shown as leaving the emitter electrode (102), hopping across the nanoparticle clusters (116), and entering the collector electrode (104).
• FIG. 1 illustrates an external circuit (128) connected to the two electrodes (106). Specifically, a first electrical conductor (130) is connected to the collector electrode (104) and the external circuit (128) and a second electrical conductor (132) is connected to the external circuit (128) and the emitter electrode (102).
• external circuit current (134) is transmitted through external circuit (128), and the same amount of electron current as flowing through the external circuit (134) will flow from the emitter electrode (102) to the collector electrode (104).
• a single cell or layer such as the configuration shown and described in FIG.
• the device (100) can generate a voltage within a range extending between about 0.25 volts and 6.0 volts, depending on the contact potential difference (discussed further herein) induced between the emitter electrode (102) and the collector electrode (104) as a function of the materials used for each.
• the device (100) nominally generates between about 0.75 volts and 5.0 volts.
• the device generates about 0.75 volts.
• the device (100) can generate an electrical current within a range of approximately 1 milliampere (ma) to approximately 10 ma. Further, in some embodiments, the device (100) generates approximately 0.75 milliwatts per square centimeter (mW/cm ). Accordingly, nano-scale energy conversion device (100) generates sufficient electrical current to power small loads, e.g., a micro-circuit.
• the emitter electrode (102) is manufactured with a tungsten (W) nanoparticle surface (136) and a cesium oxide (CS2O) coating (138) that at least partially covers the W nanoparticle surface (136).
• the collector electrode (104) is manufactured with a gold (Au) nanoparticle surface (140) and a CS2O coating (142) that at least partially covers the Au nanoparticle surface (140).
• W nanoparticles are electro sprayed onto one side of polymer base that includes a nanometal film, i.e., an atomic-scale lattice of nanometal atoms, on one side of the polymer base.
• the W nanoparticles form a surface layer on the nanometal film.
• the CS2O coating (138) on the W nanoparticle surface (136) is layered on the surface (136) through a template.
• the polymer base is a sacrificial component for assembly that is removed with acetone (described further herein).
• the Au nanoparticles are electro sprayed onto the nanometal film on a polymer base to form the Au nanoparticle surface (140) and the CS O coating (142) is layered on the Au nanoparticle surface (140) through a template, and the polymer base is removed.
• the use of the templates with particular electrospray and nanofabrication techniques form deposited layers of CS O (138) and (142) in one or more predetermined patterns on the W nanoparticle surface (136) and the Au nanoparticle surface (140).
• a percentage of coverage of each of the two surfaces (136) and (140) with the respective CS O coating layers (138) and (142) is within a range of at least 50% up to 70%, and in at least one embodiment, is about 60%.
• the CS O coatings (138) and (142) reduce the work function values of the electrodes (102) and (104) from the work function values of W (typically 4.55 eV) and Au (typically 5.1 eV), respectively.
• the emitter electrode (102) has a work function value of 0.88 electron volts (eV) and the collector electrode (104) has a work function value of 0.65 eV. Accordingly, the lower work function values of the electrodes (102) and (104) are essential to the operation of the nano scale energy conversion device (100) as described herein.
• W and Au are selected for the electrodes (106) due to at least some of their metallic properties (e.g ., strength and resistance to corrosion) and the measured change in work function when the thermionic emissive material of CS O is layered thereon.
• Alternative materials may be used, such as noble metals including, and without limitation, rhenium (Re), osmium (Os), ruthenium (Ru), tantalum (Ta), iridium (Ir), rhodium (Rh), palladium (Pd), and platinum (Pt), or any combination of these metals.
• non-noble metals such as aluminum (Al) and molybdenum (Mo) may also be used.
• Al nanoparticles may be used rather than W nanoparticles to form surface (136)
• Pt nanoparticles may be used rather than Au nanoparticles to form surface (140). Accordingly, the selection of the materials to use to form the nanoparticle surfaces (136) and (140) is principally based on the work functions of the electrodes (106), and more specifically, the difference in the work functions once the electrodes (106) are fully fabricated.
• the nano-scale energy conversion device (100) generates electric power through harvesting heat energy (144).
• the emitter electrode (102) receives the heat energy (144) from sources that include, without limitation, heat generating sources and ambient environments, and generates electrons (126) that traverse the cavity (110) via the nanoparticle clusters (116). The electrons (126) reach the collector electrode (104) and external circuit current (134) is transmitted to the external circuit (128).
• nano-scale energy conversion device (100) generates electrical power through placement in ambient, room temperature environments. Accordingly, the nano- scale energy conversion device (100) harvests heat energy (144), including waste heat, to generate useful electrical power.
• a flow chart (200) is provided illustrating a process for manufacturing a nano-scale energy conversion device.
• a diagram (300) is provided illustrating a cutaway view of an embodiment of a partially constructed nano-scale energy conversion device (300) (not shown to scale).
• an emitter electrode (302) is fabricated (202) by positioning (204) a nanometal film (328) on one side of a base, such as a polymer base (330) (shown in phantom).
• the polymer base (330) is approximately 2 nm thick (where this value should be considered non-limiting) and the nanometal film (328) is approximately 3.7 angstroms thick.
• the polymer base (330) is used as a sacrificial assembly component.
• the nanometal film (328) is positioned proximate to an electrospray nozzle of an electrospray device (see FIG. 5, electrospray nozzle (512)).
• Emitter electrode nanoparticles are selected (206) for deposition (208) on the nanometal film (328).
• the combination of the nanoparticle material and the deposited thermionic emissive material has a combined work function value greater than the work function value of a collector electrode (306) (fabricated as described further elsewhere herein).
• the difference of the work function values of the two electrodes (302) and (306) is above a predetermined value to maximize electron transfer between the two electrodes (302) and (306).
• a partial list of the appropriate nanoparticle materials for the emitter electrode (302) is provided elsewhere herein.
• At least one layer of W nanoparticles (338) is deposited (208) through electrospray onto the nanometal film (328) to form a nanoparticle surface (304) on the nanometal film (328).
• the thickness of the layer of nanoparticles to form nanoparticle surface (304) is approximately 2 nm ( i.e ., the approximate thickness of a nanoparticle), where the 2 nm value should be considered non-limiting.
• one or more metal materials in the form of nanoparticles are selected as the nanoparticle surface (304) for the emitter electrodes (302) at least partially as a function of decreasing the work function value of the electrodes (302) and (306) and maintaining a work function value differential between the electrodes (302) and (306) above a predetermined value.
• the polymer base (330) is removed (210) through an acetone solution, thereby rendering the polymer base (330) as a sacrificial material. Accordingly, the W nanoparticle surface (304) on the nanometal film (328) is ready to receive a thermionic emissive material thereon.
• At least one layer of a thermionic electron emissive material (308) is deposited (212) on at least a portion of the W nanoparticle surface (304).
• a monolayer of the thermionic electron emissive material (308) is deposited (212) on about at least 50% to about 70% of the surface of the W nanoparticle surface (304).
• about 60% of the surface of the W nanoparticle surface (304) receives a monolayer of the material (308).
• a plurality of layers of the thermionic electron emissive material (308) is deposited on about 60% of the W nanoparticle surface (304).
• the deposited thermionic electron emissive material (308) is selected to decrease the work function value of the emitter electrode (302) to a value below that of the work function value of the material selected for the W nanoparticle surface (304).
• a table (400) is provided illustrating elemental work function values of bulk materials.
• the work function value of W is 4.55 eV.
• the deposition of CS2O (308) on the W nanoparticle surface (304) decreases the work function value of emitter electrode (302) to about 0.88 eV.
• the combination of materials is positioned to create the desired work function values, and modifying the combination of materials can change the work function value of the combination.
• the selection of the thermionic electron emissive material (308) to deposit on the nanoparticle surface (304) is partially based on the desired work function value of the electrode (302) (and electrode (306)) and chemical compatibility between the nanoparticle surface (304) and the deposited material (308).
• Deposition materials include, but are not limited to, thorium, aluminum, cerium, and scandium, as well as oxides of alkali or alkaline earth metals, such as cesium, barium, calcium, and strontium.
• a diagram is provided illustrating a perspective view of a process (500) for depositing a thermionic electron emissive material on an electrode substrate, i.e., a nanoparticle surface such as W nanoparticle surface (136/304) and Au nanoparticle surface (140/310).
• a template (504) is positioned proximate to a substrate (506).
• the template (504) includes a pattern (508) of openings corresponding to a desired deposition pattern on the substrate (506).
• the template (504) is positioned over one side of the substrate (506) as shown by the arrow (524).
• the substrate (506) is grounded to facilitate direct deposition of droplets on the substrate (506) to form a pattern of the deposited deposition material(s).
• the substrate (506) with the overlaid template (504) is positioned proximate to an electrospray nozzle (512) of an electrospray device (not shown).
• An emission of the thermionic electron emissive material issues from the electrospray nozzle (512) as monodispersed droplets (514) is characterized by nanoparticles of uniform size in a dispersed phase.
• An electrospray of the droplets (514), hereinafter referred to as electrospray produces monodisperse particles to support deposition of the thermionic electron emissive material in the nanometric scale range.
• the electrospray (514) includes a solution of 0.1 molar (M) CS2O nanoparticles in ethanol, where the droplet diameter is 10 microns.
• the pattern (508) includes a range of 30-50 micron diameter holes with a center-to-center distance ranging from about 60-200 microns, staggered at about 30-60 degree angles, and preferably 45 degree angles.
• the electrospray (514) with CS2O nanoparticles is directed toward the template (504) to form a monolayer (516) as the template (504) and the substrate (506) traverse the electrospray (514) as shown by the arrow (526).
• 1014 CS O atoms per square centimeter (cm 2 ) is the target concentration for the substrate (506).
• a third step (518) the template (504) is separated from the substrate (506) as shown by the arrow (528) to leave a patterned thermionic electron emissive material (520) on electrode substrate (506) to form an emitter electrode (522).
• a patterned thermionic electron emissive material (520) on electrode substrate (506) to form an emitter electrode (522).
• four distinct lines of deposited material, collectively referred to as deposited material (520) are overlaid on the W substrate (506).
• This pattern is merely an example pattern and should not be considered limiting.
• the pattern of thermionic electrons may vary as long as the pattern enables operation of the electrode (522).
• a monolayer of patterned thermionic electron emissive material (520), i.e., CS O, is formed on a W substrate (506) to achieve coverage of the substrate (506) in excess of at least 50% to about 70%, with 60% being an optimal coverage.
• the thickness of the layer of patterned thermionic electron emissive material (520) is approximately 2 nm, where the 2 nm value should be considered non-limiting.
• Exemplary electrospray and nano-fabrication technique(s) and associated equipment including three-dimensional printing and four-dimensional printing (in which the fourth dimension is varying the nanoscale composition during printing to tailor properties) for forming the layers, films, and coatings discussed herein, are set forth in U.S. Application Publication No. 2015/0251213.
• FIG. 6 a diagram is provided illustrating a graphical representation (600) of work function values as a function of particle size.
• the graph (600) includes a first axis (602), represented herein as a vertical axis (602) that indicates a change in work function value (Df), where the vertical axis has a range from 0 to 1.2 in increments of 0.2 and in units of eV.
• the graph (600) also includes a second axis (604), represented herein as a horizontal axis that indicates particle size, where the second axis (604) extends from 0 to 60 in increments of 10 and in units of nanometers (nm).
• the graph (600) also includes a curve (606) representing the relationship between the particle size and the change in work function value associated with the size.
• the selection of nanoparticle size impacts its work function value.
• the work function value changes more than 1 eV as the nanoparticle cluster approaches that of a single atom.
• the work function value approaches measurements associated with bulk materials. This property of a work function value of a material increasing with decreasing particle size enables the tailoring of each individual application of the nano-scale energy conversion device (100). Accordingly, selecting the particular nanoparticle sizes for the spray depositions (520) on the emitter and collector electrodes (102)/(302) and
• FIG. 7 a diagram is provided illustrating an overhead view (700) of a covalently-bonded dipole (702) deposited on the nanoparticle surface (136/304/506/704) of an electrode (302/306) through an electrospray (514) deposition of the thermionic electron emissive material on the electrode nanoparticle surface/substrate (136/304)/(506/704).
• the nanoparticles in the CS2O deposited on the electrode nanoparticle surface (704) form covalent bonds that in turn form the surface dipoles (702) (only one shown in FIG. 7).
• a positive charge (706) and an opposing negative charge (708) are formed by charged nano-droplets in the electrospray (514) as they collide with the surface (704).
• the charges (706) and (708) induce an electric field (710) between the charges (706) and (708) such that the dipole (702) acts as a nano-antenna that modifies the proximate dipole moment in the vicinity of the dipole (702) through inducement of electromagnetic waves proximate thereto as a function of the induced electric field (710).
• covalently-bonded dipoles (702) deposited on an electrode nanoparticle surface (704) create a low work function electrode when the coverage area is optimized.
• the electrodes e.g., W emitter electrode (302) and the Au collector electrode (306) have dimensions of 20-50 millimeters (mm) long by 20-50 mm wide and 4-100 nm thick.
• the lOOnm thickness is based on charge penetration from the emitter electrode (102/302) into the nanofluid (112) and from the collector electrode
• electrodes (102/302) and (104/306) are approximately 4 nm thick.
• the collector electrode (306) is fabricated (214) in a manner substantially similar to that for the emitter electrode (302).
• a nanometal film (332) is positioned (216) on one side of a polymer base (334) (shown in phantom).
• the polymer base (334) is approximately 2 nm thick (where this value should be considered non limiting) and the nanometal film (332) is approximately 3.7 angstroms thick.
• the nanometal film (332) is positioned proximate to an electrospray nozzle of an electrospray device (see FIG. 5, electrospray nozzle (512)).
• Collector electrode nanoparticles are selected (218) for deposition (220) on the nanometal film (332).
• the combination of the nanoparticle material and the deposited thermionic emissive material has a combined work function value less than the work function value of the emitter electrode (302) (fabricated as described elsewhere herein).
• the difference of the work function values of the two electrodes (302) and (306) is above a predetermined value to maximize electron transfer between the two electrodes (302) and (306).
• a partial list of the appropriate nanoparticle materials for the collector electrode (306) is provided elsewhere herein.
• At least one layer of Au nanoparticles (336) is deposited (220) through electrospray onto the nanometal film (332) to form a nanoparticle surface (310) on the nanometal film (332).
• the thickness of the layer of nanoparticles to form nanoparticle surface (332) is approximately 2 nm ( i.e ., the approximate thickness of a nanoparticle), where the 2 nm value should be considered non-limiting.
• the polymer base (334) is removed (222) through an acetone solution, thereby rendering the polymer base (334) as a sacrificial material. Accordingly, the Au nanoparticle surface (310) on the nanometal film (332) is ready to receive a thermionic emissive material thereon.
• At least one layer of a thermionic electron emissive material (312) is deposited (224) on at least a portion of the Au nanoparticle surface (310).
• a monolayer of the thermionic electron emissive material (312) is deposited on about at least 50% to about 70% of the surface of the Au nanoparticle surface (310).
• about 60% of the surface of the Au nanoparticle surface (310) receives a monolayer of the material (312).
• a plurality of layers of the thermionic electron emissive material (312) is deposited on about 60% of the Au nanoparticle surface (310).
• the deposited thermionic electron emissive material (312) is selected to decrease the work function value of the collector electrode (306) to a value below that of the work function value of the material selected for the Au nanoparticle surface (310).
• the table (400) indicates that the work function value of Au is 5.1 eV.
• Deposition of CS2O (312) on the Au nanoparticle surface (310) decreases the work function value of the collector emitter electrode (306) to 0.65 eV.
• one or more metal materials in the form of nanoparticles are selected as the nanoparticle surface (310) for the collector electrodes (306) at least partially as a function of decreasing the work function value of the electrodes (302) and (306) and maintaining a work function value differential between the electrodes (302) and (306) above a predetermined value.
• the electrodes (302) and (306) are fabricated, assembly (200) of the nano scale energy conversion device (100)/(300) continues. Specifically, one of the collector electrode (306) (as shown in FIG. 3) or the emitter electrode (302) is positioned on a surface (not shown) for support. A template (not shown in FIG. 2) is employed to fabricate (226) a plurality of insulator posts (or columns, standoffs, or micro-pillars) (314) through
• the template is a graphite template.
• the insulator posts (314) are fabricated with a dielectric material, such as, and without limitation, alkanethiol, sol-gel with aerogel-like properties, corona dope, super corona dope, silicon, silicon-oxide, polymer, any dielectric material, or a combination including at least one of the foregoing.
• the templates are constructed to allow for electro-spraying of the alkanethiol such that overspray onto the thermionic electron emissive materials (308) and (312) is minimized.
• one or more insulator walls are formed that divide the cavity (316) into multiple cavities (316).
• the height (318) of the insulator posts (314) may be in a range of, for example, 1 nanometer (nm) to less than 10 nm. Therefore, the cavity (316) extends between the electrodes (302) and (306) for a distance in the range from 1 nanometer (nm) to less than 10 nm.
• the width (320) of the insulator posts (314) may be in a range of, for example, 1 nanometer (nm) to 10 nm.
• the width (322) of the cavity (322) may be in a range of, for example, 1 nanometer (nm) to 10 nm.
• the insulator posts (314) are shown as cubical or cubical like structures and substantially similar in shape and size to that of the cavity (322), although this configuration is not limiting.
• the distance between insulator posts (314) is within a range defined by about 5-6 nm to about 1 cm.
• the dimensions and configurations of the insulator posts (314) and cavities (316) are determined based on the planned employment of the nano-scale energy conversion devices (100)/(300).
• insulator posts (314) are fabricated on one of the two electrodes (302) and (306) at a predetermined height to maintain a predetermined distance between the two electrodes (302) and (306) within the nano-scale energy conversion device (100)/(300).
• the electrodes (302) and (306) and the insulator posts (314) are coupled (228) together. As described above, and shown in FIG. 3, the insulator posts (314) are deposited on the collector electrode (306). The electrode on which the insulator posts (314) were not formed, as shown in FIG. 3, the emitter electrode (302), is lowered to rest on top of the insulator posts (314) as shown by the arrows (326). An adhesive material (324) is spot- deposited at the outside ends of the nano-scale energy conversion device (100)/(300) to adhere the electrodes (302) and (306) and insulator posts (314) as a unit.
• this aspect of the assembly is completed when the device (100)/(300) is sealed or encased with one of silicon or silicon dioxide casing segments, a sealant such as a hot melt adhesive, or by electro- spraying an alkanethiol film gasket around the edge of the device on all sides, with the exception of one side remaining unsealed to facilitate addition of a nanofluid (as discussed further elsewhere herein).
• the positioning of the electrodes (302) and (306) and the insulator posts (314) define (230) a cavity therebetween (316).
• a diagram is provided illustrating a cutaway view of an embodiment of a nanofluid (800) including a plurality of Au and Ag nanoparticle clusters (802) and (804), respectively, suspended in a dielectric medium (806).
• the dielectric medium (806) is one of water, silicone oil, or alcohol.
• the dielectric medium (806) is a sol-gel with aerogel-like properties and low thermal conductivity values that reduce heat transfer therethrough, e.g., thermal conductivity values as low as 0.013 watts per meter-degrees Kelvin (W/m-K) as compared to the thermal conductivity of water at 20 degrees Celsius (°C) of 0.6 W/m-K.
• the nanoparticle clusters (802) and (804) have work function values that are greater than the work function values for the electrodes (234).
• the work function values of the Au nanoparticle clusters (802) and the Ag nanoparticle clusters (804) are 4.1 eV and 3.8 eV, respectively.
• At least one layer of a dielectric coating such as a monolayer of alkanethiol material (808), is deposited, e.g., electrosprayed, on the nanoparticles (236) to form a dielectric barrier thereon.
• the alkanethiol material at step (236) includes, but is not limited to dodecanethiol and decanethiol.
• the deposit of the dielectric coating, such as alkanethiol reduces coalescence of the nanoparticle clusters (802) and (804).
• the nanoparticle clusters (802) and (804) have a diameter in the range of 1 nm to 3 nm.
• the nanoparticle clusters (802) and (804) have a diameter of 2 nm.
• the nanoparticle clusters of Au (802) and Ag (804) are tailored to be electrically conductive with charge storage features (i.e., capacitive features), minimize heat transfer through the cavities (110) and (316) with low thermal conductivity values, minimize ohmic heating, eliminate space charges in the cavities (110) and (316), and prevent arcing.
• the plurality of Au and Ag nanoparticle clusters (802) and (804), respectively, are suspended (238) in the dielectric medium (806).
• the nanofluid (800), including the suspended nanoparticle clusters (802) and (804), provides a conductive pathway for electrons to travel across the cavities (110) and (316) from the emitter electrode (102) and (302) to the collector electrode (104) and (306) through charge transfer.
• the Au nanoparticle clusters (802) are dodecanethiol functionalized gold nanoparticles, with a particle size of 1-3 nm, at about 2% (weight/volume percent) and suspended in toluene.
• the Ag nanoparticle clusters (804) are dodecanethiol functionalized silver nanoparticles, with a particle size of 1-3 nm, at about 0.25% (weight/volume percent) and suspended in hexane.
• the particle size of both the Au and Ag nanoparticle clusters (802) and (804) is at or about 2 nm.
• the Au and Ag cores of the nanoparticle clusters (802) and (804) are selected for their abilities to store and transfer electrons.
• a 50%-50% mixture of Au and Ag nanoparticle clusters (802) and (804) is used.
• a mixture in the range of 1-99% Au-to-Ag could be used as well.
• Electron transfers are more likely between nanoparticle clusters (802) and (804) with different work functions.
• a mixture of nearly equal numbers of two dissimilar nanoparticle clusters (802) and (804) provides good electron transfer. Accordingly, nanoparticle clusters are selected based on particle size, particle material (with the associated work function values), mixture ratio, and electron affinity.
• conductivity of the nano fluid (800) can be increased by increasing concentration of the nanoparticle clusters (802) and (804).
• concentration of the nanoparticle clusters (802) and (804) can be increased.
• concentration for the conductance of the nanofluid can be found at lower concentrations of nanoparticles, such as less than 0.5 mole/liter, 0.4 to 0.5 mole/liter, or even lower
• the nanoparticle clusters (802) and (804) may have a concentration within the nanofluid (800) of about 0.1 mole/liter to about 2 moles/liter.
• the Au and Ag nanoparticle clusters (802) and (804) each have a concentration of at least 1 mole/liter.
• the stability and reactivity of colloidal particles are determined largely by a ligand shell formed by the alkanethiol coating (808) adsorbed or covalently bound to the surface of the nanoparticle clusters (802) and (804).
• the nanoparticle clusters (802) and (804) tend to aggregate and precipitate, which can be prevented by the presence of a ligand shell of the non-aggregating polymer alkanethiol coating (808) enabling these nanoparticle clusters (802) and (804) to remain suspended.
• Adsorbed or covalently attached ligands can act as stabilizers against agglomeration and can be used to impart chemical functionality to the nanoparticle clusters (802) and (804). Over time, the surfactant nature of the ligand coatings is overcome and the lower energy state of agglomerated nanoparticle clusters is formed. Therefore, over time, agglomeration may occur due to the lower energy condition of nanoparticle cluster accumulation and occasional addition of a surfactant may be used.
• the nanofluid (802) is loaded (240) into the cavities (110) and (316) by, for example, capillary and vacuum processes through the remaining unsealed side of nano-scale energy conversion device (100)/(300). Assembly is completed when the remaining unsealed side of the nano-scale energy conversion device (100)/(300) is sealed (242) or encased with one of silicon or silicon dioxide casing segments, a sealant such as a hot melt adhesive, or by electro spraying an alkanethiol film gasket around the remaining unsealed side of the device.
• a sealant such as a hot melt adhesive
• a plurality of Au and Ag nanoparticle clusters (802) and (804) are mixed together in a dielectric medium (806) to form a nanofluid (112)/(800), the nanofluid (112)/(800) is inserted into the cavities (110)/(316), and the nano-scale energy conversion device (100)/(300) is fully sealed.
• the dimensions of the nano-scale energy conversion device (100)/(300) is approximately 20-50 mm long by approximately 20-50 mm wide by approximately 9-19 nm thick (about 4 nm for each electrode (102/302 and 104/306) and about 1 nm to less than about 10 nm for the cavity (110/316) therebetween).
• the thickness of the device (100/300) is determined based on the desired electron flow therein and the other two dimensions are scalable based on the desired overall power output of the device
• a flow chart is provided illustrating a process (900) for generating electric power with the nano- scale energy conversion device (100).
• an emitter electrode (102) is provided (902) and a collector electrode (104) is provided (904), where the work function value of the collector electrode (104) is less than the work function value of the emitter electrode (102).
• the emitter electrode (102) and the collector electrode (104) are positioned (906) a predetermined distance from each other, i.e., about 1 nm to less than about 10 nm.
• FIG. 10 a diagram is provided illustrating a cutaway view of an embodiment of the nano- scale energy conversion device (1000) showing a relationship between the work functions of an emitter electrode (1002) (WF e ), collector electrode (1004) (WF C ), and nanofluid (1006) (WF nf ) therein.
• FIG. 10 also shows a pair of insulator posts (1008) separating the electrodes (1002) and (1004). The difference between the WF e and WF C establishes (908) a contact potential difference (CPD) between the two electrodes (1002) and (1004).
• CPD contact potential difference
• a voltage differential is induced across the nanofluid (1006) due to the dissimilar metals of electrodes (1002) and (1004), e.g., W and Au, respectively, both including at least a monolayer of CS2O over about 60% of the opposing surfaces thereof.
• the value for WF e is 0.88 eV and the value for WF C is 0.65 eV, to induce a VCPD of 0.23 eV.
• the VCPD induces an electric field (ECPD) that has to be overcome to transmit electrons through the nanofluid (1006) from the emitter electrode (1002) to the collector electrode (1004). Accordingly, as described further herein, this induced CPD enables thermionic emission of electrons from the emitter electrode (1002) toward the collector electrode (1004).
• the nanofluid (1006) including a plurality of Au nanoparticle clusters (1010) and Ag nanoparticle clusters (1012) is provided (910).
• the work functions of the Au nanoparticle clusters (1010) and Ag nanoparticle clusters (1012) are 4.1 eV and 3.8 eV, respectively. Therefore, a collective work function WF nf is greater than WF e which is greater than WF C . This relationship of the work function values of the Au and Ag
• nanoparticle clusters (1010) and (1012) optimizes the transfer of electrons to the nanoparticle clusters (1010) and (1012) through Brownian motion and electron hopping (discussed further herein). Accordingly, the selection of materials within the nano-scale energy conversion device (1000) optimizes electric current generation and transfer therein through enhancing the release of electrons from the emitter electrode (1002) and the conduction of the released electrons across the nanofluid (1006) to the collector electrode (1004).
• FIG. 11 a diagram is provided illustrating a graphical representation (1100) of the effect of the emitter work function value being larger than the collector work function value.
• the emitter electrode (1102) and the collector electrode (1104) are separated by the cavity (1106) that is filled with nanofluid (1108).
• a thermal distribution function (1110) of the electrons in the emitter electrode (1102) above the electrochemical potential (the Fermi level (m e )) as a function of the distance from the surface (1112) of the electrode (1102) is shown.
• the work function (WF e ) of the emitter electrode (1102) extends from the Fermi level (m,.) of the emitter electrode (1102) to an electrical potential of the emitter electrode (E e ).
• a thermal distribution function (1114) of the electrons in the collector electrode (1104) above the electrochemical potential (the Fermi level (m, )) as a function of the distance from the surface (1116) of the electrode (1104) is shown.
• the work function (WF C ) of the collector electrode (1104) extends from the Fermi level (m, ) of the collector electrode (1104) to the electrical potential of the collector electrode ( E c ).
• the Fermi level (m e ) of the collector electrode (1104) is shifted upward due to the electrical potential of a load (eVi oad ) connected to the electrodes (1102) and (1104) inducing a contact potential difference voltage (V CPD ) across the cavity (1108), where eVi oad and V CPD are equal to each other.
• An electrical potential function (E) is shown declining from the surface (1112) of the emitter electrode (1102) to the surface (1116) of the collector electrode (1104), i.e., from E e to E c linearly as the electrons traverse the nanofluid (1106) and the cavity (1108) as indicated by the arrow (1118).
• the emitter work function (WF e ) is greater than the collector work function (WF C ) so that electrons are accelerated toward the collector electrode (1104) and not accelerated back towards the emitter electrode (1102). Accordingly, the selection of the materials for the emitter electrode (1102) and the collector electrode (1104) with the associated work function and Fermi level values determining operational functionality of the nano-scale energy conversion device (100).
• the work function (WF e ) of the emitter electrode (1102) equals the combination of an external load and the work function (WF C ) of the collector electrode (1104).
• the nanofluid (1202) includes a plurality of nanoparticle clusters (1204) suspended in a dielectric medium (1206).
• the plurality of nanoparticle clusters (1204) includes Au nanoparticle clusters (1208) and Ag nanoparticle clusters (1210).
• the Au nanoparticle clusters (1208) have a work function value of about 4.1 eV and the Ag nanoparticle clusters (1210) have a work function value of about 3.8 eV.
• nanoparticle clusters (1204) are much greater than the work function values of the emitter electrode (102) (0.88 eV) and the collector electrode (104) (0.65 eV).
• the nanoparticle clusters (1204) are coated with alkanethiol to form a dielectric barrier (1212) thereon to reduce coalescence of the nanoparticle clusters (1204).
• the nanoparticle clusters (1204) have a diameter of about 2 nm.
• the nanoparticle clusters (1204) are tailored to be electrically conductive with capacitive ( i.e ., charge storage) features while minimizing heat transfer therethrough. Accordingly, suspended nanoparticle clusters (1204) provide a conductive pathway for electrons to travel across the cavity (110) from the emitter electrode (102) to the collector electrode (104) through charge transfer.
• a net electron current from the emitter electrode (102) to the collector electrode (104) via the nanoparticle clusters (1204) is the primary and dominant current of the nano scale energy conversion device (100).
• the nanoparticle clusters (1204) transfer charge physically ⁇ i.e., undergo transient charging) due to the ionization of the nanoparticle clusters (1204) upon receipt of an electron and the electric field generated by the differently charged electrodes (102) and (104).
• the nanoparticle clusters (1204) become ionized in collisions when they gain or lose an electron (1214).
• Positive and negative charged nanoparticle clusters (1204) in the nanofluid (1202) migrate to the negatively charged collector electrode (104) and the positively charged emitter electrode (102), respectively, providing a current flow. This ion current flow is in the opposite direction from the electron current flow, but much less in magnitude than the electron flow.
• Electrode separation may be selected at an optimum width to maximize ion formation and minimize ion recombination.
• the electrode separation is slightly less thanlO nm.
• the nanoparticle clusters (1204) have a maximum dimension of about 2 nm, so the electrode separation is about 3 to 5 nanoparticle clusters (1204). This separation distance provides sufficient space within the cavity for nanoparticle clusters (1204) to move around and collide, while minimizing ion recombination.
• an electron can hop from the emitter electrode (102) to a first nanoparticle cluster (1204) and then to a second, third, fourth, or fifth nanoparticle cluster (1204) before hopping to the collector electrode (104).
• a reduced quantity of hops mitigates ion recombination opportunities. Accordingly, ion recombination in the nanofluid (1202) is minimized through an electrode separation distance selected at an optimum width to maximize ion formation and minimize ion recombination.
• the electrons of the collector electrode (104) have a higher Fermi level than the electrons of the emitter electrode (102) due to the lower work function of the collector electrode (104).
• the difference in Fermi levels drives a net electron current that transfers electrons from the collector electrode (104) to the emitter electrode (102) until the Fermi levels are equal, i.e., the electrochemical potentials are balanced and thermodynamic equilibrium is achieved.
• the transfer of electrons between the emitter electrode (102) and the collector electrode (104) results in a difference in charge between the emitter electrode (102) and the collector electrode (104).
• This charge difference sets up the voltage of the contact potential difference (V CPD ) and an electric field between the emitter electrode (102) and the collector electrode (104), where the polarity of the V CPD is determined by the material having the greatest work function. With the Fermi levels equalized, no net current will flow between the emitter electrode (102) and the collector electrode (104). Accordingly, electrically coupling the emitter electrode (102) and the collector electrode (104) with no external load results in attaining the contact potential difference between the electrodes (102 and 104) and no net current flow between the electrodes (102) and (104) due to attainment of
• thermodynamic equilibrium between the two electrodes (102) and (104).
• the nano-scale energy conversion device (100) can generate electric power (e.g ., at room temperature) with or without additional heat input.
• Heat added to the emitter electrode (102) will raise its temperature and the Fermi level of its electrons. With the Fermi level of the emitter electrode (102) higher than the Fermi level of the collector electrode (104), a net electron current will flow from the emitter electrode (102) to the collector electrode (104) through the nanofluid (1202). If the external circuit (128) is connected, the same amount of electron current will flow through the external circuit current (134) from the collector electrode (104) to the emitter electrode (102). The heat energy added to the emitter electrode (102) is carried by the electrons (1214) to the collector electrode (104).
• the bulk of the added energy is transferred to the external circuit (128) for conversion to useful work and some of the added energy is transferred in collisions to the collector electrode (104) and eventually lost to ambient as waste energy.
• the temperature of the electrode (102) decreases as the highest energy electrons are emitted, and the electron transmission from the emitter electrode (102) increases, thereby generating more current.
• the emitter electrode (102) releases (912) electrons onto the nanoparticle clusters (1204), energy is stored in the nano-scale energy conversion device (100). Accordingly, the nano-scale energy conversion device (100) generates, stores, and transfers charge and moves heat energy if a temperature difference exists, where added thermal energy causes the production of electrons to increase from the emitter electrode (102) into the nanofluid (1202).
• the nanofluid (1202) is used to transfer charges from the emitter electrode (102) to one of the mobile nanoparticle clusters (1204) (via intermediate contact potential differences) from the collisions of the nanoparticle cluster (1204) with the emitter electrode (102) induced by Brownian motion (914) of the nanoparticle cluster (1204).
• Unitary nanoparticle clusters aggregate more quickly than mixed nanoparticle clusters.
• the nanoparticle clusters (1204) include a voltage feedback mechanism that prevents the hopping of more than a predetermined number of electrons to the nanoparticle cluster (1204). This prevents more than the allowed number of electrons from residing on the nanoparticle cluster simultaneously. In an embodiment, only one electron (1214) is permitted on any nanoparticle cluster (1204) at any one time.
• a single electron (1214) hops onto the nanoparticle cluster (1204).
• the electron (1214) does not remain on the nanoparticle cluster (1204) indefinitely, but hops off to either the next nanoparticle cluster (1204) or the collector electrode (104) through collisions resulting from the Brownian motion of the nanoparticle clusters (1204).
• the electron (1214) does remain on the nanoparticle cluster (1204) long enough to provide the voltage feedback required to prevent additional electrons (1214) from hopping
• the nano-scale energy conversion device (100) does not require pre-charging by an external power source in order to introduce electrostatic forces. This is due to the device (100) being self-charged with triboelectric charges generated upon contact between the nanoparticle clusters (1204) due to Brownian motion. Accordingly, the electron hopping across the nanofluid (1202) is limited to one electron (1214) at a time residing on a nanoparticle cluster (1204).
• the process through which electrons are emitted above the Fermi level and are replaced with electrons below the Fermi energy is sometimes referred to as an inverse Nottingham effect. Accordingly, the low work function value of about 0.88 eV for the emitter electrode (102) allows for the replacement of the emitted electrons with electrons with a lower energy level to induce a cooling effect on the emitter electrode (102).
• a plurality of nano-scale energy conversion devices (100) are distinguished by at least one embodiment having the thermoelectric energy conversion features described herein.
• the nanofluid (1202) is selected for operation of the nano- scale energy conversion devices (100) within more than one temperature range.
• the temperature range of the associated nano-scale energy conversion device (100) is controlled to modulate a power output of the device (100).
• the rate of thermionic emission therefrom increases.
• the operational temperature ranges for the nanofluid (1202) are based on the desired output of the nano-scale energy conversion device (100), the temperature ranges that optimize thermionic conversion, the temperature ranges that optimize thermoelectric conversion, and fluid characteristics.
• the nanofluid (1202) are designed for different energy outputs of the device (100).
• the temperature of the nanofluid (1202) should be maintained at less than 250°C to avoid deleterious changes in energy conversion due to the viscosity changes of the silicone oil above 250°C.
• the temperature range of the nanofluid (1202) for substantially thermionic emission is approximately room temperature ( i.e ., about 20°C to about 25°C) up to about 70-80°C, and the temperature range of the nanofluid for thermionic and thermo-electric conversion is above 70-80°C, with the principle limitations being the temperature limitations of the materials.
• the nanofluid (1202) for operation including thermoelectric conversion includes a temperature range that optimizes the thermoelectric conversion through optimizing the power density within the nano- scale energy conversion device (100), thereby optimizing the power output of the device (100).
• a mechanism for regulating the temperature of the nanofluid (1202) includes diverting some of the energy output of the device (100) into the nanofluid (1202). Accordingly, the cavities (110) of specific embodiments of the nano-scale energy conversion device (100) may be filled with the nanofluid (1202) to employ thermoelectric energy conversion with thermionic energy conversion above a particular temperature range, or thermionic energy conversion by itself below that temperature range.
• the dielectric medium (1206) has thermal conductivity values less than about 1.0 watts per meter-degrees Kelvin (W/(m-K)). In at least one embodiment, the thermal conductivity of the dielectric medium (1206) is as low as about 0.013 watts per meter-degrees Kelvin (W/(m-K)), as compared to the thermal conductivity of water at about 20 degrees Celsius (°C) of 0.6 W/(m-K).
• the nanofluid (1202) minimizes heat transfer through the cavity (110) with low thermal conductivity values. Since the heat transport in a low thermal conductivity nanofluid (1202) can be small, a high temperature difference between the two electrodes (102) and (104) can be maintained during operation. These embodiments are designed for those nano scale energy conversion devices (100) that employ thermionic emission only, where minimal heat transfer through the nanofluid (1202) is desired.
• nano-scale energy conversion devices In some alternative embodiments of nano-scale energy conversion devices (100), greater heat transfer through the nanofluid (1202) is desired.
• the nano-scale energy conversion device (100) has a cavity (110) dimension of less than about 10 nm. In this predetermined distance range of about 1 nm to less than about 10 nm, thermal conductivity values and electrical conductivity values of the nanofluid (1202) are enhanced over thermal and electrical conductivity values of the nanofluid (1202) when the predetermined distance of the cavity is greater than about 100 nm. This increase of thermal and electrical conductivity values of the nanofluid (1202) is due to a number of factors.
• the first factor is that of enhanced phonon and electron transfer between the plurality of nanoparticle clusters (1204) within the nanofluid (1202), enhanced phonon and electron transfer between the plurality of nanoparticle clusters (1204) and the first electrode (102), and enhanced phonon and electron transfer between the plurality of nanoparticle clusters (1204) and the second electrode (104).
• a second factor is the enhanced influence of Brownian motion of the nanoparticle clusters (1204) in the more confining volume seen in the scale of less than about 10 nm. As the distance between the electrodes (106) decreases below about 10 nm, the fluid continuum characteristics of the nanofluid (1202) with the suspended nanoparticle clusters (1204) is altered. For example, as the ratio of particle size to volume of the cavity (110) increases, the random and convection like effects of Brownian motion in a dilute solution dominate.
• nanoparticle clusters (1204) and the electrodes (102) and (104) increase thermal and electrical conductivity values due to the enhanced phonon and electron transfer.
• a third factor is the at least partial formation of nanoparticle cluster (1204) matrices within the nanofluid (1202).
• the formation of the matrices is based on the factors of time and/or concentration of the nanoparticle clusters (1204) in the nanofluid (1202).
• the nanoparticle clusters (1204) will form matrices within the nanofluid (1202) as a function of close proximity to each other with some of the nanoparticle clusters (1206) remaining independent from the matrices.
• a fourth factor is the predetermined nanoparticle cluster (1204) density, which in an embodiment is about one mole per liter. Accordingly, the very small dimensions of the cavity (110) of less than about 10 nm causes an increase in the thermal and electrical conductivity values of the nanofluid (1202) therein.
• the nanoparticle clusters (1204) are extremely thin and they are often considered to have only one dimension, i.e., their characteristic length. This extreme thinness restricts electrons and holes in a process called quantum confinement, which increases electrical conductivity. The collision of particles with different quantum confinement facilitates transfer of charge to the electrodes (102) and (104).
• a nanoparticle cluster's (1204) small size also increases the influence of its surfaces, thereby tending to increase thermal conductivity.
• the embodiments of nano-scale energy conversion device (100) have an enhanced electrical conductivity value greater than about 1 Siemens per meter (S/m). Also, the embodiments of device (100) with the enhanced thermal conductivity have a thermal conductivity value greater than about 1 W/m-K.
• the release of electrons from the emitter electrode (102) through thermionic emission as described herein is an energy selective mechanism.
• a Coulombic barrier in the cavity (110) between the emitter electrode (102) and the collector electrode (104) is induced through the interaction of the nanoparticles (1204) with the electrodes (102) and (104) inside the cavity (110).
• the Coulombic barrier is at least partially induced through the number and material composition of the plurality of nanoparticle clusters (1204).
• the Coulombic barrier induced through the nanofluid (1202) provides an energy selective barrier on the order of magnitude of about 1 eV. Accordingly, the nanofluid (1202) provides an energy selective barrier to electron emission and transmission.
• the energy selective barrier is overcome through the thermionic emission of electrons at a higher energy level than would be otherwise occurring without the barrier.
• the barrier continues to present an obstacle to further transmission of the electrons (1214) through the nanofluid (1202).
• Smaller gaps on the order of about 1-10 nm facilitates electron hopping, i.e., field emission, of short distances across the cavity (110).
• the energy requirements for electron hopping are much lower than the energy requirements for thermionic emission, therefore the electron hopping has a significant effect on the energy generation characteristics of the device (100).
• the design of the nanofluid (1202) enables energy selective tunneling (hopping) that is a result of the special form of the barrier (which has wider gap for low energy electrons) which results in electrons above the Fermi level being the principal hopping component.
• the direction of the electron hopping is determined through the selection of the different materials for the electrodes (102) and (104) and their associated work function and Fermi level values.
• the electron hopping across the nanofluid (1202) transfers heat energy with electrons (1214) across the cavity (110) while maintaining a predetermined temperature gradient such that the temperature of the fluid (1214) is relatively unchanged during the electron transfer. Accordingly, the emitted electrons transport heat energy from the emitter electrode (102) across the cavity (110) to the collector electrode (104) without increasing the temperature of the nano fluid (1202).
• FIG. 13 a diagram is provided illustrating an embodiment of employment of the nano-scale energy conversion device (1300).
• Heat energy (1302) from a source enters the emitter electrode (1304).
• Electrons (1306) are thermionic ally emitted (1318) from the emitter electrode (1304).
• the electrons (1306) traverse the cavity (1308) that is filled with nanofluid (1310) as described herein.
• the electrons (1306) reach (1320) the collector electrode (1312) that collects the electrons (1306) to generate an output electron flow (1314) that is transmitted through a first electrical conductor (1322) to a load (1316) to perform work.
• the load (1316) is connected by a second electrical conductor (1324) to the emitter (1304).
• Electrical current represented by arrow (1326) flows in the opposite direction to electron flow (1314). Accordingly, the nano-scale energy conversion device (1300) harvests heat energy (1302), including waste heat and ambient heat, to generate electrical power (1314).
• FIG. 14 a diagram is provided illustrating a system (1400) of stacked or grouped nano- scale energy conversion devices (1402) that generates electric power from heat (1404), which in an embodiment is waste heat or waste heat by-product.
• the system (1400) includes a plurality of nano-scale energy conversion devices (1402) within an insulated casing (1406).
• Each nano-scale energy conversion device (1402) is capable of producing at least 0.024 watts/cell and the system (1400) can reach a power density of about 1550 watts/liter, therefore, about 64,583 devices (1402) would be involved.
• a system (1400) to power a typical home would require about a 2 liter system.
• Stacked nano-scale energy conversion devices (1402) (in series or in parallel) define the power flux to obtain an electric power system of desired current and voltage characteristics.
• heat removal capabilities are enhanced through the additional devices (1402).
• the nano- scale energy conversion devices (1402) are scalable and configurable to provide electric power under a variety of uses.
• a diagram is provided illustrating a waste heat harvesting system (1500) that includes a nano-scale energy conversion group (1502) coupled to an electronic chip (1504), such as a semi-conductor chip that harvests electrical energy from waste heat from the electronic chip (1504).
• a system (1500) is suitable for use in mobile phones and other portable electronic devices.
• the electronic chip (1504) is affixed to the nano-scale energy conversion group (1502) with an adhesive (1506), e.g., without limitation, an epoxy adhesive.
• the group of stacked nano-scale energy conversion devices (1502) includes, e.g., and without limitation, about 35 stacked nano-scale energy conversion devices.
• the quantity of stacked nano-scale energy conversion devices may range depending on the size and dimensions of the semi-conductor chip. For example, in an embodiment, the quantity may range from a minimum of 1 to in excess of 1,000 stacked nano-scale energy conversion devices. Similarly, in an embodiment, the stacking of multiple nano-scale energy conversion devices forms layers thereof.
• the conversion group (1502) is cooled by both radiation heat transfer (1508) and natural convection heat transfer (1510).
• the nano-scale energy conversion group (1502) is driven by a temperature difference where the electronic chip (1504) is operating at about 100°C.
• the harvested electrical power does not need to be used to cool the system (1500).
• the nano-scale energy conversion group (1502) includes a predetermined number of nano-scale energy conversion devices for multiplying currents and voltages as necessary. Accordingly, a nano scale energy conversion group (1502) can be cooled by combined natural convection and radiation, and there may be no need to install any power-consuming fluid movers.
• FIG. 16 a diagram is provided illustrating an electric power generation system (1600) that includes an array (1602) of nano- scale energy conversion devices (1604) coupled to an array of solar cells (1606) that harvests electrical energy from heat byproduct (1608) from the solar cell array (1606).
• An energy storage device (1610) such as, and without limitation, an ultra-capacitor, is electrically connected to the array (1602) of nano-scale energy conversion devices (1604). Integration of the nano-scale energy
• the integration of the nano- scale energy conversion devices (1604) augments other thermal power sources such as hot water, geothermal sources, and automotive waste heat sources, to enhance the generation of electrical power. Accordingly, the nano- scale energy conversion devices (1604) can be integrated with multiple energy-harvesting devices to produce a greater energy-density device that would otherwise not be accomplished without the integration.
• the present disclosure is directed generally to an ultra-long life energy source, such as a battery, and more particularly is directed to a nano-scale energy conversion device. Ionization is provided therein by the combination of electron tunneling and thermionic emission of the nano- scale energy conversion device. Charge transfer therein is effected through conductive nanoparticles suspended in a fluid ( e.g . , a nanofluid) undergoing collisions driven by thermally-induced Brownian motion.
• a fluid e.g . , a nanofluid
• the design of this device enables ambient energy extraction at low and elevated temperatures (including room temperature). To this end, the electrodes are very close to each other to allow electrons to travel the distance between the electrodes.
• thermionic converters With respect to thermionic converters, the electrical efficiency of these devices depends on the very low work function materials deposited on the emitter electrode (cathode) and the collector electrode (anode). The efficiency of two low work function electrodes can be increased by developing cathodes with sufficient thermionic emission of electrons operating even at room temperature. These low work function cathodes and anodes provide copious amounts of electrons.
• a tunneling device comprises two low work function electrodes separated by a designed nanofluid.
• Cooling by electrode emission refers to the transport of hot electrons across the nanofluid gap, from the object to be cooled (cathode) to the heat rejection electrode (anode).
• the coupling of several technologies including: the electrospray- deposition of two low work function electrodes including cesium-oxide on tungsten and gold, respectively; an energy selective electron-transfer thermionic emission and quantum hopping of electrons; a nanofluid that is tailored as a thermoelectric element to conduct electricity while minimizing heat transfer within the device; and thermal communication from the anode electrical connection that is in thermal contact with the device and the outside heat reservoir. This coupling of technology produces a viable thermionic power generator.
• the nano-scale energy conversion devices of embodiments described herein facilitate generating electrical energy via a long-lived, constantly-recharging battery for any size-scale electrical application.
• the devices of embodiments described herein provide a battery having a conversion efficiency superior to presently available single and double conversion batteries.
• the devices of embodiments described herein may be fabricated as an integral part of, and provide electrical energy for, an integrated circuit.
• the devices of embodiments described herein are a light-weight and compact multiple-conversion battery having a relatively long operating life with an electrical power output at a useful value.
• the nanoparticle clusters of embodiments described herein are multiphase nanocomposites that include thermoelectric materials. The combination of thermoelectric and thermionic functions within a single device further enhances the power generation capabilities of the nano-scale energy conversion devices of embodiments described herein.
• the conversion of ambient heat energy into usable electricity enables energy harvesting capable of offsetting, or even replacing, the reliance of electronics on conventional power supplies, such as electrochemical batteries, especially when long-term operation of a large number of electronic devices in dispersed locations is required.
• Energy harvesting distinguishes itself from conventional batteries and hardwire power owing to inherent advantages, such as outstanding longevity measured in years, little maintenance, and minimal disposal and contamination issues.
• the nano-scale energy conversion devices described herein demonstrate a novel electric generator with low cost for efficiently harvesting thermal energy (without the need for an initial temperature differential or thermal gradient to start the electron flow).
• the nano-scale energy conversion devices of embodiments described herein are scalable across a large number of power generation requirements.
• the devices may be designed for applications requiring electric power in the milliwatts (mW), watts (W), kilowatts (kW), and megawatts (MW) ranges.
• Examples of devices for the mW range include, but are not limited to, those devices associated with the Internet of Things (IoT) (home appliances, vehicles (communication only)), handheld portable electronic devices (mobile phones, medical devices, tablets), and embedded systems (RFIDs and wearables).
• IoT Internet of Things
• RFIDs and wearables embedded systems
• devices for the watts range include, but are not limited to, handheld sensors, networks, robotic devices, cordless tools, drones, appliances, toys, vehicles, utility lighting, and edge computing.
• Examples of devices in the kW range include, but are not limited to, residential off-grid devices (rather than backup fossil fuel generators), resilient/sustainable homes, portable generators, electric and silent transportation (including water-faring), and spacecraft.
• Examples of devices in the MW range include, but are not limited to,
• industrial/data center/institutional off-grid devices e.g ., uninterruptible power supplies
• resilient complexes e.g., urban centers, commercial and military aircraft, flying cars, and railway/locomotive/trucking/shipboard transportation.
• the nano-scale energy conversion devices as heat harvesting devices that efficiently convert waste heat energy to usable electric energy facilitates flexible uses of the minute power generators. Accordingly, the nano-scale energy conversion devices and the associated embodiments as shown and described in FIGS. 1-16, provide electrical power through conversion of heat in most known environments, including ambient, ambient temperature environments.
• the nano-scale energy conversion devices are shown as configured to harvest waste heat from stationary or relatively stationary conditions.
• the nano-scale energy conversion devices may be configured to harvest heat or waste heat while in motion. Accordingly, the scope of protection of the embodiment(s) is limited only by the following claims and their equivalents.

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• 2020
  • 2020-02-21 EP EP20712763.0A patent/EP3931858A1/de active Pending
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