Recognition of energy-saving and detection of flammable gases

Abstract

Sensor (100; 300) for flammable gases, comprising: at least one first electrode (102; 304; 302; 1002; 1102) formed of a first metal; at least one second electrode (104; 308; 1004; 1104) formed from a metal different from that of the first electrode, wherein either the first electrode or the second electrode is made of palladium, wherein the non-palladium electrode is made of a platinum-silver alloy, and wherein the platinum-silver alloy comprises silver from about 20% to about 25% and ranges therebetween and platinum from about 74% to about 79% and ranges therebetween; and a gas-permeable catalytic material (108; 305; 502; 1008; 1108) formed from one or more layers of nanoparticles at an active reaction junction between the first electrode and the second electrode, wherein the active reaction junction between the first electrode and the second electrode forms a thermocouple.

Description

Field of the invention

[0001] The present invention relates to gas detection techniques and, more particularly, to energy-saving sensors for flammable gases using a thermocouple design. Background of the invention

[0002] The detection of flammable gases is important for many industries and human activities, ranging from residential safety to mining operations. For example, methane detection is particularly important for a number of areas, including oil and gas facility operations, cattle ranching, greenhouse gas monitoring, natural gas monitoring, and more.

[0003] In such applications, many sensors must be installed over extended periods (often at remote locations). Thus, a battery-powered sensor with a long lifetime (e.g., on the order of 5 years) and very low power consumption would be desirable.

[0004] However, existing combustion sensors rely on electrical heating elements to operate the sensing element at high temperatures. These electrical heating elements typically consume prohibitively large amounts of power (on the order of approximately 50 milliwatts (mW) to approximately 150 mW). Furthermore, many commercially available devices are limited to high gas concentrations.

[0005] Thus, a room-temperature, low-power, and cost-effective sensor for detecting flammable gases such as methane would be desirable. Such a sensor would ideally be capable of measuring gas concentrations in the part-per-million (ppm) range.

[0006] JP 2005-98844 A describes a gas sensor that, even in a compact form, generates high heat output per unit area and provides sufficient electromotive force. Detection occurs by converting the heat generated by the gas reaction on the surface of a catalytically active layer into a voltage using a thermoelectric material. The catalytic layer is porous and can be formed by self-organizing processes such as anodic oxidation of aluminum.

[0007] US 2007 / 0 212 263 A1 describes a micro-thermoelectric gas sensor with a thermoelectric conversion unit, a microheater, and a catalyst layer arranged thereon, which enables catalytic combustion of combustible gas. The sensor also includes a detection unit with an electrode structure on a membrane of defined thickness. Furthermore, a method for the precise placement of functional materials such as catalysts or resistors on a substrate is described, whereby the microstructure of the material is specifically controlled.

[0008] JP 2005-183 795 A describes a compact gas sensor with a thermocouple pattern on a flexible substrate. A catalytically active thin film on the back promotes gas oxidation, while the resulting temperature difference is detected via the thermocouple.

[0009] JP 2007-248223 A describes a gas sensor with high selectivity that operates at room temperature and is easy to fabricate. It consists of two doped iron silicide layers on an insulator substrate, with a Pt catalyst layer for selective hydrogen detection at one end and electrodes at the other end. Brief description of the invention

[0010] The invention is described by the features of the independent claims. Embodiments are specified in the dependent claims.

[0011] The present invention provides energy-saving flammable gas sensors using a thermocouple design. In one aspect of the invention, a flammable gas sensor is provided. The flammable gas sensor comprises: at least one first electrode; at least one second electrode formed from a material different from that of the first electrode; and a catalytic material, particularly formed from one or more layers of nanoparticles, at an active reaction junction between the first electrode and the second electrode, wherein the active reaction junction between the first electrode and the second electrode forms a thermocouple.

[0012] In a further aspect of the invention, a detection unit is provided. The detection unit comprises: a plurality of sensors, each having at least one first electrode, at least one second electrode formed from a material different from that of the first electrode, and a catalytic material, in particular formed from one or more layers of nanoparticles, at an active reaction junction between the first electrode and the second electrode, wherein the active reaction junction between the first electrode and the second electrode forms a thermocouple. The plurality of sensors can each comprise a different catalytic material.

[0013] In yet another aspect of the invention, a method for detecting flammable gas is provided. The method comprises: providing a flammable gas sensor comprising: at least one first electrode; at least one second electrode formed from a material different from that of the first electrode; and in particular, a catalytic material formed from one or more layers of nanoparticles at an active reaction junction between the first electrode and the second electrode, wherein the active reaction junction between the first electrode and the second electrode forms a thermocouple; and measuring a voltage difference across the first electrode after the catalytic material has been exposed to the flammable gas.

[0014] A more complete understanding of the present invention, as well as further features and advantages of the present invention, will become apparent by reference to the following detailed description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic illustrating elements of the flammable gas sensor according to an embodiment of the present invention; Fig. 2 is a diagram showing the behavior of the flammable gas sensor of Fig. 1 when placed in a container with a temporary concentration of methanol vapor according to an embodiment of the present invention; Fig. 3 is a schematic illustrating a flammable gas sensor with a cold junction according to an embodiment of the present invention; Fig. 4 is an exemplary system for processing sensor data according to an embodiment of the present invention; Fig. Figure 5 is a schematic illustrating the active reaction junction surrounded by the catalytic material according to one embodiment of the present invention; Fig. 6 is a schematic diagram illustrating the operation of the present flammable gas sensor according to an embodiment of the present invention; Fig. 7 is a schematic diagram illustrating a multi-sensor unit according to an embodiment of the present invention; Fig. 8 is a diagram illustrating an exemplary data processing apparatus according to an embodiment of the present invention; Fig. 9 is a diagram illustrating an exemplary methodology for detecting a flammable gas according to an embodiment of the present invention; Fig. 10 is a schematic illustrating an exemplary configuration of the present flammable gas sensor, wherein the active reaction junction includes the first and second electrodes making contact via a porous, electrically conductive catalyst according to an embodiment of the present invention; and Fig. 11 is a schematic illustrating an exemplary configuration of the present flammable gas sensor, wherein the active reaction junction includes the first and second electrodes in direct physical and electrical contact with each other and with a non-electrically conductive catalyst according to an embodiment of the present invention. Detailed description of preferred embodiments

[0015] Provided herein is a sensor that operates at room temperature (i.e., from approximately 15°C to approximately 30°C and ranges therebetween), is sensitive to flammable gases, and operates at the microwatt (µW) energy level. As described in more detail below, the sensor operates like a thermocouple using dissimilar metals and a catalytic junction comprising surface nanoparticles to catalyze the reaction of low concentrations of flammable gases with oxygen at room temperature. Suitable catalytic nanoparticles include, but are not limited to, platinum (Pt), palladium (Pd), and ruthenium (Ru).

[0016] As used herein, the term "flammable gas" refers to hydrocarbon gases and vapors, for example, hydrogen, methane (and other alkanes), methanol, butane, propane, and natural gas.

[0017] The elements of this flammable gas sensor are Fig. 1. The present sensor uses two dissimilar metals with a gas-porous catalytic interface (as the active region) to detect flammable gas in the presence of oxygen (O 2 ), thereby releasing excess amounts of hydrogen (H 2 ), heat and ultimately the reaction products carbon dioxide (CO 2 ) and water (H 2O). According to an exemplary embodiment, the active region of the sensor forms part of a thermocouple. The formation of hydrogen and other reaction products temporarily changes the work function of the metals. In addition, heat develops from the catalysis process and, due to the dissimilar metals used in the sensor's construction, creates a detectable voltage across the electrodes. In particular, a temperature gradient within a conductor leads to an increase in an internal electric field. This is called the Seebeck effect or thermoelectric effect. See, for example, Safa Kasap, "Thermoelectric Effects in Metals: Thermocouples", An e-Booklet, pages 1-11 (2001). Based on the principle of a thermocouple, it is possible to use different (i.e.With electrode materials (e.g. having different Seebeck coefficients) it is possible to detect a net voltage difference between the first and second electrode.

[0018] As in Fig. 1, the gas sensor 100 includes a first electrode 102 and a second electrode 104 attached to an inert substrate 106. The first / second electrodes 102 and 104 may be attached to the inert substrate 106 using, for example, an adhesive such as epoxy resin.

[0019] According to an exemplary embodiment, the first electrode 102 and the second electrode 104 are each configured as strips with a high aspect ratio (a length L and a width B, where L >> B) and are attached to the inert substrate 106 such that the strips are oriented perpendicular to each other and intersect approximately at the midpoint of this strip. See Fig. 1. Furthermore, each stripe can be a thin film, which can have a thickness of, for example, approximately 1 nanometer (nm) to approximately 5 nm and ranges in between.

[0020] The first / second electrodes 102 and 104 are formed from dissimilar materials. For example, according to an exemplary embodiment, one of the (first or second) electrodes is formed from platinum (Pt) or Pt-containing alloys, while the other electrode is formed from palladium (Pd) or Pd-containing alloys. For example, the first electrode 102 is formed from Pt and the second electrode 104 is formed from Pd, or vice versa. In an exemplary embodiment, the Pt electrode (102 or 104) is an alloy of Pt and silver (Ag) to avoid hydrogen embrittlement. By way of example only, the Pt / AG alloy comprises Ag from about 20% to about 25% and regions therebetween and Pt from about 74% to about 79% and regions therebetween. Suitable materials for the inert substrate 106 include, but are not limited to, quartz, silicon dioxide, aluminum oxide, aluminum nitride, mica, boron nitride, glass, and combinations thereof.

[0021] In this exemplary embodiment, a gas-permeable catalyst is present between the first electrode 102 and the second electrode 104. The term "gas-permeable" means that the catalyst material itself is configured to be permeable to ambient gases and / or that the catalyst is supported on a material that is permeable to ambient gases. For example, the catalyst may be composed of one or more layers of catalytic nanoparticles, as described in detail below. Such nanoparticle layers are porous and thus permeable to gases. In this case, the catalyst is also electrically conductive, i.e., electrical contact can be established between the first electrode 102 and the second electrode 104 via the catalyst. Accordingly, the first electrode 102 and the second electrode 104 do not have to be in direct (physical) contact with each other (see Fig. 1) to form a thermocouple, since an electrical connection is provided via the catalyst (i.e., catalyst 108). Alternatively, the catalytic material may be supported by a porous, gas-permeable material (such as porous ceramic). In that case, the material surrounding the catalyst may not be electrically conductive; thus, direct physical / electrical contact between the first electrode 102 and the second electrode 104 is required to form a thermocouple at the active region.

[0022] In the Fig. 1, a catalytic material 108 is present between the first electrode 102 and the second electrode 104. In particular, the catalytic material 108 is present at the intersection of the intersecting first electrode 102 and second electrode 104. In this example, the catalytic material 108 makes physical and electrical contact with both the first electrode 102 and the second electrode, but the first electrode 102 does not make direct physical contact with the second electrode 104. In this example, the catalytic material 108 is electrically conductive. The catalytic material 108 is also porous / gas permeable. Thus, in this configuration, the catalytic material 108 acts as a gas permeable spacer, preventing the first and second electrodes 102 / 104 from making direct physical contact with each other. The Fig. 1 configured sensor causes a detectable voltage to be generated in the presence of a flammable gas and oxygen.

[0023] According to an exemplary embodiment, the catalytic material 108 is formed from one or more layers of nanoparticles. By way of example only, suitable nanoparticles for the sensor include, but are not limited to, Pt nanoparticles (e.g., a Pt nanopowder such as platinum black), Pd nanoparticles, and / or Ru nanoparticles. By way of example only, platinum is a strong catalyst for methane gas. See, for example, Singh et al., "Review: An Overview of Recent Development of Platinum-Based Cathode Materials for Direct Methanol Fuel Cells," Int. J. Electrochem. Sci., 9 (July 2014) 5607-5639. Palladium is a suitable catalyst for butane gas. See, for example, published U.S. patent application number 2013 / 0072738 by Jung et al. entitled “Supported Catalyst for Direct Dehydrogenation of n-Butane and Preparing Method of Butenes from n-Butane Using the Same”.Ruthenium, or ruthenium in combination with platinum and / or palladium, is a suitable catalyst for methanol. See, for example, U.S. Patent No. 6,429,167, issued to Maeno et al., entitled "Alumina-Supported Ruthenium Catalyst," and U.S. Patent No. 6,682,837, issued to Gorer, entitled "Method for Producing Electricity Using a Platinum-Ruthenium-Palladium Catalyst in a Fuel Cell." Varying the composition of the catalytic material can tune the sensitivity of the sensor to different gases. Thus, as described in detail below, embodiments are contemplated herein that utilize multiple sensors comprising different catalytic materials, thereby enabling the detection of different gases.

[0024] Layers of (e.g., Pt, Pd, and / or Ru) nanoparticles are electrically conductive and porous. As described above, electrical contact can thus be established between the first and second electrodes 102 / 104 via the catalytic material 108 without the first and second electrodes 102 / 104 being in direct physical contact with each other. Ambient gas can permeate the porous catalytic material, where it is decomposed by the catalytic material, as described above, in a reaction that generates heat. The heat is detected by the thermocouple.

[0025] The sensor 100 responds to a variety of flammable hydrocarbons, including methanol (MeOH). See, for example, Fig. 2. Fig. Figure 2 illustrates the behavior of sensor 100 in response to a temporary concentration of methanol vapor in a container. Voltages in the microvolt to millivolt range were observed in response to the presence of flammable gases such as methane, methanol, etc. In this example, the concentration of methanol vapor varied from approximately 0 parts per million (ppm) to approximately 1,000 ppm, and the corresponding sensor output voltages were in the range of 1×10 -6 Volts up to 1×10 -4 Volt. See Fig. 2. The electrical behavior of the sensor is repeatable and returns to a base voltage after exposure.

[0026] Although Pt and Pd were chosen as the electrode materials in the example above, it is worth noting that other electrode materials can be used to create dissimilar alloys useful for the flammable gas sensor, including, but not limited to, niobium (Nb), tantalum (Ta), vanadium (V), iron (Fe), nickel (Ni), and tin (Sn). As provided above, Pt nanoparticles, Pd nanoparticles, and / or Ru nanoparticles are viable options for the catalyst material.

[0027] As provided above, heat develops from the catalysis process and, due to the dissimilar metals (thermocouple) used in the electrodes, creates a detectable voltage across the first / second electrode. However, local temperature effects (such as ambient temperatures dependent on the sensor location) can contribute a thermoelectric potential to the sensor voltage. Therefore, in an alternative embodiment, the sensor described above is constructed with a reference junction to cancel the effects of local temperature. See Fig. 3.

[0028] As in Fig. 3, the sensor 300 includes two identical (i.e., formed of the same material) first electrodes 302 and 304 on an inert substrate 306. These two first electrodes 302 and 304 are parallel to each other and do not intersect. A second electrode 308 is formed perpendicular to the first electrodes 302 and 304. The second electrode 308 makes electrical and physical contact with the first electrode 302 to form a reference junction. The reference junction is very similar to a cold junction in a thermocouple circuit (see below), providing a reference reading away from the heat source.An active reaction junction (recognition site) is formed at the other first electrode 304, where catalytic material 305 is in both physical and electrical contact with the first electrode 304 and the second electrode 308 (however, the first electrode 304 and the second electrode 308 are not in contact with each other). Suitable materials for the inert substrate, the first and second electrodes, and the catalytic material have been provided above.

[0029] As also described above, a thermocouple is formed by using first / second electrodes made of dissimilar materials. For example, the first electrodes 302 and 304 may be formed of Pt, and the second electrode 308 may be formed of Pd. The intersection of the first electrode 302 and the second electrode 308 is a reference junction. The active reaction junction may be formed by placing the catalytic material (e.g., Pt, Pd, and / or Ru nanoparticles) in both physical and electrical contact with the first electrode 304 and the second electrode 308.

[0030] An electrical contact is made with electrodes 302 and 304 to measure the sensor voltage. In practice, this can be achieved by connecting the two electrical contacts to the input of a high-impedance amplifier 402. See, for example, system 400 in Fig. 4. The amplified sensor voltage is then digitized by an analog-to-digital converter 404, which is connected to a computer 406 for processing, storing, and transmitting the sensor data. An exemplary device that may be configured to serve as computer 406 is described below in connection with the description of Fig. 8 described.

[0031] With further reference to Fig. 3, any of the materials described above may be used, as long as the electrodes utilize dissimilar materials. For example, in an alternative embodiment, the material used for the first electrodes 302 and 304 may be interchanged with that used for the second electrode 308. In particular, the first electrodes 302 and 304 may be formed of Pd, while Pt forms the bridging second electrode 308.

[0032] Two electrical contacts are made with the first electrodes 302 and 304, as described above. An additional electrical contact can be made with the bridging second electrode 308 to enable independent monitoring of both the sensor and the reference junction, if desired.

[0033] For example, instead of placing the catalytic layer between the electrodes, it is also possible to surround the junction (of the electrodes) with the catalytic material. See Fig. 5. A reference junction configuration (such as the one from Fig. 3) is in Fig. 5, and identical structures are numbered accordingly. For example, the active reaction site is as in Fig. 5 (e.g., at the junction between electrode 304 and (dissimilar) electrode 308) is enclosed by the catalytic material 502, which in turn is enclosed by a porous (gas-permeable) housing 504. Contained within the housing is the reference junction (e.g., at the junction between electrode 302 and (dissimilar) electrode 308). According to an exemplary embodiment, the housing 504 is formed of (porous) alumina.

[0034] Fig. 6 is a schematic diagram 600 illustrating the operation of the present flammable gas sensor. As in Fig. 6, the sensor utilizes a thermocouple design in which, as described above, there are at least two electrodes (i.e., a first electrode and a second electrode) made of dissimilar materials (e.g., Pt and Pd or other combinations as provided above). A catalytic material (e.g., Pt, Pd, and / or Ru nanoparticles) is present at the “hot” junction of the electrodes. This catalytic material acts as a heat source for the thermocouple circuit. For example, as provided above, the heat is a byproduct of the catalysis process when a flammable gas (see Fig. 6) in the presence of oxygen at the catalytic layer into carbon dioxide (CO 2 ) and water (H 2 O) is split.

[0035] The presence of heat creates a voltage difference across the electrodes, which can be measured using a voltmeter. A junction between the electrodes away from the heat source is called a "cold junction" or "reference junction" because it can provide a measurement away from the heat source and is thus free from local temperature effects. A cold / reference junction has been used, for example, in connection with the description of Fig. 3 and Fig. 5 described above. This reference allowed for the exclusion of thermal effects from the signal. It is preferable to place the cold junction close to, but isolated from, the heat source on the same substrate.

[0036] It is important that the first / second electrodes only connect to each other at the hot and / or cold junctions; otherwise, the sensor readings would be inaccurate. Thus, mounting the sensor on an inert (i.e., electrically inert, thermoreactively inert, etc.) substrate serves to insulate the electrodes.

[0037] As provided above, different catalysts can be used in the same device to provide sensitivity to different gases. See Fig. 7. The Fig. The detection device 700 shown in Figure 7 comprises multiple iterations of the flammable gas sensor described above, i.e., Sensor A, Sensor B, Sensor C, etc., except that each sensor in the device 701 comprises a different catalytic material (i.e., Catalytic Material I, Catalytic Material II, Catalytic Material III, etc.). As described above, suitable catalytic materials for use in accordance with the present sensors include, but are not limited to, Pt nanoparticles, Pd nanoparticles, and / or Ru nanoparticles. Thus, according to an exemplary embodiment, the detection device 700 comprises at least one Sensor A having Pt nanoparticles as the catalyst, at least one Sensor B having Pd nanoparticles as the catalyst, and at least one Sensor C having Ru nanoparticles as the catalyst, i.e., as Catalytic Material I, Catalytic Material II, and Catalytic Material III, respectively.Using different catalytic materials, the device 700 is capable of detecting a variety of different gases.

[0038] With reference to Fig. Figure 8 shows a block diagram of a data processing device 800 that may be implemented according to the present techniques. For example, device 800 may be configured to serve as computer 406 in system 400.

[0039] The device 800 includes a computer system 810 and removable media 850. The computer system 810 includes a processor device 820, a network interface 825, a memory 830, a media interface 835, and an optional display 840. The network interface 825 enables the computer system 810 to connect to a network, while the media interface 835 enables the computer system 810 to interact with media such as a hard disk drive or a removable media 850.

[0040] Processor device 820 may be configured to implement the methods, steps, and functions disclosed herein. Memory 830 could be distributed or local, and processor device 820 could be distributed or a single device. Memory 830 could be implemented as electrical, magnetic, or optical memory, or any combination of these or other types of storage devices. Furthermore, the term "memory" should be broadly interpreted to encompass any information that can be read from or written to an address in addressable space accessed by processor device 820. With this definition, information on a network accessible via network interface 825 is still within memory 830 because processor device 820 can retrieve the information from the network.It should be noted that each distributed processor comprising processor device 820 generally includes its own addressable memory space. It should also be noted that part or all of computer system 810 may be incorporated into an application-specific integrated circuit or a general-purpose integrated circuit.

[0041] The optional display 840 is any type of display suitable for interaction with a human user of the device 800. Generally, the display 840 is a computer monitor or other similar display.

[0042] Fig. 9 is a schematic illustrating an exemplary methodology 900 for detecting a flammable gas and using the present sensors. In step 902, a sensor or a system of the sensors described above is provided. After the catalytic material has been exposed to a flammable gas (which generates heat as described above), the voltage difference across the electrodes is measured in step 904. Step 904 may be performed using a voltmeter. In step 906, the sensor signal is amplified (for example, using an AD8236 sense amplifier available from Analog Device, Norwood, MA). In step 908, the output of the amplifier is connected to an analog-to-digital converter, which digitizes the (amplified) signal. See also Fig. 4. The digitized signal can then be further processed, analyzed, etc., in step 910, e.g. using a computer for data processing.

[0043] A variety of different electrode and catalyst configurations are contemplated herein. For example, the basic components of the present sensor 100 include, as described in connection with the description of Fig. 1 above, first and second electrodes 102 / 104 and a catalytic material 108 at an active reaction junction between the first and second electrodes 102 / 104. The active reaction junction between the first and second electrodes 102 / 104 forms a thermocouple junction. According to the present techniques, the first and second electrodes may not have direct physical contact with each other at the active reaction junction (as in the Fig. 1, in which electrical contact between the first and second electrodes 102 / 104 is provided via the catalyst 108) or there may be direct physical as well as electrical contact between the first and second electrodes at the active reaction junction. In the former case, the catalytic material is both porous and electrically conductive. In the latter case, the catalytic material may be supported / contained in an electrically non-conductive porous material. Each of these exemplary configurations will now be described with reference to the Fig. 10 and Fig. 11 further described.

[0044] Fig. 10 illustrates the exemplary configuration in which the first and second electrodes (in this example, designated by reference numerals 1002 and 1004, respectively) make electrical contact via the catalytic material 1008. In particular, the catalytic material 1008 is present at an active reaction junction between the first electrode 1002 and the second electrode 1004 in the same manner as described above. The active reaction junction between the first electrode 1002 and the second electrode 1004 forms a thermocouple. In this example, the first electrode 1002 and the second electrode 1004 do not make direct physical contact with each other. However, the catalytic material 1008 (which is both porous and electrically conductive) makes direct physical contact with both the first electrode 1002 and the second electrode 1004.Thus, continuity is provided between the first electrode 1002 and the second electrode 1004 by the catalytic material 1008. As provided above, porous electrically conductive catalysts include, but are not limited to, layers of Pt, Pd, and / or Ru nanoparticles.

[0045] In this example, the first electrode 1002 is in electrical, thermal, and mechanical contact with the porous catalytic material 1008. The porous catalytic material 1008 is similarly in electrical, thermal, and mechanical contact with the second electrode 1004. The assembly forms a combination of thermoelectric junctions that operate as if the first electrode 1002 and the second electrode 1004 were in direct contact. The porous catalytic material 1008 allows the gas to penetrate and react, thereby increasing the junction temperature. As described above, the junction temperature is evident as a thermoelectric voltage across the first electrode 1002 and the second electrode 1004.

[0046] As highlighted above, the catalyst may be supported by a porous, electrically non-conductive material. In this case, the active reaction junction may comprise the first and second electrodes (designated, respectively, by reference numerals 1102 and 1104 in this example) in direct physical (and electrical) contact with each other at the active reaction junction. See Fig. 11. As in Fig. 11, the catalytic material 1108 is present as above at an active reaction junction between the first electrode 1102 and the second electrode 1104. The active reaction junction between the first electrode 1102 and the second electrode 1104 forms a thermocouple. In this example, the catalytic material 1108 is supported by an electrically non-conductive porous material. In particular, the catalytic material 1108 is as shown in Fig.11 shown distributed within a porous (but electrically non-conductive) material.

[0047] Accordingly, to ensure electrical contact, the first electrode 1102 and the second electrode 1104 are in direct physical and electrical contact with each other to form a direct (thermocouple) connection between the electrodes. According to an exemplary embodiment, the catalyst comprises Pt, Pd, and / or Ru nanoparticles, and the porous, electrically non-conductive material comprises porous ceramic, sintered particles, lithographically patterned nanowires, pressed nanowires, and / or any other shaped porous structures known in the art.

[0048] In this example, both the first electrode 1102 and the second electrode 1104 are in thermal and mechanical contact with the porous, electrically non-conductive material. The first electrode 1102 is in electrical, thermal, and mechanical contact with the second electrode 1104. This arrangement forms a thermocouple between the first electrode 1102 and the second electrode 1104. The porous, electrically non-conductive material allows the gas to penetrate and react with the catalytic material 1108, thereby increasing the temperature of the material. The porous, electrically non-conductive material is in thermal contact with the thermocouple junction between the electrodes.The reactions of flammable gases with the catalytic material 1108 in the porous, electrically non-conductive material thereby heats the thermocouple junction and is detected based on a thermoelectric voltage response to the junction temperature.

[0049] Although illustrative embodiments of the present invention have been described herein, it should be understood that the invention is not limited to these precise embodiments and that various changes and modifications may be made by one skilled in the art without departing from the scope of the invention.

Claims

[1] Sensor (100; 300) for flammable gases, comprising: at least one first electrode (102; 304; 302; 1002; 1102) formed of a first metal; at least one second electrode (104; 308; 1004; 1104) formed from a metal different from that of the first electrode, wherein either the first electrode or the second electrode is made of palladium, wherein the non-palladium electrode is made of a platinum-silver alloy, and wherein the platinum-silver alloy comprises silver from about 20% to about 25% and ranges therebetween and platinum from about 74% to about 79% and ranges therebetween; and a gas-permeable catalytic material (108; 305; 502; 1008; 1108) formed from one or more layers of nanoparticles at an active reaction junction between the first electrode and the second electrode, wherein the active reaction junction between the first electrode and the second electrode forms a thermocouple. [2] A flammable gas sensor according to claim 1, wherein the catalytic material is electrically conductive and porous. [3] The flammable gas sensor of claim 2, wherein the catalytic material is selected from the group consisting of: platinum nanoparticles, palladium nanoparticles, ruthenium nanoparticles, and combinations thereof. [4] A flammable gas sensor according to claim 2, wherein the first electrode is in direct physical contact with the catalytic material, wherein the second electrode is in direct physical contact with the catalytic material, and wherein the first electrode and the second electrode are not in direct physical contact at the active reaction junction. [5] A flammable gas sensor according to claim 1, wherein the catalytic material is distributed within a porous, electrically non-conductive material. [6] A flammable gas sensor according to claim 5, wherein the first electrode and the second electrode are in direct physical contact at the active reaction junction. [7] A flammable gas sensor according to claim 1, further comprising: an inert substrate to which the first electrode and the second electrode are attached. [8] The flammable gas sensor of claim 7, wherein the inert substrate comprises a material selected from the group consisting of: quartz, silicon dioxide, aluminum oxide, aluminum nitride, mica, boron nitride, glass, and combinations thereof. [9] A flammable gas sensor according to claim 7, wherein the first electrode and the second electrode are each configured as strips arranged at right angles to each other on the substrate. [10] The flammable gas sensor of claim 9, wherein the strips each have a thickness of about 1 nanometer to about 5 nanometers and ranges therebetween. [11] A flammable gas sensor according to claim 9, wherein the catalytic material is disposed between the first electrode and the second electrode such that the catalytic material is in physical contact with both the first electrode and the second electrode. [12] A flammable gas sensor according to claim 9, wherein the catalytic material encloses the first electrode and the second electrode. [13] A flammable gas sensor according to claim 9, wherein the first electrode, the second electrode and the catalytic material are encased in a porous casing. [14] A flammable gas sensor according to claim 13, wherein the porous housing comprises porous alumina. [15] A flammable gas sensor according to claim 1, further comprising: a plurality of first electrodes, wherein the second electrode bridges the plurality of first electrodes and thereby creates a plurality of connections between the plurality of first electrodes and the second electrode, and wherein one of the plurality of connections is the active reaction junction and another of the plurality of connections is the reference junction.

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