Abstract:
An electrochemical sensor system includes a filter comprising a micro-porous solid possessing a large surface area, wherein the solid porous material may contain alkaline materials and the filter is located within a container sealed with a cap, and includes a water reservoir containing water or a water-based solution and a heater disposed proximate to the water reservoir. The heater can be utilized to heat the water reservoir. This sensor system further comprises a heater and hydrogen generating chamber disposed proximate to the charcoal filter within the container. Additionally, a layer comprising water trapped within a polymer matrix can be provided wherein the layer is located below the heater and hydrogen generating chamber within the container in order to slow down water evaporation and provided extended electrochemical sensing capabilities for the electrochemical sensor system.

Description:
TECHNICAL FIELD  
       [0001]     Embodiments are generally related to sensing. Embodiments are also related to hydrogen detection. Embodiments are additionally related to sensory arrays for hydrogen detection. Embodiments are further related to electrochemical hydrogen sensors.  
       BACKGROUND OF THE INVENTION  
       [0002]     Electrochemical hydrogen (H 2 ) sensors are utilized in a number of sensing applications, including fuel cells, transformer monitoring systems, in the monitoring of chemical, petroleum, plastic, space and glass industries. An H 2  sensor can be of tremendous value in such applications, not only from a safety standpoint, but are also economically beneficial.  
         [0003]     The earliest H 2  sensors were based on palladium (Pd). Hydrogen absorbs on Pd surfaces and diffuses into its bulk, altering its electrical properties. This type of sensor, however, undergoes phase change at high H 2  concentrations. Such a scenario could result in an expansion of the Pd lattice. This problem was overcome by alloying palladium with nickel. Using Pd-Ni alloy, sensors can detect hydrogen from ppm to 100% concentrations.  
         [0004]     Such sensors, however, are affected by gases like carbon monoxide (CO), sulfur dioxide (SO 2 ), hydrogen sulfide (H 2 S), VOCs, oil vapor and the so forth. In applications such as those involving high humidity with and the presence of SO 2 , H 2 S and NO 2 , for example, Pd—Ni can become poisoned or corroded. Further, VOC and oil vapor can cause problems for Pd H 2  sensors.  
         [0005]     Electrochemical sensors could be utilized in H 2  detection and possess many advantages over conventional tin oxide based or Pd based sensors. The freezing/boiling of the water reservoir, however, limits the working temperature range of electrochemical sensors. As the temperature of the cell decreases, the chemical reaction, which the user “sees” as a signal decreases. At some point, depending upon the electrolyte, the cell current stops. Usually, upon returning to a normal temperature, the cell reactivates.  
         [0006]     If an electrochemical sensor is to be utilized in temperatures below its normal operating temperature range, the cell should be heated. In general, the lowest temperature at which a cell can be expected to function properly over long periods of time is  0 C. Additionally, there is cross-sensitivity among H 2 , CO, CH4, and C 2 H 2 , etc., which can cause false alarms.  
         [0007]     The embodiments disclosed herein therefore address the aforementioned problems associated with conventional electrochemical sensing systems.  
       BRIEF SUMMARY  
       [0008]     The following summary is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole.  
         [0009]     It is, therefore, one aspect of the present invention to provide for an improved sensor system.  
         [0010]     It is another aspect of the present invention to provide for an improved electrochemical sensor system.  
         [0011]     It is yet another aspect of the present invention to provide for a hydrogen sensor system.  
         [0012]     The aforementioned aspects of the invention and other objectives and advantages can now be achieved as described herein. In accordance with one embodiment, an electrochemical sensor system can be provided, which includes a filter comprising a micro-porous solid possessing a large surface area, wherein the filter is located within a container sealed with a cap. Such a system further can include a heater and hydrogen generating chamber disposed proximate to the charcoal filter within the container. Additionally, a layer comprising water trapped within a polymer matrix can be provided wherein the layer is located below the heater and hydrogen generating chamber within the container in order to slow down water evaporation and provided extended electrochemical sensing capabilities for the electrochemical sensor system. The water trapped within the polymer matrix generally can comprise a water-gel. Additionally, one or more hydrophobic layers can be disposed between the filter and the water-gel, which can include or be associated with an antiseptic solution.  
         [0013]     Additionally, a gas diffusion control layer can be disposed between the heater and hydrogen generating chamber and the hydrophobic layers, wherein a plurality of holes are formed from the gas diffusion control layer, which link the heater and hydrogen generating chamber to one or more of the hydrophobic layers. Additionally, one or more electrolytes and catalyst electrodes can be disposed between a first hydrophobic layer and a second hydrophobic layer. The container can be configured from nickel-plated steel. The cap can also be formed from nickel-plated steel. The micro-porous solid can posses a large surface area in a range of approximately 200 m 2 /g to 1000 m 2 /g. In applications like high humidity with presence of SO2, H2S and NO2, the hydrogen sensitive electrodes, i.e., Pd or Pd—Ni will get poisoned or corroded. Alkaline porous materials are added to the micro-porous solid to get rid of those corrosive gases before they could reach the electrodes.  
         [0014]     In another embodiment, an electrochemical sensor system can be provided, which includes a filter comprising a micro-porous solid possessing a large surface area, wherein the filter is located within a container sealed with a cap. A heater and hydrogen-generating chamber can also be disposed proximate to the charcoal filter within the container. Additionally, a water-gel layer comprising water trapped within a polymer matrix can be provided, wherein the water-gel layer is located below the heater and hydrogen-generating chamber within the container in order to slow down water evaporation and wherein the water-gel includes an antiseptic solution. One or more hydrophobic layers are also disposed between the filter and the water-gel.  
         [0015]     Additionally, a gas diffusion control layer can be disposed between the heater and hydrogen generating chamber and at least one hydrophobic layer, wherein a plurality of holes are formed from the gas diffusion control layer, which link the heater and hydrogen generating chamber to the at least on hydrophobic layer. Finally, one or more electrolyte and catalyst electrodes can be disposed between a first hydrophobic layer and a second hydrophobic layer of the at least one hydrophobic layer, thereby providing extended electrochemical sensing capabilities for the electrochemical sensor system. The container itself can comprise nickel-plated steel. The cap can also be configured from nickel-plated steel.  
         [0016]     In accordance with a third embodiment, an electrochemical sensor system can be provided, which includes an array of electrochemical sensors associated with a sensor package, wherein each sensor among the array of sensors is classified according to its response to a set of analytes and wherein each sensor is configured from a different catalyst and/or coating. Additionally, each catalyst and/or coating selected responds different to one or more members among a group of analytes thereby producing a unique signature for each analyte thereof and providing multiple electrochemical sensing capabilities thereof. An electrode(s) is also associated with each sensor of the array.  
         [0017]     The set of analytes and the electrode(s) can be selected from a list of materials respectively including, but not limited to, one or more of the following types of analytes and electrode materials: Carbon monoxide: Platinum, Ruthenium; Hydrogen Sulphide: Platinum, Gold; Oxygen: Platinum, Gold, Silver, Rhodium; Hydrogen: Palladium, Platinum, Gold; Sulphur Dioxide: Gold; and Carbon Dioxide: Platinum, Silver. The array of electrochemical sensors associated with the sensor package can include, for example, one, two, three, four or more sensors, depending upon design considerations.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate embodiments and, together with the detailed description of the invention, serve to explain the principles of the embodiments disclosed herein.  
         [0019]      FIG. 1  illustrates a sensor system, which can be implemented in accordance with one embodiment;  
         [0020]      FIG. 2  illustrates a sensor system, which can be implemented in accordance with an alternative embodiment;  
         [0021]      FIG. 3  illustrates a sensor system, which can be implemented in accordance with another embodiment; and  
         [0022]      FIG. 4  illustrates a sensor system, which can be implemented in accordance with an additional embodiment.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment of the present invention and are not intended to limit the scope of the invention.  
         [0024]      FIG. 1  illustrates a sensor system  100 , which can be implemented in accordance with one embodiment. System  100  can be implemented as an electrochemical sensor with an extended life and wide working temperature range. System  100  can include a nickel-plated steel housing  103  (e.g., a can) that encases an active charcoal filter  106  located adjacent a heater and H 2  generating chamber  118 . In such a hydrogen generating chamber  118 , the heater can heat up the metal hydrides to release hydrogen. The generated hydrogen can be used for self-testing or self-calibrating of the sensors. A pressure-releasing hole  114  can be located between or integrated with the active charcoal filter  106  and chamber  118 .  
         [0025]     One or more diffusion holes  110 ,  112  can be provided respectively adjacent charcoal filter  106  and chamber  118 . One or more larger holes  116 ,  117  can also be located near chamber  118 . A gas diffusion control layer  104  can be configured below charcoal filter  106  and chamber  118  and may be configured from a material, such as, for example, stainless steel. Holes  110 ,  112 ,  116 , and  117  can be configured from the diffusion control layer  104 .  
         [0026]     A hydrophobic layer  119  configured from example, Teflon, can be located below the diffusion control layer  104  and above a layer  120  comprising electrolyte (e.g., Nafion) and one or more catalyst electrodes. A layer  121  can be located between layer  120  and a layer  122  composed of hydrophobic Teflon. A washer  124  can be located below layer  122 . A hole  128  can be configured from washer  124 , which in turn is located above a layer  126  that can be composed of water or water/gel with an antiseptic solution. Heaters  129  and  130  can be located either inside or outside of the sensor.  
         [0027]     System  100  addresses the fact that freezing of an electrolyte/water reservoir and boiling of such an electrolyte/water reservoir limits the working temperature of electrochemical sensors. As the temperature of the cell decreases, the chemical reaction, which the user “sees” as a signal decreases. At some point, depending upon the electrolyte, the cell current stops. Usually, upon returning to a normal temperature, the cell reactivates. If an electrochemical sensor is to be utilized in temperatures below its normal operating temperature range, the cell should be heated. In general, the lowest temperature at which a cell can be expected to function properly over long periods of time is 0° C.  
         [0028]     In the configuration of system  100 , the heaters  129  or  130  can be utilized when electrochemical cells associated with system  100  are applied in temperatures below its normal operating temperatures. Water-gels, such as those located in layer  126  can be utilized to slow down waver evaporation to extend the life of sensor system  100 . Water-gels can be regarded as water trapped in a polymeric matrix. Evaporation of water is slowed by the polymer matrix and can be further slowed by the incorporation of hygroscopic materials facilitating ion movement within the gel.  
         [0029]      FIG. 2  illustrates a sensor system  200 , which can be implemented in accordance with an alternative embodiment. System  200  includes a cap  202 , which can be configured as a nickel-plated cap and located above a can  224  that can also be formed from nickel-plated steel, similar to the nickel-plated steel housing  103  depicted in  FIG. 1 . Additionally, system  200  includes a gasket  204 , which can be formed from a material such as 66-nylon. An active charcoal filter  206  is contained within cap  202 . Note that the active charcoal filter  206  of  FIG. 2  is similar to the active charcoal filter  106  depicted in  FIG. 1 . Note that although actives charcoal filters  106  and  206  are depicted respectively in  FIGS. 1-2 , such filters can be  
         [0030]     A gas diffusion control stainless film  208  can be disposed below cap  202  above a hydrophobic Teflon membrane  214 ,  220 , while surrounding a proton exchange membrane  216  (i.e. with a catalyst). A layer  218  can also be provided, which can be, for example, water or water-gel (with an antiseptic solution).  
         [0031]     System  200  can be implemented in accordance with common materials for physical sorption, such as activated charcoal, silica, alumina gels, zeolites, porous polymers (e.g., Tenax, XAD, Chromosorb). Adsorbents tend to be micro-porous solids processing large surface areas (e.g., 200 to 1000 m2g). A high degree of discrimination can be achieved by the use of size-specific materials, having a controlled pore size slightly larger than the kinetic diameter of the desired analyte. Such a configuration excludes all larger species form the pores entirely. Molecules significantly smaller than the chosen analyte though are able to fit into the pores, and possess smaller interaction energy due to the size mismatch.  
         [0032]      FIG. 3  illustrates a sensor system  300 , which can be implemented in accordance with another embodiment. System  300  includes two electrodes  308 ,  310  that border an electrolyte (e.g., Nafion) membrane  302 . Note the electrolyte membrane  302  and electrodes  308 ,  310  form a layer, which is analogous to layer  120  of  FIG. 1 . Thus, electrodes  308 ,  310  can function as catalyst electrodes. A polymer selective permeable filter (e.g., Gore-Tex or carbel coating)  306  can be positioned adjacent electrode  310 . Similarly, a polymer selective permeable filter (e.g., Gore-Tex or carbel coating  304 ) can be located adjacent electrode  308 .  
         [0033]     A suggested width of the filter  306  layer can be, for example, 0.3 mm, while a suggested width of the electrode  308 ,  310  can be, for example, 0.05 mm. A suggested width of the membrane  302  can be, for example, 0.06 mm. Note that such widths are suggestions only and it can be appreciated that such values can vary, depending upon particular embodiments and design considerations.  
         [0034]      FIG. 4  illustrates a sensor system  400 , which can be implemented in accordance with an additional embodiment. System  400  can be implemented as a sensor package in which a heater, such as, for example, the heater  130  depicted in  FIG. 1 , can be located within this multiple-sensor system  400 . System  400  can thus be utilized to implement systems  100 - 300  depicted and described herein. System  400  additionally includes a plurality of electrochemical sensors  402 ,  404 ,  406 ,  408 , which can be implemented, for example, in accordance with the embodiments of sensors  100 ,  200 ,  300  of  FIGS. 1, 2 ,  3 .  
         [0035]     Thus, for example, system  400  can include individual sensors  402 ,  404 ,  406 ,  408 , each of which is embodied as, for example, system  100 , including the nickel-plated steel housing  103  (e.g., a can) that encases an active charcoal filter  106  located adjacent a heater and H 2  generating chamber  118 , the pressure-releasing hole  114  located between or integrated with the active charcoal filter  106  and chamber  118 , one or more diffusion holes  110 ,  118  and so forth.  
         [0036]     System  400  is directed toward the fact that hydrogen sensors are utilized for fuel cell and transformer monitoring, but cross-sensitivity among H2, CO, CH4, C2H2 and the like can cause false alarms. Thus, the sensors  402 ,  404 ,  406 ,  408  are arranged as an array configuration. The selectivity of sensor system  400  takes advantage of chemo-metrics. A minimum number of sensors for system  400  can be utilized. Sensors exhibiting similar responses are preferably eliminated.  
         [0037]     A selection of one or more of sensors  402 ,  404 ,  406 ,  408  is preferably based on its sensitivity, selectivity, stability and/or cost. Improvements are achieved by utilizing selective permeable filters. Interferences, however, may not always be known prior to the use of sensors. Thus, applications that require the simultaneous monitoring for multiple analytes require multiple sensors. In such cases, an array of sensors  402 ,  404 ,  406 ,  408 , each bearing a catalyst/coating with a different degree of selectivity for the analytes of interest, can be implemented.  
         [0038]     In terms of pattern-recognition analysis, a sensor can be classified according to its response to a set of analytes. Each sensor  402 ,  404 ,  406 ,  408  of the array of sensors depicted in  FIG. 4  can be designed with a different catalyst/coating, wherein each catalyst/coating is selected to respond differently to the members of a set of analytes. The combination of responses thereof should produce a unique “fingerprint” for each analyte.  
         [0039]     In general, system  400  includes an array of electrochemical sensors  402 ,  404 ,  406 ,  408  associated with a sensor package  401 , wherein each sensor  402 ,  404 ,  406 ,  408  of the array is classified according to its response to a set of analytes. Additionally, each sensor is configured from a different catalyst and/or coating. Note that each catalyst and/or coating selected responds differently to one or more members among a group of analytes thereby producing a unique signature for each analyte thereof and providing multiple electrochemical sensing capabilities for sensor system  400 .  
         [0040]     The efficiency of the array of sensors  402 ,  404 ,  406 ,  408  depends on the uniqueness of the catalyst/coating responses thereof. A suggested list of analyte/electrode materials, which can be utilized in accordance with system  400 , include, for example, the following: 
        Carbon monoxide: Platinum, Ruthenium     Hydrogen Sulphide: Platinum, Gold     Oxygen: Platinum, Gold, Silver, Rhodium     Hydrogen: Palladium, Platinum, Gold     Sulphur Dioxide: Gold     Carbon Dioxide: Platinum, Silver        
 
         [0047]     Although four sensors  402 ,  404 ,  406 ,  408  are illustrated in  FIG. 4 , it can be appreciate that an embodiment be implemented in an array configuration in which only two such sensors are utilized. Thus, in one embodiment of  FIG. 4 , a two sensor array can be implemented, wherein one sensor is more sensitive to H 2 , but less to CO, while the other sensor is more sensitive to CO, and less to H 2 . In such an embodiment, the first sensors can be implemented as a Pt electrode Nafion-based sensor, while the second sensor can be implemented as a Pd electrode Nafion-based sensor. Both such sensors can be equipped with self-test calibration features. Because the first and second sensors possess cross-sensitivity with H 2  and CO, the response from both sensors will be used to determine the concentration of H 2  and CO.  
         [0048]     In such an embodiment, the Pt electrode can possess an H 2  equivalent of 25% CO, and the Pd electrode can possess an H 2  equivalent of 150% CO. Thus, if the reading from the first sensor to the second sensor is A and B, respectively, the H 2  and CO concentrations can be determined according to the following formulation (assuming H 2  and CO concentrations are X and Y ppm): 
 
From Pt electrode: 0.25X+Y=A 
 
From Pd electrode: X+0.67Y=B 
 
         [0049]     The description as set forth is not intended to be exhaustive or to limit the scope of the invention. Many modifications and variations are possible in light of the above teaching without departing from the scope of the following claims. It is contemplated that the use of the present invention can involve components having different characteristics. It is intended that the scope of the present invention be defined by the claims appended hereto, giving full cognizance to equivalents in all respects.