Patent Publication Number: US-2011053008-A1

Title: Water vapor transfer membrane and paper integrated assembly

Description:
TECHNICAL FIELD 
     The invention relates to a fuel cell and more particularly to humidification of fuel cells. 
     BACKGROUND 
     Fuel cells are used as an electrical power source in many applications. In particular, fuel cells are proposed for use in automobiles to replace internal combustion engines. A commonly used fuel cell design uses a solid polymer electrolyte (“SPE”) membrane or proton exchange membrane (“PEM”), to provide ion transport between the anode and cathode. 
     In proton exchange membrane type fuel cells, hydrogen is supplied to the anode as fuel and oxygen is supplied to the cathode as the oxidant. The oxygen can either be in pure form (O 2 ) or air (a mixture of O 2  and N 2 ). PEM fuel cells typically have a membrane electrode assembly (“MEA”) in which a solid polymer membrane has an anode catalyst on one face, and a cathode catalyst on the opposite face. The anode and cathode layers of a typical PEM fuel cell are formed of porous conductive materials, such as woven graphite, graphitized sheets, or carbon paper to enable the fuel to disperse over the surface of the membrane facing the fuel supply electrode. Each electrode has finely divided catalyst particles (for example, platinum particles), supported on carbon particles, to promote oxidation of hydrogen at the anode and reduction of oxygen at the cathode. Protons flow from the anode through the ionically conductive polymer membrane to the cathode where they combine with oxygen to form water, which is discharged from the cell. The MEA is sandwiched between a pair of porous gas diffusion layers (“GDL”), which in turn are sandwiched between a pair of non-porous, electrically conductive elements or plates. The plates function as current collectors for the anode and the cathode, and contain appropriate channels and openings formed therein for distributing the fuel cell&#39;s gaseous reactants over the surface of respective anode and cathode catalysts. In order to produce electricity efficiently, the polymer electrolyte membrane of a PEM fuel cell must be thin, chemically stable, proton transmissive, non-electrically conductive and gas impermeable. In typical applications, fuel cells are provided in arrays of many individual fuel cell stacks in order to provide high levels of electrical power. 
     The internal membranes used in fuel cells are typically maintained in a moist condition. This helps avoid damage to or a shortened life of the membranes, as well as to maintain the desired efficiency of operation. For example, lower water content of the membrane leads to a higher proton conduction resistance, thus resulting in a higher ohmic voltage loss. The humidification of the feed gases, in particular the cathode inlet, is desirable in order to maintain sufficient water content in the membrane, especially in the inlet region. Humidification in a fuel cell is discussed in commonly owned U.S. patent application Ser. No. 10/797,671 to Goebel et al.; commonly owned U.S. patent application Ser. No. 10/912,298 to Sennoun et al.; and commonly owned U.S. patent application Ser. No. 11/087,911 to Forte, each of which is hereby incorporated herein by reference in its entirety. 
     To maintain a desired moisture level, an air humidifier is frequently used to humidify the air stream used in the fuel cell. The air humidifier normally consists of a round or box type air humidification module that is installed into a housing of the air humidifier. Examples of this type of air humidifier are shown and described in U.S. patent application Ser. No. 10/516,483 to Tanihara et al., and U.S. Pat. No. 6,471,195, each of which is hereby incorporated herein by reference in its entirety. 
     Membrane humidifiers have also been utilized to fulfill fuel cell humidification requirements. For the automotive fuel cell humidification application, such a membrane humidifier needs to be compact, exhibit low pressure drop, and have high performance characteristics. 
     Designing a membrane humidifier requires a balancing of mass transport resistance and pressure drop. To transport water from wet side to dry side through a membrane, water molecules must overcome some combination of the following resistances: convectional mass transport resistance in the wet and dry flow channels; diffusion transport resistance through the membrane; and diffusion transport resistance through the membrane support material. Compact and high performance membrane humidifiers typically require membrane materials with a high water transport rate (i.e. GPU in the range of 10,000-16,000). GPU or gas permeation unit is a partial pressure normalized flux where 1 GPU=10 −6  cm 3  (STP)/(cm 2  sec cm Hg). As a result, minimizing the transport resistance in the wet and dry flow channels and the membrane support material becomes a focus of design. 
     Accordingly, there is a need for improved materials and methodologies for humidifying fuel cells. 
     SUMMARY OF THE INVENTION 
     The present invention solves one or more problems of the prior art by providing in at least one embodiment a membrane humidifier assembly. The membrane humidifier assembly includes a first flow field plate adapted to facilitate flow of a first gas thereto and a second flow field plate adapted to facilitate flow of a second gas thereto. A polymeric membrane is disposed between the first and second flow fields. A first diffusion layer is disposed between first flow field plate and the polymeric membrane. A second diffusion layer is disposed between second flow field plate and the polymeric membrane. The polymeric membrane is adapted to permit transfer of water between the first flow field plate and the second flow field plate. The polymeric membrane includes a polymeric substrate and a polymer layer disposed on the polymeric substrate. The polymeric layer adhered to the first diffusion layer. The polymer layer characteristically includes a first polymer having fluorinated cyclobutyl groups disposed on the polymeric substrate. 
     Other exemplary embodiments of the invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while disclosing exemplary embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  provides a schematic of a fuel cell system including a membrane humidifier assembly for humidifying a cathode inlet airflow to a fuel cell stack; 
         FIG. 2A  is a schematic cross section of a membrane humidifier assembly perpendicular to the flow of gas to a first flow field plate; 
         FIG. 2B  is a cross section of a membrane humidifier assembly with a peripheral sealing edge; 
         FIG. 3  is a schematic cross section of a membrane humidifier assembly perpendicular to the cross section of  FIG. 2A ; 
         FIG. 4  is a schematic cross section of a variation of a membrane humidifier assembly perpendicular to the flow of gas to a first flow field plate; 
         FIG. 5  is a flow chart illustrating the preparation of a polymeric membrane useful in a membrane humidifier; 
         FIG. 6A  is a schematic cross section of a polymer membrane comprising a single layer; 
         FIG. 6B  is a schematic cross section of a diffusion layer coated with a polymeric layer; 
         FIG. 6C  is a schematic cross section of a diffusion layer with a microporous layer coated with a polymeric layer; 
         FIG. 6D  is a schematic cross section of a diffusion layer coated with a polymeric layer disposed over a substrate; 
         FIG. 6E  is a schematic cross section of a substrate coated with a selective polymeric layer disposed over a diffusion layer coated with a microporous layer; 
         FIG. 6F  is a schematic cross section of a substrate coated with a selective polymeric layer disposed over a diffusion layer; and 
         FIG. 7  is a bar chart providing performance results for humidifiers incorporating embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Reference will now be made in detail to presently preferred compositions, embodiments and methods of the present invention, which constitute the best modes of practicing the invention presently known to the inventors. The Figures are not necessarily to scale. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for any aspect of the invention and/or as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     Except in the examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred. Also, unless expressly stated to the contrary: percent, “parts of,” and ratio values are by weight; the term “polymer” includes “oligomer,” “copolymer,” “terpolymer,” and the like; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among the constituents of a mixture once mixed; the first definition of an acronym or other abbreviation applies to all subsequent uses herein of the same abbreviation and applies mutatis mutandis to normal grammatical variations of the initially defined abbreviation; and, unless expressly stated to the contrary, measurement of a property is determined by the same technique as previously or later referenced for the same property. 
     It is also to be understood that this invention is not limited to the specific embodiments and methods described below, as specific components and/or conditions may, of course, vary. Furthermore, the terminology used herein is used only for the purpose of describing particular embodiments of the present invention and is not intended to be limiting in any way. 
     It must also be noted that, as used in the specification and the appended claims, the singular form “a,” “an,” and “the” comprise plural referents unless the context clearly indicates otherwise. For example, reference to a component in the singular is intended to comprise a plurality of components. 
     Throughout this application, where publications are referenced, the disclosures of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this invention pertains. 
     With reference to  FIG. 1 , a schematic of a fuel cell system incorporating a membrane humidifier assembly is provided. Fuel cell system  10  includes fuel cell stack  12 . Compressor  14  provides a flow of air to the cathode side of the stack  12  on a cathode input line  16 . The flow of air from the compressor  14  is sent through membrane humidifier assembly  18  to be humidified. A cathode exhaust gas is output from the stack  12  on a cathode output line  20 . The cathode exhaust gas includes a considerable amount of water vapor and/or liquid water as a by-product of the electrochemical process in the fuel cell stack  12 . As is well understood in the art, the cathode exhaust gas can be sent to membrane humidifier assembly  18  to provide the humidification for the cathode inlet air on the line  16 . 
     With reference to  FIGS. 2A ,  2 B, and  3 , schematic cross sections of a membrane humidifier assembly are provided. The membrane humidifier of this embodiment may be used in any application in which it is desirable to transfer water from a wet gas to a dry gas such as the fuel cell system of  FIG. 1 .  FIG. 2A  is a cross section of a membrane humidifier assembly perpendicular to the flow at which dry gas is introduced.  FIG. 2B  is a cross section of a membrane humidifier assembly with a peripheral sealing edge.  FIG. 3  is a cross section of a membrane humidifier assembly perpendicular to the cross section of  FIG. 2A . Membrane humidifier assembly  18  includes first flow field plate  22  adapted to facilitate flow of a first gas to membrane humidifier assembly  18 . Membrane humidifier assembly  18  also includes second flow field plate  24  adapted to facilitate flow of a second gas thereto. In a refinement, first flow field plate  22  is a wet plate and second flow field plate  24  is a dry plate. Polymeric membrane  26  is disposed between the first flow field plate  22  and second flow field plate  24 . In one variation, polymeric membrane  26  includes polymeric substrate  30  and selective polymeric layer  32 . In a refinement, polymeric substrates  30  spatially vary in hydrophilicity and strength to capitalize on the pressure difference in humidifier assembly  18  and water vapor transfer. These substrates can also be customized for the adhesive used in the final device manufacturing. In another refinement, selective polymeric layer  32  spatially varies in composition yielding different strength and water vapor transfer characteristics. Selective polymeric layer  32  includes a polymer having fluorinated cyclobutyl groups (e.g., perfluorocyclobutyl groups) as set forth below in more detail. In a refinement of the present embodiment, polymeric membrane  26  has a permeance of equal to or greater than 6000 GPU, and typically in the range of 6000-16,000 GPU. Polymeric membrane  26  is adapted to permit transfer of water from the first gas to the second gas. For the embodiment shown and described herein, the membrane humidifier assembly  18  for a cathode side of the fuel cell is described. However, it is understood that the membrane humidifier assembly  18  can be used for an anode side of the fuel cell or otherwise as desired. It should be appreciated that in a variation, a membrane humidifier assembly is provided in which the membrane of U.S. Pat. Appl. No. 2008/0001313 is replaced by polymeric membrane  26 . The entire disclosure of this patent application is hereby incorporated herein by reference. 
     First flow field plate  22  includes a plurality of flow channels  36  formed therein. The channels  36  are adapted to convey a wet gas from the cathode of the fuel cell to an exhaust (not shown). In a refinement of the present embodiment, channels  36  are characterized by a width W CW  and a depth H CW . A land  38  is formed between adjacent channels  36  in flow field plate  22 . The land  38  includes a width W LW . It should be appreciated that any conventional material can be used to form the first flow field plate  22 . Examples of useful materials include, but are not limited to, steel, polymers, and composite materials, for example. 
     Second flow field plate  24  includes a plurality of flow channels  40  formed therein. The channels  40  are adapted to convey a dry gas from a source of gas (not shown) to the cathode of the fuel cell. As used herein, wet gas means a gas such as air and gas mixtures of O 2 , N 2 , H 2 O, H 2 , and combinations thereof, for example, that includes water vapor and/or liquid water therein at a level above that of the dry gas. Dry gas means a gas such as air and gas mixtures of O 2 , N 2 , H 2 O, and H 2 , and combinations thereof, for example, absent water vapor or including water vapor and/or liquid water therein at a level below that of the wet gas. It is understood that other gases or mixtures of gases can be used as desired. Channels  40  include a width W CD  and a depth H CD . A land  42  is formed between adjacent channels  40  in second flow field plate  24 . The land  42  includes a width W LD . It should be appreciated that any conventional material can be used to form the dry plate  24  such as steel, polymers, and composite materials, for example. 
     In a refinement of the present embodiment, W CW  and W CD  are each independently from about 0.5 mm to about 5 mm. In another refinement, W LW  and W LD  are each independently from about 0.5 mm to about 5 mm. In still another refinement, H CW  and H CD  are each independently from about 0.1 to about 0.5 mm. In another refinement, H CW , H CD  are each about 0.3 mm. 
     Still referring to  FIGS. 2A ,  2 B, and  3 , a diffusion medium or diffusion layer  44  is disposed adjacent the first flow field plate  22  and abuts the lands  38  thereof. Similarly, a diffusion medium or diffusion layer  46  is disposed adjacent the dry side plate  24  and abuts the lands  42  thereof. Selective polymer layer  32  is adhered to diffusion layer  44 . In one refinement, selective polymer layer  32  is adhered to diffusion layer  44  by penetration of polymer layer  32  into diffusion layer  44 . The diffusion media  44 ,  46  are formed from a resilient and gas permeable material such as carbon fabric, paper, polyester and glass fiber, for example. In a refinement of the present invention, diffusion media  44 ,  46  each independently have a thickness from about 0.05 to about 0.2 mm. In another variation, media  44 ,  46  each independently have a thickness from about 0.05 to about 0.15 mm. In still another variation, media  44 ,  46  each independently have porosity in the range of 50-95%. In yet another variation, media  44 ,  46  each independently have porosity from about 79 to about 90%. In another refinement, diffusion media  44 ,  46  are characterized by pores having a pore size from about 0.01 to about 100 micrometers. In another refinement, the pore size is from about 1 to about 50 micrometers. To mitigate against intrusion of the diffusion media  44 ,  46  into the channels  36 ,  40 , which results in higher pressure drops in the channels  36 ,  40 , it is desirable for the diffusion media  44 ,  46  to have a modulus of elasticity larger than 40,000 kPa, and more desirable to for the modulus to be larger than 100,000 kPa. 
     In another variation as set forth in  FIG. 2B , the first flow field plate  22  includes peripheral sealing section  52  and the second flow field plate  24  includes peripheral sealing section  54 . In a refinement, sealing surface  52  completely surrounds flow field plate  22  and sealing surface  52  completely surrounds flow field plate  24 . 
     Membrane humidifier assembly  18  advantageously allows the transfer of water from wet side channels  36  to the dry side channels  40 . Although operation of the present invention is not restricted to any particular theory of operation, several transport modes are believed to be involved in the functioning of membrane humidifier assembly  18 . Convection mass transport of water vapor occurs in the channels  36 ,  40  while diffusion transport occurs through the diffusion media  44 ,  46 . Water vapor is also transported by diffusion through the polymeric membrane  26 . Additionally, if a pressure differential exists between the channels  36  and channels  40 , water is transferred through polymeric membrane  26  by hydraulic forces. Temperature differences between the channels  36  and channels  40  may also affect the transport of water. Finally, there is also an enthalpy exchange between the channels  36  of the wet side plate  22  and the channels  40  of the dry side plate  24 . 
     During operation, the wet gas is caused to flow through the channels  36  formed in first flow field plate  22 . The wet gas is received from a supply of wet gas. Any conventional means can be used to deliver the wet gas to the channels  36  such as a supply header in communication with the channels  36 , for example. In the embodiment depicted in  FIG. 1 , the wet gas is supplied from an exhaust stream from fuel cell stack  12 . The wet gas exits the channels  36  to the exhaust. The dry gas is caused to flow through the channels  40  formed in second flow field plate  24 . Any conventional means can be used to deliver the dry gas to the channels  40  such as a supply header in communication with the channels  40 , for example. The dry gas then exits the channels  40 . In the embodiment depicted in  FIG. 1 , the dry gas is supplied from compressor  14  (not shown). 
     In a variation of the present embodiment, the temperature of the wet gas is typically lower than the temperature of the dry gas. The temperature of the dry air from the compressor may be about 180 degrees Celsius, and the temperature of the wet air from the fuel cell exhaust may be about 80-95 degrees Celsius. If an air cooler (not shown) is used to cool the dry air supplied from the compressor, the temperature may be in the range of 95-105 degrees Celsius. It is understood that other temperature ranges can be used without departing from the scope and spirit of the invention. As a result of the temperature difference between the wet gas and the dry gas, the dry gas is also cooled during the humidification thereof. The cooling effect also increases the relative humidity of the newly humidified gas (the dry gas), thus minimizing a drying effect of the gas on components of the fuel cell. 
     During flow of the wet gas through the channels  36  and the flow of the dry gas through the channels  40 , the wet gas is in cross flow with the dry gas. It is understood that a counter-flow of the gas streams can also be used to facilitate a transport of water vapor from wet gas stream to the dry gas stream. For a fuel cell humidification application, the water transfer effectiveness requirement is typically low. As a result, there is little expected performance difference between counter-flow and cross-flow design. 
     It is useful to characterize the construction of membrane humidifier assembly  18  by defining a channel area ratio AR c  by the following equation: 
       AR c   =W   C /( W   C   +W   L ) 
     where W c  is a channel width and W L  is a channel depth. In a variation, the channel area ratios AR c  are in the range of 75-85% with a channel width W c  of between 0.5 mm and 5 mm and channel depths between 0.1 mm and 0.5 mm. Such channel area ratios AR c  and channel widths W c  are chosen to maximize a membrane area utilization under the lands  38 ,  42  and minimize the intrusion of the membrane  26  or other structures into the flow channels  36 ,  40 . In a refinement, flow of gas through the channels  36 ,  40  is laminar thereby minimizing the pressure drop through the channels  36 ,  40  while maximizing the water vapor transport through the diffusion media  44 ,  46  and the membrane  26 . In another variation, the flow is turbulent through channels  36 ,  40 . 
     With reference to  FIG. 4 , a variation of a membrane humidifier assembly is provided.  FIG. 4  is a cross section of a membrane humidifier assembly perpendicular to the flow at which dry gas is introduced. Membrane humidifier assembly  18  includes first flow field plate  22  adapted to facilitate flow of a first gas to membrane humidifier assembly  18 . Membrane humidifier assembly  18  also includes second flow field plate  24  adapted to facilitate flow of a second gas thereto. In a refinement, first flow field plate  22  is a wet plate and second flow field plate  24  is a dry plate. 
     Polymeric membrane  26  is disposed between the first flow field plate  22  and second flow field plate  24 . In the present variation, polymeric membrane  26  includes polymeric substrate  30  and selective polymeric layers  32 ,  33 . In a refinement, polymeric substrate  30  spatially varies in hydrophilicity and strength to capitalize on the pressure difference in humidifier assembly  18  and water vapor transfer. These substrates can also be customized for the adhesive used in the final device manufacturing. In another refinement, selective polymeric layers  32 ,  33 —spatially vary in composition yielding different strength and water vapor transfer characteristics. Selective polymeric layers  32 ,  33  each independently include a polymer having perfluorocyclobutyl groups as set forth below in more detail. 
     Diffusion medium or diffusion layer  44  is disposed adjacent the first flow field plate  22  and abuts the lands  38  thereof. Diffusion layer  44  may contain microporous layer (“MPL”) (not shown). Similarly, a diffusion medium or diffusion layer  46  is disposed adjacent the dry side plate  24  and abuts the lands  42  thereof. Selective polymer layer  32  is adhered to diffusion layer  44  while selective polymer layer  33  is adhered to substrate  30 . In one refinement, selective polymer layer  32  is adhered to diffusion layer  44  by penetration of polymer layer  32  into diffusion layer  44  or microporous layer  50  (not shown) on diffusion layer  44 . In a refinement of the present embodiment, polymeric membrane  26  has a permeance of equal to or greater than 6000 GPU, and typically in the range of 6000-16,000 GPU. 
     Polymeric membrane  26  is adapted to permit transfer of water from the first gas to the second gas. For the embodiment shown and described herein, the membrane humidifier assembly  18  for a cathode side of the fuel cell is described. However, it is understood that the membrane humidifier assembly  18  can be used for an anode side of the fuel cell or otherwise as desired. It should be appreciated that in a variation, a membrane humidifier assembly is provided in which the membrane of U.S. Pat. Appl. No. 2008/0001313 is replaced by polymeric membrane  26 . The entire disclosure of this patent application is hereby incorporated herein by reference. Membrane humidifier assembly  18  also includes diffusion media  44 ,  46  as set forth above. Moreover, the construction of first flow field plate  22  and second flow field plate  24  is the same as that set forth above. 
     With reference to  FIG. 5 , a schematic flow chart illustrating a method of forming the polymeric membranes set forth above is provided. Assembly methods can vary to optimize cost, durability, and performance. Layers can be annealed individually or together. Layers can be wet or dry hot pressed. In this variation, polymeric substrate  30  is coated with a liquid precursor to polymeric layer  32 . Polymeric layer  32  at least partially penetrates into substrate  32 . Similarly, diffusion layer  44  is coated with a liquid precursor to polymeric layer  33 . Polymeric layer  33  at least partially penetrates into diffusion layer  44 . Polymeric substrate  30  includes sufficient porosity so that the liquid precursors to polymer layers  32 ,  33  are imbibed therein during formation. Therefore, polymeric substrate  30  is characterized by a predetermined void volume. Typically, the void volume is from 30 volume percent to 95 volume percent of the total volume of the substrates. Polymeric substrate  30  may be formed from virtually any polymeric material having the requisite void volume. Expanded polytetrafluoroethane (ePTFE) is particularly useful for this application. 
     As set forth above, polymeric layers  32 ,  33  each include a polymer having perfluorocyclobutyl groups. As set forth above, polymeric membrane  26  includes a first polymer having perfluorocyclobutyl groups. Suitable polymers having cyclobutyl moieties are disclosed in U.S. Pat. Pub. No. 2007/0099054, U.S. patent application Ser. No. 12/197,530 filed Aug. 25, 2008; Ser. No. 12/197,537 filed Aug. 25, 2008; Ser. No. 12/197,545 filed Aug. 25, 2008; and Ser. No. 12/197,704 filed Aug. 25, 2008; the entire disclosures of which are hereby incorporated by reference. In a variation, the first polymer has a polymer segment comprising polymer segment 1: 
       E 0 -P 1 -Q 1 -P 2    1
 
     wherein: 
     E o  is a moiety having a protogenic group such as —SO 2 X, —PO 3 H 2 , —COX, and the like; 
     P 1 , P 2  are each independently absent, —O—, —S—, —SO—, —CO—, —SO 2 —, —NH—, NR 2 —, or —R 3 —, 
     R 2  is C 1-25  alkyl, C 1-25  aryl or C 1-25  arylene; 
     R 3  is C 1-25  alkylene, C 1-25  perfluoroalkylene, perfluoroalkyl ether, alkylether, or C 1-25  arylene; 
     X is an —OH, a halogen, an ester, or 
     
       
         
         
             
             
         
       
     
     R 4  is trifluoromethyl, C 1-25  alkyl, C 1-25  perfluoroalkylene, C 1-25  aryl, or E 1 (see below); and 
     Q 1  is a fluorinated cyclobutyl moiety. In a refinement, polymer segment 1 is repeated 1 to 10,000 times. 
     In variation of the present invention, the first polymer comprises polymer segments 2 and 3: 
       [E 1 (Z 1 ) d ]-P 1 -Q1-P 2    2
 
       E 2 -P 3 -Q 2 -P 4    3
 
     wherein: 
     Z 1  is a protogenic group such as —SO 2 X, —PO 3 H 2 , —COX, and the like; 
     E 1  is an aromatic containing moiety; 
     E 2  is an unsulfonated aromatic-containing and/or aliphatic-containing moiety; 
     X is an —OH, a halogen, an ester, or 
     
       
         
         
             
             
         
       
     
     d is the number of Z 1  attached to E 1 ; 
     P 1 , P 2 , P 3 , P 4  are each independently absent, —O—, —S—, —SO—, —CO—, —SO 2 —, —NH—, NR 2 —, or —R 3 —; 
     R 2  is C 1-25  alkyl, C 1-25  aryl, or C 1-25  arylene; 
     R 3  is C 1-25  alkylene, C 1-25  perfluoroalkylene, perfluoroalkyl ether, alkylether, or C 1-25  arylene; 
     R 4  is trifluoromethyl, C 1-25  alkyl, C 1-25  perfluoroalkylene, C 1-25  aryl, or another E 1  group; and 
     Q 1 , Q 2  are each independently a fluorinated cyclobutyl moiety. In one refinement, d is equal to the number of aromatic rings in E 1 . In another refinement, each aromatic ring in E 1  can have 0, 1, 2, 3, or 4 Z 1  groups. 
     In another variation of the present embodiment, the first polymer comprises segments 4 and 5: 
     
       
         
         
             
             
         
       
     
     wherein: 
     Z 1  is a protogenic group such as —SO 2 X, —PO 3 H 2 , —COX, and the like; 
     E 1 , E 2  are each independently an aromatic-containing and/or aliphatic-containing moiety; 
     X is an —OH, a halogen, an ester, or 
     
       
         
         
             
             
         
       
     
     d is the number of Z 1  attached to R 8 ; 
     P 1 , P 2 , P 3 , P 4  are each independently absent, —O—, —S—, —SO—, —CO—, —SO 2 —, —NH—, NR 2 —, or —R 3 —; 
     R 2  is C 1-25  alkyl, C 1-25  aryl or C 1-25  arylene; 
     R 3  is C 1-25  alkylene, C 1-25  perfluoroalkylene, perfluoroalkyl ether, alkylether, or C 1-25  arylene; 
     R 4  is trifluoromethyl, C 1-25  alkyl, C 1-25  perfluoroalkylene, C 1-25  aryl, or another E 1  group; 
     R 8 (Z 1 ) d  is a moiety having d number of protogenic groups; and 
     Q 1 , Q 2  are each independently a fluorinated cyclobutyl moiety. In a refinement of this variation, R 8  is C 1-25  alkylene, C 1-25  perfluoroalkylene, perfluoroalkyl ether, alkylether, or C 1-25  arylene. In one refinement, d is equal to the number of aromatic rings in R 8 . In another refinement, each aromatic ring in R 8  can have 0, 1, 2, 3, or 4 Z 1  groups. In still another refinement, d is an integer from 1 to 4 on average; 
     In another variation of the present embodiment, the first polymer comprises segments 6 and 7: 
       E 1 (SO 2 X) d -P 1 -Q 1 -P 2    6
 
       E 2 -P 3 -Q 2 -P 4    7
 
     connected by a linking group L 1  to form polymer units 8 and 9: 
     
       
         
         
             
             
         
       
     
     wherein: 
     Z 1  is a protogenic group such as —SO 2 X, —PO 3 H 2 , —COX, and the like; 
     E 1  is an aromatic-containing moiety; 
     E 2  is an unsulfonated aromatic-containing and/or aliphatic-containing moiety; 
     L 1  is a linking group; 
     X is an —OH, a halogen, an ester, or 
     
       
         
         
             
             
         
       
     
     d is a number of Z 1  functional groups attached to E 1 ; 
     P 1 , P 2 , P 3 , P 4  are each independently absent, —O—, —S—, —SO—, —SO 2 —, —CO—, —NH—, NR 2 —, or —R 3 —, and 
     R 2  is C 1-25  alkyl, C 1-25  aryl or C 1-25  arylene; 
     R 3  is C 1-25  alkylene, C 1-25  perfluoroalkylene, or C 1-25  arylene; 
     R 4  is trifluoromethyl, C 1-25  alkyl, C 1-25  perfluoroalkylene, C 1-25  aryl, or another E 1  group; 
     Q 1 , Q 2  are each independently a fluorinated cyclobutyl moiety; 
     i is a number representing the repetition of polymer segment 6 with i typically from 1 to 200; and
         j is a number representing the repetition of a polymer segment 7 with j typically being from 1 to 200. In one refinement, d is equal to the number of aromatic rings in E 1 . In another refinement, each aromatic ring in E 1  can have 0, 1, 2, 3, or 4 Z 1  groups. In still another refinement, d is an integer from 1 to 4 on average.       

     In still another variation of the present embodiment, the first polymer comprises polymer segments 10 and 11: 
       E 1 (Z 1 ) d -P 1 -Q 1 -P 2    10
 
       E 2 (Z 1 ) f -P 3    11
 
     wherein: 
     Z 1  is a protogenic group such as —SO 2 X, —PO 3 H 2 , —COX, and the like; 
     E 1 , E 2  are each independently an aromatic or aliphatic-containing moiety wherein at least one of E 1  and E 2  includes an aromatic substituted with Z 1 ; 
     X is an —OH, a halogen, an ester, or 
     
       
         
         
             
             
         
       
     
     d is the number of Z 1  functional groups attached to E 1 ; 
     f is the number of Z 1  functional groups attached to E 2 ; 
     P 1 , P 2 , P 3  are each independently absent, —O—, —S—, —SO—, —SO 2 —, —CO—, —NH—, NR 2 —, or —R 3 —; 
     R 2  is C 1-25  alkyl, C 1-25  aryl, or C 1-25  arylene; 
     R 3  is C 1-25  alkylene, C 1-25  perfluoroalkylene, perfluoroalkyl ether, alkyl ether, or C 1-25  arylene; 
     R 4  is trifluoromethyl, C 1-25  alkyl, C 1-25  perfluoroalkylene, C 1-25  aryl, or another E 1  group; and 
     Q 1  is a fluorinated cyclobutyl moiety, 
     with the proviso that when d is greater than zero, f is zero and when f is greater than zero d is zero. In one refinement, d is equal to the number of aromatic rings in E 1 . In another refinement, each aromatic ring in E 1  can have 0, 1, 2, 3, or 4 Z 1  groups. In still another refinement, d is an integer from 1 to 4 on average. In one refinement, f is equal to the number of aromatic rings in E 2 . In another refinement, each aromatic ring in E 2  can have 0, 1, 2, 3, or 4 Z 1  groups. In still another refinement, f is an integer from 1 to 4 on average. 
     Example for Q 1  and Q 2  in the above formulae are: 
     
       
         
         
             
             
         
       
     
     In each of the formulae 2-11, E 1  and E 2  include one or more aromatic rings. For example, E 1  and E 2 , include one or more of the following moieties: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Examples of L 1  include the following linking groups: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     where R 5  is an organic group, such as an alkyl or acyl group. 
     In another embodiment of the present invention, polymeric membrane  26  includes a polymer blend. The polymer blend of this embodiment includes a first polymer and a second polymer. The first polymer includes the polymer segment 1 set forth above. The first polymer is different than the second polymer. In one variation, the second polymer is a non-ionic polymer. 
     In a refinement, the non-ionic polymer is a fluorine-containing polymer such as a fluoro-elastomer or fluoro-rubber. The fluoro-elastomer may be any elastomeric material comprising fluorine atoms. The fluoro-elastomer may comprise a fluoropolymer having a glass transition temperature below about 25° C. or preferably, below 0° C. The fluoro-elastomer may exhibit an elongation at break in a tensile mode of at least 50% or preferably at least 100% at room temperature. The fluoro-elastomer is generally hydrophobic and substantially free of ionic group. 
     The fluoro-elastomer may be prepared by polymerizing at least one fluoro-monomer such as vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, vinylfluoride, vinylchloride, chlorotrifluoroethylene, perfluoromethylvinyl ether, and trifluoroethylene. The fluoro-elastomer may also be prepared by copolymerizing at least one fluoro-monomer and at least one non-fluoro-monomer such as ethylene, propylene, methyl methacrylate, ethyl acrylate, styrene and the like. The fluoro-elastomer may be prepared by free radical polymerization or anionic polymerization in bulk, emulsion, suspension and solution. Examples of fluoro-elastomers include poly(tetrafluoroethlyene-co-ethylene), poly(vinylidene fluoride-co-hexafluoropropylene), poly(tetrafluoroethylene-co-propylene), terpolymer of vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene, and terpolymer of ethylene, tetrafluoroethylene and perfluoromethylvinylether. Some of the fluoro-elastomers are commercially available from Arkema under trade name Kynar Flex® and Solvay Solexis under the trade name Technoflon®, from 3M under the trade name Dyneon®, and from DuPont under the trade name Viton®. For example, Kynar Flex 2751 is a useful copolymer of vinylidene fluoride and hexafluoropropylene with a melting temperature between about 130° C. and 140° C. The glass transition temperature of Kynar Flex 2751 is about −40 to −44° C. The fluoro-elastomer may further comprise a curing agent to allow crosslinking reaction after being blended with a first polymer that includes a perfluorocyclobutyl moiety. 
     In another variation of this embodiment, the second polymer is a perfluorosulfonic acid polymer (PFSA). In a refinement, such PFSAs are a copolymer containing a polymerization unit based on a perfluorovinyl compound represented by: 
       CF 2 ═CF—(OCF 2 CFX 1 ) m —O r —(CF 2 ) q —SO 3 H
 
     where m represents an integer of from 0 to 3, q represents an integer of from 1 to 12, r represents 0 or 1, and X 1  represents a fluorine atom or a trifluoromethyl group and a polymerization unit based on tetrafluoroethylene. 
     In a variation of this embodiment, the second polymer is present in an amount from about 5 to about 70 weight percent of the total weight of the polymer blend. In a further refinement, the second polymer is present in an amount from about 10 to about 60 weight percent of the total weight of the polymer blend. In still another refinement, the polymer having polymer segment 1 is present in an amount from about 30 to about 95 weight percent of the total weight of the polymer blend. In still another refinement, the polymer having polymer segment 1 (i.e., the first polymer) is present in an amount from about 40 to about 90 weight percent of the total weight of the polymer blend. 
     The following examples illustrate the various embodiments of the present invention. Those skilled in the art will recognize many variations that are within the spirit of the present invention and scope of the claims. 
     Table 1 and  FIGS. 6A-F  provide a set of membranes used to evaluate the performance of membrane humidifier assemblies made in accordance with embodiments set forth above. Example 1 corresponds to  FIG. 6A  with the polymeric membrane having a single selective layer of a PFSA polymer. Example 2 corresponds to  FIG. 6B  with diffusion layer  44  being a polyester paper and selective polymer layer  32  being a perfluorocyclobutyl polymer (PFCB) containing 0% Kynar Flex 2751 (KF). Example 3 corresponds to  FIG. 6C  with diffusion layer  44  being a carbon paper coated with microporous layer  50  and selective polymer layer  32  being a perfluorocyclobutyl polymer containing 40% Kynar Flex 2751. Example 4 corresponds to  FIG. 6D  with polymeric substrate being polypropylene, selective polymer layers  32  being a perfluorocyclobutyl polymer containing 30% Kynar Flex 2751, and diffusion layer  44  being a polyester paper. Example 5 corresponds to  FIG. 6C  with diffusion layer  44  being a carbon paper coated with microporous layer  50  and selective polymer layer  32  being a perfluorocyclobutyl polymer containing 30% Kynar Flex 2751. Example 6 corresponds to  FIG. 6E  with polymeric substrate  30  being a Donaldson 1326 ePTFE support (D1326), diffusion layer  44  being a carbon paper coated with microporous layer  50  and selective polymer layer  32  being a perfluorocyclobutyl polymer containing 30% Kynar Flex 2751. Example 7 corresponds to  FIG. 6F  with polymeric substrate  30  being a Donaldson 1326 ePTFE support (D1326), diffusion layer  44  being a glass fiber layer and selective polymer layer  32  being a perfluorocyclobutyl polymer containing 30% Kynar Flex 2751. Example 8 corresponds to  FIG. 6F  with polymeric substrate  30  being a Donaldson 1326 ePTFE support (D1326), diffusion layer  44  being a polyester layer and selective polymer layer  32  being a perfluorocyclobutyl polymer containing 30% Kynar Flex 2751. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 Comparatives 
                 25 μm PFSA baseline 
               
               
                 Example 1 
               
               
                 Example 2 
                 Method 1 Single Layer Paper 
               
               
                 Example 3 
                 Method 2 coated Gas Diffusion Medium with 
               
               
                   
                 Microporous Layer 
               
               
                 Example 4 
                 Method 2 coated on Tonen on paper (paper removed) 
               
               
                 Example 5 
                 Free Standing Film hot pressed on gas diffusion medium 
               
               
                   
                 with microporous layer 
               
               
                 Example 6 
                 Method 1 hot pressed to gas diffusion medium with 
               
               
                   
                 microporous layer 
               
               
                 Example 7 
                 Method 1 hot pressed to glass fiber based gas diffusion 
               
               
                   
                 medium 
               
               
                 Example 8 
                 Method 1 hot pressed to polyester gas diffusion medium 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 1 
     PFSA Baseline 
     A membrane using a standard perfluorosulfonic acid polymer membrane is used as a baseline. 
     EXAMPLE 2 
     Method 1 Single Layer Composite 
     Perfluorocyclobutyl-Graft-Perfluorosulfonic Acid Ionomer Blend on Crane Paper Support Structure 
     A solution of perfluorocyclobutyl-graft-perfluorosulfonic acid ionomer (1 gram, Tetramer Technologies) in N,N-dimethylacetamide (DMAc, 9 grams) with a 30 wt. % solids solution of Kynar Flex 2751 (Arkema, 2.857 g of a 15 wt. % solution in DMAc) is coated using a 3-mil Bird applicator (Paul N. Gardner) directly onto window pane glass. The coated glass is then heated on a heated platen at 40° C. for 10 minutes. Crane paper is then laid on top of the wet coating and the wet film soaked into the support which is then heated in an oven at 80° C. until dry. A coated support is obtained with a water vapor transfer of 9827 gpu; however, the coating is not leak free. The upper limit of the TCT735 coating thickness is believed to be 7-8 μm thick. When other coatings are made by placing Crane paper on top of a wet film that had been dried at 40° C. for 15 minutes, the wet film soaks into the support paper and the resulting composites after drying 15 minutes at 80° C. are not leak free. In all cases where the wet coating soaks into the Crane paper, the resultant composite is not leak free. The composite prepared after 15 minutes at 40° C. and then 15 minutes at 80° C., is compression molded at 150° C. for 3 minutes between Kapton® film. The composite is then delaminated while the laminate is still warm and the composite is not leak free. 
     EXAMPLE 3 
     Method 2 Single Layer Coated Gas Diffusion Medium With Microporous Layer 
     Perfluorocyclobutyl-Graft-Perfluorosulfonic Acid Ionomer Blend on GDL With MPL 
     A 10 wt % solution, in N,N-dimethylacetamide is prepared using a perfluorocyclobutyl-graft-perfluorosulfonic acid (PFCB-g-PFSA) ionomer prepared from the reaction of the potassium salt of 2-(2-iodotetrafluoroethoxy)tetrafluoroethanesulfonyl fluoride, CAS#: [66137-74-4] with the aryl brominated perfluorocyclobutyl polymer (90,000 Mw) polymerized from a 16,000 Mw biphenyl perfluorocyclobutane oligomer and a hexafluoroisopropylidene-bis-trifluorovinyl ether monomer. A blend solution is prepared by adding 3 g of a 10 wt % solution of Kynar Flex 2751 in N,N-dimethylacetamide to 7 g of the 10 wt % PFCB-g-PFSA solution. The gas diffusion layer is held down on a vacuum table at 50° C. and coated uniformly with a 10 wt % perfluorocyclobutyl ionomer blend solution on the microporous layer (MPL) and is dried over a 15 minute period. The resultant integrated water vapor transfer membrane is used as a water vapor transfer membrane in a humidifier for a hydrogen-air fuel cell system that is operated at less than 100° C. 
     EXAMPLE 4 
     Method 2 Single Layer Coated Tonen Polypropylene Porous Support 
     Perfluorocyclobutyl-Graft-Perfluorosulfonic Acid Ionomer Blend on GDL With MPL 
     A 10 wt % solution, in N,N-dimethylacetamide is prepared using a perfluorocyclobutyl-graft-perfluorosulfonic acid (PFCB-g-PFSA) ionomer prepared from the reaction of the potassium salt of 2-(2-iodotetrafluoroethoxy)tetrafluoroethanesulfonyl fluoride, CAS#: [66137-74-4] with the aryl brominated perfluorocyclobutyl polymer (90,000 Mw) polymerized from a 16,000 Mw biphenyl perfluorocyclobutane oligomer and a hexafluoroisopropylidene-bis-trifluorovinyl ether monomer. A blend solution is prepared by adding 3 g of a 10 wt % solution of Kynar Flex 2751 in N,N-dimethylacetamide to 7 g of the 10 wt % PFCB-g-PFSA solution. The Tonen polypropylene porous support is placed on a sheet of paper and held down on a vacuum table at 50° C. and coated uniformly with a 10 wt % perfluorocyclobutyl ionomer blend solution and is dried over a 15 minute period. The resultant integrated water vapor transfer membrane is used as a water vapor transfer membrane in a humidifier for a hydrogen-air fuel cell system that is operated at less than 100° C. 
     EXAMPLE 5 
     Free-Standing Film Hot Pressed to Gas Diffusion Medium With a Microporous Layer 
     Perfluorocyclobutyl-Graft-Perfluorosulfonic Acid Ionomer Blend Hot Dressed to GDL With MPL 
     A 10 wt % solution, in N,N-dimethylacetamide is prepared using a perfluorocyclobutyl-graft-perfluorosulfonic acid (PFCB-g-PFSA) ionomer prepared from the reaction of the potassium salt of 2-(2-iodotetrafluoroethoxy)tetrafluoroethanesulfonyl fluoride, CAS#: [66137-74-4] with the aryl brominated perfluorocyclobutyl polymer (90,000 Mw) polymerized from a 16,000 Mw biphenyl perfluorocyclobutane oligomer and a hexafluoroisopropylidene-bis-trifluorovinyl ether monomer. A blend solution is prepared by adding 3 g of a 10 wt % solution of Kynar Flex 2751 in N,N-dimethylacetamide to 7 g of the 10 wt % PFCB-g-PFSA solution. The 10 wt % solution is then coated on a clean sheet of extruded Teflon™ at 50° C. and dried over a 15 minute period. The resultant single layer composite membrane film is pressed at 120° C. and 4000 lbs for two minutes in contact with gas diffusion media. The resultant diffusion media membrane composite is used as a water vapor transfer membrane in a humidifier for a hydrogen-air fuel cell system that is operated at less than 100° C. 
     EXAMPLE 6 
     Method 1 Single Layer Composite Membrane Hot Pressed to Gas Diffusion Medium With a Microporous Layer 
     Perfluorocyclobutyl-Graft-Perfluorosulfonic Acid Ionomer Blend Hot Dressed to GDL With MPL 
     A 5 wt % solution, in N,N-dimethylacetamide is prepared using a perfluorocyclobutyl-graft-perfluorosulfonic acid (PFCB-g-PFSA) ionomer prepared from the reaction of the potassium salt of 2-(2-iodotetrafluoroethoxy)tetrafluoroethanesulfonyl fluoride, CAS#: [66137-74-4] with the aryl brominated perfluorocyclobutyl polymer (90,000 Mw) polymerized from a 16,000 Mw biphenyl perfluorocyclobutane oligomer and a hexafluoroisopropylidene-bis-trifluorovinyl ether monomer. A blend solution is prepared by adding 3 g of a 5 wt % solution of Kynar Flex 2751 in N,N-dimethylacetamide to 7 g of the 5 wt % PFCB-g-PFSA solution. The 5 wt % solution is then coated on a clean sheet of extruded Teflon™ at 50° C. and the ePTFE support (example Donaldson 1326) is laid-down on top of the wet layer such that the solution is able to contact the porous support. The ePTFE structure remains opaque and the wet-film is dried over a 15 minute period. The resultant single layer composite membrane film is peeled from the Teflon™ backing film and pressed at 120° C. and 4000 lbs for two minutes with the backing film side of the WVT membrane in contact with the gas diffusion media. The resultant diffusion media membrane composite is used as a water vapor transfer membrane in a humidifier for a hydrogen-air fuel cell system that is operated at less than 100° C. 
     EXAMPLE 7 
     Method 1 Single Layer Composite Membrane Hot Pressed Glass Fiber Based Gas Diffusion Medium 
     Perfluorocyclobutyl-Graft-Perfluorosulfonic Acid Ionomer Blend Hot Dressed to GF-GDL 
     A 5 wt % solution, in N,N-dimethylacetamide is prepared using a perfluorocyclobutyl-graft-perfluorosulfonic acid (PFCB-g-PFSA) ionomer prepared from the reaction of the potassium salt of 2-(2-iodotetrafluoroethoxy)tetrafluoroethanesulfonyl fluoride, CAS#:[66137-74-4] with the aryl brominated perfluorocyclobutyl polymer (90,000 Mw) polymerized from a 16,000 Mw biphenyl perfluorocyclobutane oligomer and a hexafluoroisopropylidene-bis-trifluorovinyl ether monomer. A blend solution is prepared by adding 3 g of a 5 wt % solution of Kynar Flex 2751 in N,N-dimethylacetamide to 7 g of the 5 wt % PFCB-g-PFSA solution. The 5 wt % solution is then coated on a clean sheet of extruded Teflon™ at 50° C. and the ePTFE support (example Donaldson 1326) is laid-down on top of the wet layer such that the solution is able to contact the porous support. The ePTFE structure remains opaque and the wet-film is dried over a 15 minute period. The resultant single layer composite membrane film is peeled from the Teflon™ backing film and pressed at 120° C. and 4000 lbs for two minutes with the backing film side of the WVT membrane in contact with glass fiber based gas diffusion media. The resultant diffusion media membrane composite is used as a water vapor transfer membrane in a humidifier for a hydrogen-air fuel cell system that is operated at less than 100° C. 
     EXAMPLE 8 
     Method 1 Single Layer Composite Membrane Hot Pressed to Polyester Gas Diffusion Medium 
     Perfluorocyclobutyl-Graft-Perfluorosulfonic Acid Ionomer Blend Hot Dressed to GDL With MPL 
     A 5 wt % solution, in N,N-dimethylacetamide is prepared using a perfluorocyclobutyl-graft-perfluorosulfonic acid (PFCB-g-PFSA) ionomer prepared from the reaction of the potassium salt of 2-(2-iodotetrafluoroethoxy)tetrafluoroethanesulfonyl fluoride, CAS#: [66137-74-4] with the aryl brominated perfluorocyclobutyl polymer (90,000 Mw) polymerized from a 16,000 Mw biphenyl perfluorocyclobutane oligomer and a hexafluoroisopropylidene-bis-trifluorovinyl ether monomer. A blend solution is prepared by adding 3 g of a 5 wt % solution of Kynar Flex 2751 in N,N-dimethylacetamide to 7 g of the 5 wt % PFCB-g-PFSA solution. The 5 wt % solution is then coated on a clean sheet of extruded Teflon™ at 50° C. and the ePTFE support (example Donaldson 1326) is laid-down on top of the wet layer such that the solution is able to contact the porous support. The ePTFE structure remains opaque and the wet-film is dried over a 15 minute period. The resultant single layer composite membrane film is peeled from the Teflon™ backing film and pressed at 120° C. and 4000 lbs for two minutes with the backing film side of the WVT membrane in contact with a polyester gas diffusion media. The resultant diffusion media membrane composite is used as a water vapor transfer membrane in a humidifier for a hydrogen-air fuel cell system that is operated at less than 100° C. 
     Experimental Results 
       FIG. 7  provides experimental results at a common screening point for materials for water vapor transfer within a humidified, hydrogen-air fuel cell system. Grams of water transferred across the membrane are measured from a wet inlet stream of 80° C., 85% relative humidity, 10 slpm dry gas flow, and 160 kPaa to a dry inlet stream of 80° C., 0% relative humidity, 11.5 slpm dry gas flow, 80° C., and 183 kPaa.  FIG. 7  also indicates acceptable levels for automotive fuel cell applications. 
     The above description of embodiments of the invention is merely exemplary in nature and, thus, variations thereof are not to be regarded as a departure from the spirit and scope of the invention.