Abstract:
A structural reinforcement for a pressurized plastic electrochemical cell stack is described with a first endplate and a second endplate, wherein the first endplate and the second endplate are each connected to a structural reinforcement along an axial direction such that the reinforcement extends through the first endplate and the second endplate and provides for compressing the first endplate and the second endplate against a bilithic or monolithic plastic electrochemical cell stack internal to the reinforcement, thereby sealing a gas generation cell within the reinforcement and thus providing enhanced creep resistance of the electrochemical cell stack.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The disclosure relates generally to electrochemical cell structures, and more specifically, to electrochemical cell structures having a plastic internal stack configuration, wherein the plastic internal stacks are prevented from leaking and restrained from creep caused by internal pressure during operation. 
         [0002]    Electrochemical cells are energy conversion devices that are usually classified as either fuel cells or electrolyzers. By way of example, electrolysis cells can function as hydrogen generators by electrolytically decomposing water to produce hydrogen and oxygen gases. Fuel cells use the hydrogen by electrochemically reacting a hydrogen gas with an oxidant across an exchange membrane or electrolyte to generate electricity and produce water. 
         [0003]    Alkaline electrolysis systems have been commercially available for several decades. Direct current voltage of about 1.7V to about 2.2V is applied to two electrodes that are positioned within a liquid electrolyte. At the positive electrode, oxygen is produced and at the negative electrode, hydrogen forms. An ion-permeable diaphragm keeps the gases separated. 
         [0004]    Conventional electrochemical systems currently have many individual component parts including multiple electrode pairs, diaphragms, gaskets, bolts and other miscellaneous pieces that add to the complexity of the system assembly and drive the manufacturing costs up. For example, hydrogen generating electrochemical cell structures are manufactured with metal plates normally bolted together manually, with gaskets used between the plates to electrically insulate them from one another. The materials are normally expensive and assembly requires intensive and therefore high labor costs. 
         [0005]    The general configuration and fabrication difficulties of conventional electrochemical systems that include stack assemblies are discussed in reference to  FIG. 1 . As shown, a typical stack assembly  10  includes a plurality of repeating units  12 . Each repeat unit  12  includes an anode  14 , a bipolar plate  16 , a cathode  18 , and a diaphragm  20 . Any large-scale implementation of an alkaline electrolysis stack may include a hundred or more repeat units  12 . Each repeat unit  12  requires electrical coupling between the anode  14 , the bipolar plate  16 , and the cathode  18 , also commonly referred to as the electrode assembly  22 . Direct current voltage  24  is applied to the anode  14  and the cathode  16  in the presence of an electrolyte (not shown), which for alkaline electrolysis is typically a potassium hydroxide solution. Each electrode assembly  22  must be separated by a diaphragm  20 , primarily to keep the hydrogen and oxygen gases being generated from mixing between adjacent electrode assemblies  22 . All of the repeat units  12  within a stack must be positioned within some type of housing and surrounded by non-conductive gasketing. Sealing technologies, piping or manifolds to distribute the electrolyte and to capture the hydrogen and oxygen gases. Hundreds of possibly thousands of connections and bolts or other fasteners are used to assemble this type of stack, further impacting the fabrication costs. 
         [0006]    Newly developed electrochemical cell structures have involved the use of stack housings formed of non-conductive materials to achieve high chemical resistance and low assembly cost. However, the use of non-conductive materials, e.g., plastics, introduces materials that are not creep resistant and are therefore impractical for stacks with internal pressure. Internal pressure is an advantage in electrolysis because it raises the system efficiency and lowers the cost and potential necessity of post-stack compressors. 
         [0007]    Accordingly, there is a need for a low cost electrochemical cell structure in which plastic stack housings are utilized and resists pressure related creep. 
       SUMMARY OF THE INVENTION 
       [0008]    This disclosure describes structural reinforcements for electrochemical cell stack modules comprising one or more non-conductive frames. In one embodiment, an electrochemical cell stack module comprises an electrochemical cell stack comprising one or more non-conductive frames, wherein the one or more non-conductive frames support at least one of an anode, a cathode, a top diaphragm, and a lower diaphragm of a repeat plate; and a structural reinforcement configured for containing the electrochemical cell stack, the structural reinforcement comprising a first rigid member, a second rigid member and at least one connector fixedly attached to the first and second rigid members along an axial or longitudinal direction and adapted to compress the first rigid member and the second rigid member against each end of the electrolyzer. 
         [0009]    In another embodiment, the electrochemical cell stack module comprises an electrochemical cell stack comprising one or more non-conductive frames, wherein the one or more non-conductive frames support at least one of an anode, a cathode, a top diaphragm, and a lower diaphragm of a repeat plate; and a structural reinforcement configured for containing the electrochemical cell stack, the structural reinforcement comprising a cylindrical sleeve having an inner diameter equal to or slightly larger than the cylindrically shaped electrochemical cell stack. 
         [0010]    In yet another embodiment, the electrochemical cell stack module comprises a cylindrically shaped electrochemical cell stack comprising one or more non-conductive frames, wherein the one or more non conductive frames support at least one of an anode, a cathode, a top diaphragm, and a lower diaphragm of a repeat plate; and a structural reinforcement configured for containing the electrochemical cell stack, the structural reinforcement comprising a cylindrical sleeve having an inner diameter equal to or slightly larger than the cylindrically shaped electrochemical cell stack, a first rigid member disposed against one end of the cylindrical sleeve, a second rigid member disposed against an other end of the cylindrical sleeve. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The disclosure and embodiments thereof will become apparent from the following description and the appended drawings, in which the like elements are numbered alike: 
           [0012]      FIG. 1  is a prior art schematic representation of an alkaline electrolysis system. 
           [0013]      FIG. 2  is a partial exploded perspective view of an electrochemical cell stack that includes non-conductive frames for supporting various components of the electrolyzer. 
           [0014]      FIG. 3  is perspective view of an electrode insert for the electrochemical cell stack of  FIG. 2 . 
           [0015]      FIG. 4  is a perspective view of end caps for the electrochemical cell stack of  FIG. 2 . 
           [0016]      FIG. 5  is a top view of the electrochemical cell stack of  FIG. 2 . 
           [0017]      FIG. 6  is a side view of the electrochemical cell stack shown in  FIG. 5 . 
           [0018]      FIG. 7  is a perspective exploded view of a structural reinforcement for limiting longitudinal deflection during operation of an electrochemical cell stack module including non-conductive frames in accordance with one embodiment. 
           [0019]      FIG. 8  is a perspective view of a structural reinforcement for limiting longitudinal deflection during operation of an electrolyzer including non-conductive frames in accordance with another embodiment. 
           [0020]      FIG. 9  is a perspective view of a structural reinforcement for limiting radial or circumferential deflection during operation of an electrochemical cell stack module including non-conductive frames in accordance with another embodiment. 
           [0021]      FIG. 10  is a perspective view of a two-piece cylindrical structural reinforcement for an electrochemical cell stack module. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    The disclosure describes various structural reinforcements for an electrochemical cell stacks configured with non-conductive stacks that minimize and/or prevent pressure related creep. Advantageously, the structural reinforcements described herein permit internal pressure to build up within the stacks with minimal and/or without any pressure related creep, resulting in increased the system efficiency. The structural reinforcement can be used with electrolyzers of a bilithic or a monolithic design. As used herein, the term electrochemical cell is generic and intended to encompass electrolytic cells, galvanic cells, as well as fuels cells such as, but not limited to, solid oxide fuel cells, polymer electrolyte membrane type fuel cells, alkaline fuel cells, and the like. 
         [0023]      FIGS. 2-6  illustrate various views of an exemplary electrolyzer  100  that includes non-conductive frames for supporting various components of the electrolyzer. As will be discussed herein, the structural reinforcements described herein can be configured to limit longitudinal and/or radial deflection as a result of using the non-conductive frames in the electrolyzer, e.g., electrolyzer  100 . The electrolyzer  100  comprises an anode  102  and a cathode  104  spaced apart from the anode  102 . A bipolar plate  106  is interposed between the anode  102  and the cathode  104  to enable an electrical connection therebetween. As best shown in  FIG. 3 , the anode  102 , bipolar plate  106  and cathode  104  are joined together to create an electrode insert  108 . The electrochemical cell structure  100  ( FIG. 2 ) further comprises an electrode frame  110 . The circularly shaped electrode frame  110  comprises an electrolyte inlet  112 , a first electrolyte flow path  114  on a top surface  116 , a second electrolyte flow path  117  on a bottom surface  118  (shown with dotted lines), a seat  120 , an oxygen flow path  122  on a top surface  116  and a hydrogen flow path  124  on a bottom surface  118  (shown with dotted lines). An electrode insert  108  is positioned on a seat  120 . The electrochemical cell structure  100  further comprises a top diaphragm  126 , a top diaphragm frame  128 , a bottom diaphragm  130  and a bottom diaphragm frame  132 . For purposes of discussion, in this embodiment, the top diaphragm frame  128 , the top diaphragm  126 , the electrode insert  108 , the electrode frame  108 , the bottom diaphragm  130  and the bottom diaphragm frame  132  form a repeat plate  134 . An implementation of an alkaline electrolysis stack would include many, for example between about 10 to about 100, individual repeat plates  134 . As shown in  FIG. 4 , each stack is typically capped with an end cap  140 , an anode  102  and a current collector  142  at one end and an end cap  140 , a cathode  104  and a current collector  142  at an opposite end. 
         [0024]    In operation, an electrolyte is introduced via an inlet  112  ( FIG. 2 ) and is distributed to the anode  102  by a first flow path  114  and to the cathode  104  by a second flow path  117 . In addition, the electrolyte flows through the top membrane  126  and the bottom membrane  130  and creates an ionic bridge between adjacent repeat plates  134 . A DC current is applied to the electrode inserts  108  and a portion of the electrolyte dissociates into oxygen and hydrogen at each anode  102  and cathode  104 , respectively, within a representative stack. The oxygen and a portion of the electrolyte flow through oxygen flow path  122  to oxygen outlet  123  and the hydrogen and a portion of the electrolyte flow through hydrogen flow path  124  to hydrogen outlet  125 . Additional flow paths (not shown) are provided between adjacent repeat plates  134  to allow the electrolyte to flow to one of the inlets  112 , the oxygen outlet  123  and the hydrogen outlet  125 . 
         [0025]    As shown best in  FIG. 2 , the top diaphragm support  128 , the electrode frame  110  and the bottom diaphragm support  132  components, of each repeat plate  134  are made of a non-conductive materials, and typically, although not necessarily, have the same general geometry. For purposes of clarity, these combined components are referred to as nonconductive frame  150 . In one embodiment, non-conductive frame  150  comprises a material having a maximum working temperature in a range between about 60 degrees Celsius to about 120 degrees Celsius. This temperature range would support most alkaline electrolysis applications. In another embodiment, nonconductive frame  150  comprises a material having a maximum working temperature in a range between about 60 degrees Celsius to about 300 degrees Celsius. This temperature range would support most alkaline electrolysis and fuel cell applications as well as most proton exchange membranes (PEM) and acid electrolysis applications. 
         [0026]    In an embodiment, the nonconductive frame  150  comprises a polymer, typically a polymer chemically resistant to caustic to avoid degradation during prolonged exposure to bases like KOH or NaOH. In another embodiment, the nonconductive frame  150  can also comprise a hydrolytically stable polymer. Suitable polymers include, but are not limited to, polyethylene, fluorinated polymers, polypropylene, and polysulfone, polyphenylenesulfide, polystyrene, and blends thereof. In preferred embodiments, the nonconductive frame  150  is manufactured with one or more polymers from the NORYL® resin family. 
         [0027]    In reference to  FIGS. 5 and 6 , repeat plate  134  is depicted as a single unit. Each repeat plate  134  is constructed to provide an inlet  11  of the electrolyte. As best shown in  FIG. 6 , the electrolyte splits in to two streams on either side of the bipolar plate  106  and dissociates in to H 2  and O 2 . The diaphragms  126  and  130  bound each side of the electrode insert to ensure the H 2  and O 2  do not mix between adjacent repeat plates  134 . The construction of the exemplary repeat plate  134  is relatively simple and avoids the use of seals or gaskets. As depicted, the electrode inset  108  and the diaphragms  126  and  130  are supported and encased within the single piece non-conductive frame of repeat plate  134 . The flow paths for the electrolyte are also defined by the single piece non-conductive frame of repeat plate  134 , essentially removing any need for gasketing within said system. 
         [0028]      FIG. 7  illustrates a structural reinforcement  200  for an electrolyzer such as the one discussed above, (e.g., electrolyzer  100 ) that minimizes longitudinal deflection. The structural reinforcement includes rigid members  202  and  204  that form a sandwich about the electrolyzer  100 . The rigid members  202 ,  204  are fastened to one another with at least one connector, e.g., fastener  206  so as to contain the electrolyzer  100  there between and minimize and/or prevent creep related to the nonconductive frame  150 . The rigid members can be formed of any material sufficiently rigid to prevent creep from the stacked non-conductive frames  150  used in the electrolyzer  100 . Likewise, the rigid members can be of any shape suitable to be configured to retain and prevent creep in the electrolyzer  100  during operation. 
         [0029]    In one embodiment, the rigid members  202 ,  204  are fastened to one another with at least one connector  206  extending through the electrolyzer stack as shown in  FIG. 7 . Optionally, the current collector (see  FIG. 4 , current collector  142 ) can function as the rigid members  202  and/or  204 . In other embodiments, each rigid member  202 ,  204  is fixedly attached directly to the electrolyzer stack. 
         [0030]    In another embodiment, the rigid members  202 ,  204  are configured to be of a larger lateral dimension than the electrolyzer  100 . In this embodiment, the rigid members  202 ,  204  have a portion that overlies the boundaries of the electrolyzer  100 . The rigid members can thus be externally fastened about the periphery with a suitable fastener, e.g., bolts, clamps, tie rods, straps, and the like. 
         [0031]    In another embodiment, the fasteners are internally positioned within the flow channels of the electrolyzer (see  FIG. 2 , for example flow paths  114 ,  117 ,  122 , and/or  124 ). The fasteners can be disposed within chemically resistant sleeves or can be formed of chemically resistant materials suitable for the environment in which they are disposed. Of course, one of skill in the art will appreciate that the fasteners should also be made of a creep resistant material. 
         [0032]      FIG. 8  illustrates a structural reinforcement  300  for limiting longitudinal deflection in accordance with another embodiment. The structural reinforcement comprises at least two rigid members in the form of straps  302 ,  304  disposed at each end of the electrolyzer  100 . A fastener  306  secures the straps against the ends of the electrolyzer so as to prevent creep of the nonconductive frame  150  during operation. In the embodiment shown, the straps are externally fastened relative to the electrolyzer. Optionally, the fastener could be disposed within the flow channels of the electrolyzer as previously described. 
         [0033]      FIG. 9  illustrates structural reinforcement  400  for limiting radial deflection. Those of skill in the art will appreciate that the electrolyzer can have an overall cylindrical shape. The structural reinforcement  400  comprises a cylindrical sleeve  402  having an inner diameter slightly larger than the outer diameter of the electrolyzer  100 . Optionally, a material  404  is disposed in the space between the outer surface of the electrolyzer stack and the inner surface of the cylindrical sleeve. The material transfers mechanical load from the electrolyzer stack to the cylindrical shell and resists creep deformation of the electrolyzer stack. In various embodiments, the material can comprise a liquid, a gel, a particulate, a creep-resistant solid, a combination thereof, and the like. In this manner, radial deflection is prevented. The cylindrical sleeve  402  can be formed of a composite, plastic, or metal that is sufficiently rigid so as minimize and/or prevent creep that is manifested in the radial direction. It should also be noted that additional reinforcement or limiting longitudinal deflection could be combined with the cylindrical sleeve  402  of structural reinforcement  400 . For example, rigid members such as those shown in  FIGS. 7 and 8  can be utilized in addition to the cylindrical sleeve  402 . A suitable connector can be used to fasten the rigid members to the corresponding ends of the cylindrical sleeve, e.g., by adhesive, by bolts, by welding, and the like. 
         [0034]      FIG. 10  illustrates the structural reinforcement  400  for limiting radial deflection, wherein the cylindrical shape is formed of two crescent shaped portions  406 ,  408 . Although a two-piece construction is illustrated, one of skill in the art will appreciate that more than two pieces can be used to form the cylindrical shape of the structural reinforcement. Moreover, the various pieces are not intended to be limited to any particular shape. 
         [0035]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and can include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.