BACKGROUND
The invention relates generally to electrochemical cell structures and more specifically to electrochemical cell structures having single-piece nonconductive frames that support the anode, the cathode and the electrolyte and define flowpaths for working fluids and for byproducts of ionic exchange.
Electrochemical cells are energy conversion devices that are usually classified as either electrolysis cells or fuel cells. Electrolysis cells can function as hydrogen generators by electrolytically decomposing water to produce hydrogen and oxygen gases. Fuel cells electrochemically react a hydrogen gas with an oxidant across an exchange membrane or electrolyte to generate electricity and produce water.
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.
For electrochemical systems, especially alkaline electrolysis systems, to become economically feasible the manufacturing costs associated with these systems must markedly improve. Current systems require numerous process steps during assembly, with each step adding cost to the overall system. Additionally, conventional systems currently have many individual component parts including multiple electrodes, diaphragms, gaskets, bolts and other miscellaneous parts that add to the complexity of the system assembly and drive the manufacturing costs up.
Accordingly, there is a need for an improved electrochemical cell that promotes an overall reduction in the number of component parts and simplifies the associated manufacturing and fabrication process.
BRIEF DESCRIPTION
An electrochemical cell structure comprises an anode, a cathode spaced apart from the anode and an electrolyte in ionic communication with each of the cathode and the anode. A single-piece nonconductive frame supports each of the anode, the cathode and the electrolyte and defines flowpaths for working fluids and for byproducts of ionic exchange.
DRAWINGS
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
FIG. 1 is a side cross-sectional view of one embodiment of the instant invention.
FIG. 2 is a schematic representation of an alkaline electrolysis system.
FIG. 3 is schematic representation of an exemplary alkaline electrolysis stack arrangement.
FIG. 4 is an exploded view of one embodiment of the instant invention.
FIG. 5 is a side view of an electrode insert in accordance with one embodiment of the instant invention.
FIG. 6 is a perspective view of end caps in accordance with one embodiment of the instant invention.
FIG. 7 is a top view of electrochemical cell structure in accordance with one embodiment of the instant invention.
FIG. 8 is a side view of the electrochemical cell structure shown in FIG. 7.
FIG. 9 is a flow chart representation of one method of fabrication of the instant invention.
FIG. 10 is a flow chart representation of another method of fabrication of the instant invention.
FIG. 11 is a schematic representation of an alkaline electrolysis system in accordance with the instant invention.
DETAILED DESCRIPTION
An electrochemical cell structure 10 comprising an anode 12, a cathode 14 spaced apart from the anode 12, an electrolyte 16 in ionic communication with each of the anode 12 and the cathode 14, and a single-piece nonconductive frame 18, is shown in FIG. 1. The single-piece nonconductive frame 18 supports the anode 12, the cathode 14 and the electrolyte 16 and defines a plurality of flowpaths 20 for working fluids (not shown) or byproducts of ionic exchange (not shown). As shown in FIG. 1, because the elements are encased in the single-piece nonconductive frame 18 and the flowpaths 20 are defined by the same, the construction is efficient and effective (no gaskets or seals are required) and the fabrication process is simplified.
One type of electrochemical cell structure is utilized within an alkaline electrolysis system 30, as schematically shown in FIG. 2. Water (H2O) is supplied into the system 30 via inlet 32 and is circulated by pump 34. The water is combined with a base, typically Potassium Hydroxide (KOH) or Sodium Hydroxide (NaOH), to form a liquid alkaline electrolyte 36, which electrolyte 36 is circulated by pump 34 to electrolyzer 38. Electrolyzer 38 includes an anode 40 (+ electrode), a diaphragm 42 and a cathode 44 (− electrode). Direct current voltage 46 is applied to the anode 40 and the cathode 44 in the presence of the electrolyte 36. The direct current voltage, typically a voltage in the range between about 1.7V to about 2.2V, splits the water into its constituents of hydrogen (H2) at the cathode 44 and oxygen (O2) at the anode 40. Diaphragm 42 keeps the H2 and O2 gases separated. The O2 gas in mixture with electrolyte 36 is transported to an oxygen separator 48. After separation from the electrolyte 36, the O2 gas is stored, vented, or otherwise utilized and a portion of the electrolyte 50 is recirculated by pump 34 into system 30. The H2 gas in mixture with liquid electrolyte 36 is transported to a hydrogen separator 52. After separation from the electrolyte 36, the H2 gas is captured and stored, burned, electrochemically reacted or otherwise utilized and a portion of the electrolyte 54 is recirculated by pump 34 into system 30.
As discussed above, in order for electrochemical systems, especially alkaline electrolysis systems, to become economically feasible the manufacturing costs associated with these systems must markedly improve. Current systems require numerous process steps during assembly, with each step adding cost to the overall system. Additionally, conventional systems currently have many individual component parts including multiple electrodes, diaphragms, gaskets, bolts and other miscellaneous parts that add to the complexity of the system assembly and drive the manufacturing costs up.
One particularly difficult and expensive fabrication area is the stack assembly within these electrochemical systems. Taking an alkaline electrolysis stack as an exemplary stack arrangement, the general configuration and fabrication difficulties can be discussed in reference to FIG. 3. As shown in FIG. 3, a typical stack assembly 56 includes a plurality of repeat units 58. Each repeat unit 58 includes an anode 60, a bipolar plate 62, a cathode 64 and a diaphragm 66. Any large-scale implementation of an alkaline electrolysis stack may include as many as a hundred or more repeat units 58. Each repeat unit 58 requires electrical coupling between the anode 60, the bipolar plate 62 and the cathode 64, referred to as the electrode assembly 65. Each electrode assembly 65 must be separated by a diaphragm 66, primarily to keep the hydrogen and oxygen gases from mixing between adjacent electrode assemblies 65. All of the repeat units 58 within a stack must be positioned within some type of housing, and surrounded by nonconductive gasketing, sealing technologies, and piping or manifolds to distribute the electrolyte and to capture the hydrogen and oxygen gases. Hundreds or possibly thousands of connections and bolts or other fasteners are used to assemble this type of stack, further impacting the fabrication costs.
In accordance with one embodiment of the instant invention, an electrochemical cell structure 100 is shown in FIGS. 4-8. Electrochemical cell structure 100 is shown in an exploded view to better demonstrate the constituent parts in FIG. 4. Electrochemical cell structure 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. In one embodiment of the invention, as best shown in FIG. 5, anode 102, bipolar plate 106 and cathode 104 are joined together to create an electrode insert 108. Electrochemical cell structure 100 (FIG. 4) further comprises an electrode frame 110. 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 top surface 116 and a hydrogen flow path 124 on bottom surface 118 (shown with dotted lines). Electrode insert 108 is positioned on seat 120. 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. 6, 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.
In operation, an electrolyte is introduced via inlet 112 (FIG. 4) and is distributed to the anode 102 by first flow path 114 and to the cathode 104 by 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 an oxygen outlet 123 and the hydrogen and a portion of the electrolyte flow through hydrogen flow path 124 to a 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 inlet 112, the oxygen outlet 123 and the hydrogen outlet 125.
As shown best in FIG. 4, 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 nonconductive 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, nonconductive 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 membrane (PEM), polybenzimidazole (PBI), and acid electrolysis and fuel cell applications.
In one embodiment of the instant invention, 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 comprises a hydrolytically stable polymer. In another embodiment, the nonconductive frame 150 is selected from the group consisting of polyethylene, fluorinated polymers, polypropylene, and polysulfone polyphenyleneoxide, polyphenylenesulfide, polystyrene and blends thereof.
In reference to FIGS. 7 and 8, repeat plate 134 is depicted as a single unit. Each repeat plate 134 is constructed to provide an inlet 112 for the electrolyte. As best shown in FIG. 8, the electrolyte splits into two streams on either side of the bipolar plate 106 and dissociates into H2 and O2. The diaphragms 126 and 130 bound each side of the electrode insert to ensure the H2 and O2 do not mix between adjacent repeat plates 134. The construction of this exemplary repeat plate 134 is simple and avoids the use of seals or gaskets. As depicted, the electrode insert 108 and the diaphragms 126 and 130 are supported and encased within the single-piece nonconductive frame of repeat plate 134. The flow paths for the electrolyte are also defined by the single-piece nonconductive frame of repeat plate 134, essentially removing any need for gasketing within the system.
In one embodiment of the invention, the electrochemical cell structure is fabricated according to the process discussed in reference to FIG. 9. First an electrode assembly is positioned within a first nonconductive frame piece S1. As discussed above, the electrode assembly typically comprises an anode, a cathode and a bipolar plate. Next, a second nonconductive frame piece is applied to the first nonconductive frame piece to sandwich the electrode assembly therebetween S2. Next, the first and second nonconductive frame pieces are joined together to form a single-piece nonconductive frame unit about the electrode assembly S3. Additional nonconductive frame pieces and additional component parts may be added as per requirements, for example, a diaphragm frame and a diaphragm. Multiple single-piece nonconductive frame units are joined together to form an electrochemical stack structure having a single-piece nonconductive frame. In one embodiment, the frame pieces or units are joined together by adhesive. In another embodiment, the frame pieces or units are joined together using ultrasonic or laser welding. In yet another embodiment, the frame pieces or units are joined together by applying heat or current to melt the pieces or units together.
In another embodiment, the electrochemical cell structure is fabricated according to the process discussed in reference to FIG. 10. First at least one and typically a plurality of electrode assemblies are positioned within a molding apparatus S4. As discussed above, the electrode assembly typically comprises an anode, a cathode and a bipolar plate. Next, a heated molding material, typically a polymer, is dispensed into the molding apparatus and flows around the provided electrode assemblies S5. Finally, the molding material is cooled and the electrochemical cell structure is removed from the molding apparatus S6. In this embodiment, the single-piece nonconductive frame is formed in place around the electrode assemblies, thereby further simplifying the fabrication process. The flow channels and pathways are predefined in the molding apparatus to ensure proper flow of working fluids and ionic byproducts during use. Additional component parts can be included if required, for example, diaphragms may be positioned within the molding apparatus prior to S5.
One embodiment of the instant invention is depicted in FIG. 11. Water (H2O) is supplied into the system and is circulated by pump 34. The water is combined with an alkaline base, typically Potassium Hydroxide (KOH) or Sodium Hydroxide (NaOH), to form a liquid alkaline electrolyte that is circulated by pump 34 to the inlet 112 formed in the single-piece nonconductive frame 150. A plurality of electrode inserts 108 is positioned within the single-piece nonconductive frame and is separated from adjacent electrode inserts 108 by diaphragms, as discussed above. The electrolyte flows though the inlet 112 and to each of the respective electrode inserts 108. Direct current voltage is applied to the electrode inserts 108 in the presence of the electrolyte. The direct current voltage splits the water into its constituents of hydrogen (H2) at the cathode and oxygen (O2) at the anode. The diaphragms keep the H2 and O2 gases separated. The O2 gas in mixture with electrolyte is transported via oxygen outlet 123 (defined by single-piece nonconductive frame 150) to an oxygen separator. After separation from the electrolyte, the O2 gas is stored, vented, or otherwise utilized and a portion of the electrolyte is recirculated by pump 34 into the system. The H2 gas in mixture with liquid electrolyte is transported via hydrogen outlet 125 (defined by single-piece nonconductive frame 150) to a hydrogen separator. After separation from the electrolyte, the H2 gas is captured and stored, burned, electrochemically reacted or otherwise utilized and a portion of the electrolyte is recirculated by pump 34 into the system.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.