The invention relates in general to fuel cells and, more particularly, to high temperature proton exchange medium fuel cells.
A fuel cell electrochemically combines hydrogen and oxygen to produce electricity. Byproducts of the energy-generating electrochemical reaction in a fuel cell include water vapor and carbon dioxide. The electrochemical reaction also generates heat. In a stack plate fuel cell where numerous plates are stacked together and sandwich multiple electrochemical layers, heat dissipation from internal portions of the stack remains a challenge. Current heat management techniques rely on thermal cooling layers disposed adjacent to each electrochemical layer and between each set of plates. For a fuel cell having a stack of numerous plates and electrochemical layers, conventional heat removal techniques for each layer would significantly increase the fuel cell package thickness, volume, and size, thereby rendering the fuel cell impractical or infeasible for many applications. Historically, some of the most difficult operations in high temperature fuel cells are temperature control and temperature spread across the membrane-electrode-assembly (MEA) of the fuel cell. Thus, there is a need for a system that can effectively manage heat within a fuel cell.
Aspects of the invention are directed to a high temperature proton exchange medium (PEM) fuel stack system with enhanced thermal management features. The fuel cell can include a plurality of membrane-electrode-assemblies (MEA) separated by bipolar plates. The bipolar plates can comprise a plurality of repeating units and two non-repeating units, one on each end of the stack of repeating units. The upper and lower edges of the repeating units and non-repeating units are configured such that a plurality of fins is formed therein. A coolant, such as air, can be passed along the fins in the upper edges of the units in a first direction. A coolant, such as air, can be passed along the fins in the lower edges of the units in a second direction that is opposite the first direction.
Alternatively or in addition, a plurality of channels can be formed on both major surfaces of the repeating units and on one surface of each of the non-repeating units. The channels can extend along a serpentine path. Fuel, such as hydrogen, can be supplied to the channels on one side of each repeat unit, and on one side of one of the non-repeat units. Oxidant, such as air, can be supplied to the channels on the channels on the opposite side of each repeat unit and on one side of the other one of the non-repeat units.
Such features can keep the temperature of the fuel cell within acceptable limits.
Embodiments of the invention are directed to a thermal management system for a high temperature PEM fuel cell. The term “high temperature PEM fuel cell” means a fuel cell that operates at a temperature of at least about 120° C. In some instances, a high temperature fuel cell can operate in a temperature range of about 120° C. to about 200° C. Various possible aspects of the invention will be explained herein, but the detailed description is intended only as exemplary. Embodiments of the invention are shown in
Referring to
A fuel cell assembly 10 can also include two non-repeat units 14″. A “non-repeat unit” is a bipolar plate with a flow field on only one side of the bipolar plate 14. An example of a non-repeat 14″ unit is shown in
When the components are assembled, a plurality of cells 28 is formed, as shown in
The upper and lower edges 20, 22 of the bipolar plates 14, both for repeating units 14′ and non-repeating units 14″, can be configured so that a portion of the material of the plate 14 is removed, thereby leaving a protrusion or fin 40. That is, The fin 40 can be thin relative to the thickness of the rest of the plate 14, i.e., thinner than central portion 18. In one embodiment, material can be removed from the front and back side of the plate 14 in the edge region such that the fin 40 is centrally located along the respective edge of the plate. However, in other embodiments, the fin 40 can be closer to or at one of the sides of the plate 14. In one embodiment, the non-repeat units 14″ can have material removed on only one face of the plate, as shown in
When the plurality of plates 14 is stacked together in the fuel cell assembly 30, a plurality of fins is formed along the top 42 and bottom 44 of the fuel cell assembly 30. There can be any suitable spacing between the fins 40. In one embodiment, the fins 40 can be spaced about 0.20 inches apart. The spacing between each neighboring pair of fins 40 can be the same or the spacing can be different between at least one pair of fins 40 of neighboring plates. Any suitable coolant, such as air, can be supplied by at least one coolant source 60 to the space between the fins 40 and flow laterally along the fins 40. Any suitable structure for coupling the coolant source(s) 60 to the fuel cell assembly 30 can be used in the various embodiments of the invention. For example, a coolant source can be a blower, a gas cylinder, or any other source of gas in fluid connection with the fins 40 in fuel cell assembly.
On one side of each repeat unit 14′ and on one side of only one of the non-repeat units 14″, hydrogen can enter into an individual cell by way of slot 1. The slot 1 can have any suitable configuration. The flow can then split into a plurality of channels 50. In one embodiment, there can be eight channels. In one embodiment, the channels can have a depth of about 0.040 inches. The channels can be generally parallel to each other over their entire path. The channels can have any suitable size, shape and configuration. The channels 50 can be formed by recesses in the plate 14 or by raised structures formed on the face of the plate 14. The channels 50 can be substantially identical to each other or at least one of the channels 50 can be different from the other channels 50 in one or more respects. The channels 50 can extend across each bipolar plate 14 in a direction from one lateral end 24 to the opposite lateral end 24. The channels 50 can be generally serpentine. In one embodiment, the channels 50 can turn on itself five times before exiting through the slot 3, as is shown in
On the other side of each repeat unit 14′ and on one side of the second of the non-repeat units 14″, air can enters into an individual cell by way of slot 2. The air can be transported from the slot 2 to the surface of the bipolar plate 14 using angled channels (not shown). The flow can then split into a plurality of channels (not shown). There can be any suitable quantity of channels. In one embodiment, there can be eight channels. In one embodiment, the channels can have a depth of about 0.040 inches.
The channels can be generally parallel to each other over their entire path. The channels can have any suitable configuration. The channels can be substantially identical to each other or at least one of the channels can be different from the other channels in one or more respects. The channels can extend across each bipolar plate 14 from one lateral end 24 to the opposite lateral end 24. The channels can be generally serpentine. In one embodiment, the channels can turn on itself five times before exiting through the slot, as is shown in
The channels for the hydrogen can be substantially identical to the channels for the air. As they are situated on the opposite side of a repeating plate, the direction of flow of the hydrogen can be opposite to the direction of flow of air. In some instances, the channels for the hydrogen can be different from the channels for the air in one or more respects.
This combination of fins, slots and serpentine channels can reduce the risk of a MEA impingement.
Because of the exothermic reaction that occurs in the MEA, a maximum of 55 W of heat can be generated per cell. In some cases, the MEA manufacturer recommends operating the fuel cell at a temperature of 140° C. to 180° C.; however, the temperature spread across the MEA should be as low as possible. To maintain a small temperature spread, the cells can be cooled by supplying air to the space between fins and passing air along the fins. Air can be introduced into the fins using a counter flow strategy, as shown in
Before operating the high temperature fuel cell assembly 30, heaters 75 can be used to heat-up the stack to 140° C., as is shown in
To minimize temperature spread, the coolant flow must be even across each fuel cell. Accordingly, two coolant sources 60, such as knife blowers, can be used to create substantially even flow and can be positioned on both side of the stack to provide a counter flow strategy. The knife blowers can be used to direct air or any other type of coolant gas into the fuel cell assembly 30. This counter flow strategy will minimize the temperature spread across the MEA.
While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Thus, it will be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention.
This application claims the benefit of Provisional Application Ser. No. 61/266,480 entitled “HIGH TEMPERATURE PEM FUEL CELL WITH THERMAL MANAGEMENT SYSTEM”, filed Dec. 3, 2009, which is herein incorporated by reference in its entirety
Number | Date | Country | |
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61266480 | Dec 2009 | US |