Exemplary embodiments pertain to the art of fuel cells, and in particular to direct methanol fuel cells.
The increased use of electrical power in, for example, aircraft systems and other portable and mobile environments, requires advanced electrical storage systems and/or a chemical to electrical power conversion system to generate adequate amounts of electrical power. Both high system efficiency and high power density of the conversion system are required.
Fuel cell-based power systems, such as direct methanol fuel cell (DMFC)-based power systems, are promising power sources for such applications due to the high energy density and the ease of transport and storage of methanol, and relatively simple system structure, with a reaction of methanol and oxygen outputting water and carbon dioxide, and producing electrical energy. Typical DMFC systems, however, can only operate with diluted methanol fuel, typically 1.6 to 9.6 percent by weight of methanol, diluted with water. Such systems usually have a pure methanol reservoir, and mix the pure methanol with product water to get a diluted fuel flow. This adds complexity and high flows plus a mixing reservoir which is extra mass and volume. Further, utilizing highly diluted methanol fuel decreases power and energy density of the system. Using higher methanol concentrations typical leads to lower cell performance due to higher methanol crossover.
An alternative approach is a vapor feed DMFC, in which a higher methanol concentration solution is evaporated before feeding into the cell. In such systems, however, the cells must always be maintained at a high temperature, above the fuel's boiling point, to prevent fuel condensation. This approach increases system complexity and energy usage, and results in difficulties in system operation, especially at a cold start condition. Additionally, water management is always a challenge for typical DMFC systems having solid plates, leading to lower cell performance, especially when operating with a high methanol concentration solution via a vapor feed.
In one embodiment, a direct methanol fuel cell includes a cathode electrode, an anode electrode and a membrane located between the anode electrode and the cathode electrode. An anode hydrophilic microporous plate (HMP) is located at an anode side of the fuel cell. The anode HMP has a front side and a back side opposite the front side, and the front side is positioned closer to the anode electrode than the back side. An anode gas diffusion layer is located in an anode chamber defined between the anode electrode and the anode HMP. A flow of methanol fuel is introduced into the back side of the anode hydrophilic microporous plate or to the anode chamber.
Additionally or alternatively, in this or other embodiments the flow of methanol fuel has a concentration of between 1% and 100% by weight of methanol.
Additionally or alternatively, in this or other embodiments the flow of methanol fuel is introduced into the fuel cell in a liquid phase.
Additionally or alternatively, in this or other embodiments a blower is located at the anode side to internally circulate gases in the anode chamber.
Additionally or alternatively, in this or other embodiments one or more valves are configured to selectably direct the liquid flow of methanol fuel to the back side of the anode HMP or to the anode chamber.
Additionally or alternatively, in this or other embodiments the flow of methanol fuel is selectably introduced to a back side of the anode HMP or to the anode chamber based on a concentration of methanol in the flow of methanol fuel.
Additionally or alternatively, in this or other embodiments a cathode hydrophilic microporous plate (HMP) is located at a cathode side of the fuel cell. The cathode HMP has a front side and a back side opposite the front side. The front side is located closer to the cathode electrode than the back side. A cathode gas diffusion layer is located between the cathode electrode and the cathode HMP. A liquid flow of deionized water or a water-based solution is introduced into the back side of the cathode HMP.
Additionally or alternatively, in this or other embodiments the anode electrode, the cathode electrode and the membrane are constructed as a membrane electrode assembly.
Additionally or alternatively, in this or other embodiments the anode gas diffusion layer is one of hydrophilic or hydrophobic.
Additionally or alternatively, in this or other embodiments the cathode gas diffusion layer is one of hydrophilic or hydrophobic, and a hydrophilic gas diffusion layer is preferred.
In another embodiment, a method of operating a direct methanol fuel cell includes providing a fuel cell, including a cathode electrode, an anode electrode, and a membrane located between the anode electrode and the cathode electrode. An anode hydrophilic microporous plate (HMP) is located at an anode side of the fuel cell. The anode HMP has a front side and a back side opposite the front side. The front side is located closer to the anode electrode than the back side. An anode gas diffusion layer is located in an anode chamber defined between the anode electrode and the anode HMP, and a flow of methanol fuel is selectably into the back side of the anode HMP or to the anode chamber.
Additionally or alternatively, in this or other embodiments the flow of methanol fuel is selectably introduced to the back side of the anode HMP or to the anode chamber based on a concentration of methanol in the flow of methanol fuel.
Additionally or alternatively, in this or other embodiments the flow of methanol fuel is introduced to the fuel cell at the anode chamber when a concentration of methanol in the flow of methanol fuel is less than or equal to 15% by weight of methanol.
Additionally or alternatively, in this or other embodiments the flow of methanol fuel is introduced to the fuel cell at the back side of the anode HMP when a concentration of methanol in the flow of methanol fuel is greater than 15% by weight of methanol.
Additionally or alternatively, in this or other embodiments the flow of methanol fuel is introduced into the fuel cell in a liquid phase.
Additionally or alternatively, in this or other embodiments the flow of methanol fuel introduced into the back side of anode HMP is maintained under a negative pressure against the gases pressure in the anode chamber.
Additionally or alternatively, in this or other embodiments the operating pressure of the flow of methanol fuel in the back side of anode HMP is about 0.5 lbf/in2 to 10 lbf/in2 less than the gases pressure in the anode chamber,
Additionally or alternatively, in this or other embodiments the gases in the anode chamber are internally circulated via a blower to enhance evaporation and diffusion of the methanol vapor from the anode HMP to anode electrode.
Additionally or alternatively, in this or other embodiments the flow of methanol fuel is selectably directed to the back side of the anode HMP or to the anode chamber via operation of one or more valves.
Additionally or alternatively, in this or other embodiments the method includes providing a cathode hydrophilic microporous plate (HMP) located at a cathode side of the fuel cell. The cathode HMP has a front side and a back side opposite the front side. The front side is located closer to the cathode electrode than the back side. A cathode gas diffusion layer is located between the cathode electrode and the cathode hydrophilic microporous plate. A liquid flow of deionized water or a water-based solution is circulated at the back side of the cathode HMP under a negative pressure against the gases pressure in the cathode chamber, and an oxidant is introduced into the cathode chamber.
The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:
and
A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.
Referring to
The anode side 12 includes a hydrophilic microporous plate (HMP) 24 working as anode bipolar plate, which may or may not have flow channels superimposed on one side or both sides of the anode HMP 24. In some embodiments, the anode side 12 also includes an anode gas diffusion layer (GDL) 26. The anode GDL 26 is located closer to the MEA 16 than is the anode HMP 24. As shown in
Referring again to
The fuel cell 10 structure described herein is effectively usable with a methanol flow of fuel 28 in a wide range of concentrations from, for example, 1 percent by weight methanol to 100 percent by weight methanol. Shown in
Referring now to
In other embodiments, such as shown in
As illustrated, the fuel cell 10 may be provided with one or more valves 42 and fuel input lines 44. Depending on a methanol concentration of the flow of fuel 28, a controller 46 commands opening and/or closing of valves 42 to direct the liquid phase flow of fuel 28 either to the back side 30 of the anode HMP 24 or to the front side 31 of the anode HMP 24. In some embodiments, operation of the fuel cell 10 may be started with a liquid flow of fuel 28 with a relatively high concentration of methanol, for example 100% methanol, and the liquid flow of fuel 28 is introduced to the back side 30 of the anode HMP 24 under a small negative pressure against the gases pressure in the anode GDL 26. As the fuel cell 10 operates, product water produced by the fuel cell 10 may be added to the flow of fuel 28, thus diluting the flow of fuel 28 over time. As the flow of fuel 28 is diluted to be of a low methanol concentration in a range of about 15% by weight or less of methanol, the operation of the valves 42 may be changed to selectably direct the flow of fuel 28 to the front side 31 of the anode HMP 24 at the anode chamber 35. Such an operation can gain excellent fuel utilization and efficiency.
The fuel cell 10 disclosed herein having an anode HMP 24 and a cathode HMP 32 provides improved water management in the fuel cell 10 and a vapor fuel feed without heating of the liquid flow of fuel 28 and without requiring high operating temperature of the fuel cell 10. Further, the fuel cell 10 can efficiently operate with a wide range of methanol solutions, from a very diluted methanol solution up to 100% methanol. Utilizing high to pure concentrations of methanol fuel significantly improves the overall system power and energy density, and reduces fuel storage needed. The fuel cell 10 may further operate at a wide range of fuel cell 10 temperatures, from above 0 degrees Celsius up to the fuel 28 or water boiling point, which depends on the system's operating pressure. Further, since heating of the flow of fuel 28 is not needed, the fuel cell 10 has a simple start-up and shutdown.
The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.
While the present disclosure has been described with reference to an exemplary embodiment or embodiments, 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 present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.