Hydrophilic anode gas diffusion layer

Details Hydrophilic anode gas diffusion layer Hydrophilic anode gas diffusion layer

2002-08-30

2004-11-23

Ryan, Patrick (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Having magnetic field feature

C429S006000, C429S006000, C429S047000

Reexamination Certificate

active

06821661

ABSTRACT:

BACKGROUND
The invention generally relates to an anode gas diffusion layer for a fuel cell and methods for preparation and use thereof.
A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a polymer electrolyte membrane (PEM), often called a proton exchange membrane, that permits only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is reacted to produce protons that pass through the PEM. The electrons produced by this reaction travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the protons to form water. The anodic and cathodic reactions are described by the following equations:
H
2
→2H
+
+2
e
−
  (1)
at the anode of the cell, and
O
2
+4H
+
+4
e
−
→2H
2
O  (2)
at the cathode of the cell.
A typical fuel cell has a terminal voltage of up to about one volt DC. For purposes of producing much larger voltages, multiple fuel cells may be assembled together to form an arrangement called a fuel cell stack, an arrangement in which the fuel cells are electrically coupled together in series to form a larger DC voltage (a voltage near 100 volts DC, for example) and to provide more power.
The fuel cell stack may include flow field plates (graphite composite or metal plates, as examples) that are stacked one on top of the other. The plates may include various surface flow field channels and orifices to, as examples, route the reactants and products through the fuel cell stack. A PEM is sandwiched between each anode and cathode flow field plate. Electrically conductive gas diffusion layers (GDLs) may be located on each side of each PEM to act as a gas diffusion media and in some cases to provide a support for the fuel cell catalysts. In this manner, reactant gases from each side of the PEM may pass along the flow field channels and diffuse through the GDLs to reach the PEM. The PEM and its adjacent pair of catalyst layers are often referred to as a membrane electrode assembly (MEA). An MEA sandwiched by adjacent GDL layers is often referred to as a membrane electrode unit (MEU), or also as an MEA.
A fuel cell system may include a fuel processor that converts a hydrocarbon (natural gas or propane, as examples) into a fuel flow for the fuel cell stack. For a given output power of the fuel cell stack, the fuel flow to the stack must satisfy the appropriate stoichiometric ratios governed by the equations listed above. Thus, a controller of the fuel cell system may monitor the output power of the stack and based on the monitored output power, estimate the fuel flow to satisfy the appropriate stoichiometric ratios. In this manner, the controller regulates the fuel processor to produce this flow, and in response to the controller detecting a change in the output power, the controller estimates a new rate of fuel flow and controls the fuel processor accordingly.
The fuel cell system may provide power to a load, such as a load that is formed from residential appliances and electrical devices that may be selectively turned on and off to vary the power that is demanded by the load. Thus, the load may not be constant, but rather the power that is consumed by the load may vary over time and abruptly change in steps. For example, if the fuel cell system provides power to a house, different appliances/electrical devices of the house may be turned on and off at different times to cause the load to vary in a stepwise fashion over time. Fuel cell systems adapted to accommodate variable loads are sometimes referred to as “load following” systems.
FIG. 1
depicts an exemplary fuel cell stack assembly
10
, an assembly that includes a stack
12
of flow field plates that are clamped together under a compressive force. To accomplish this, the assembly
10
includes end plate
16
and spring plate
20
that are located on opposite ends of the stack
12
to compress the flow plates that are located between the plates. Besides the end plate
16
and spring plate
20
, the assembly
10
may include a mechanism to ensure that a compressive force is maintained on the stack
12
over time, as components within the stack
12
may settle, or flatten, over time and otherwise relieve any applied compressive force.
As an example of this compressive mechanism, the assembly
10
may include another end plate
14
that is secured to the end plate
16
through tie rods
18
that extend through corresponding holes of the spring plate
20
. The spring plate
20
is located between the end plate
14
and the stack
12
, and coiled compression springs
22
may reside between the end plate
14
and spring plate
20
. The tie rods
18
slide through openings in the spring plate
20
and are secured at their ends to the end plates
14
and
16
through nuts
15
and
17
. Due to this arrangement, the springs
22
remain compressed to exert a compressive force on the stack
12
over time even if the components of the stack
12
compress.
To establish connections for external conduits (hoses and/or pipes) to communicate the reactants, coolants and product with the manifold passageways of the stack
12
, the assembly
10
may include short connector conduits, or pipes
24
, that may be integrally formed with the end plate
16
to form a one piece end plate assembly (for example, pipes
24
may be welded to end plate
16
).
FIG. 2
depicts a surface
100
of an exemplary flow field plate
90
. The surface
100
includes flow channels
102
for communicating a coolant to remove heat from the fuel cell stack
10
. Flow channels
120
(see
FIG. 3
) on an opposite surface
119
of the plate
90
may be used for purposes of communicating hydrogen (for an anode plate configuration) or air (for a cathode plate configuration) to a fuel cell MEU.
An opening
170
of the plate
90
forms part of a vertical inlet passageway of the manifold for introducing hydrogen to the flow channels
120
(see FIG.
3
); and an opening
168
of the plate
90
forms part of a vertical outlet passageway of the manifold for removing hydrogen from the flow channels
120
. Similarly, openings
174
and
164
in the plate
90
form partial vertical inlet and outlet passageways, respectively, of the manifold for communicating an air flow (that provides oxygen to the fuel cells); and openings
162
and
166
form partial vertical inlet and outlet passageways, respectively, of the manifold for communicating the coolant to the flow channels
102
. While flow field channels generally have uniform square or circular cross-sectional profiles, channels are also known that have trapezoidal cross-section profiles (channel walls are not perpendicular to channel floors), and square and trapezoidal profiles with channel walls and floors intersected at selected angles or in rounded portions.
As shown in
FIG. 3
, the flow field plate
90
may be designed so that a gasket
190
may be formed on either surface
119
or
100
of plate
90
. Conventionally, each flow field plate includes a gasket groove on one side to receive a gasket. However, the gasket
190
may also be adhered to or formed on either side of the plate
90
.
Referring to
FIG. 4
, an example of a fuel cell
38
is shown such as those included in the stack shown in
FIG. 1
, utilizing flow field plates
40
and
42
such as those shown in
FIGS. 2 and 3
. As an example, fluid flow field plate
40
might serve as an anode side of the fuel cell, circulating reformate through flow field channels
54
. Similarly, fluid flow field plate
42
might serve as a cathode side of the fuel cell, circulating air through flow field channels
56
. Catalysts
46
and
48
, which facilitate chemical reactions, are applied to the anode and cathode sides, respectively, of solid electrolyte
44
. The MEA (including PEM
44
and catalyst layers
46
and
48
) is sandwiched between anode and cathode GDLs
50
and
52

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