WO2007053560A2

WO2007053560A2 - Method of operating a fuel cell stack

Info

Publication number: WO2007053560A2
Application number: PCT/US2006/042344
Authority: WO
Inventors: Michael K. Budinski; Craig S. Gittleman; Christopher L. Lewis; Daniel P. Miller; Yeh-Hung Lai
Original assignee: General Motors Corp
Current assignee: Motors Liquidation Co
Priority date: 2005-10-31
Filing date: 2006-10-31
Publication date: 2007-05-10
Anticipated expiration: 2008-04-30
Also published as: US20070122662A1; US8232011B2; CN101300703B; DE112006003028T5; WO2007053560A3; DE112006003028B4; CN101300703A

Abstract

One aspect of the invention includes the discovery that pinholes in the membrane of the membrane electrode assembly may be caused by hygroexpansive ratcheting.

Description

METHOD OF OPERATING A FUEL CELL STACK

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims the benefit of U.S. Provisional Application number 60/731 ,804 filed October 31 , 2005.

TECHNICAL FIELD

[0002] The present invention relates to a method, and more particularly, to a method of operating a fuel cell stack.

BACKGROUND

[0003] One of the key challenges in the race to commercialize fuel cells for vehicle applications is developing membrane electrode assemblies (MEAs) that can meet industry durability targets. Polymer electrolyte membranes (PEMs) are some of the most promising membranes for automotive applications. These membranes serve to conduct protons from the anode electrode to the cathode electrode of the fuel cell while preventing the crossover of reactant gases: hydrogen and oxygen. State-of-the-art PEM fuel cells for high power density operations utilize perfluorosulfonic acid (PFSA) membranes which may be about 25 microns thick or less. To be successful in automotive applications, these membranes must survive ten years of vehicle operation or 5500 hours of operation including transient conditions and start-stop and freeze-thaw cycles. The requirements on the chemical and mechanical stability of these thin membranes are significantly more demanding compared to the thicker membranes (100-200 μm) used in the past. Fuel cells cannot operate effectively if even small amounts of these gases are allowed to permeate through the membrane through, for example, microscopic pinholes in the membrane. Ultimately, fuel cells fail because such pinholes develop and propagate within the polymer membranes.

SUMMARY OF EXEMPLARY EMBODIMENTS A method of operating a fuel cell stack to prevent mechanical failure of fuel cell membranes due to hygroexpansive ratcheting comprising: providing a plurality of fuel cells each comprising a membrane and an anode electrode catalyst layer and a cathode electrode catalyst layer; the membrane and electrodes being interposed between bipolar plates, each bipolar plate have a face including a reactant flow field defined, at least in part, by a plurality of lands and channels; humidifying the fuel cell stack; cycling the humidity in the fuel cell stack from a condition below 100 percent relative humidity to a condition at 100 percent relative humidity or where there is condensation of water, and wherein at least two of the following conditions (a-h) are met:

(a) wherein the cycling of the humidity comprises drying the fuel cell stack at a rate less than 0.2 λ/sec; (b) the membrane comprises an extruded membrane;

(c) the planar expansion of the membrane during the cycling of the humidity is equal to or less than 25 percent;

(d) the magnitude if the humidity cycle is less than 50% relative humidity;

(e) wherein each of the anode electrode catalyst layer and the cathode electrode catalyst layer are substantial free of cracks;

(f) operating the fuel cell stack at potentials below 700 mV;

(g) wherein the lowest compression between the gas diffusion media and the MEA over each channel is at least 0.2 MPa; or

(h) wherein a conductive restrictive layer underlies or overlies at least one of the anode electrode catalyst layer or the cathode electrode catalyst layer to restrict the planar expansion of the membrane, to prevent the membrane from being pinched in a crack formed in one of the anode electrode catalyst layer or the cathode electrode catalyst, or to arrest the propagation of an incipient crack in one of the electrode catalyst layers. Anther embodiment of the invention includes a product comprising: a polyelectrolyte membrane and an anode electrode catalyst layer and a cathode electrode catalyst layer over opposite faces of the membrane; a conductive restrictive layer underlying or overlying at least one of the anode electrode catalyst layer or the cathode electrode catalyst layer to restrict the planar expansion of the membrane, to prevent the membrane from being pinched in a crack formed in one of the anode electrode catalyst layer or the cathode electrode catalyst or to arrest the propagation of an incipient crack in one of the electrode catalyst layers.

[0006] Other embodiments of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS [0007] Exemplary embodiments of the invention will become more fully understood from the detailed description and the accompanying drawings which are briefly described as follows. [0008] Figure 1 illustrates a step in hygroexpansion ratcheting discovered in the course of developing an embodiment of this invention. [0009] Figure 2 illustrates a step in hygroexpansion ratcheting discovered in the course of developing an embodiment of this invention. [0010] Figure 3 illustrates a step in hygroexpansion ratcheting discovered in the course of developing an embodiment of this invention. [0011] Figure 4 illustrates a step in hygroexpansion ratcheting discovered in the course of developing an embodiment of this invention. [0012] Figure 5 illustrates a step in hygroexpansion ratcheting discovered in the course of developing an embodiment of this invention. [0013] Figure 6 is a graphic illustration of the crossover leak as a function of the number of humidity cycles during inert RH cycling for several membranes. [0014] Figure 7 is the graphic illustration of tear test results for several membranes. [0015] Figure 8 is a graphic illustration of the result of dimensional stability testing performed on several membranes. [0016] Figure 9 is a graph illustrating crossover leak as a function of number of humidity cycles for a membrane. [0017] Figure 10 is a graph illustrating the results of a test of the crossover leak as a function of the number of humidity cycles during inert RH cycling of a

PTFE, hydrocarbon and partially fluorinated hydrocarbon membranes. [0018] Figure 11 illustrates a fuel cell according to one embodiment of the invention. [0019] Figure 12 illustrates a fuel cell according to one embodiment of the invention. [0020] Figure 13 is a graph illustrating the amount of fluoride released during steady state and RH cycling operation for various membranes. [0021] Figure 14 illustrates a portion of a fuel cell according to one embodiment of the invention. [0022] Figure 15 is a graph illustrating the improvement in cycles to failure of a fuel cell having electrodes with no mud-cracks according to one embodiment of the invention compared to a fuel cell having electrodes with mud-cracks. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0023] The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0024] During operation, PEM fuel cells will see temperatures ranging from subzero to 100⁰C and a variety of humidification levels including exposure to liquid water. As the PFSA membranes absorb water they undergo significant volumetric swelling. Nafion^® NR-111 (25 μm solution-cast) absorbs 50 Wt% of water at 100°C, and undergoes 10% and 15% linear expansion at 23⁰C and 100⁰C respectively. Upon dehydration, PFSA membranes shrink to smaller than their original size. For example Nafion^® shrinks by about 7% and 11% from its initial area upon dehydration after soaking in water at 80⁰C and 100⁰C respectively. These membranes will experience tensile, compression and shear stresses as their dimensions change with fluctuations in temperature and humidity levels while constrained in fuel cell architectures. The membranes also experience other stresses during fuel cell operation. For example, membranes are compressed between sheets of carbon based diffusion media at pressures up to 3.5 MPa. As with other engineering materials, mechanical fatigue can reduce the membrane strength over time, leading to mechanical membrane degradation and reduced fuel cell durability.

[0025] Furthermore, the glass transition temperature for perfluorosulfonic acid membranes such as Nafion^® occurs within fuel cell operating temperatures ranging from 60-100⁰C. Thus, the polymer experiences structural as well as dimensional changes during fuel cell operation. Perfluorosulfonic acid membranes are susceptible to chemical attack by hydroxyl and other radicals, which subsequently impact the mechanical integrity of the membrane.

[0026] One embodiment of the invention includes the discovery that pinholes in the membrane of a membrane electrode assembly may be caused by hygroexpansive ratcheting. The process of hygroexpansive ratcheting of a membrane electrode assembly is illustrated in Figures 1-5. Referring now to Figure 1, a fuel cell stack 10 includes a fuel cell unit which includes a membrane electrode assembly that includes an ionic membrane 100 having a first face 12 and an opposite second face 14, and a first catalyst layer 16 overlying the first face 12 and a second catalyst layer 18 overlying the second face 14. For example, the first catalyst layer 16 may serve as an anode and the second catalyst layer 18 may serve as a cathode. The membrane 100, first catalyst layer 16 and second catalyst layer 18 may be subject to restraints 401 , 402, 403 and/or 404 which apply force Ri, R₂, R₃ and R₄ respectively. In embodiment wherein a fibrous gas diffusion media layer such as carbon fiber paper is used, the restraints 401 , 402, 403 and 404 are each fibers of the gas diffusion media layer.

[0027] Referring now to Figure 2, the membrane electrode assembly which includes the ionic membrane 100 and the first catalyst layer 16 and the second catalyst layer 18 swells during a wet state operation of the fuel cell. The electrode membrane assembly, most particularly the ionic membrane 100, swells primarily in the thickness direction because the planar constraints such as those provided by 401 , 402, 403 or 404 cause planar compressive stresses. A force F is exerted on the membrane electrode assembly in an inward or compressive direction indicated by arrows 36 towards the center of the space between adjacent restraints 401 and 402, or 304 and 404. The upheaval of the ionic membrane 100 causes the catalyst layers 16 and 18 to form cracks 38 therein. With time, the stresses on the MEA will decay as a consequence of material flow or creep.

[0028] Referring now to Figure 3, when the humidity in the fuel cell is reduced or the fuel cell is in a dry state, the membrane electrode assembly shrinks, particularly the ionic membrane 100. Because of stress relaxation that occurred during the aforementioned swollen state, a tensile force F is exerted on the membrane electrode assembly, as it shrinks, in a outwardly direction as indicated by arrows 36 away from the center of the space between adjacent restraints and towards the points of compression applied by restraints 401 and 402, or 403 and 404. The cracks 38 in the first catalyst layer 16 and the second catalyst layer 18 widens to expose separation ends 40 in each of the catalyst layers 16 and 18. With time, the tensile stress decays as a consequence of material flow or creep.

[0029] Referring now to Figure 4, when the fuel cell is operated again in a humidified state, the membrane electrode assembly, particularly the ionic membrane 100 swells and a protuberance 42 of the ionic membrane 100 extends into the crack 38 between the separation ends 40 of the first catalyst layer 16 or the second catalyst layer 18. As the membrane electrode assembly swells a force F is exerted on the membrane electrode assembly inwardly in the direction of arrows 36 towards the center of the space between adjacent restraints 401 and 402, or 403 and 404. With time, the stresses on the MEA will decay as a consequence of material flow or creep.

[0030] Referring now to Figure 5, as the humidity in the fuel cell is reduced or the fuel cell is in a dry state, the membrane electrode assembly including the ionic membrane 100 shrinks. Because of stress relaxation that occurred during the aforementioned swollen state, a tensile force F is exerted on the membrane electrode assembly, particularly the ionic membrane 100, in an outward direction as indicated by arrows 36 away from the centers of the space between adjacent restraint and towards the points of compression applied by restraints 401 and 402, or 403 and 404. The protuberance 42 is trapped between the separation ends 40 of each of the first catalyst layer 16 and second catalyst layer 18 as the membrane 100 continues to shrink. As a result, a crack or tear 44 may develop in the ionic membrane 100. With continued wet-dry cycling, the tears 44 may eventually extend through the thickness of the ionic membrane 100. That is, pinholes may develop through the thickness of the ionic membrane 100.

[0031] Although Figures 1-5 illustrate a failure mechanism involving the fibers of a gas diffusion media, failures of the membrane or MEA through hygroexpansive ratcheting may involve forces applied by the lands of the bipolar plates, and may occur in the presence of other materials such as a microporous layer overlying the gas diffusion media layer. Cracks in the electrodes and pinholes in the membrane may develop under a variety of circumstances in which the membrane undergoes hydroexpansion.

[0032] The invention includes the discovery that pinhole development in the ionic membrane may be significantly reduced or eliminated utilizing an ionic membrane produced from an extrusion process. These extruded membranes exhibit superior durability as will be appreciated from the following.

[0033] A variety of membranes were subjected to cyclic stresses by intermittently flowing wet and dry air over the membrane in a non-operating fuel cell. Membrane electrode assemblies with anode and cathode platinum loadings of 0.4 mg/cm² were built in 50 cm² cells using flow fields with 2 mm wide straight channels separated by 2 mm wide lands. The membrane electrode assemblies were compressed between two pieces of commercially available carbon fiber gas diffusion media. The cycle consisted of flowing 2.0 SLPM of 150% RH air (9O⁰C dew point at 80⁰C) over both the anode and cathode sides of the membrane electrode assembly for two minutes followed by flowing 2.0 SLPM of dry air over both sides of the cell for two minutes. The tests ran isothermally at 8O⁰C with no backpressure. To ensure that any failures that occurred were induced solely by mechanical stresses, no hydrogen gas was used and no current was drawn from the cell during the test. Membrane failure was determined by periodically measuring the flow of air across the membrane with a 3 psi pressure applied to one side of the cell.

[0034] The mechanical properties of the membrane were also evaluated.

Data was collected for both the machine and transverse direction for all samples. Tensile tests were conducted using ASTM method D882. The tests were conducted at 23⁰C and 50% RH using a 25 mm wide sample with 50 mm between the grips and a loading rate of 500 mm/min. Tests were also conducted with the membrane submerged in the deionized water at 8O⁰C. Tear tests were conducted using ASTM method D624 (Die B). The tests were conducted at 23°C and 50% RH with a loading rate of 50 mm/min. The peak load and the energies to break are determined as described in the ASTM procedures. Averages and standard deviations for both the tensile and tear tests were based on five replicate samples.

[0035] The dimensional stability of the PFSA membranes was measured as well. The membranes were cut into 200 mm x 125 mm sheets. The membranes were equilibrated at 23°C and 35% RH overnight before recording the initial dimensions. The membranes were then dried at 80⁰C for one hour and the dimensions were measured. The membranes were subsequently soaked in the deionized water at 80⁰C for two hours and the dimensions were measured again. The membranes were then dried again at 80⁰C for one hour and the dimensions were measured. Finally the membranes were allowed to equilibrate at 23⁰C and 35% RH overnight before recording the final dimensions.

[0036] There are a variety of PFSA membranes available with equivalent weights ranging from 700-1100. The membrane processing method can also vary. DuPont manufactures a solution-cast form of a hydrolyzed Nafion® 1100 EW 25 μm membranes as NR-111 (currently sold as NRE-211). Ion Power, Inc., manufactures an alternative form of hydrolyzed Nafion® 1100 EW 25 μm membranes as N111-IP. Both these Nation® membranes are homogenous and are made using 1100 EW Nafion®. There are also methods of mechanically reinforcing PFSA membranes. For example, WL Gore manufactures expanded polytetrafluoethylene (ePTFE) micro reinforced composite PFSA membranes under the Gore Primea® product line. These reinforced membranes have been shown to have improved tear resistance and dimensional stability compared to homogeneous membranes.

[0037] Homogeneous DuPont NR-111, the homogeneous Ion Power N111-IP and the composite Gore Primea® series 57 membranes were tested for durability under inert relative humidity cycling conditions described above. Two cells were run for each type of membrane electrode assembly. The progression of crossover leak as a function of the number of humidity cycles is shown in Figure 6. Failures in these tests were defined as 10 seem crossover. The NR-111 fails after about 4000 cycles, whereas after 20,000 cycles there is no detectable leak in the N111-IP membrane. Composite Gore Primea® membrane electrode assemblies fail due to crossover between 6,000-7,000 cycles. These results indicate that the mechanical reinforcement is not sufficient to prevent mechanical failure caused by humidity cycling.

[0038] Mechanical properties of membranes used were measured to determine if there was any correlation between these properties and the results of the humidity cycling tests. Tensile test results of NR-111 , N111-1 P and Gore Primea® membranes are shown in Table 1 below. Tensile strength, yield strength, elongation at break and Young's Modulus are reported. None of these properties stands out as significantly different for the N111-IP compared to the other membranes that would suggest that N111-IP would exhibit superior durability in the humidity cycling test.

Table 1

Membrane NR-111 N111-IP Gore™ Primea^® unit MD +/- TD +/. MD +/- TD +/- MD +/- TD +/-

50% RH, 23°C

Tensile

Strength MPa 30.5 3.9 28.0 3.0 32.6 3.6 37.5 4.0 35.0 1.4 32.3 3.3

Yield Strength

(2% offset) MPa 14.4 0.0 14.0 0.2 14.1 0.6 14.9 0.2 18.0 0.5 15.6 0.8

Elongation % 253 49 235 36 176 19 141 20 196 37 147 29

Young's

Modulus MPa 272 21 253 17 304 8 319 7 324 51 340 19 submerged, 80⁰C

Tensile

Strength MPa 8.9 2.9 9.5 2.1 17.2 5.5 16.1 8.4 18.4 0.7 15.1 0.8

Yield Strength

(2% offset) MPa 4.4 0.3 4.6 0.2 5.0 5.0 5.3 0.4 5.2 0.2 4.1 0.1

Elongation % 159 127 188 117 193 81 127 90 153 22 157 26

Young's

Modulus MPa 23.9 3.8 25.1 5.1 45.0 5.6 51.5 4.2 58.0 2.7 28.3 1.7

[0039] The tear test results are summarized in Figure 7. The peak load and the energy to break the membranes are recorded. It was found that the Nafion® N111-IP exhibits the lowest peak load and the smallest energy to break of these three membranes tested. Thus, its superior durability in the humidity cycling test cannot be attributed to better tear resistance. Also, while the composite Gore Primea® membrane is the most tear resistant, it is not resistant to humidity cycling induced failure. This enhancement in tear resistance has been attributed to the ePTFE reinforcement.

[0040] The results of the dimensional stability tests are shown in Figure 8.

The percent swelling is defined as the area change from the initial dimensions to those measured after soaking for two hours at 8O⁰C. The percent shrinking is defined as the area change from the initial dimensions to those measured after drying for one hour at 80⁰C after the soak which are recorded as negative values. The percent swollen-shrunken is defined as the area change from the swollen dimensions after soaking for two hours at 80⁰C to the shrunken dimensions after drying for one hour at 8O⁰C. The Nafion N111-IP exhibits the smallest amount of swelling when submerged at 8O⁰C and also the smallest difference in area change between the swollen and the shrunken states. The above illustrates that cycling between dry (less than 5% RH) operation and exposure to liquid water causes mechanical failure of some of the PFSA membranes. However, under expected operating conditions of a fuel cell, the membranes may never be completely dried out. Therefore, the impact of humidity cycling without completely drying out the membranes was examined. Figure 9 shows results of humidity cycling of Gore Primea® membrane electrode assemblies from either 0%, 50%, or 80% relative humidity to supersaturated conditions. In these tests, the relative humidity cycle consist of 2.5 minutes at 150% relative humidity followed by 3.5 minutes at drier conditions. All tests were conducted at 80⁰C and no backpressure. The time to crossover failure increased from 4000 to 7000 to 14000 cycles and the magnitude of the relative humidity swing is decreased. The results indicate that the smaller the magnitude of humidity swing, the longer the life of the membrane. However, even relatively small humidity swings, such as from 80% relative humidity to liquid water, will eventually lead to mechanical membrane failure. These types of relative humidity swings would certainly be expected during fuel cell operations.

[0042] While PFSA membranes are chemically very stable, they are known to degrade in the fuel cell environment via hydroxyl-radical attack, strongly enhanced by the presence of trace cation contamination. The mechanism is quite complicated, depending on ionomer structure, cation level, catalyst components, electrode design, relative humidity, temperature, current density, and other factors.

[0043] To evaluate the impact of chemical degradation on membrane mechanical failure, in-situ 50 cm² relative humidity cycling tests have been conducted with reactive gases (H₂ and air) and at a constant current density of 0.1 A/cm². In these tests both the anode and cathode stoichiometries were 20 to provide essentially uniform relative humidity throughout the cell. The other conditions were identical to the inert gas RH cycling test described above (2 min. 0% RH feed/2 min. 150% RH feed, 8O⁰C, 0 kPag). Failure in these tests was identified at 10 seem crossover leak. The results for both homogeneous 25 μm Nafion® 1100 EW membranes and the reinforced Gore Primea® membrane electrode assemblies are shown in Table 2 below. For all membranes, operation at 0.1 A/cm² significantly accelerates membrane failure. The failure times for the DuPont NR-111 and the Gore Primea® membrane electrode assemblies are reduced by a factor of 5 relative to the inert humidity cycling test. The Ion Power N111-IP did not fail in the inert test after 20,000 cycles, but developed crossover leaks after 1800 humidity cycles at 0.1 A/cm², indicating at least a ten-fold lifetime reduction. Clearly chemical degradation of PFSA membranes causes mechanical weakening.

Table 2: Comparison of RH cycling with inert gases at 0.1 A/cm²

[0044] In order to quantify the magnitude of chemical degradation during these tests, the water exhausted from the fuel cell was collected and the fluoride composition was measured using ion chromatography. It is well known that hydrogen fluoride (HF) is a byproduct of oxidative degradation of PFSA polymers (Journal of Power Sources, Volume 131, Issues 1-2, 14 May 2004, Pages 41-48, Curtin et al). Thus, an indication of the degree of membrane degradation can be determined by measuring the HF content in the water exhausted from the fuel cell. At the beginning of these tests, each cell was run at constant feed conditions with fully humidified inlets for 24 hours. Water was also collected during this 24 hour period of steady state operation and the fluoride composition was measured using ion chromatography. The amount of fluoride released during steady state and RH cycling operation of the cells are compared in Figure 13. The results in Figure 13 show that for all three membranes tested the fluoride release rate (FRR) is approximately 10 times higher during RH cycling than during steady state operation. These results indicate that the degree of chemical degradation of PFSA membranes is accelerated by RH cycling.

[0045] Thus it is recommended that RH cycling be avoided especially during conditions known to accelerate the attack of PFSA polymers. At the conditions of the experiments described above, the cell potential was generally above 700 mV. Additional experiments have shown that chemical degradation of PFSA membranes increases with increasing cell potential (E. Endoh, S. Terazano, H. Wϊdjaja, Y. Takimoto, Electrochem. Solid-State Lett. 7, A209- A211). Efforts should be made to limit RH swings when operating a fuel cell at potentials above 70OmV.

[0046] Tests were also run on a variety of hydrocarbon and partially- fluorinated hydrocarbon proton-conductive membranes for mechanical durability. The results from the in-situ humidity cycling (0-150% relative humidity) test at 80⁰C are shown in Figure 10. None of the hydrocarbon or partially-fluorinated hydrocarbon polymer membranes lasted more than 400 cycles before developing a crossover leak. This is an order of magnitude lower than the least durable of the PFSA membranes.

[0047] Referring to Figure 11, one embodiment of the invention includes a fuel cell stack including a plurality of fuel cells 10 including an extruded ionic membrane 100 having a first catalyst layer 16 on one face 12 thereof and a second catalyst layer 18 on a second face 14 thereof. A first bipolar plate 20 overlies the first catalyst layer 16. A variety of additional layers may optionally be interposed between the bipolar plate 20 and the first catalyst layer 16. The first bipolar plate 20 includes a reactant gas flow field defined in part by a first land 24 and a second land 26 separated by a channel 28. A second bipolar plate 22 is provided over the second catalyst layer 18, and again, additional optional layers may be interposed between the second bipolar plate 20 and the second catalyst layer 18. The second bipolar plate 22 includes a reactant gas flow field defined in part by a first land 30 and a second land 32 separated by a channel 34. In one embodiment of the invention a first microporous layer 46 overlies the first catalyst layer 16 and similarly a second microporous layer 48 overlies the second catalyst layer 18. Alternatively, as shown in Figure 14, a first conductive restrictive layer 200, such as aramid or polytetrafluoroethlene fibers, with an ionomer, may be placed over or adhered to the membrane electrode assembly to limit the buckling of the MEA. In embodiments wherein the first conductive resistive layer 200 is adjacent the membrane 100, the conductive resistive layer 200 must be proton conducting. Alternatively, the restrictive layer 200 may be, for example, expanded polytetrafluoroethylene and an ionomer. A second conductive restrictive layer 202, as an alternative to or in addition to the first conductive restrictive layer 200, may be placed over one or more of the catalyst layers 16, 18. The second conductive restrictive layer 202 may be made of the same materials as the first conductive restrictive layer 200. Alternatively, the second conductive restrictive layer 202 may be, for example, an electrically conductive epoxy layer. The catalyst layers 16, 18 are known in the art and may include an unsupported catalyst or a catalyst supported on particles, such as carbon, and further including an ionomer. Referring again to Figure 11 , a first gas diffusion media material 50 may overlie the first microporous layer 46 and a second gas diffusion media 52 may overlie the second microporous layer 48. A first bipolar plate 20 may overlie the gas diffusion media and a second bipolar plate 22 may overlie the second gas diffusion media 52.

[0049] Referring now to Figure 12, another embodiment of the invention includes a fuel cell stack 10 similar to that illustrated in Figure 11 , however in this case, a first sealing gasket 54 overlies a first face 12 of the ionic membrane 100 and a second sealing gasket 56 overlies the second face 14 of the ionic membrane 100. As indicated above, in an alternative embodiment, the first and second sealing gaskets 54, 56 may overlie the first catalyst layer 16 and second catalyst layer 18 respectively.

[0050] One embodiment of the invention includes operating a fuel cell wherein the rate of drying δλ/δ time is less than 0.2 λ per second. Again, Lamda (λ) as used herein is defined as the number of water molecules per unit proton in the ionomer (H₂O/H⁺) - physically, it is the level of hydration. The membrane mechanical life, determined by the number of cycles to reach gas crossover leak in RH cycling test, is directly related to membrane stress. In turn, membrane stress is a strong function of water content, dehydration rate, temperature, and heating/cooling rate. The relationship between membrane stress and fatigue life can be represented using a fatigue life curve, which as in common mechanical engineering practice is referred to as an S-N curve. According to the S-N curve, higher membrane stresses generally correspond to lower fuel cell durability. The present inventors have recognized that membrane stress can be minimized by properly controlling variables like membrane dehydration rate, water content, and temperature. By minimizing membrane stress, the membrane fatigue life can be prolonged. In one embodiment of the invention, we have established an S-N curve for Gore Primea® MEA through a series of RH cycling tests under various test conditions which include different ranges of RH changes from hydrated to dehydrated states, range of cycling frequencies, and range of temperatures. The membrane stress for each condition was determined through a suitable membrane stress model. An example of a suitable membrane stress model which we developed is as follows:

where values for the membrane hydration λ, Δλ, the membrane temperature T, the coefficient of hygro expansion β, and the uniaxial creep compliance D are input from material tests and fuel cell system tests, and where λ, Δλ represent the water content of the membrane in terms of the number of water molecules per acid site with an unit of H₂θ/H⁺, ε,y is a strain tensor, σ represents stress, t represents time, δy is the Kronecker delta, B is the bulk creep compliance, s is the dilatational component of the applied stress, s,jis the deviatoric component of the applied stress, and ξ is an integration variable representing time. See Third International Conference on Fuel Cell Science, Engineering and Technology, Ypsilanti, Ml May 23-25, 2005 Yeh-Hung Lai, Viscoelastic Stress Model and Mechanical Characterization of Perfluorosulfonic Acid (PFSA) Polymer Electrolyte Membranes. FUELCELL2005-74120. The particulars of this membrane stress model are beyond the scope of the present invention and can be gleaned from a variety of suitable teachings on stress modeling. The model is presented here merely for illustrative purposes and should not be used to limit the scope of the invention. Using the fatigue life curve, S-N curve, we have found that by carefully controlling the dehydration rate, we can significantly reduce the membrane stress, and therefore, prolong the membrane fatigue life. In a non- controlled RH cycling test condition of changing the gas flow humidity from 0%RH to 150%RH at 80⁰C with a dwell time of 2 minutes at each humidity condition, the membrane has a fatigue life of about 6000 cycles. In this test condition, it is determined that the average membrane dehydration rate is about 0.2 H₂O/H⁺ per second. By reducing the dehydration rate to 0.1 H₂O/H⁺ per second, it has been determined that the membrane fatigue life increased by 57%. Furthermore, by reducing the dehydration rate to 0.05 H₂O/H⁺ per second, we determined that the membrane fatigue life can be increased by 220%. The results are summarized in the table as follows.

[0051] In one embodiment of the invention a fuel cell stack includes a membrane electrode assembly, and bipolar plates constructed and arranged so that the planar aerial hygroexpansion of the membrane is less than 25% during a humidity cycle ranging from 80 dry to 80⁰C wet. [0052] In another embodiment of the invention a fuel cell stack includes a plurality of membrane electrode assemblies wherein the membrane is manufactured from an extrusion process. The extruded membranes may be either perfluorinated, partially fluorinated or hydrocarbon membranes

[0053] Another embodiment of the invention includes operating a fuel cell stack so that the magnitude of the humidity cycle is less than 50% RH and preferably no more than 20% RH. It is also preferable to avoid cycling between conditions where liquid water is prevalent and less than 100% RH.

[0054] In one embodiment of the invention the fuel cell includes a membrane electrode assembly including electrode layers that are substantially free of cracks. For example, the layers may include a number of cracks, provided that the number and size of the cracks do not adversely influence, to any significant extent, the cycles to failure of the membrane. Figure 15 is a graph illustrating the improvement in cycles to failure of a membrane electrode assembly (MEA) with electrodes having no mud-cracks compared to an MEA having electrodes with mud-cracks. Both MEAs contain identical GoreSelect® membranes. If 10 seem crossover leak is considered an unacceptable failure, an MEA without mud-cracks can under go approximately 6800 humidity cycles before failure compared to only approximately 3400 cycles for an MEA with electrodes having mud-cracks under the conditions that the test was run. Of course it should be understood the invention is not limited by any particular comparative illustration or test present herein. [0055] One embodiment of the invention includes operating the fuel cell stack under conditions that minimize chemical thinning of the ionomer in the membrane via hydroxyl-induced free radical depolymerization. In one embodiment of the invention the fuel cell stack is operated so as to minimize RH cycling at cell potentials greater than 700 mV.

[0056] Another embodiment of the invention includes compressing the compressible components of the fuel cell with at least 0.2MPa of compression pressure between MEA and GDM over the channels and with at least a compression uniformity of at least 0.27 in one embodiment, and at least 0.6 in another embodiment so that the membrane electrode assembly is adequately constrained from deformation and buckling between the lands of the bipolar plate flow field.

[0057] To reduce the resistance of proton conductivity in the membrane, it is normally desired to keep the polymer electrolyte membrane sufficiently hydrated. However, it is recognized that under typical operating conditions the MEA cycles through relatively wet and relatively dry states. These membrane hydration cycles are particularly prevalent during fuel cell start-up and shut-down operations and as power demand fluctuates during operation of the fuel cell. When the membrane is hydrated, the swelling in the membrane could introduce significant compressive stress that can lead to the buckling of MEA if compression pressure is not adequately applied between GDM and MEA. The buckling of the MEA can lead to the local over heating of material by significantly increasing electrical contact resistance, which can ultimately result in the formation of membrane pinholes and crossover of reactant gases. An example of increasing the membrane fatigue life using the RH cycling test compared to the prior art through the improvement in compression is summarized in the table as follows.

[0058] In this table, the lowest compression pressure between the GDM and MEA over the channel is determined by a stress model such as, but not limited to, a finite element method. The compression uniformity is determined by taking the ratio of the lowest GDM/MEA compression pressure over the channel to the averaged cell compression, which is defined by the compression load divided by the active area. In the prior art design/method, the lowest compression pressure is determined to be 0.15MPa and the compression uniformity is 0.054. By increasing the lowest GDM/MEA compression pressure to 0.38MPa and by increasing the compression uniformity to 0.27, an increase of 24% in fatigue life can obtained. Furthermore, by increasing the lowest GDM/MEA compression pressure to 0.76MPa and by increasing the compression uniformity to 0.27, we can increase the fatigue life by 80°/^

[0059] Solid polymer electrolyte membranes 100 may include ion- conductive materials. Suitable membranes useful in the present invention are described in US patent numbers 4,272,353 and 3,134,697, and in the Journal of Power Sources, Volume 29 (1990), pages 367-387.

[0060] Suitable membranes 100 may include ion exchange resin membranes. The resins include ionic groups in their polymeric structure; one ionic component for which is fixed or retained by the polymeric matrix and at least one other ionic component being a mobile replaceable ion electrostatically associated with the fixed component. The ability of the mobile ion to be replaced under appropriate conditions with other ions imparts ion exchange characteristics to these materials.

[0061] The ion exchange resins can be prepared by polymerizing a mixture of ingredients, one of which contains an ionic constituent. One broad class of cation exchange, proton conductive resins is the so-called sulfonic acid cation exchange resin. In the sulfonic acid membranes, the cation exchange groups are sulfonic acid groups which are attached to the polymer backbone.

[0062] The formation of these ion exchange resins into membranes or sheets is well known to those skilled in the art. The preferred type is perfluorinated sulfonic acid polymer electrolyte in which the entire membrane structure has ionic exchange characteristics. These membranes are commercially available, and a typical example of a commercially sulfonic perfluorocarbon, proton conductive membrane is sold by E.I. DuPont de Nemours & Company under the trade designation Nafion. Other such membranes are available from Asahi Glass and Asahi Chemical Company. The use of other types of membrane such as, but not limited to, perfluorinated cation- exchange membranes, hydrocarbon based cation-exchange membranes as well as anion-exchange membranes are also within the scope of the invention.

[0063] The anode and cathode electrode catalyst layers 16, 18 may include supported or unsupported catalyst materials. Preferably the layers 16, 18 include a group of finely divided particles, such as carbon, supporting finely divided catalyst particles, such as platinum, and an ion conductive material, such as a proton conducting ionomer, intermingled with the particles. The proton conductive material may be an ionomer such as a perfluorinated sulfonic acid polymer. Preferred catalyst materials include metal such as platinum, palladium, and mixtures of metals such as platinum and molybdenum, platinum and cobalt, platinum and ruthenium, platinum and nickel, and platinum and tin, other platinum transition-metal alloys, and other fuel cell electrocatalysts known in the art. The gas diffusion media layers 50, 52 may be of any porous material suitable for aiding in the diffusion of reactant gases from the channels 28, 34 of the bipolar plates 20, 22 respectively to the membrane 100. In one embodiment, the diffusion media layers 50, 52 include, but are not limited to, carbon fiber paper. The microporous layers 46, 48 may include a binder and particles may be deposited over each of the diffusion media layers 50, 52. In one embodiment the binder may include a hydrophobic polymer such as, but not limited to, polyvinylidene fluoride (PVdF), fluoroethylene propylene (FEP), polytetrafluoroethylene (PTFE) or other organic or inorganic hydrophobic materials. The particles and binder may be included in a liquid phase which may be, for example, a mixture of an organic solvent and water to provide dispersion. In various embodiments, the solvent may include at least one of 2-propanol, 1- propanol or ethanol, etc. The dispersion may be applied the gas diffusion media layer 50, 52 or a hydrophobic coating over the gas diffusion media layer. In another embodiment, the dispersion may be applied to an electrode. The dispersion is dried (by evaporating the solvent) and the resulting dried microporous layer may include 60-90 weight percent particles and 10-40 weight percent binder. In various other embodiments, the binder may range from 10-30 weight percent of the dried microporous layer. A suitable particle for the microporous layer includes a graphitized carbon particle available from Superior Graphite, Chicago, Illinois under the trademark PUREBLACK SCD 205-110..

[0065] When the terms "over", "overlying", "overlies", or "under",

"underlying", "underlies" are used herein with respect to the relative position of one component or layer with respect to a second component or layer, such shall mean that the first component or layer is in direct contact with the second component or layer, or that additional layers or components may be interposed between the first component or layer and the second component or layer.

[0066] The above description of embodiments is merely exemplary in nature and, and is not intended to limit the scope of the invention.

Claims

CLAIMS What is claimed is:

1. A method of operating a fuel cell stack to prevent mechanical failure of fuel cell membranes due to hygroexpansive ratcheting comprising: providing a plurality of fuel cells each comprising a membrane and an anode electrode catalyst layer and a cathode electrode catalyst layer; the membrane and electrodes being interposed between bipolar plates, each bipolar plate have a face including a reactant flow field defined, at least in part, by a plurality of lands and channels; humidifying the fuel cell stack; cycling the humidity in the fuel cell stack from a condition below 100 percent relative humidity to a condition at 100 percent relative humidity or where there is condensation of water, and wherein at least two of the following conditions (a-h) are met:

(a) wherein the cycling of the humidity comprises drying the fuel cell stack at a rate less than 0.2 λ/sec;

(b) the membrane comprises an extruded membrane;

(d) the magnitude if the humidity cycle is less than 50% relative humidity; (e) wherein each of the anode electrode catalyst layer and the cathode electrode catalyst layer are substantial free of cracks;

(f) operating the fuel cell stack at potentials below 700 mV;

(h) wherein a conductive restrictive layer underlies or overlies at least one of the anode electrode catalyst layer or the cathode electrode catalyst layer to restrict the planar expansion of the membrane, to prevent the membrane from being pinched in a crack formed in one of the anode electrode catalyst layer or the cathode electrode catalyst, or to arrest the propagation of an incipient crack in one of the electrode catalyst layers.

2. A method as set forth in claim 1 wherein at least three of the conditions (a-h) are met.

3. A method as set forth in claim 1 wherein at least four of the conditions (a-h) are met.

4. A method as set forth in claim 1 wherein at least five of the conditions (a-h) are met.

5. A method as set forth in claim 1 wherein at least six of the conditions (a-h) are met.

6. A method as set forth in claim 1 wherein at least seven of the conditions (a-h) are met.

7. A method as set forth in claim 1 wherein all eight of the conditions (a-h) are met.

8. A method as set forth in claim 1 wherein the magnitude of the humidity cycle is less than 20% relative humidity;

9. A method as set forth in claim 1 wherein the minimum compression over any channel divided by the average compression over the entire active area of a fuel cell in the fuel cell stack is at least 0.6.

10. A method as set forth in claim 1 wherein the membrane comprises an extruded membrane.

11. A method as set forth in claim 1 wherein the membrane comprises an extruded membrane comprising a perfluorosulfonic acid.

12. A method as set forth in claim 1 wherein the membrane comprises a fluoropolymer.

13. A method as set forth in claim 1 wherein the membrane comprises a hydrocarbon polymer or partially fluorinated hydrocarbon polymer.

14. A method as set forth in claim 1 further comprising an electrically conductive restrictive layer over at least one of the anode catalyst layer or cathode catalyst layer, the electrically conductive restrictive layer being constructed and arranged to restrict the expansion of the membrane during the humidifying.

15. A method as set forth in claim 1 further comprising an electrically conductive microporous layer over at least one of the anode catalyst layer or cathode catalyst layer, the microporous layer being constructed and arranged to restrict the expansion of the membrane during the humidifying.

16. A method as set forth in claim 1 further comprising an electrically conductive epoxy layer over at least one of the anode catalyst layer or cathode catalyst layer to restrict the expansion of the membrane during the humidifying.

17. A method as set forth in claim 1 further comprising restricting any humidity cycling at cell potentials greater than 70OmV.

18. A method as set forth in claim 1 wherein there is a continuous interface between the membrane and at least one of the anode or cathode catalyst layer.

19. A method as set forth in claim 23 wherein the fuel cell comprises compressible materials and wherein the compressible materials are compressed uniformly.

20. A method as set forth in claim 1 wherein the lowest compression between the gas diffusion media and the MEA over each channel is equal to or greater than 0.38 MPa.

21. A method as set forth in claim 1 wherein the lowest compression between the gas diffusion media and the MEA over each channel is equal to or greater than 0.76 MPa.

22. A method as set forth in claim 1 wherein the drying rate is equal to or less than 0.2 λ/sec.

23. A method as set forth in claim 1 wherein the drying rate is equal to or less than 0.1 λ/sec. W

24. A method as set forth in claim 1 wherein the drying rate is equal to or less than 0.05 λ/sec.

25. A process as set forth in claim 1 wherein the minimum compression over any channel divided by the average compression over the entire active area of a fuel cell is at least 0.27.

26. A method of operating a fuel cell stack to prevent mechanical failure of fuel cell membranes due to hygroexpansive ratcheting comprising: providing a plurality of fuel cells each comprising a membrane and an anode electrode catalyst layer and a cathode electrode catalyst layer; the membrane and electrodes being interposed between bipolar plates, each bipolar plate have a face including a reactant flow field defined, at least in part, by a plurality of lands and channels; humidifying the fuel cell stack; cycling the humidity in the fuel cell stack from a condition below 100 percent relative humidity to a condition at 100 percent relative humidity or where there is condensation of water, and wherein the cycling comprises drying the fuel cell stack at a rate less than 0.2 λ/sec.

27. A method as set forth in claim 26 wherein the drying rate is equal to or less than 0.1 λ/sec.

28. A method as set forth in claim 26 wherein the drying rate is equal to or less than 0.05 λ/sec.

29. A method of operating a fuel cell stack to prevent mechanical failure of fuel cell membranes due to hygroexpansive ratcheting comprising: providing a plurality of fuel cells each comprising a membrane and an anode electrode catalyst layer and a cathode electrode catalyst layer; the membrane and electrodes being interposed between bipolar plates, each bipolar plate have a face including a reactant flow field defined, at least in part, by a plurality of lands and channels; humidifying the fuel cell stack; cycling the humidity in the fuel cell stack from a condition below 100 percent relative humidity to a condition at 100 percent relative humidity or where there is condensation of water, and wherein the membrane comprises an extruded membrane.

30. A method as set forth in claim 29 wherein the membrane comprises an extruded membrane comprising a perfluorosulfonic acid.

31. A method as set forth in claim 29 wherein the membrane comprises a fluoropolymer.

32. A method as set forth in claim 29 wherein the membrane comprises a hydrocarbon polymer or partially fluorinated hydrocarbon polymer.

33. A method of operating a fuel cell stack to prevent mechanical failure of fuel cell membranes due to hygroexpansive ratcheting comprising: providing a plurality of fuel cells each comprising a membrane and an anode electrode catalyst layer and a cathode electrode catalyst layer; the membrane and electrodes being interposed between bipolar plates, each bipolar plate have a face including a reactant flow field defined, at least in part, by a plurality of lands and channels; humidifying the fuel cell stack; cycling the humidity in the fuel cell stack from a condition below 100 percent relative humidity to a condition at 100 percent relative humidity or where there is condensation of water, and wherein the planar expansion of the membrane is equal to or less than 25 percent during the cycling of the humidity.

34. A method of operating a fuel cell stack to prevent mechanical failure of fuel cell membranes due to hygroexpansive ratcheting comprising: providing a plurality of fuel cells each comprising a membrane and an anode electrode catalyst layer and a cathode electrode catalyst layer; the membrane and electrodes being interposed between bipolar plates, each bipolar plate have a face including a reactant flow field defined, at least in part, by a plurality of lands and channels; humidifying the fuel cell stack; cycling the humidity in the fuel cell stack from a condition below 100 percent relative humidity to a condition at 100 percent relative humidity or where there in condensation of water, and wherein the magnitude if the humidity cycle is less than 50% relative humidity.

35. A method as set forth in claim 34 wherein the magnitude if the humidity cycle is less than 20% relative humidity.

36. A method of operating a fuel cell stack to prevent mechanical failure of the fuel cell membrane due to hygroexpansive ratcheting comprising: providing a plurality of fuel cells each comprising a membrane and an anode electrode catalyst layer and a cathode electrode catalyst layer; the membrane and electrodes being interposed between bipolar plates, each bipolar plate have a face including a reactant flow field defined, at least in part, by a plurality of lands and channels; humidifying the fuel cell stack; cycling the humidity in the fuel cell stack from a condition below 100 percent relative humidity to a condition at 100 percent relative humidity or where there is condensation of water, and wherein each of the anode electrode catalyst layer and the cathode electrode catalyst layer are substantial free of cracks.

37. A method of operating a fuel cell stack to prevent mechanical failure of fuel cell membranes due to hygroexpansive ratcheting comprising: providing a plurality of fuel cells each comprising a membrane and an anode electrode catalyst layer and a cathode electrode catalyst layer; the membrane and electrodes being interposed between bipolar plates, each bipolar plate have a face including a reactant flow field defined, at least in part, by a plurality of lands and channels; humidifying the fuel cell stack; cycling the humidity in the fuel cell stack from a condition below 100 percent relative humidity to a condition at or above 100 percent relative humidity, and operating the fuel cell stack at potentials below 700 mV.

38. A method of operating a fuel cell stack to prevent mechanical failure of fuel cell membranes due to hygroexpansive ratcheting comprising: providing a plurality of fuel cells each comprising a membrane and an anode electrode catalyst layer and a cathode electrode catalyst layer; the membrane and electrodes being interposed between bipolar plates, each bipolar plate have a face including a reactant flow field defined, at least in part, by a plurality of lands and channels; humidifying the fuel cell stack; cycling the humidity in the fuel cell stack from a condition below 100 percent relative humidity to a condition at 100 percent relative humidity or where there is condensation of water, and wherein the lowest compression between the gas diffusion media and the MEA over each channel is at least 0.2 MPa.

39. A method as set forth in claim 38 wherein the lowest compression between the gas diffusion media and the MEA over each channel is equal to or greater than 0.38 MPa.

40. A method as set forth in claim 38 wherein the lowest compression between the gas diffusion media and the MEA over each channel is equal to or greater than 0.76 MPa.

41. A process as set forth in claim 40 wherein the minimum compression over any channel divided by the average compression over the entire active area of a fuel cell is at least 0.6.

42. A process as set forth in claim 40 wherein the minimum compression over any channel divided by the average compression over the entire active area of a fuel cell is at least 0.27.

43. A method as set forth in claim 40 wherein the fuel cell comprises compressible materials and wherein the compressible materials are compressed uniformly.

44. A method of operating a fuel cell stack to prevent mechanical failure of fuel cell membranes due to hygroexpansive ratcheting comprising: providing a plurality of fuel cells each comprising a membrane and an anode electrode catalyst layer and a cathode electrode catalyst layer; the membrane and electrodes being interposed between bipolar plates, each bipolar plate have a face including a reactant flow field defined, at least in part, by a plurality of lands and channels; humidifying the fuel cell stack; cycling the humidity in the fuel cell stack from a condition below 100 percent relative humidity to a condition at 100 percent relative humidity or where there is condensation of water, and wherein a conductive restrictive layer underlies or overlies at least one of the anode electrode catalyst layer or the cathode electrode catalyst layer to restrict the planar expansion of the membrane, to prevent the membrane from being pinched in a crack formed in one of the anode electrode catalyst layer or the cathode electrode catalyst, or to arrest the propagation of an incipient crack in one of the electrode catalyst layers.

45. A method comprising: providing a fuel cell comprising a membrane and an anode catalyst and a cathode catalyst; humidifying and drying the fuel cell in a humidity cycle; controlling the humidity cycle of the fuel cell so the planar expansion of the membrane is less than 25% during the humidity cycle.

46. A method as set forth in claim 45 wherein the membrane comprises an extruded membrane.

47. A method as set forth in claim 45 wherein the membrane comprises an extruded membrane comprising a perfluorosulfonic acid.

48. A method as set forth in claim 45 wherein the membrane comprises a fluoropolymer.

49. A method as set forth in claim 45 wherein the membrane comprises a hydrocarbon polymer or partially fluorinated hydrocarbon polymer.

50. A method as set forth in claim 45 further comprising an electrically conductive restrictive layer over at least one of the anode catalyst layer or cathode catalyst layer, the electrically conductive restrictive layer being constructed and arranged to restrict the expansion of the membrane during the humidifying.

51. A method as set forth in claim 45 further comprising an electrically conductive microporous layer over at least one of the anode catalyst layer or cathode catalyst layer, the microporous layer being constructed and arranged to restrict the expansion of the membrane during the humidity cycle.

52. A method as set forth in claim 45 further comprising an electrically conductive epoxy layer over at least one of the anode catalyst layer and cathode catalyst layer to restrict the expansion of the membrane during the humidity cycle.

53. A method as set forth in claim 45 further comprising restricting any humidity cycling at cell potentials greater than 70OmV.

54. A method as set forth in claim 45 wherein there is a continuous interface between at least one of the anode or cathode catalyst layer and the membrane.

55. A method as set forth in claim 45 wherein the fuel cell comprises compressible materials and wherein the compressible materials are compressed uniformly.

56. A method as set forth in claim 45 wherein the magnitude of the humidity cycle is less than 50% relative humidity.

57. A method as set forth in claim 45 wherein the magnitude of the humidity cycle is less than 20% relative humidity.

58. A method as set forth in claim 45 wherein the lowest compression between the gas diffusion media and the MEA over each channel is a t least 0.2 MPa.

59. A method as set forth in claim 45 wherein the lowest compression between the gas diffusion media and the MEA over each channel is equal to or greater than 0.38 MPa.

60. A method as set forth in claim 45 wherein the lowest compression between the gas diffusion media and the MEA over each channel is equal to or greater than 0.76 MPa.

61. A method as set forth in claim 45 wherein the drying is conducted at a drying rate equal to or less than 0.2 λ/sec.

62. A method as set forth in claim 45 wherein the drying is conducted at a drying rate equal to or less than 0.1 λ/sec.

63. A method as set forth in claim 45 wherein the drying is conducted at a drying rate equal to or less than 0.05 λ/sec.

64. A method as set forth in claim 45 further comprising an electrically conductive restrictive layer over at least one of the anode catalyst layer or cathode catalyst layer to restrict the expansion of the membrane during the humidifying.

65. A method as set forth in claim 45 further comprising an electrically conductive microporous layer over at least one of the anode catalyst layer or cathode catalyst layer to restrict the expansion of the membrane during the humidity cycle.

66. A method as set forth in claim 45 further comprising an electrically conductive epoxy layer over at least one of the anode catalyst layer or cathode catalyst layer to restrict the expansion of the membrane during the humidity cycle.

67. A method comprising: providing a fuel cell comprising a membrane and an anode catalyst and a cathode catalyst; humidifying and drying the fuel cell in a humidity cycle; controlling the humidity cycle of the fuel cell so the planar expansion of the membrane is less than 25% during the humidity cycle; wherein the fuel cell further comprises an electrically conductive restrictive layer over at least one of the anode catalyst layer or cathode catalyst layer to restrict the expansion of the membrane during the humidifying; restricting any RH cycling at cell potentials above 70OmV .

68. A product comprising: a polyelectrolyte membrane and an anode electrode catalyst layer over a first face of the membrane and a cathode electrode catalyst layer over a second face of the membrane; a conductive restrictive layer underlying or overlying at least one of the anode electrode catalyst layer or the cathode electrode catalyst layer to restrict the planar expansion of the membrane, to prevent the membrane from being pinched in a crack formed in one of the anode electrode catalyst layer or the cathode electrode catalyst or to arrest the propagation of an incipient crack in one of the electrode catalyst layers.

69. A product as set forth in claim 68 wherein the conductive restrictive layer comprises an electrically conductive epoxy layer over at least one of the anode catalyst layer or cathode catalyst layer to restrict the expansion of the membrane during humidifying the fuel cell.

70. A product as set forth in claim 68 wherein the conductive restrictive layer underlies one of the anode electrode catalyst layer or the cathode electrode catalyst layer and comprises an ionomer.

71. A product as set forth in claim 68 wherein the conductive restrictive layer underlies one of the anode electrode catalyst layer or the cathode electrode catalyst layer and comprises expanded polytetrafluorethylene and an ionomer.

72. A product as set forth in claim 68 wherein the conductive restrictive layer underlies at least one of the anode electrode catalyst layer or cathode electrode catalyst layer, and wherein the conductive restrictive layer comprises a cloth and an ionomer.

73. A product as set forth in claim 68 wherein the conductive restrictive layer overlies at least one of the anode electrode catalyst layer or cathode electrode catalyst layer, and wherein the conductive restrictive layer comprises a porous electrically conductive cloth, and further comprising a gas diffusion media layer and wherein the conductive resistive layer is interposed between the gas diffusion media layer and one of the electrode catalyst layers.