GAS DIFFUSION LAYER WITH LOWER GAS DIFFUSIVITY
A gas diffusion layer for use in fuel cells comprises a fiber and non-fiber material in a ratio such that the water vapor diffusion transport resistance is greater than 0.8 s/cm measured at 80 C and 150 kPa absolute gas pressure when the gas diffusion layer has a thickness less than or equal to 300 microns. Another gas diffusion layer comprises a fiber and non-fiber material in a ratio such that the water vapor diffusion transport resistance is lower than 0.4 s/cm measured at 80 C and 150 kPa absolute gas pressure when the gas diffusion layer has a thickness greater than or equal to 100 microns. Fuel cells incorporating the gas diffusion layers are also provided.
1 . A gas diffusion layer that is positionable between an electrode and a flow field in a PEM fuel cell, the gas diffusion layer comprising a fiber and non-fiber material in a ratio such that the water vapor diffusion transport resistance is greater than 0.8 s/cm measured at 80 C and 150 kPa absolute gas pressure when the gas diffusion layer has a thickness less than or equal to 300 microns.
2 . The diffusion layer of claim 1 wherein the diffusion transport resistance is greater than 1.0 s/cm
3 . The diffusion layer of claim 1 wherein the diffusion transport resistance is greater than 1.2 s/cm.
4 . The diffusion layer of claim 1 wherein the diffusion transport resistance is less than 3.0 s/cm.
5 . The diffusion layer of claim 1 wherein the binder resin is carbonized to be electrically conductive.
6 . The diffusion layer of claim 1 wherein the binder resin is non-carbonized to act as a solid filler.
7 . The diffusion layer of claim 1 wherein the binder resin comprises a combination of carbonized and non-carbonized resin.
8 . The diffusion layer of claim 5 wherein the carbonized binder resin is present in an amount of from between about 18 wt % and about 60 wt %.
9 . The diffusion layer of claim 1 having a porosity in an amount from between about 25 volume % and about 95 volume %.
10 . The diffusion layer of claim 9 having a porosity in an amount from between about 60 volume % and about 89 volume %.
11 . The diffusion layer of claim 1 wherein the fibers of the gas permeable diffusion structure comprise a woven or non-woven textile or paper.
12 . The diffusion layer of claim 1 wherein the resin-containing layer comprises carbon fiber woven or non-woven textile or paper or a carbon cloth.
13 . The diffusion layer of claim 1 further comprising a second resin-containing layer comprising a plurality of fibers and a binder resin having a resin present in a second amount that is different from the resin amount in the first layer.
14 . The diffusion layer of claim 1 further comprising one or more additional resin containing layers each individual resin-containing layer arranged adjacent the next individual resin-containing layer with each individual layer having a different content of resin from the next adjacent resin-containing layer.
15 . The diffusion layer of claim 1 further comprising a microporous layer on at least one side of the first resin-containing layer.
16 . The diffusion layer of claim 15 wherein the microporous layer comprises a carbon powder and a fluorocarbon polymer binder.
17 . The diffusion layer of claim 16 wherein the fluorocarbon polymer binder comprises a component comprising at least one of PTFE, FEP, or combinations thereof.
18 . A gas diffusion layer that is positionable between an electrode and a flow field in a PEM fuel cell, the gas diffusion layer comprising a fiber and non-fiber material in a ratio such that the water vapor diffusion transport resistance is lower than 0.4 s/cm measured at 80 C and 150 kPa absolute gas pressure when the gas diffusion layer has a thickness greater than or equal to 100 microns.
19 . The diffusion layer of claim 18 wherein the diffusion transport resistance is lower than 0.3 s/cm
20 . The diffusion layer of claim 18 wherein the diffusion transport resistance is less than 0.2 s/cm.
21 . The diffusion layer of claim 18 wherein the diffusion transport resistance is greater than 0.05 s/cm.
22 . The diffusion layer of claim 18 wherein the binder resin comprises a component selected from the group consisting of carbonized electrically conductive resins, non-carbonized resins, and combinations thereof.
23 . The diffusion layer of claim 1 further comprising one or more additional resin containing layers each individual resin-containing layer arranged adjacent the next individual resin-containing layer with each individual layer having a different content of resin from the next adjacent resin-containing layer.
24 . The diffusion layer of claim 1 further comprising a microporous layer on at least one side of the first resin-containing layer.
25 . The diffusion layer of claim 15 wherein the microporous layer comprises a carbon powder and a fluorocarbon polymer binder.
26 . A fuel cell comprising:
an anode gas flow field having one or more channels for introducing a first gas to the fuel cell,
an anode diffusion layer disposed over the anode gas flow field;
an anode catalyst layer disposed over the anode diffusion layer;
a polymeric ion conductive membrane disposed over the anode catalyst layer;
a cathode catalyst layer disposed over the polymeric ion conductive membrane;
a cathode diffusion layer disposed over the cathode catalyst layer;
a cathode gas flow field having one or more cathode plate channels for introducing a second gas to the fuel cell, the cathode flow field being disposed over the cathode diffusion layer, wherein at least one of the anode diffusion layer or the cathode diffusion layer comprises:
gas diffusion layer comprising a fiber and non-fiber material in a ratio such that the water vapor diffusion transport resistance is greater than 0.8 s/cm measured at 80 C and 150 kPa absolute gas pressure when the gas diffusion layer has a thickness less than or equal to 300 microns or such that the water vapor diffusion transport resistance is lower than 0.4 s/cm measured at 80 C and 150 kPa absolute gas pressure when the gas diffusion layer has a thickness greater than or equal to 100 microns.