Selectively coated bipolar plates for water management and freeze start in PEM fuel cells
A flow field plate for fuel cell applications includes an electrically conductive plate having a first surface defining a plurality of channels. An active area section and an inactive area section characterize the flow field channels. A hydrophobic layer is disposed over at least a portion of the inactive area section while a hydrophilic layer is disposed over at least a portion of the active area section.
1. A fuel cell comprising;
a first flow field plate having a first surface defining a first plurality of channels, each channel having a first active area region and a first inactive area region, the first active area being an interior section of the fuel cell at which electrochemical reactions are occurring characterized by presence of catalyst layers and the first inactive area being peripheral to active area region characterized by absence of catalyst layers;
a hydrophilic layer disposed only over the first active area region, wherein the hydrophilic layer has a surface energy greater than about 50 dyne/cm and a contact angle less than 50 degrees;
a hydrophobic layer disposed only over the first inactive area region wherein the hydrophobic layer has a surface energy less than about 40 dyne/cm and a contact angle greater than 50 degrees;
a second flow field plate having a second surface defining a second plurality of channels, each channel having a second active area region and a second inactive area region; and
a membrane electrode assembly interposed between the first and second flow field plates, the membrane electrode assembly including:
a polymeric ion conductive membrane;
cathode catalyst layer; and
anode catalyst layer.
2. The fuel cell of claim 1 wherein the hydrophobic layer comprises carbon nanotubes and a component selected from the group consisting of polyhexafluoropropylene, polytetrafluoroethylene, fluorinated ethylene propylene polytrifluoroethylene, chlorotrifluoroethylene, and combinations thereof.
3. The fuel cell of claim 1 further comprises a gas diffusion layer and a microporous layer disposed over the gas diffusion layer, the gas diffusion layer and the microporous layer interposed between the membrane electrode assembly and the first flow field plate, the microporous layer comprising carbon nanotubes and a component selected from the group consisting of polyhexafluoropropylene, polytetrafluoroethylene, fluorinated ethylene propylene polytrifluoroethylene, chlorotrifluoroethylene, and combinations thereof.
4. The fuel cell of claim 3 wherein the hydrophilic layer comprises a carbon layer.
5. The fuel cell of claim 3 wherein the hydrophilic layer comprises a precious metal over-coated with silica.
6. The fuel cell of claim 1 further comprising a transition region positioned between the first active area region and the first inactive area region.
7. The fuel cell of claim 1 wherein the hydrophobic layer has a contact resistance greater than about 100 degrees.
8. The fuel cell of claim 1 wherein the hydrophobic layer comprises carbon nanotubes.
9. The fuel cell of claim 1 wherein the hydrophilic layer comprises a carbon layer.
10. The fuel cell of claim 9 wherein the carbon layer is treated with a plasma.