Reversible superhydrophilic-superhydrophobic coating for fuel cell bipolar plates and method of making the same

One variation may include a method which may include depositing a hydrophilic coating over at least a portion of a fuel cell bipolar plate. The bipolar plate may include a reactant gas header opening communication with the plurality of tunnels. Moreover, the tunnels may be communicating with a plurality of channels which may be defined by reactant gas flow field which may include a plurality of lands. At least a portion of the hydrophilic coating may be reacted with the material including a hydrophobic group which may provide a hydrophobic portion. Thereafter, at least a portion of the hydrophobic portion comprising oxidizing the hydrophobic group may be removed in order to regenerate the hydrophilic coating.

TECHNICAL FIELD

The field to which the disclosure generally relates to includes fuel cell bipolar plates and methods of making the same.

BACKGROUND

A variety of fuel cells produce water as a byproduct or utilize membranes such as, but not limited to, proton exchange membranes which must be humidified for acceptable performance. Water condensation during operation or shut down can result in reactant gas flow fields or tunnels being blocked by retained water or ice.

SUMMARY OF EXEMPLARY EMBODIMENTS OF THE INVENTION

One exemplary embodiment includes a fuel cell bipolar plate having a reversible superhydrophilic-superhydrophobic coating thereon.

Another exemplary embodiment includes providing a fuel cell bipolar plate having a hydrophilic surface, reacting a material with at least a portion of the hydrophilic surface to change a portion of the surface to be hydrophobic thereby providing a hydrophobic portion, and oxidizing at least a portion of the hydrophobic portion to remove the same and regenerate the hydrophilic surface.

Another exemplary embodiment includes a method of providing a fuel cell bipolar plate having a metal oxide layer formed there over, reacting the metal oxide with a material including a hydrophobic alkyl group to create a hydrophobic portion, and oxidizing at least a portion of the hydrophobic portion to remove the same and regenerate the hydrophilic surface.

Another exemplary embodiment of the invention includes providing a fuel cell bipolar plate having a hydrophilic coating thereon comprising titanium oxide, reacting the hydrophilic coating with octadecylsilane to provide a hydrophobic portion, and oxidizing at least a portion of the hydrophobic portion to remove the same to regenerate the hydrophilic layer including titanium oxide.

Another exemplary embodiment includes a fuel cell bipolar plate including a reactant gas header opening communicating with a first portion including a plurality of tunnels defined therein, the first portion communicating with a reactant gas flow field having a plurality of channels defined therein, and a superhydrophilic-superhydrophobic coating over at least a portion of the tunnels.

Another exemplary embodiment includes a method comprising providing a fuel cell bipolar plate including a reactant gas header opening communicating with a plurality of tunnels, the tunnels communicating with a plurality of channels defined by a reactant gas flow field including a plurality lands, coating at least a portion of the fuel cell bipolar plate with a metal oxide to create a hydrophilic layer, reacting n-octadecylsilane with the hydrophilic layer to create a hydrophobic silyl hydride layer, and thereafter oxidizing and removing the hydrophobic silyl hydride layer to regenerate the hydrophilic layer.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

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

Referring now toFIG. 1, one exemplary embodiment includes a fuel cell bipolar plate10including a reactant gas header11having an opening12therein for the flow of reactant gas therethrough. The reactant gas header opening12communicates with a plurality of tunnels28defined by a first set of lands26. A cover32is provided over the tunnels28. The tunnels28direct and funnel reactant gases toward a reactant gas flow field14. The reactant gas flow field is defined by a second set of lands forming a plurality of reactant gas flow channels18. The spacing of the tunnels28is typically wider than the spacing of the channels18. In one embodiment feed ports34may be positioned between the tunnels28and the channels18. The feed ports function to provide uniform gas distribution through the bipolar plate channels and the weld line joining the cathode and anode sides of the bipolar plate that is situated between the gas channels18and fee ports34prevents reactant gases from intruding into the coolant channels and coolant from intruding into the reactant channels18. A port/tunnel design is required to enable the weld line. In one exemplary embodiment, a portion of the bipolar plate may include a layer including the reactant product of a hydrophilic material and a material including a hydrophobic group to provide a hydrophobic portion over at least a portion of the bipolar plate. In one embodiment the hydrophobic portion may cover the reactant gas flow field including at least the channel18portions thereof and the tunnels28leading to the reactant gas flow field14. In one embodiment a portion of the hydrophobic portion may be oxidized and removed to leave a hydrophilic component remaining thus converting a portion of the hydrophobic portion to a hydrophilic surface. In one embodiment, the hydrophobic group may be an alkyl group. In one embodiment, the hydrophilic component may be a metal oxide such as, but not limited to, titanium oxide. In one embodiment, the hydrophobic material may include, but is not limited to, n-octodecylsilane CH3(CH2)16(CH2SiH3). In one embodiment, the material on the fuel cell bipolar plate prior to oxidation includes a covalent M-O—Si bond, where M is a metal such as, but not limited to, titanium. In one embodiment, the use of a reversible superhydrophilic-superhydrophobic coating may be advantageous where portions to be coated with a hydrophobic coating are covered. The coating on uncovered portions of the bipolar plate may be oxidized by, for example, exposure to UV light to remove the hydrophobic group and regenerate the hydrophilic coating.

One exemplary embodiment of the invention includes a method of providing a stainless steel fuel cell bipolar plate coated with gold and cleaning the bipolar plate with open air plasma to enhance wetting. A superhydrophilic coating is applied to the bipolar plate, for example, by applying an aqueous-based titania solution via dipping, spraying or brushing the solution onto the bipolar plate and drying the same, for example, with a heat gun to form a coating thereon which is superhydrophilic. The superhydrophilic portion of the bipolar plate may be reactive with a material including a hydrophobic group. For example, the superhydrophilic bipolar plate may be dipped in about 0.1 to 10 weight percent, and preferably about five weight percent n-octadecylsilane (in hexane) solution and flash dried (20 seconds at room temperature) to generate self assembled monolayers “SAM” on the titanium oxide surface to provide a coating that is superhydrophobic. Thereafter, superhydrophilic regions may be selectively regenerated by exposing the super hydrophobic coating to UV radiation to oxidize and remove the silicon hydrophobic portion and to regenerate the titanium oxide.

In one exemplary embodiment, the hydrophilic coating is deposited over the tunnels28and the channels18. Thereafter, a hydrophobic material is reacted with the hydrophobic coating and bonded thereto to form a hydrophobic portion over at least a portion of the fuel cell bipolar plate. The hydrophobic portion may cover at least a portion of the surfaces defining the tunnels and at least a portion of the surfaces defining channels. Thereafter, the hydrophobic portion over the channels is oxidized, for example, by UV radiation to remove the hydrophobic component leaving the hydrophilic component (e.g. titanium oxide). The resultant fuel cell bipolar plate includes a hydrophobic portion over the tunnels and a hydrophilic portion over the channels. Leaving the hydrophobic portion over the tunnels28provides the advantage of facilitating liquid water purge from the channels to the headers during shut down and, as a result, shorter start times from freeze conditions are realized as ice formation in channels is eliminated allowing reactant gas to reach the electrodes for fuel cell power.

FIG. 2illustrates a portion of a fuel cell stack40including a plurality of fuel cell bipolar plates10which include a reactant gas flow field defined by a plurality of lands16and channels18. A superhydrophilic-superhydrophobic coating42may be deposited over at least a portion of the fuel cell bipolar plate10, for example over at least a portion of the surface(s)19defining the channels18and over at least a portion of the surface(s) defining the tunnel28. Thereafter, the superhydrophilic-superhydrophobic coating over the channel surface19may be exposed to UV light to remove the hydrophobic component and regenerate a hydrophilic coating102. A soft goods portion44may be sandwiched between bipolar plates10. The soft goods portion44may include a membrane46such as a proton exchange membrane including an ionomer. An anode48and a cathode50may be deposited over opposite faces of the membrane46. The cathode and the anode may include a catalyst which may be supported and may include an ionomer (e.g. on carbon particle) or not supported. A first gas diffusion media layer52may be provided over the anode48and similarly a second gas diffusion media layer56may be provided over the cathode50. The gas diffusion media layers42,54may include, but are not limited to, a plurality of fibers in the form of a porous paper, mat or felt to facilitate the diffusion of reactant gases from the channels18of the bipolar plate10to the anode48and cathode50, respectively. Optionally, a first microporous layer56may be provided between the first gas diffusion media layer52and the anode48. Likewise, a second micro porous layer58may be provided between the second gas diffusion media layer54and the cathode50. The microporous layers56,58may be constructed or arranged to control the flow of water through the soft goods portion. In one exemplary embodiment, the microporous layers56and58may include a plurality of carbon particles bound together by polytetrafluoroethylene. One or more gaskets104may be used for sealing.

Another exemplary embodiment may include a method including providing a fuel cell bipolar plate including a reactant gas header opening communicating with a plurality of tunnels, the tunnels communicating with a plurality of channels defined by a reactant gas flow field including a plurality lands, coating at least a portion of the fuel cell bipolar plate with a metal oxide to create a hydrophilic layer, reacting n-octadecylsilane with the hydrophilic layer to create a hydrophobic silyl hydride layer, and thereafter oxidizing and removing the hydrophobic silyl hydride layer to regenerate the hydrophilic layer, wherein the oxidizing and removing the hydrophobic silylhydride layer comprises exposing the silylhydride layer to open air plasma.

Another exemplary embodiment may include A method including providing a fuel cell bipolar plate including a reactant gas header opening communicating with a plurality of tunnels, the tunnels communicating with a plurality of channels defined by a reactant gas flow field including a plurality lands, coating at least a portion of the fuel cell bipolar plate with a metal oxide to create a hydrophilic layer, reacting n-octadecylsilane with the hydrophilic layer to create a hydrophobic silyl hydride layer, and thereafter oxidizing and removing the hydrophobic silyl hydride layer to regenerate the hydrophilic layer, wherein the oxidizing and removing the hydrophobic silylhydride layer comprises exposing \the silylhydride layer to UV radiation, wherein the UV radiation has different intensity across the plate surface area generating a spatial gradient of surface hydrophilicity/hydrophobicity wherein the magnitude of hydrophilicity/hydrophobicity varies over the plate surface.

Another exemplary embodiment may include a method including providing a fuel cell bipolar plate comprising a stainless steel surface providing a hydrophilic layer, the bipolar plate including a reactant gas header opening communicating with a plurality of tunnels, the tunnels communicating with a plurality of channels defined by a reactant gas flow field including a plurality lands, reacting n-octadecylsilane with the hydrophilic layer to create a hydrophobic silyl hydride layer, and thereafter oxidizing and removing the hydrophobic silyl hydride layer to regenerate the hydrophilic layer.

The above description of embodiments of the invention is merely exemplary in nature and, thus, variations thereof are not to be regarded as a departure from the spirit and scope of the invention.