Patent Application
20170250414
The present invention relates to a method to produce a gas diffusion layer and a fuel cell comprising said gas diffusion layer.
The idea of engineering water pathways through gas diffusion layers in fuel cells is a permanent topic in the operation of fuel cell stacks.
The presence of holes as engineered water pathways has been reported a few times, including ex situ and in situ measurements to study the effect of this approach. The generated holes having 80 μm diameters using a laser and an improved performance in a small scale cell (1 cm2) using this perforated gas diffusion layers has been reported. An improved stability in a 6-cells stack (area of 30 cm2) was reported in which the GDL has been modified in this way, and in an ex situ study using environmental scanning electron microscopy (ESEM) water accumulation in perforated GDLs was visualized.
Laser perforation of GDLs was also reported. Much larger holes (300 μm) and with a high hole density were used. In situ tests using polarization curves and neutron imaging have shown some improvement in certain conditions (low current and low humidity), but also increased mass transport losses for such large holes. Finally, the use of mechanical pinning was reported to create one single hole at specific locations of a single channel fuel cell (under the flow channel or under the land, and near the inlet or outlet of the cell), and the impact of this hole on water distribution was studied.
It is the objective of the present invention to provide a method to produce a gas diffusion layer and a fuel cell comprising said gas diffusion layer; said gas diffusion layer allowing higher design flexibility and lower cost.
This objective is achieved according to the present invention by a method to produce electrically conductive porous materials with distributed wettability, comprising the steps of:
a) Coating the external and internal surfaces of a porous base material made of carbon fiber or Titanium with Fluoroethylene-Propylene (FEP) and/or perfluoroalkoxy (PFA) and/or Ethylene-Tetrafluoroethylene (ETFE) or any other hydrophobic polymer;
b) Exposing the coated material to irradiation through a blocking mask such that only parts of the coated porous material are exposed;
c) Immersing the previously exposed material in a monomer solution and heating to a temperature higher than 45° C., resulting in the graft co-polymerization of monomers on the FEP layer.
Compared to the methods known in the prior art, the wettability change using radiation grafting according to the present invention is more cost-effective and allows higher design flexibility. For example, elongated in-plane water pathways cannot be realized using holes. Furthermore, a better durability is obtained due to the covalent bonding of the grafted hydrophilic compound.
With respect to a fuel cell, the objective is achieved according to the present invention by a fuel cell where a gas diffusion layer of the anode side, preferably produced by a method according to any of the preceding claims, comprises hydrophilic parts in order to achieve a distributed wettability and part of channels in an anode flow plate aligned with said gas diffusion layer are connected to a water inlet and flooded with water wherein the water channels and the hydrophilic parts of the GDL form a water supply network used to humidify the fuel cell.
Advantageous embodiments of the present invention are listed hereinafter and can be combined in any possible and/or suitable combination:
a) the base material is a porous material is an electrically conductive or non-conductive material;
b) the applied coating (a) can be distributed over the thickness in whatever configuration, such as homogeneusly distributed over the thickness (high design freedom);
c) photon-type radiation is used for irradiation, preferably in an energy range from UV to gamma sources;
d) in addition or alternatively to photon-type radiation, particle beam is used to generate initiators, such as plasma, accelerated and heavy ions;
e) the penetration depth of the irradiation is regulated in order to obtained a targeted modification depth, preferably previously produced stacks of various materials, such as gas diffusion layer and microporous layers, can be modified by the targeted modification depth;
f) any patterned design can be defined, such us parallel slits or circles;
g) lithography methods are used;
h) the monomer solution of step (c) comprises a radically activated monomer resulting in graft copolymerization of a hydrophilic polymer, such us N-nivylformamide, acrylic acid, methacrylic acid, styrene, sufonated styrene, vinylpyridine, glycerol methacrylate among others;
i) the monomer solution is used as a pure liquid or is diluted with a solvent or/and other compounds and one or more additional monomers;
j) with an additional step (d) consisting on further exposing the material to solutions and different pressure and temperature conditions in order to pursue additional chemical reaction to further reduce the contact angle or implement another desired property, such us hydrolysis or sulfonation;
k) negative pressures are additionally applied in step (c) to allow the penetration of the solution into the material pores of the porous material;
l) a surfactant or any lowering surface tension agents are added to the monomer solution to allow the penetration into the material pores;
m) the porous material is exposed to vapor phase of the monomer or any other mixture of gases;
n) the heat removal by water evaporation is sufficient to remove all the heat produced in the fuel cell, suppressing the need of an additional cooling system;
o) the water supply network is placed on the cathode side instead of the anode side;
p) the water supply network is used for the supply of water in an electrolyser stack or in a stack of fuel cells.
Preferred embodiment of the present invention are hereinafter described in more detail with respect to the attached drawings which depict in:
The present invention discloses a method of manufacturing gas diffusion layers (GDL) with a defined pattern of hydrophobic and hydrophilic regions. The interest of such materials for fuel cell applications is their potential use on the cathode side to improve the transport of oxygen in presence of liquid water, as discussed in the literature and illustrated in
A further possibility of application is to use this invention as a help for evaporation cooling in fuel cells and electrolyzers, using the hydrophilic pathways as a help to guide water injection. Other applications relying on porous supports that require through plane conduction of water or any other liquid can benefit from this material, such as microfluidics (dialysis).
The proposed method to synthesize such a material is based on radiation induced graft polymerization. The originally hydrophobic material is exposed to a beam which is masked in certain regions. Alternatives to define the exposed regions are to use lithography or a scanning pencil beam. The regions which have been exposed are “activated”. Consequently the graft copolymerization process will occur only in these regions. The synthesis process is summarized in
Currently, the realization of a first GDL hydrophobized using
Fluoro-Ethylene-Propylene and with localized grafting of Acrylic Acid as a hydrophilic compound has been demonstrated. For this example a gas diffusion layer commercially available Toray TPGH-090 was coated with 30% weight of FEP and sintered. The material was then irradiated with an electron beam of 1.5 MeV energy and 50.0 kGy dose. A mask of 2 mm thickness stainless stell was used with drilled slits of 500 μm. The irradiated material was placed into a reactor of 50 mL and 50 mbar pressure. The grafting solution (15% vol Acrylic acid in water) was pumped in after 60 min of nitrogen bubling. The reaction was brought to a temperature of 60° C.
The distribution of the different components visualized by SEM-EDX is shown in
It is believed that this method is of significant interest, since the performance of the fuel cell is improved by the use of this material. Moderate additional costs are expected due the simplicity of the process and the low cost of the chemicals involved.
General thoughts on patentability
In addition, the implementation of the evaporation cooling concept using the material above can be realized. The direct injection of liquid water in a fuel cell for the purpose of humidification and cooling has important advantages:
The practical implementation of evaporation cooling is difficult. Our studies on differential cells have shown that, on the local scale, humidification from the anode side is much more effective than from the cathode side. However, due to the permeation through the membrane and the electro osmotic drag, water injected in the anode inlet will be transported to the cathode side.
The present invention now uses a design that provides some of the channels on the anode side (for example, each 3rd channel) as water supply channels being completely flooded with water (these supply channels are connected to another manifold than the hydrogen supply channels). To transport the water efficiently to the regions between the water supply channels, elongated hydrophilic water pathways are created in the GDL (using the method described above). To avoid gas bubbling into the water supply channels, those can optionally be covered by a hydrophilic region as illustrated in
The key interest of the present invention resides in the fact that the use of the common components can be maintained and nothing is particularly added compared to the classical fuel cell technology. The extra cost of the present GDL modification method is offset by the system cost reduction due to the suppression of external humidifiers. Even further, if the evaporation cooling is, as targeted, sufficient to remove all the heat produced, a further cost and size reduction by suppressing the coolant circulation and by using monolithic separator plates can be realized. Such a design is illustrated in
The present invention provides a significant advantage compared to other proposed ideas due to the following features:
On the evaporation cooling (application) disclosure, the significant advantage of the present inventions resides in the fact that no additional layer is included, and that no layer is significantly bulkier or expensive than in classical fuel cell designs (as opposed, for example, to the water transport plates of the UTC design). Thus, the following advantages are realizable:
| Number | Date | Country | Kind |
|---|---|---|---|
| 14184065.2 | Sep 2014 | EP | regional |
| 15165515.6 | Apr 2015 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/069284 | 8/21/2015 | WO | 00 |
