Patent Application
20110136047
This disclosure relates to fuel cell catalyst supports and methods of manufacturing the same.
Cost and durability issues have made it difficult to commercialize fuel cells. Fuel cells utilize a catalyst that creates a chemical reaction between a fuel, such as hydrogen, and an oxidant, such as oxygen, typically from air. The catalyst is typically platinum loaded onto a support, which is usually a high surface area carbon.
Some durability issues are attributable to the degradation of the support caused by corrosion. Electrochemical studies have indicated that the corrosion depends strongly on surface area and morphology structure of carbon. For example, it has been reported that carbon with high surface area, such as Ketjen Black, can corrode severely at potentials experienced during start and stop cycling of the fuel cell causing a dramatic loss in fuel cell performance. Accordingly, to overcome this particular durability issue, it may be desirable to use a support other than carbon that is more chemically and electrochemically stable.
One possible alternative support for a catalyst is a metal oxide. Metal oxides can have a high surface area and good corrosion resistance, which are desirable for fuel cell applications. However, most of these high surface area metal oxides are not conductive and are extremely hydrophilic. Hydrophilic supports can cause problems, such as electrode flooding, which leads to significant drop in cell performance, especially at high current densities. As result, existing metal oxides supports cannot be applied in low temperature fuel cells.
What is therefore needed is a modified metal oxide that is more suitable for use in a fuel cell environment.
A fuel cell catalyst support is disclosed that includes a support structure having a metal oxide/phosphate, modified with a boron carbide layer, using a chemical or mechanical process, for example. The metal catalyst layer (active layer) is supported on top of the boron carbide layer.
These and other features of the disclosure can be best understood from the following specification and drawings, the following of which is a brief description.
An example fuel cell 10 is schematically illustrated in
The anode 14 and cathode 18 typically include a catalyst arranged on a catalyst support. The catalyst support provides the support structure upon which a thin layer of catalyst is deposited. Typically, the catalyst is platinum and the catalyst support is carbon, such as ketjen black, carbon fibers or graphite.
This disclosure relates to a catalyst support 30 having a metal oxide and/or metal phosphate support structure 32, as shown in
Metal oxides/phosphates are typically hydrophilic, which limit their use in certain applications due to electrode flooding, particularly in the low temperature fuel cells. In addition, most of these materials are electrically isolating. Catalyst supports typically must be somewhat conductive to ensure electrons at the catalyst layer pass through the support without experiencing an undesirable amount of resistance. Thus, a catalyst support must not only more hydrophobic, but also conductive to be suitable in fuel cells. To this end, a boron carbide (B4C) layer 34 is provided as an intermediate layer between the metal oxide/phosphate support structure 32 and the catalyst layer 36, schematically depicted in
While the catalyst support 30 is schematically shown as discrete, uniform layers, it should be understood that the catalyst support 30 comprises boron carbide 34 arranged between the metal oxide/phosphate support structure 32 and the catalyst layer 36. Boron carbide 34 can fully or partially cover the metal oxide/phosphate surface. Example catalysts include noble metals, such as platinum, palladium, gold, ruthenium, rhodium, iridium, osmium, or alloys thereof. A secondary metal can also be used to reduce the amount of noble metal used. Example secondary metals include transition metals, such as cobalt, nickel, iron, copper, manganese, vanadium, titanium, zirconium and chromium.
The boron carbide layer 34 forms a conductive and corrosion resistant shell on the support structure 32. In one example in which titanium oxide with a high surface area is used as the support structure 32, a high surface area layer of boron carbide can be achieved correspondingly. Boron carbide provides improved hydrophobicity to the catalyst support 30.
The boron carbide layer 34 can be chemically or mechanically deposited onto the support structure 32. An example, chemical process of forming a boron carbide layer on the metal oxide/phosphate support structure is depicted in
The boron carbide layer 34 can also be deposited mechanically on an outer surface of the support structure 32 by blasting the support structure 32 with carbon particles and a source of boron, for example, by a ball milling process.
Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US08/76948 | 9/19/2008 | WO | 00 | 2/3/2011 |
