Honda (Minato-Ku, Tokyo, JP) and Symyx Technologies, Inc. (Santa Clara, CA) share U.S. Patent 7,662,740 for a freeze-drying method to produce a more active fuel cell nanocatalyst comprised of platinum, chromium, and copper, and nickel. The concentration of platinum is less than 50 atomic percent, and/or the concentration of chromium is less than 30 atomic percent, and/or the concentration of copper, nickel, or a combination thereof is at least 35 atomic percent. The alloy catalysts exhibit favorable electrocatalytic activity while having reduced amounts of platinum, as compared to a platinum standard.
In this regard it is to be further noted that each component (e.g., metal) of the catalyst may be deposited separately, each for example as a separate layer on the surface of the electrode, membrane, etc. Alternatively, two or more components may be deposited at the same time. Additionally, when the catalyst comprises or consists essentially of an alloy of these metals, the alloy may be formed and then deposited.
The loading, or surface concentration, of a catalyst on the membrane or electrode is based in part on the desired power output and cost for a particular fuel cell. In general, power output increases with increasing concentration; however, there is a level beyond which performance is not improved. Likewise, the cost of a fuel cell increases with increasing concentration. Thus, the surface concentration of catalyst is selected to meet the application requirements.