Freeze Dried Nanoscale Platinum-Chromium-Copper/Nickel Fuel Cell Catalyst Is Cheaper and More Active than Platinum Standard Say Honda and Symyx Scientists

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. 

The freeze-dry method may be used to produce supported catalyst alloy powders that are heavily loaded with nanoparticle deposits of a catalyst alloy that comprises one or more non-noble metals, wherein the deposits have a relatively narrow size distribution

The nanocatalyst alloy was developed by inventors Konstantinos Chondroudis,  Alexander Gorer, Martin Devenney, Ting He, Hiroyuki Oyanagi, Daniel M. Giaquinta, Kenta Urata, Hiroichi Fukuda, Qun Fan, Peter Strasser, and Keith James Cendak

Although platinum is considered to be the most efficient and stable single-metal electrocatalyst for fuel cells, it is costly. Additionally, an increase in electrocatalyst activity over platinum is desirable, if not necessary, for wide-scale commercialization of fuel cell technology. However, the development of cathode fuel cell electrocatalyst materials faces longstanding challenges. The greatest challenge is the improvement of the electrode kinetics of the oxygen reduction reaction. In fact, sluggish electrochemical reaction kinetics have prevented attaining the thermodynamic reversible electrode potential for oxygen reduction.

 A second challenge is the stability of the oxygen electrode (cathode) during long-term operation. Specifically, a fuel cell cathode operates in a regime in which even the most unreactive metals are not completely stable. Thus, alloy compositions that contain non-noble metal elements may have a rate of corrosion that would negatively impact the projected lifetime of a fuel cell. The corrosion may be more severe when the cell is operating near open circuit conditions (which is the most desirable potential for thermodynamic efficiency). 

The alloy catalyst may be employed in the absence of a support particle. More specifically, it is to be noted that a metal catalyst comprising platinum, chromium, and copper and/or nickel, may be directly deposited (e.g., sputtered) onto, for example, (i) a surface of one or both of the electrodes (e.g., the anode, the cathode or both), and/or (ii) one or both surfaces of a polyelectrolyte membrane, and/or (iii) some other surface, such as a backing for the membrane (e.g., carbon paper).

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. 

FIG. 1 is a photograph of a TEM image of a carbon support with freeze dried platinum chromium, copper,  and nickel catalyst nanoparticles deposited on the carbon support.

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.

For example, a fuel cell designed to meet the requirements of a demanding application such as an extraterrestrial vehicle will usually have a surface concentration of catalyst sufficient to maximize the fuel cell power output. For less demanding applications, economic considerations dictate that the desired power output be attained with as little catalyst as possible. Typically, the loading of catalyst is between about 0.01 and about 6 mg/cm². Experimental results to date indicate that in some embodiments the catalyst loading is preferably less than about 1 mg/cm², and more preferably between about 0.1 and 1 mg/cm².