U.S. Patent Application 20090297924 reveals a scheme for the production of silica coated Pt--Ru (platinum-ruthenium) alloy nanoparticles which are effective in preventing CO poisoning of the Pt catalyst surface and which do not migrate, agglomerate and deteriorate during prolonged fuel cell operation. Inventors Yuzuru Shimazaki (Sendai-shi, JP) Yoshio Kobayashi (Tohoku University, Sendai-shi, JP) Mikio Konno (Tohoku University, Sendai-shi, JP) produced polymer electrolyte fuel cell (PEFC) electrodes in which the catalyst particles are prevented from mutually aggregating/agglomerating together due to transfer on the carbon support and which show no substantial decrease in catalytic activity even after a long period of use. PEFC fuel cells are also known as PEMFC, or proton exchange fuel cell. Although nanoparticles are capable of providing an extremely large active surface area, when a PEFC electrode utilizing nanoparticles is used for a prolonged period of time, the catalyst nanoparticles on carrier of the PEFC electrode because of the nano-size thereof migrate and aggregate together to result in a rapid loss of activity.
The Ru--Pt alloy nanoparticles are coated with a silica layer with a thickness of about 1-2 nm to give encapsulated nanoparticles. The silica coat layer is very thin, hence will not prevent a substance(s) from diffusing therethrough. Thus, it secures high activity and prolonged life simultaneously. A catalyst comprising the encapsulated nanoparticles showed an initial catalytic activity level equivalent to the levels of the products currently on the market and, further, the decrease in activity thereof was found suppressed by the effect of encapsulation in silica spheres.
The nanoparticles can be said to be encapsulated nanoparticles with the surface being coated with a porous substance comprising an inorganic oxide such as silica. The encapsulated nanoparticles have a very thin porous substance layer, such as a silica layer, with a thickness of about 0.5 to 2 nm as formed around each nanoparticle with a particle diameter of about 2-3 nm. It has been established that the catalyst prepared by using the encapsulated nanoparticles as coated with a porous substance such as silica produces no particular phenomenon of inhibiting the diffusion of substances involved in the reaction and shows no particular decreases in activity.
The aggregation of nanoparticles can be inhibited by catalyst nanoparticles containing Pt wherein a porous matter containing an inorganic oxide is disposed on the surface of the catalyst nanoparticles.When use is made of nanoparticles whose surface has undergone specific modification, excellent catalytic activity can be realized.
The catalyst carrying the encapsulated nanoparticles was allowed to stand in an aqueous solution of sulfuric acid and the durability of the catalyst in acidic solution was evaluated in terms of particle diameter, surface area, and methanol oxidation current-based activity. As a result, even after 1000 hours of standing in sulfuric acid, no increase was found in particle diameter, and no decreases were found in surface area and catalytic activity (on the other hand, a commercial catalyst evaluated in the same manner showed an activity decrease of about 30% after 1000 hours of standing).