Toyota researchers have developed a fuel cell catalyst carrier that bears a catalytic nano metal densely by coordinating the catalytic metal to a specified compound. The material has excellent catalytic activity and can improve power generation efficiency when used as a catalyst for fuel cells. The new catalyst is expected to contribute “to spreading the use of fuel cells,” according to Toyota researchers in U.S. Patent Application 20100015506.
FIG. 1 is a flow diagram of the preparation of a catalyst material using 2-(1H-pyrrol-3-ylpyridine) as a polymerizable ligand. The materials have higher catalytic performance and serviceability, particularly as electrode material for fuel cells.
Heat treating (burning) the catalyst material results in further improvement of oxidation reduction performance of the catalyst material. Thus, the catalyst material having undergone heat treatment (burning) may have a sufficient catalytic performance required when it is used for fuel cells etc., thereby having serviceability.
The peak potential of oxygen reduction obtained by cyclic voltammetry (cv) and rotating disk electrode (RDE) measurement is 0.54 V vs. SCE and the number of the electrons involved in the reaction is close to 4. This performance is comparable to the catalyst performance of platinum or its alloys which are currently used as an electrode catalyst material for the cathodes (oxygen or air electrodes) of fuel cells. This clearly shows that the catalyst material can be used as an electrode catalyst material for the cathodes (oxygen or air electrodes) of fuel cells.
Recently, many investigations have been made of electrode systems, as electrode catalysts, which have undergone surface modification with a macrocyclic compound, such as porphyrin, chlorophyll, phthalocyanine, tetraazaannulene or Schiff base, or a derivative thereof. These electrode systems are expected to be applied, as electrode catalysts which take the place of platinum (Pt) and its alloys, to the cathode of (oxygen-hydrogen) fuel cells, such as phosphoric acid fuel cells or polymer electrolyte fuel cells, by utilizing the electrochemical multielectron reduction properties of molecular oxygen (O2) due to such electrode catalysts.
However, the catalytic activity of the electrode systems utilizing any of the above macrocyclic compounds is insufficient to use for fuel cells. Under these circumstances, there have been demands for development of catalyst materials having higher catalytic performance and serviceability.
To solve the above problem, inventors Naoko Iwata, Makoto Yuasa, Kenichi Oyaizu, Ken Tanaka, Yuichi Iai, Masakuni Yamamoto, Shinichi Sasaki and Shigeru Kido examined the reasons that the electrode catalysts utilizing a macrocyclic compound do not have sufficiently high catalytic activity.
To solve the above problem, inventors Naoko Iwata, Makoto Yuasa, Kenichi Oyaizu, Ken Tanaka, Yuichi Iai, Masakuni Yamamoto, Shinichi Sasaki and Shigeru Kido examined the reasons that the electrode catalysts utilizing a macrocyclic compound do not have sufficiently high catalytic activity.
As a result, they inferred from the examination that in the catalyst systems utilizing a macrocyclic compound, the density of active species is lowered when the species are supported on a catalyst support, whereby the catalytic activity of the catalyst systems is decreased. They found that if a catalyst support is coated with a heteromonocyclic compound or a polynuclear polymer derived from the heteromonocyclic compound, a lot of M-N4 structure where a catalytic metal is coordinated is formed, whereby a catalyst material with high catalytic activity is obtained.
The Toyota scientists created a durable catalyst material that includes a conductive material whose surface is coated with a polynuclear polymer formed by polymerization of a specific monomer, characterized in that the specific monomer or the polynuclear polymer formed by polymerization of the specific monomer is used as a polymerizable ligand and a catalytic metal is coordinated to the coordination sites of the polymerizable ligand. And they have finally reached the present catalyst formulation.
After dedicating their efforts to this investigation, Toyota’s inventors have found that when the polymerizable ligand is a ligand obtained by electrochemical polymerization under the specified conditions (voltage applied, solvent, supporting electrolyte), the resultant catalyst material bears active species densely and has significantly improved catalytic activity.
The Toyota scientists created a durable catalyst material that includes a conductive material whose surface is coated with a polynuclear polymer formed by polymerization of a specific monomer, characterized in that the specific monomer or the polynuclear polymer formed by polymerization of the specific monomer is used as a polymerizable ligand and a catalytic metal is coordinated to the coordination sites of the polymerizable ligand. And they have finally reached the present catalyst formulation.
After dedicating their efforts to this investigation, Toyota’s inventors have found that when the polymerizable ligand is a ligand obtained by electrochemical polymerization under the specified conditions (voltage applied, solvent, supporting electrolyte), the resultant catalyst material bears active species densely and has significantly improved catalytic activity.
Further, after examining the characteristics of the conductive materials to be used as a support, the inventors found that when the conductive material has a specified specific surface area and average particle size, the resultant catalyst material has significantly improved catalytic activity. They have found that repeating the electrochemical polymerization and/or the coordination of a catalytic metal (metallation) more than one time is effective in increasing the density of active species supported on a catalyst support and in improving the catalytic activity of the catalytic material.
Also Toyota researchers found that using an ancillary ligand when repeating the electrochemical polymerization and/or the coordination of a catalytic metal (metallation) more than one time is effective in improving the coordination property of a catalytic metal, and they have reached the present invention. They have found that when a noble metal and a transition metal are coordinated to the coating layer at the same time, the resultant catalyst material has significantly improved catalytic activity.
Heat treating (burning) the catalyst material results in further improvement of oxidation reduction performance of the catalyst material. Thus, the catalyst material having undergone heat treatment (burning) may have a sufficient catalytic performance required when it is used for fuel cells etc., thereby having serviceability.
