Hitachi Maxell , subsidiary of Hitachi, has announced development of a new catalyst used for oxygen-reduction reactions at the cathode of a polymer electrolyte fuel cell (PEFC).
The new catalyst is gold-platinum (AuPt) nano-particle 2 to 3nm in size and can generate approximately 4.8 times the oxygen-reduction current per unit area than commercial platinum catalysts.
PEFCs are a promising clean-energy source for automobiles, homes, and mobile devices. Platinum is commonly used as the catalyst for the oxygen-reduction reaction in PEFCs, but platinum is expensive precious metal, so reducing material cost for PEFCs by minimising the amount of platinum used, while improving its catalytic effect is an important R&D topic.
Increasing the surface area of the catalyst by reducing particle size is an effective way of improving catalytic activity. It has also been reported that the addition of base metals such as iron, cobalt and nickel to platinum also improves the oxygen-reduction reaction rate, but these kinds of base metals dissolve easily in the acidic environment of a PEFC where the catalyst is working, which is a problem.
Hitachi Maxell has developed a new catalyst for oxygen-reduction reactions in PEFCs. The new catalyst is a composition of platinum and gold and is resistant to acidic environments.
It was difficult to synthesise gold particles smaller than 5nm due to its relatively low melting point, but by applying a proprietary nano-level particle synthesising technology, Hitachi Maxell has succeeded in developing a high-activity structure in which the gold and platinum are not fully alloyed for the new catalyst.
Using citric acid as a reducing agent, AuPt catalyst particles 2 to 3nm in size were synthesised at 373K. Compared with platinum catalysts, this new AuPt catalyst achieves approximately 4.8 times higher oxygen-reduction current per unit area.
X-ray diffraction analysis revealed that the gold and platinum are not fully alloyed and it is supposed that this structure results in the improved the oxygen-reduction reaction activity.
This success represents a large step closer to fuel cells that are practical for applications requiring large current, such as automobiles and homes.
Hitachi Maxell presented this new technology for synthesising a highly-active AuPt catalyst at the 101st catalysis conference held March 29 at the Tower Hall Funabori in Tokyo.
Hitachi Maxell will continue nano-technology research and development towards practical applications in polymer-electrolyte and direct-methanol fuel cells.