A new catalyst developed by Hitachi Maxell Ltd. can generate about 4.8 times the oxygen-reduction current per unit area than existing platinum catalysts. The new catalyst, for use at the cathode of a polymer electrolyte fuel cell (PEFC), is a gold-platinum particle 2 to 3 nm in size. Platinum is a common catalyst for the oxygen-reduction reaction in PEFCs, but it is an extremely expensive precious metal, so reducing material cost for PEFCs by minimizing the amount of platinum used, while improving its catalytic effect is an important R&D topic.
Besides reducing particle size to increase surface area, the addition of base metals such as iron, cobalt, and nickel to platinum also improves the oxygen-reduction reaction rate. But these metals dissolve easily in the acidic environment of a PEFC where the catalyst is working, which is a problem. Maxell’s new catalyst is resistant to acidic environments.
It was difficult to synthesize gold particles smaller than 5 nm due to its relatively low melting point. However, a proprietary nano-level particle-synthesizing technology, allowed Maxell to develop a high-activity structure in which the gold and platinum are not fully alloyed in the new catalyst. Using citric acid as a reducing agent, the gold-platinum catalyst particles were synthesized at 373°K. Maxell intends to continue nano-technology R&D towards practical applications in polymer-electrolyte and direct-methanol fuel cells.
Hitachi Maxell Ltd