Showa Denko’s Pt-Substitute Catalyst Cuts Fuel Cell Costs
Show a Denko KK of Japan has developed a catalyst for polymer electrolyte fuel cells (PEFC) to replace expensive platinum (Pt)-based catalysts. The new catalyst adds carbon (C), nitrogen (N) and other elements to niobium (Nb) and titanium (Ti) oxides (Fig 1). The development was advanced as part of the “non-precious metal oxide-based cathode for PEFCs” project of the New Energy & Industrial Technology Development Organization (NEDO) of Japan, by a group headed by Professor Ken-Ichiro Ota of Yokohama National University of Japan.
In PEFCs, catalysts promote the chemical reaction between hydrogen (H) and oxygen (O). Pt, currently used as the catalyst, is a rare metal that costs over Yen4,000 per gram, and the high cost of catalysts has been a major obstacle to widespread adoption of PEFCs.
Another problem is that Pt dissolves in the air electrode, which is in an oxidizing environment. The development of a substitute has been a major priority from the viewpoint of durability as well. Nb- and Ti-based oxides face few restrictions in terms of resources, and because they are oxides they are less susceptible to being dissolved than Pt. Material cost, says a source at Showa Denko, is “… no more than 5% of the platinum catalyst.”
Catalytic Strength Index
The newly developed Nb- and Ti-based oxide catalysts have oxidation/reduction potential (ORP, an index of catalytic strength) of 1V or better, about the same as Pt, suggesting high performance as catalysts (Fig 2). When it comes to performance in fuel cells, however, “Platinum performance is still four or five times higher,” says a source at Showa Denko. The firm joined the NEDO project in July 2008, and says there is still considerable room for improvement. For example, the catalyst particles are large at about 40nm, but they expect performance to rise with smaller particle sizes.
According to Showa Denko, cell evaluation for fuel cell applications indicated an open voltage of 1V or higher, and a durability of at least 500 hours. Performance verification testing is still under way, with new records being set that make it the most effective Pt-substitute catalyst in the world at present. The remaining issue is establishing a volume production method. “We still can’t assure stable performance in 4-gram batches,” reveals an engineer at the firm.
