The National Science Foundation's (NSF) Tokyo Office periodically receives and disseminates reports on research developments in Japan that are related to the Foundation's mission. NSF-sponsored researchers currently working in Japan prepare many of these reports. These reports present information for use by NSF program managers and policy makers; they are not statements of NSF policy. .
Mr. Ted H. Yu, a graduate student in Material Science and Mineral Engineering at University of California, Berkeley, prepared the following report. Mr. Yu is a participant in the 1999 Summer Institute sponsored in the United States by NSF/NIH/USDA and the Science and Technology Agency and Japan Science and Technology Corporation in Japan. Dr. Tatsuhiro Okada of Department of Polymer Physics at National Institute of Materials and Chemical Research in Tsukuba, hosted Mr. Yu. Mr. Yu can be reached via email at: tyu@OCF.Berkeley.EDU
As an alternative to the combustion engine, Polymer Electrolyte Membrane (PEM) fuel cells have the potential to provide energy with lower emissions. One of the major concerns facing PEM fuel cells is its high cost. One of the high cost components of PEM fuel cells is the platinum catalyst. Not only does platinum (Pt) make fuel cells expensive, it is also very rare. It is estimated that there is not enough Pt in the world to power every car with a PEM fuel cells.
Alternative catalysts have been searched for extensively by scientists. It was discovered that Co-N compounds can carry out oxygen reduction similar to Pt. However, the level of performance is not as good as Pt. Whereas, Pt can carry out oxygen reduction of ~98%, the highest Co-N can perform is ~67% in basic solution. The performance drops to ~33% in neutral and acidic solutions.
Dr. Okada's group has discovered that a mixture of Porphyrin (a Co-N compound) and Pt can achieve oxygen reduction almost as high as that of pure Pt. Unfortunately, the price of Porphyrin is just as high as the price of Pt. My research this summer has been the analysis of the mixture of Co dqph (a Co-N compound) and Pt. Unlike Porphyrin, Co dqph is a very cheap Co-N compound.
The theory of why mixed catalysts of Co-N and Pt perform well is as follows. Oxygen catalytic reduction involves many steps. It is believed that Co-N compounds cannot carry out one of the steps in oxygen reduction very well. The Pt can compensate for the step that Co-N performs poorly. Thus, overall oxygen reduction remains high.
Synthesis:
To make Co dqph: 0.036 g of dqph and 10 ml of ethanol were bubbled
under nitrogen for 5 minutes. .025 g of Co (II) Acetate Tetrahydrate
was then added. The solution was mixed for 2 hours under nitrogen.
Afterwards, the solution was Rotovapped for 15 minutes to get
rid of the ethanol.
Mixed Catlysts:
Mixed catalysts of the following concentration were prepared:
Weight Percentage:
(%Pt/%Co-N)
(100/0)
(80/20)
(60/40)
(50/50)
(40/60)
(20/80)
(0/100)
Graphite was then added to the catalysts for electronic conductivity. The final powder mixture contains 20% mixed catalyst and 80% graphite.
Heat Treatment:
It was discovered by Dr. Okada's group that heat treatment between
600 C and 800 C greatly improves the performance of Co-N catalysts.
The heat treatment was performed in a quartz tube. The quartz
tube was heated to 600 C inside a furnace for two hours.
Electrode:
After heat treatment, 5 mg of the powder mixture was mixed with
100 mg of Nafion solution and 0.100 ml of ethanol. The solution
was mixed with a stir bar. Afterwards, 0.020 ml of the solution
was placed onto a graphite electrode. The electrode was then heated
for 2 hours at 80 C. Afterwards, it is ready for performance testing.
Cyclic Voltammetry:
The electrode was then placed in 0.005 M H2SO4 solution. The performance
of the electrode was determined by cyclic voltammetry. Using -0.1
V as the control voltage, the current at this voltage was compared
to see which Pt/Co-N mixture performed the best.
Results:
As expected, the 100/0, Pt/Co-N mixture had the highest current
and performed the best. However, the 80/20 and 60/40 mixture had
performances almost as high as the 100% Pt catalyst. This data
is encouraging, but more research needs to be done on this topic
to confirm these results due to the large possible sources of
error during the experimental procedures.
Thanks:
I would like to thank NSF and JISTEC for funding the Summer Institute
in Japan. I would like to thank NIMC for hosting me this summer.