Journal: Chemical Communications, 2011, ASAP
Authors: Lin Gana,b, Hongda Dua, Baohua Lia, and Feiyu Kanga,b
Affiliation: aInstitute of Advanced Materials, Graduate School at Shenzhen, Tsinghua University; bLaboratory of Advanced Materials, Department of Materials Science and Engineering, Tsinghua University
Image of graphite nanofibers
There are multiple issues involved in the development of fuel cells. One of the most pressing is the need for an efficient way to catalyze the reduction of oxygen. Most fuel cells today use carbon-supported platinum catalysts; however these are not long lasting nor are they very efficient. One way to improve the specs of these catalysts is to optimize the carbon support structure. In this paper the authors investigate the use of graphite nanofibers (GNFs) as the carbon support for these catalysts.
In general, the more the carbon is in the form of graphite (the more graphitization), the more resistant the support is to corrosion and the higher the electron conductivity, which could be important to the catalytic properties of the material; however, the higher the amount of graphitization, the less able the metal catalyst is to become deposited onto the surface. The less metal catalyst in the material, the lower the catalytic abilities. The authors discuss how it is difficult to deposit metals onto the surface of carbon nanotubes (CNTs), because of the lack of surface defects; however the GNFs should have more surface defects but still a high amount of graphitization.
The authors synthesized the GNFs from carbon nanofibers (CNFs). The CNFs have exposed graphitic edges, which disperse the platinum catalyst fairly uniformly. In the formation of GNFs, the graphitic edges largely coalesce thereby increasing the amount of graphitization. The researchers hoped that this would increase durability, but still allow for good deposition of catalyst. They used transmission electron microscopy (TEM) to compare the dispersion of platinum catalyst on GNFs to their CNF precursors and found that it was comparable. Additionally, tests showed that the GNF loaded with catalyst performed better than the CNF version in a test using a direct-methanol fuel cell possibly due to higher electron conductivity, because of the higher graphitization. Additionally, the GNF material was shown to be more durable in accelerated durability tests. The authors succeeded in making catalytic support that is more durable and has higher catalytic abilities than previous materials.