AmericanChemicalSociety.com
Reports: GB10 47532-GB10: A Novel Approach for Controlled Synthesis of Single-Walled Carbon Nanotube-Supported Pt Nanoparticle Catalysts and Electrochemical Properties
1. Objectives
Fuel cells have been receiving increased attention recently due to the depletion of fossil fuels and the increase in environmental pollution. Among different types of fuel cells, direct methanol and ethanol fuel cells are excellent power sources due to their high energy density, low pollutant emission, low operating temperature (60 - 100 °C) and ease of handling liquid fuel. However, there remain some critical obstacles inhibiting broad applications of direct methanol and ethanol fuel cells, including low electrocatalytic activity of anodes for methanol and ethanol oxidation reactions and the high cost of noble metal platinum (Pt)-based catalysts. In order to enhance the catalytic activity and reduce the usage of Pt- based catalysts, one strategy is to explore novel carbon materials to effectively disperse catalyst particles. During the past year, we have investigated effects of different carbon nanotube supported catalysts on methanol and ethanol electro-oxidation, as well as synthesized Pt and Pt-Ru nanoparticles on graphene sheets, and explored their electrocatalytic activity for methanol and ethanol oxidation.
2. Findings
2.1 Effects of Different Carbon Nanotube Supported Catalysts on Methanol and Ethanol Electro-Oxidations
For both methanol and ethanol electro-oxidations, single-walled carbon nanotube (SWCNTs)-supported Pt and Pt-Ru catalysts demonstrated higher forward peak current density, larger ratios of forward peak current density to reverse peak current density, and lower charge transfer resistances in comparison to multi-walled carbon nanotube (MWCNTs)-supported Pt and Pt-Ru catalysts. These results suggest that SWCNTs can effectively enhance the electrocatalytic activities of Pt and Pt-Ru nanoparticles for methanol and ethanol oxidations, and thereby efficiently convert chemical energy to electrical energy. Our experimental results clearly demonstrate that SWCNTs are more desirable candidates as catalyst supports for both direct methanol and ethanol fuel cells compared with MWCNTs.
2.2 Graphene-Supported Platinum and Platinum-Ruthenium Nanoparticles with High Electrocatalytic Activity for Methanol and Ethanol Oxidations
In 2005, graphene, a mono-atomic sheet of hexagonally arranged carbon atoms, was successfully synthesized. Graphene has exhibited excellent electrical conductivity and extremely high specific surface area (2600 m2/g), and therefore, graphene should be explored as a support material to improve electrocatalytic activity of catalyst particles for methanol and ethanol oxidations. In our study, Pt and Pt-Ru nanoparticles were synthesized on graphene sheets, and their electrocatalytic activity for methanol and ethanol oxidations was investigated. Experimental results demonstrate that, in comparison to the widely-used Vulcan XC-72R carbon black catalyst supports, graphene-supported Pt and Pt-Ru nanoparticles demonstrate enhanced efficiency for both methanol and ethanol electro-oxidations with regard to diffusion efficiency, oxidation potential, forward oxidation peak current density, and the ratio of the forward peak current density to the reverse peak current density. For instance, the forward peak current density of methanol oxidation for graphene- and carbon black-supported Pt nanoparticles is 19.1 mA/cm2 and 9.76 mA/cm2, respectively; and the ratios are 6.52 and 1.39, respectively; the forward peak current density of ethanol oxidation for graphene- and carbon black-supported Pt nanoparticles is 16.2 mA/cm2 and 13.8 mA/cm2, respectively; and the ratios are 3.66 and 0.90, respectively. These findings favor the use of graphene sheets as catalyst supports for both direct methanol and ethanol fuel cells.
3. Student Training and Development
The execution of this proposed research not only has significant impact on the career development of the PI, but also provides invaluable opportunities for both graduate and undergraduate students to participate in cutting-edge research in the areas of nanomaterials and nanoparticle catalysts. During the period from September 1, 2009 to August 31, 2010, nine students (1 high school student, 3 undergraduates, and 5 graduate students) have participated in this project. Among them, Tracey Tang, a senior at Greenwood Laboratory School, received the 3rd place award in the category of Senior Physics at the 50th Annual Ozarks Science & Engineering Fair (Springfield, MO, April 6-8, 2010) for her project: Photoelectrical Properties of MWCNT/TiO2 Solar Cell. Patrick M. Margavio, a senior in Physics, was awarded 1st place in the Collegiate Division of Physics, Mathematics, Engineering, and Computer Science for his project, Effect of Chirality on Carbon Nanotube Based Thin Film Solar Cells, at the 2010 Missouri Academy of Science Annual Meeting (Springfield, MO, April 16-17, 2010).
