Carbon Nanotube Free-Standing Film of Pt/MWNTs as a Bifunctional Component in Hydrogen Proton Exchange Membrane Fuel Cel
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1018-EE03-01
Carbon Nanotube Free-Standing Film of Pt/MWNTs as a Bifunctional Component in Hydrogen Proton Exchange Membrane Fuel Cells Jason M. Tang1,2, Kurt Jensen1,3, Paul Larsen1,3, Wenzhen Li1,3, Mikhail E. Itkis4, Yushan Yan1,3, and Robert C. Haddon1,2 1 Department of Chemical & Environmental Engineering, University of California, Riverside, Riverside, CA, 92521 2 Department of Chemistry, University of California, Riverside, Riverside, CA, 92521 3 Bourns College of Engineering รณ Center for Environmental Research & Technology, University of California, Riverside, Riverside, CA, 92521 4 Center for Nanoscale Science and Engineering, University of California, Riverside, Riverside, CA, 92521 ABSTRACT Conventional fuel cell architecture on one side of the membrane electrode assembly consists of a carbon backing layer, hydrophobic microporous layer (MPL), and a catalyst layer, which is in contact with the solid proton exchange membrane. Pt nanoparticles are deposited onto multi-walled carbon nanotubes (Pt/MWNTs) and a free-standing film of Pt/MWNTs is fabricated to act as the MPL and the catalyst layer in hydrogen fuel cells. The free-standing film of Pt/MWNTs condenses two functions into one bifunctional layer that simplifies the fuel cell fabrication procedure. Fuel cell polarization performance improves when using the free-standing film of Pt/MWNTs without the MPL resulting in higher a higher peak performance of 1.2 W/cm2 in comparison with 1.0 W/cm2 when in the presence of a MPL.
INTRODUCTION A conventional electrocatalyst support used in hydrogen proton exchange film fuel cells (PEMFCs) is carbon black. Other carbon based supports found in the literature are aerogels, fibers, or carbon nanotubes.1,2 According to recent studies multi-walled carbon nanotubes and single-walled carbon nanotubes have been shown to exhibit enhanced durability and resistance to corrosion in an acceleration of simulated fuel cell operating conditions.3,4 This investigation shows the use of MWNTs as a catalyst support exhibiting a bifunctional ability to act as a catalyst layer and hydrophobic microporous layer (MPL). Conventional fuel cell architecture uses a hydrophobic (MPL) composed of carbon black and polytetrafluoroethylene (PTFE).5 However, use of a Pt/MWNT catalyst layer eliminates the need for the MPL.
EXPERIMENTAL DETAILS Electrocatalyst preparation and fuel cell fabrication MWNTs used in this study were purchased from the MER Corporation (Catalog # MRCMW). These MWNTs were first surface oxidized under refluxing conditions under acidic conditions in a mixture of 1.0 M H2SO4/2.0 M HNO3 for 6 hours. The oxidized MWNTs were then filtered out from the acid mixture using a filtration membrane and subsequently rinsed with water before drying. Pt was then deposited onto the MWNTs by using ethylene glycol as a reduction agent to make the Pt supported on MWNTs (Pt/MWNT). Upon suspending the MWNTs in ethylene glycol by ultrasonication, the pH was adjusted to above 10 as measured by litmus paper by addition of a previously prepared 1
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