SWNT−MWNT Hybrid Architecture for Proton Exchange Membrane Fuel Cell Cathodes

Abstract

A thin film of single-wall carbon nanotubes (SWNTs) and SWNT−multiwall carbon nanotube (MWNT) hybrids loaded with Pt have been evaluated as the cathode catalyst layer in proton exchange membrane fuel cells. The optimum Pt loading and thickness for SWNT films is found to be in the range of 20−100 µg Pt/cm2 and 0.3−1.4 µm, respectively. In this optimum range, Pt-SWNT thin films show excellent proton conductivity and are able to reach peak performance without additional nafion in the catalyst layer. Cathode-specific mass activity of Pt on a SWNT support is found to decrease as the Pt loading and thickness increase due to mass transfer limitations. Addition of Pt-MWNTs to Pt-SWNT thin films is found to increase the mass transport characteristics and cathode-specific mass activity. A SWNT−MWNT hybrid support shows three times higher mass activity than a SWNT support at about the same power output, and the optimum hybrid is found for a blend composed of 20−30 µgPt/cm2 on SWNTs and 5−10 µgPt/cm2 on MWNTs.