Integration of carbon aerogels in PEM fuel cells

We prepared resorcinol-formaldehyde (RF) aerogel films with a high molar ratio of resorcinol/catalyst (R/C) of about 1500 and a low mass ratio of 30%. At the onset of the gelation process, organic fibers or carbon fiber fleece were added to the sol in order to increase the mechanical stability. Upon pyrolysis the RF-aerogel as well as the organic fibers were transformed into porous nanostructured carbon. The thickness of the films was about 500 mum and below. As previously shown, the addition of fibers modifies the gelation and thus the structure of the carbon network as well as the particle and pore sizes in characteristic ways. To investigate this influence, samples with different fiber types and contents were prepared. Scanning electron microscopy was used to determine the particle and pore sizes. The largest pore sizes obtained were in the range of several microns. The highest electrical conductivity reached was about 28 S/cm for a sample with almost 80% porosity. Tests of single cells prepared with carbon aerogel sheets show that films with a rather coarse structure in the interior and a micron thin fine structured top and bottom layer are most suitable as gas diffusion electrodes in polymer electrolyte membrane (PEM) fuel cells. The top and bottom layer promote the formation of low resistance electrical contacts between the gas diffusion electrodes and the polymeric membrane as well as the current collector. (C) 2001 Elsevier Science B.V. All rights reserved.