Direct growth of carbon nanotubes forests on carbon fibers to replace microporous layers in proton exchange membrane fuel cells

Abstract

A novel microporous layer structure for fuel cell application has been developed based on the direct growth of thin multiwall carbon nanotubes forests on the carbon fiber support of a commercial gas diffusion media free of hydrophobic treatment. The growth process is a hot filaments assisted chemical vapor deposition coupled with a specific catalyst dedicated to the growth of carbon nanotubes on carbon support. The so obtained carbon nanotube forests are perpendicularly aligned all along the carbon fibers and cover the surface of the gas diffusion media, providing a unique and new structure of microporous layer. The carbon nanotubes composing the forests are about 10 μm–20 μm long, with about 6 walls for an average diameter of 7.5–8 nm. Fuel cell testing demonstrated a performance improvement up to 30% compared to the best state of the art gas diffusion media, even in the presence of liquid water in the fuel cell, which is the main issue limiting performances.