Can Carbon Coating Improve the Durability of Carbon Xerogels as Catalyst Supports for Proton Exchange Membrane Fuel Cell Electrodes?

Abstract

A carbon xerogel (CX) with a pore size of ∼70 nm was selected as support for a fuel cell electrocatalyst. While carbon xerogels offer excellent mass transport properties, their amorphous nature reduces their resistance to carbon corrosion under the oxidizing conditions of PEMFC operation. To tackle this, a partially graphitized carbon layer was deposited on the xerogel surface using chemical vapor deposition (CVD). This layer covers a large part of the micropores but keeps intact the interconnected meso/macropore network of the CX. The carbon-coated CX was also post-treated at 1500 °C under an inert atmosphere for further crystallization. Pt nanoparticles (20 wt %) were then deposited on both pristine and CVD-treated CXs by reduction of hexachloroplatinic acid in liquid phase; the resulting catalysts were evaluated with respect to their electrochemical activity and compared to a commercial carbon black-supported catalyst. The catalyst on the post-treated supports exhibited initial catalytic activities comparable to those obtained on pristine CX. After accelerated aging in RDE configuration, despite a decrease in the catalytic surface of Pt, specific activities increased while mass activities remained stable. In the Membrane-Electrodes Assembly configuration, the catalyst supported on the carbon xerogel post-treated with chemical vapor deposition and subsequent high-temperature treatment at 1500 °C exhibited encouraging durability behavior. This behavior was attributed to differences in Pt nanoparticle growth on post-treated carbon xerogel supports. Moreover, it was observed that these post-treatments do not negatively affect mass transport inside the electrode, since the meso/macropore texture remained intact.