XPS study of electrodes formed from a mixture of carbon black and PTFE powder

Kurzfassung

Gas diffusion electrodes for electrochemical devices frequently consist of polytetrafluorethylene (PTFE) and are carbon black supported catalysts. The hydrophilic and hydrophobic character determines the moisturewetting wetting behavior, which is important for the media transports in the gas diffusion electrodes. The main components of gas diffusion electrodes are an organic binder, typical PTFE, and a catalyst, for applications with acid electrolyte a noble metal catalyst, which frequently is supported by carbon black. The chemical surface composition of electrodes prepared in different ways from a mixture of carbon black and PTFE and mechanically and thermally modified were determined by X-ray photoelectron spectroscopy (XPS). The XPS measurements show differences between electrodes wet prepared from a suspension and electrodes prepared with the dry preparation technique of the DLR (Deutsches Zentrum für Luft- und Raumfahrt). During the preparation of the electrodes by the dry preparation technique the carbon black is enriched on the surface. Due to the mechanical stressing the enrichment of the carbon black is reduced. By tempering the PTFE concentration on the surface can be increased. The results of the XPS measurements were related to the wetting behavior; a concentration of approximately 20 weight% (wt%) PTFE is the limit between hydrophilic and hydrophobic surfaces.