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Gas diffusion electrodes for electrochemical devices frequently consist of polytetrafluroethylene (PTFE) and carbon black-supported catalysts. The hydrophilic or hydrophobic character determines the wetting behaviour, which is important for media transport in the gas diffusion electrodes. The main components of the gas diffusion electrodes are an organic binder (typically PTFE) and a catalyst (for applications with acid electrolyte, a noble metal catalyst) that frequently is supported by carbon black. The chemical surface compositions 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 DLR (Deutsches Zentrum für Luft-und Raumfahrt). During preparation of the electrodes by the dry technique, the carbon black is enriched on the surface. Mechanical modification reduces the enrichment of the carbon black and tempering increases the PTFE concentration on the surface. The results of the XPS measurements were related to the wetting behaviour: a concentration of ∼20 wt.% PTFE marks the transition between hydrophilic and hydrophobic surfaces.

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