Hydrophobic carbon layer

Effect of PTFE Content in the Hydrophobic Carbon Layer of thie GDL on Cell Performance... 

The air gas-diffusion electrode developed in this laboratory [2] is a double-layer tablet comprising a porous hydrophobic gas layer and a catalytic layer in which the catalyst is placed. The gas layer of the electrode is prepared from hydrophobic material carbon black modified with PTFE by a special technology [3], The catalytic layer contains a porous catalyst. 

The porous hydrophobic film of previous electrode designs has now been substituted with a new layer based on a mixture of particles of hydrophobic carbon and PTFE binder. This mixture is very similar in composition to the catalytic layer. This particular modification provides several advantages ... 

It is well known that Nafion ionomer contains both hydrophobic and hydrophilic domains. The former domain can facilitate gas transport through permeation, and the latter can facilitate proton transfer in the CL. In this new design, the catalyst loading can be further reduced to 0.04 mg/cm in an MEA [10,11]. However, an extra hydrophobic support layer is required. This thin, microporous GDL facilitates gas transport to the CL and prevents catalyst ink bleed into the GDL during applications. It contains both carbon and PTFE and functions as an electron conductor, a heat exchanger, a water removal wick, and a CL support. 

A review appeared on piezoelectric quartz crystals used as detectors for phenols in air, after coating with Triton X-100 and 4-aminoantipyrine (78), or with activated carbon cloth impregnated with various compounds, such as poly(vinyl pyrrolidone). A piezoelectric sensor was proposed for determination of trace amounts of phenol and alkylphenols in air. The problems attaining selectivity of the adsoption membranes and operating conditions were addressed . An AT-cut quartz crystal, coated with a hydrophobic PVC layer and operating in the thickness shear mode, has been used to detect 4-aminophenol, after conversion to a hydrophobic indophenol dye and adsorption on the polymer layer. The mode of preparation of the PVC coating affects the sensitivity of the detector , a... 

Superhydrophobic surfaces based on poly(methyl methacrylate) (PMMA) with flower-like structures were prepared by controlling the aminolysis reaction of surface ester groups and the surface morphology of PMMA. The effects of the aminolysis time and the processing temperature in stearic acid solution on the surface wettability and surface morphology were examined in detail. The combination of rough surface morphology and the presence of hydrophobic carbon chtiins on the top layer was responsible for the super-hydrophobicity. 

For the comparison of deposition methods the samples with approximately the "same" thickness (interval 73-85 run) were chosen. From the values of contact angle measured with water drop presented we can resume that the most hydrophobic is pristine PET. Due to coverage of the substrate by the carbon layers we observed lower values of contact angle. This... 

The preparation of a GDL involves the use of a substrate, carbon cloth or paper [6-8], which are in general commercially available. They are usually treated to have hydrophobic/hydrophilic properties, typically using polytetrafluoroethylene (PTFE) [9]. A microporous carbon layer, made with carbon and PTFE with controlled porosity is applied to the substrate in the catalyst layer side or to both sides [10]. This improves the gas and water transport properties. 

The first step is the preparation of a gas diffusion medium, which usually consists of a thin layer of uncatalyzed carbon and PTFE on a hydrophobized carbon cloth or paper. The following step involves the preparation of eatalyst-PTFE suspension. The catalyst is first dispersed in distilled water, using a combination of stirring and sonication. The PTFE emulsion is added and the PTFE flocculated onto the catalyst powder. The pH of the catalyst... 

Such a PTFE-bonded hydrophobic catalyst layer is a breakthrough in catalyst layer preparation technology for PEMFCs. First, this technique uses a carbon-... 

On either side of each catalyst layer are the gas diffusion layers (GDLs) or gas diffusion media (GDM), both terms being used in literature. These are typically made of hydrophobic carbon fiber paper or cloth, termed the substrate, with a hydrophobic microporous layer (MPL) applied to the catalyst side, made of carbon particles with a hydrophobic binder. The hydrophobic-ity is typically achieved through application of PTFE to the substrate and by mixing the PTFE with the carbon particles in a carbon ink to be coated on the substrate. The GDLs serve a number of functions ... 

---