Hydrophilic-hydrophobic and sorption properties of the catalyst layers of electrodes in a proton-exchange membrane fuel cell: A stage-by-stage study

Abstract

In the electrodes of a proton-exchange membrane fuel cell, the hydrophilic-hydrophobic properties of the catalyst layers (CL), which contain a carbon substrate (CS), an ionomer in the form of Nafion resin, and a platinum catalyst, are investigated with standard contact porosimetry. Regularities in the influence of ionomer on the hydrophilic-hydrophobic properties of ten different CS, including Vulcan XC-72 carbon black, are investigated. The following plots are obtained: pore distribution curves with respect to radii, water desorption isotherms, moisture content distribution curves with respect to capillary pressure and to the free energy of binding water to material, and the wetting angle of water for the samples under investigation as a function of pore radius. It is established that both a hydrophobic effect and a hydrophilic effect occur in CL as a result of ionomer application to the CS under investigation. It is concluded that these different effects are determined by the orientation of the sulfonate groups (inside and outside) in the resin particles. This orientation depends on the extent of the binding of sulfonate groups to the CS surface by adsorption. CS surface properties are determined by the type and concentration of surface groups. Thus, the phenomenon of ionogenic-group inversion is established. When platinum is applied to CS, the CL become partially hydrophilic.