4.5 ION TRANSPORT IN CATHODE CATALYST LAYERS
Catalyst layers, coated on the electrolyte membrane surface, contain the electrolyte ionomer phase to conduct protons. The ionomer content usually ranges from 0.1 to 0.4, forming a proton conducting network. The ionic resistance of a catalyst layer may not be small, yielding a certain amount of ohmic loss. In catalyst layers, water is transported in both void space and electrolyte ionomer. The layer’s ionic conductivity is determined by water content in the ionomer phase.
4.5.1 Variation in Water Content in Catalyst Layers
(1) Water Vapor Concentration
Without liquid water, diffusion is a major mechanism for water transport in both ionomer and gaseous phases. At phase equilibrium between the ionomer ...