Hydrogen oxidation on partially immersed Nafion(R)-coated electrodes

The mass transport of hydrogen on partially immersed Nafion(R)-coated electrodes (Nafion(R)\Pt\highly oriented pyrolytic graphite) was investigated as a model of the three-phase region of the gas-diffusion electrodes in proton-exchange membrane fuel cells. On raising the electrode from a position at which the Nafion(R) coating was fully immersed in the electrolyte solution (h = 0 mm), the dependence of the H-2 oxidation current on h was similar to that reported for a partially immersed flat platinum electrode. In contrast, on raising from a partially immersed position (h = 3 mm), the current was independent of h, and higher than that when raising from h = 0 mm at a given Nafion(R) thickness. When raising from h = 3 mm, the Nafion(R) coating above the intrinsic meniscus was not covered with a thin liquid electrolyte film, but functioned solely as a supermeniscus. This made hydrogen diffusion easier, resulting in the observed higher current. From the above results, useful implications for the design of gas-diffusion electrodes in PEMFCs are demonstrated.