Rate limiting proton hydration in the hydrogen electrode of the polymer electrolyte membrane fuel cell

We show how one can obtain information on the three-phase contact of the electrode in the polymer electrolyte fuel cell, using nonequilibrium thermodynamics in combination with impedance spectroscopy. The isothermal hydrogen adsorption and reaction at the E-TEK electrode of a polymer electrolyte fuel cell with a Nafion (R) 117 membrane is investigated at 30 degrees C and 1 bar. We have earlier reported that adsorption and diffusion of gas to the three-phase contact is rate-limiting. We proceed to show how charge transfer and hydration and transport into the membrane play a role. The adsorption/diffusion step takes place in a layer located before the platinum surface, while the charge transfer takes place at (predominantly) the metal particle surface, while the third step is on the membrane side of the metal surface.