Evaluation of the net water transport through electrolytes in Proton Exchange Membrane Fuel Cell

Abstract

Electro-osmotic drag and back diffusion are the primary water transport mechanisms in PEMFC (Proton Exchange Membrane Fuel Cell) electrolytes. These two phenomena occur competitively in the membrane, and ultimately determine the net water movement. The chemical compositions of reactants and product (i.e., H 2, O 2, and H 2O) in a porous catalyst layer vary with respect to the electro-chemical reactions and water transport through the membrane. The tendency of the chemical compositions was estimated by analyzing the net water transport coefficient ( α), defined as the ratio of the reaction rate to the water transport rate. New criteria were suggested for predicting species mole fractions from the flow direction, and these were validated by CFD analysis. The hydrogen mole fraction had different tendencies to rise or fall based on the flow direction at α = 0.5, while the oxygen mole fraction extreme was located at α = −0.75. Finally, α was shown to influence the membrane conductivity and activation losses, which are the main factors that contribute to fuel cell performance.