New expressions to determine the water diffusion coefficient in the membrane of PEM fuel cells

A set of mathematical expressions is presented to allow the determination of the water content in a PEMFC membrane, and facilitate the calculation of the water balance under variable conditions of hydration on both sides of it. The study is based on a cooperative model of water diffusion through the membrane, which avoids discontinuities in the calculations, gives a natural path to avoid the Schroeder's paradox, correctly predicting the value limit of ponding of water content, and presents a good behaviour to temperature variation. The model has been tested with Nafion® 117 literature data. Its features are coherent with physical models.