The distribution and diffusion coefficient of water inside a Nafion® membrane in a running fuel cell under transient conditions analyzed by operando time-resolved CARS spectroscopy

The performance and stability of polymer electrolyte membrane fuel cells (PEMFCs) are directly affected by the distribution of water molecules inside the membrane. In this study, coherent anti-Stokes Raman scattering (CARS) spectroscopy was used to measure the distribution of water in a Nafion® membrane under transient conditions after increasing the current density. At the cathodic surface of the membrane, an overshoot in amount of water was observed as a result of the increase in the rate of water production and electro-osmosis, while at the other locations in the membrane was observed a gradual increase of water as a result of water transport. The calculation of the water diffusion coefficient during power generation was subsequently carried out, which was consistent with the results of the previous values obtained statically.