Temperature dependence of the water distribution inside a Nafion membrane in an operating polymer electrolyte fuel cell. A micro-Raman study

In situ confocal micro-Raman spectroscopy was used to probe the interior of the electrolyte membrane of a polymer electrolyte fuel cell (PEFC) at various temperatures (40-110 °C) and humidities (dry-90% RH). No changes in the Raman spectra for functional groups involved in the polymer were found under humidified and dry conditions, except for the sulfonic acid group. With increasing relative humidity, the band intensity for S-O stretching (ν(S-O)) in the latter increased, and the peak shifted toward lower wavenumber. By analyzing the Raman peaks, water distributions through the Nafion membrane thickness were successfully evaluated in the operating PEFC. It was found that the back-diffusion of water produced at the cathode to the anode, humidifying the membrane, was clearly detectable, and also the rate of water transport in the membrane increased with increasing cell temperature.