New insights into the temperature-water transport-performance relationship in PEM fuel cells

Three-dimensional numerical simulations of a single straight-channel PEMFC at three different operating temperatures (343 K, 353 K, and 363 K) and at a relative humidity RH = 90% were carried out, by using potentiostatic conditions ranging from 0.27 to 1.0 V. This study aimed at gaining further insights into the complex and tightly coupled interactions taking place inside the fuel cell, relating water generation and transport with local temperature distributions and cell performance. A sensitivity analysis concluded that the higher the operating temperature is, the better the electrical performance of the PEMFC, for the range of operating temperatures analyzed. This feature was further investigated at high current densities (j = 2.25 and 2.57 A/cm2), where the increase of the operating temperature (in the range of study) resulted in an enhancement of the water diffusivity and the electro-osmotic drag, improving the ionic conductivity. Additionally, the dimensionless temperature distribution across the cell width was found to be similar in all the cases. Profile-like curves displaying under-rib/under-channel characteristics are presented and analyzed to understand the role of water and its interaction with the different phenomena occurring within the cell. It was demonstrated that colored scatter plots are convenient tools that contribute to explain existing relationships between the water-related magnitudes.