Investigating Evaporation in Gas Diffusion Layers for Fuel Cells with X-ray Computed Tomography

Publication Type

Journal Article

Date Published

10/2017

Authors

Iryna V. Zenyuk, Adrien Lamibrac, Jens Eller, Dilworth Y. Parkinson, Federica Marone, Felix N. Büchi, Adam Z. Weber

DOI

Abstract

Understanding evaporation in porous media and the associated water distribution for a given saturation is critical for optimizing many different technologies including polymer–electrolyte fuel cells. In these devices, heat and mass-transport are coupled due to the two-phase transport of water and operating temperatures from subzero to 80 °C. Especially critical is understanding phase change in the mixed wettability, carbon gas-diffusion layers (GDLs). While previous works have measured evaporation rates empirically for a given saturation, there remains a need to explore the mechanisms governing evaporation, which are tied directly to the internal water distribution. In this article, liquid-water evaporation rates in GDLs are measured in situ using synchrotron X-ray computed tomography (CT). X-ray CT allows visualizing the evaporating water-front location and interfacial water/air surface area, thereby enabling true surface-area based evaporation rates. It is found that the overall specific evaporation rate is essentially constant as a function of saturation and that the water/air interfacial area scales almost linearly with saturation. To isolate transport and kinetic contributions to the overall evaporation rate, we systematically varied gas flow rate and composition. A three-dimensional mathematical model with direct meshes of liquid-water evaporation fronts from the X-ray CT studies allowed for the determination that the evaporation is transport limited. The overall results provide insight into evaporation phenomena in porous media.

Journal

The Journal of Physical Chemistry C

Volume

120

Year of Publication

2016

Issue

50

ISSN

1932-7447

Organization

Research Areas

Laboratory

LBNL

Type

Analysis, Materials, User Facilities