Effective-Diffusivity Measurement of Partially-Saturated Fuel-Cell Gas-Diffusion Layers

In proton-exchange-membrane fuel cells, flooding of the cathode gas-diffusion layer (GDL) hinders the gaseous reactant transport and thereby limits cell performance. The understanding of the effective diffusivity of the reactants through the GDL is essential for performance optimization and material design. In this paper, the effective diffusivities of unsaturated and partially-saturated GDLs are experimentally examined using an ex-situ electrochemical limiting-current method for various, uncompressed GDLs including different PTFE loadings. For unsaturated (including PTFE loadings) and partially-saturated (no PTFE) GDLs, the experimental results follow a power law with respect to porosity and saturation, respectively. PTFE treatment favorably changes the liquid distribution for improved gas-transport pathways, and a new correlation is proposed using a cumulative log-normal distribution function; however, the impact of PTFE on the overall effective diffusivity depends on the specific GDL structure. This work provides insights for fuel-cell models and transport phenomena, which can lead to the optimal GDL material design and cell operation. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.024211jes] All rights reserved.