Measurement of effective gas diffusion coefficients of catalyst layers of PEM fuel cells with a Loschmidt diffusion cell

Abstract

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In this work, using an in-house made Loschmidt diffusion cell, we measure the effective coefficient of dry gas (O 2 -N 2 ) diffusion in cathode catalyst layers of PEM fuel cells at 25 • C and 1 atmosphere. The thicknesses of the catalyst layers under investigation are from 6 to 29 m. Each catalyst layer is deposited on an Al 2 O 3 membrane substrate by an automated spray coater. Diffusion signal processing procedure is developed to deduce the effective diffusion coefficient, which is found to be (1.47 ± 0.05) × 10 −7 m 2 s −1 for the catalyst layers. Porosity and pore size distribution of the catalyst layers are also measured using Hg porosimetry. The diffusion resistance of the interface between the catalyst layer and the substrate is found to be negligible. The experimental results show that the O 2 -N 2 diffusion in the catalyst layers is dominated by the Knudsen effect. Crown

Improved experimental method for measuring gas diffusivity through thin porous media

“…The experimental uncertainty in the GDL diffusivity measurements conducted by Zamel et al is large, as will be shown, and grows exponentially large for the measurement of thinner materials pertinent to the development of PEMFCs such as the microporous layer and catalyst layer . This study builds upon the work by Dong et al, who determined the theoretical accuracy of measuring diffusivity of porous media with the Loschmidt cell method, with the design of a new Loschmidt cell that can measure submillimeter thick materials such as the gas diffusion (∼200 μ m ), microporous (∼50 μ m ), and catalyst layers (∼10 μ m ) with a high level of accuracy.…”

Effective transport properties for polymer electrolyte membrane fuel cells – With a focus on the gas diffusion layer

“…Using a Loschmidt cell apparatus described earlier in Section 2.2.1, Shen et al [125] measured the diffusion coefficient of the catalyst layer. In order to make these measurements, the catalyst layer was spared onto a porous membrane and the diffusion coefficient of this assembly was measured.…”

Effective diffusivity of polymer electrolyte fuel cell gas diffusion layers: An overview and numerical study

“…Apparently such an uncertainty resulted in a significant underestimation of the MPL effective diffusivity measured by Chan et al [17]. Likewise, the effective diffusivity of the catalyst layers measured by Shen et al [20] is expected to be highly underestimated. Similarly, the effective diffusivity of the MPL estimated by Zhang et al [34] is lower than those estimated by Nanjundappa et al [28] and El Hannach et al [35] by an order of magnitude.…”

“…[17]. The effective diffusivity of SolviCore MPL is 5 times less than that of its carbon substrate GDLs tested: a set of untreated, PTFE-treated and MPL-coated GDLs, namely Toray (060-and 120-series), SGL Sigracet (10-and 25-series) and SolviCore Shen at al [20]. Analytical Equation (22) in the paper [36].…”

“…This limitation is mainly due to the infinitesimally small cross-section of the GDL that imposes a technical challenge in estimating the effective diffusivity in the in-plane directions. Most of the experimental investigations to estimate the effective diffusivity of the GDLs are ex-situ in which closed diffusion cells [4,17,20,21], open diffusion cells [19] and electrochemical diffusimetry [6,18] were employed. There are two approaches to experimentally evaluate the effects of porosity on the effective diffusivity of the GDL, namely through (i) changing the PTFE content of the GDL (e.g.…”