Abstract
Gas diffusion layers (GDLs) are commonly known as one of the critical water management components in polymer electrolyte fuel cells with significant impact on the electrochemical cell performance. Increasing levels of liquid saturation in GDLs, especially during high-current-density operation, limit gas transport from the flow field channels to the catalyst layer surfaces and hence reduce cell performance. To provide GDL material selection and modification guidelines, a thorough understanding of the underlying structural factors of GDL materials and their influence on water management is required. In this work, operando X-ray tomographic microscopy (XTM) was employed to investigate the liquid saturation behavior for three commercial GDL materials during i-E curves and current jump characterization. Liquid volume fractions, saturation profiles and cluster distributions were analyzed to understand observed discrepancies in cell performance. Furthermore, saturation-dependent relative diffusivities were derived via direct numerical simulations, and the impact of GDL substrates on cell performance is thoroughly discussed with respect to structure and thermal properties.
Highlights
The aim of this work is to evaluate the underlying critical structure factors of three representative Gas diffusion layers (GDLs) substrates on polymer electrolyte fuel cells (PEFCs) performance at the typical start-up temperature of 25 °C
The underlying critical structure factors of three representative commercial GDL substrates all without micro porous layer (MPL) (Freudenberg H2315 I6, Toray TGP-H-060 and SGL 24BA) on PEFC performance at the typical start-up temperature of 25 °C are investigated through the analysis of the liquid water accumulating in the GDL pore space
The cells were operated at differential cell conditions to mimic cell inlet conditions with dry cathode feed gas, as it is the case if no humidifier is implemented in the PEFC peripherals, and wet anode feed gas due to hydrogen recirculation at the anode
Summary
The aim of this work is to evaluate the underlying critical structure factors of three representative GDL substrates on PEFC performance at the typical start-up temperature of 25 °C. The liquid saturation behavior and gas diffusion properties are derived to comparatively study the effects of the individual GDL structures and their impact on cell performance differences is elaborated. The high frequency resistance (HFR) was recorded by a Tsuruga E3566 AC milliohm meter (Tsuruga Electric Co., Japan) at a frequency of 1 kHz. Subsecond Operando XTM imaging.—Subsecond operando Xray tomographic microscopy (XTM) was employed to investigate liquid water saturation processes in the gas diffusion layers of PEFCs at the TOMCAT beamline of the Swiss Light Source (SLS) at Paul Scherrer Institut (PSI). The XTM scan time was set to 0.1 s (0.33 ms exposure time, 300 projections), in order to capture the fast liquid dynamics within the GDL and reduce X-ray dose so to enable multiple experiments with up to 300 scans. Figure 3. 3D renderings of three different GDL substrates (a) Freudenberg I6; (b) Toray TGP-H-060; (c) SGL 24BA) and their corresponding continuous pore size distribution (cPSD) with Gaussian fitting for peak position determination (d), (e) and (f), respectively
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