The properties of porous transport layers (PTL) in electrolysis devices and their effects on cell performance have been studied extensively in recent literature. This paper provides a detailed analysis with regards to the transport in the catalyst layer (CL). The work demonstrated that the catalyst loading affects the sensitivity of electrolysis performance to PTL properties, particularly those of the PTL surface in contact with the CL. It was demonstrated that upon reducing catalyst loading, PTL properties had an increased effect on the performance of PEMWE cells. While we observed mild performance variations among PTLs when using a high anode catalyst loading, strong correlations between PTL surface properties and cell performance existed at a low catalyst loading. PTL properties affected performance by influencing the in-plane conductivity and permeability of the CL. The variation of apparent exchange current density and apparent CL bubble coverage with the stoichiometric flow rate was studied at low anode feed rates. This led to the emergence of a PTL grain size effect on apparent bubble coverage at high catalyst loading. We provide a descriptive analysis of the phenomena causing voltage losses in PEMWE devices. These findings are important for electrochemical modeling and designing the PTL/CL interface.

X-ray computed tomography (CT) is a nondestructive three-dimensional (3D) imaging technique used for studying morphological properties of porous and nonporous materials. In the field of electrocatalysis, X-ray CT is mainly used to quantify the morphology of electrodes and extract information such as porosity, tortuosity, pore-size distribution, and other relevant properties. For electrochemical systems such as fuel cells, electrolyzers, and redox flow batteries, X-ray CT gives the ability to study evolution of critical features of interest in ex situ, in situ, and operando environments. These include catalyst degradation, interface evolution under real conditions, formation of new phases (water and oxygen), and dynamics of transport processes. These studies enable more efficient device and electrode designs that will ultimately contribute to widespread decarbonization efforts.

In this paper, direct-modeling-based Lattice Boltzmann Method (LBM) combined with in-situ flow visualization, is used to explore fundamentally the transport of liquid-water inside the gas-diffusion layers (GDLs) used in polymer electrolyte fuel cells. Studies of the water evolution, water saturation, and breakthrough pressure inside a GDL with single and multiple injection points under land and channel geometries are explored. The model and experiment demonstrate good agreement between geometries of GDLs provided in this study which were obtained by a three-dimensional (3-D), reconstructed micro-structure from micro X-ray computed tomography (CT). The overall predictions of water evolution within the GDL agree well with the data visualized from the X-ray CT experiment for all cases studied. It also reveals that the liquid-water saturation profiles inside the GDL and breakthrough pressure are different when the location of the water injection point is altered, thereby providing analysis as to the impact of microporous layers or catalyst-layer functioning. Moreover, the uncompressed GDL undergoes a significantly different mechanism of water transport than that of the compressed GDL. Furthermore, the predictions show that the wettability variation is one of the key factors of the saturation characteristics.

Proton exchange membrane fuel cells (PEMFC) require a gas diffusion layer (GDL) to aid in the transport of liquid fuel to the catalyst layer. In this work, direct modeling using the Lattice Boltzmann Method (LBM) was applied to X-ray CT scans of four different carbon gas diffusion layers to understand the mass transport properties through the samples. Three injection orientations were used to study local saturation levels, water evolution through the sample, and mass transport behavior at breakthrough conditions. The LBM, combined with computational fluid dynamic modeling techniques, can accurately predict liquid saturation at the macro and micro scale, which provides more insight into the mass transport phenomena through the GDL. The change of pore structure and orientation in both the in-plane and through-plane determines the path that liquid water must take, which could aid or impact PEMFC performance. The outcomes from this work will also benefit any research that needs knowledge of internal mass transport qualities of gas diffusion media.