Phosphoric Acid Invasion in High Temperature PEM Fuel Cell Gas Diffusion Layers

In this work, liquid phosphoric acid was injected into polymer electrolyte membrane fuel cell (PEMFC) gas diffusion layers (GDLs) to visualize the invasion patterns developed at breakthrough. Three-dimensional (3D) images of the GDLs were obtained through X-ray computed tomography, and equivalent pore networks were generated as the basis for pore network simulations using OpenPNM. Strong qualitative agreement was obtained between the simulated and experimentally observed liquid phosphoric acid invasion patterns, which provided validation for the numerical modeling. Different GDL materials were evaluated by examining the effects of a micro porous layer (MPL) and pore size distribution on the saturation and distribution of phosphoric acid. The MPL was shown to restrict liquid phosphoric acid from entering the carbon fiber substrate. The overall phosphoric acid saturation at breakthrough was found to decrease significantly for samples containing an MPL due to the smaller pore sizes. Further, the influence of cracks in an MPL on overall saturation at breakthrough was investigated. It was observed that a crack-free MPL provided a more effective physical barrier to restrict the undesired leaching of liquid phosphoric acid through the GDL

OpenPNM: A Pore Network Modeling Package

Pore network modeling is a widely used technique for simulating multiphase transport in porous materials, but there are very few software options available. This work outlines the OpenPNM package that was jointly developed by several porous media research groups to help address this gap. OpenPNM is written in Python using NumPy and SciPy for most mathematical operations, thus combining Python's ease of use with the performance necessary to perform large simulations. The package assists the user with managing and interacting with all the topological, geometrical, and thermophysical data. It also includes a suite of commonly used algorithms for simulating percolation and performing transport calculations on pore networks. Most importantly, it was designed to be highly flexible to suit any application and be easily customized to include user-specified pore-scale physics models. The framework is fast, powerful, and concise. An illustrative example is included that determines the effective diffusivity through a partially water-saturated porous material with just 29 lines of code

Synchrotron X-ray Radiography and Tomography of Vanadium Redox Flow Batteries—Cell Design, Electrolyte Flow Geometry, and Gas Bubble Formation

The wetting behavior and affinity to side reactions of carbon‐based electrodes in vanadium redox flow batteries (VRFBs) are highly dependent on the physical and chemical surface structures of the material, as well as on the cell design itself. To investigate these properties, a new cell design was proposed to facilitate synchrotron X‐ray imaging. Three different flow geometries were studied to understand the impact on the flow dynamics, and the formation of hydrogen bubbles. By electrolyte injection experiments, it was shown that the maximum saturation of carbon felt was achieved by a flat flow field after the first injection and by a serpentine flow field after continuous flow. Furthermore, the average saturation of the carbon felt was correlated to the cyclic voltammetry current response, and the hydrogen gas evolution was visualized in 3D by X‐ray tomography. The capabilities of this cell design and experiments were outlined, which are essential for the evaluation and optimization of cell components of VRFBs

Comparative characterization of phenolic and other polar compounds in Spanish melon cultivars by using high-performance liquid chromatography coupled to electrospray ionization quadrupole-time of flight mass spectrometry

Melon (Cucumis melo L.), belonging to the Cucurbitaceae family, is a significant source of phytochemicals which provide human health benefits. High-performance liquid chromatography coupled to electrospray ionization mass spectrometry quadropole-time of flight (HPLC-ESIQTOF-MS) was used for the comprehensive characterization of 14 extracts from 3 Spanish varieties of melon (Galia, Cantaloupe, and Piel de Sapo). A total of 56 different compounds were tentatively identified, including: amino acids and derivatives, nucleosides, organic acids, phenolic acids and derivatives, esters, flavonoids, lignans, and other polar compounds. Of these, 25 were tentatively characterized for the first time in C. melo varieties. Principalcomponent analysis (PCA) was applied to gain an overview of the distribution of the melon varieties and to clearly separate the different varieties. The result of the PCA for the negative mode was evaluated. The variables most decisive to discriminate among varieties included 12 of the metabolites tentatively identified.CIDAF (Centro de Investigación y desarrollo del Alimento Funcional), Departamento de química analítica. Grupo FQM-297

Up-Scaled Microfluidic Fuel Cells With Porous Flow-Through Electrodes

In this work, an experimental microfluidic fuel cell is presented with a novel up-scaled porous electrode architecture that provides higher available surface area compared to conventional microfluidic fuel cells, providing the potential for higher overall power outputs. Our proof-of-concept architecture is an up-scaled flow-through fuel cell with more than nine times the active electrode surface area of the flow-through architecture first proposed by A Microfluidic Fuel Cell With Flow-Through Porous Electrodes," J. Am. Chem. Soc., 130, pp. 4000-4006). Formic acid and potassium permanganate were employed as the fuel and oxidant, respectively, both dissolved in a sulfuric acid electrolyte. Platinum black was employed as the catalyst for both anode and cathode, and the performances of carbon-based porous electrodes including cloth, fiber, and foam were compared to that of traditional Toray carbon paper (TGP-H-120). The effects of catalyst loading were investigated in a microfluidic fuel cell containing 80 pores per linear inch carbon foam electrodes. A discussion is also provided of current density normalization techniques via projected electrode surface area and electrode volume, the latter of which is a highly informative means for comparing flow-through architectures

Establishing Accuracy of Watershed-Derived Pore Network Extraction for Characterizing In-Plane Effective Diffusivity in Thin Porous Layers

The work presented in this paper reports a versatile and customizable watershed-based pore network extraction tool. It was used to build pore networks from microscale computed tomography images of highly porous carbon-fiber materials. The extracted networks were used to characterize the structural properties (pore and throat diameter, and porosity distributions) and to predict the dry, in-plane, effective diffusivities of two commercial gas diffusion layers under various levels of compression. The relationship between compression and effective diffusivity was used to accurately predict experimental values available in the literature to within 10% of the reported values for compressive strains less than 0.55. Through this work, we validate the accuracy of watershed-derived pore networks for predicting in-plane effective diffusivities, further establishing the reliability of watershed-derived pore network modeling for fuel cell applications

Role of the microporous layer in the redistribution of phosphoric acid in high temperature PEM fuel cell gas diffusion electrodes

In this work, pore network modelling was used to investigate the leaching of phosphoric acid PA in the gas diffusion electrode GDE of high temperature polymer electrolyte membrane fuel cells HT PEMFCs . A HT PEMFC GDE composed of a catalyst layer, a microporous layer MPL and a fibrous substrate was assembled, and its three dimensional 3D geometry was imaged using synchrotron X ray microcomputed tomography. The spatial distribution of pore spaces and their connections were identified based on the 3D geometry, and an equivalent pore network of the GDE was obtained for simulating the PA transport with an invasion percolation algorithm. The predicted mass redistribution of PA in the GDE was found to be in excellent agreement with experimental values reported in the literature. The presence of the MPL encouraged the containment of PA within the CL and discouraged PA leaching toward the channe