bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fundamental Understanding of Water Movement in Gas Diffusion Layer Under Different Arrangements Using Combination of Direct Modeling and Experimental Visualization
Authors: Satjaritanun Pongsarun , Shimpalee Sirivatch , Weidner John W. , Shum Andrew , Zenyuk Iryna V. , Weber Adam Z. , Hirano Shinichi 
Published: February 2020

The purpose of this work is to use direct modeling based Lattice Boltzmann Method (LBM) [1-3] with combination of flow visualization to fundamentally understand the transport of liquid water and air inside the gas diffusion layers (GDLs) used in polymer electrolyte membrane fuel cells (PEMFC). Studies of the water evolution, water saturation, and breakthrough pressure inside GDL under different arrangements are the primary focus in this work. The model geometries of GDLs provided in this study were obtained by three dimensional reconstructed micro-structure from micro X-ray computed tomography (CT) as shown in Figure 1. The experimental setup was similar to that in Ref. 3 with the addition of multiple water injection points and also the compression pressure that can represent the effect of land area of the PEMFC flow-field.
The overall predictions of water profile evolution within the GDL agree with the data visualized from the X-ray CT experiment for all cases studied. They also reveal that the water saturation profiles inside the GDL samples and breakthrough pressure are different when the location of water injection point is changed. In addition, the non-compressed GDL provides significantly different mechanism of water transport compared to compressed GDL. Figure 2 shows example of the predictions and experimental data of water evolution inside the SGL10BA GDL with and without compression. The results clearly show that without compression, water spreads to the side of the GDL before it moves up to the top of the GDL. For the compressed GDL, the water transports directly to the top of GDL, where breakthrough pressure is reached. This work will also be extended to include the effect of non-uniform wettability of GDL on water transport and saturation.
References:
1. Frisch, B. Hasslacher, Y. Pomeau, Physical review letters 56 (14) (1986) 1505-1508.
2. R. McNamara, G. Zanetti, Physical Review Letters 61 (1988) 2332-2335.
3. P. Satjaritanun, J.W. Weidner, S. Hirano, Z. Lu, Y. Khunatorn, S. Ogawa, S.E. Litster, A.D. Shum, I.V. Zenyuk, S. Shimpalee, Journal of the Electrochemical Society, 164 (11) (2017) E3359-E3371.
4. I. V. Zenyuk, A. Lamibrac, J. Eller, D.Y. Parkinson, F. Marone, F. N. Büchi, A.Z. Weber, Phys. Chem. C 120 (2016) 28701−28711.

Figure 1
From Catalyst Layer to Flow Field: Analysis of Electrolyte Redistribution in HT-PEFC By Operando X-Ray Tomographic Microscopy
Authors: Halter Jonathan , Schmidt Thomas J. , Büchi Felix N 
Published: February 2020

High temperature polymer electrolyte fuel cells are based on a polybenzimidazole membrane, imbibed with phosphoric acid as the electrolyte. Phosphoric acid shows a high degree of mobility within the membrane and, as was shown by Eberhardt et.al [1], can also invade the pores of the anode gas diffusion layer (GDL) after a current step from 0.2 Acm2 to 0.8 Acm2 and even invade the channel of the flow field, where it is removed from the fuel cell. The loss of electrolyte is a mayor degradation mode of HT-PEFCs and may also affect the performance of a HT-PEFC.
In recent years, synchrotron based operando x-ray tomographic microscopy of HT-PEFCs has been applied for visualizing and quantifying phosphoric acid redistribution in the GDL [1]. In the present work, this technique was used to quantify phosphoric acid saturation in the anode GDL after a current step (s. figure 1) and correlated it with operando electrochemical impedance spectroscopy measurement.
The synchrotron imaging parameters were optimized to enable the quantification of the acid redistribution in the GDL, the microporous layer and the catalyst layer. For the first time, phosphoric acid redistribution in the cracks of both, microporous and catalyst layers, was evaluated and quantified, allowing the determination of flooding time constants for the cracks in both layers. The redistribution of acid in both, anode and cathode catalyst layers, is quantified and compared.
References:

S.H. Eberhardt et.al., J. Electrochem. Soc., 162 (3), F310-F316

Figure 1
Oxygen Transport Resistance in PEMFC Catalyst Layer Based on Ultra-Micro Electrode (UME) Theory
Authors: Lu Zijie , Wang Chunmei , Sulek Mark , Waldecker James 
Published: February 2020

Hydrogen fuel cell is a promising zero-emission automotive powertrain for larger vehicles with long-distance requirements. However, its cost must be reduced to achieve real commercial use. Minimizing use of precious metal catalysts and increasing the fuel cell power density have been the most viable means to reduce the stack cost. Focus of advanced research is shifting to improve the fuel cell power density (> 1 W/cm2) with low Pt-loaded catalyst layers (≤ 0.125 mgPt/cm2 total).
One of the emerging issues with the low loaded fuel cell electrode is the dramatic increase of oxygen transport resistance with Pt loading reduction. This has been observed for both diluted (with addition of carbon particles to maintain the layer thickness) and undiluted (thinner) electrodes. The mechanism for the transport resistance increase in low Pt loaded electrode is not well understood and the quantitative modeling of the resistance is scarce. In this work we propose a simple explanation to the oxygen transport in the catalyst layer based on the assumption that each active Pt particle functions as a semi-spherical nano-electrode, which is covered by a layer of proton conducting matter (ionomer, water film, or a combination of two). Without any other assumption, the oxygen transport resistance in the catalyst layer can be analytically determined, for the case of limiting current density, as
(see image file for the equation)
This work identifies several critical factors that influence the oxygen transport resistance, including the CL thickness, the Pt particle density, and the diffusivities of oxygen in proton conducting phase and in CL voids. Figure 1 shows the influence of the CL thickness and the Pt particle density, the two most influencing factors, on the oxygen transport resistance, as an example. From this work it is possible to reduce the oxygen transport resistance by optimizing the layer structure.
(see image file for the plot)
Figure 1. The influence of the CL thickness (left) and the Pt particle density (right) on the oxygen transport resistance in the catalyst layer.

Figure 1
The Effect of pH on Fuel-Cell Catalyst-Layer Inks
Authors: Berlinger Sarah A. , Dagan Nicholas , McCloskey Bryan D. , Weber Adam Z. 
Published: February 2020

Fuel cell catalyst layers are cast from inks containing a solvent, an ionomer, and catalyst particles. Though there are generally accepted material classes (water/alcohol mixtures for the solvent, perfluorosulfonic acid (PFSA) polymers, and Pt-alloy based catalyst particles supported on carbon), there are no standard ratios or metrics for ink formulation. As such, ink recipes have been highly empirical to date, with little understanding of the governing interactions controlling resultant properties and behavior. This study therefore aims to systematically investigate the effect of pH on ink aggregation and rheology.
Solvent choice greatly influences the morphology of PFSAs in solution1-4, which in turn alters pH. Starting with a solvent-ionomer compositional matrix, solvent versus pH effects are decoupled. Using dynamic and electrophoretic light scattering, rheology, and direct visualization with cryo electron microscopy, particle-solvent-ionomer systems are then studied to understand aggregation, stability, and rheology under various pH conditions.
Acknowledgements
This work was mainly funded under the Fuel Cell Performance and Durability Consortium (FC PAD) funded by the Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02-05CH11231. S.A.B also acknowledges support from National Science Foundation Graduate Research Fellowship under Grant No. DGE 1106400.
References

Welch, C.; Labouriau, A.; Hjelm, R.; Orler, B.; Johnston, C.; Kim, Y. S., Nafion in Dilute Solvent Systems: Dispersion or Solution? ACS Macro. Lett.
2012,
1 (12), 1403-1407.

Ma, C.-H.; Yu, T. L.; Lin, H.-L.; Huang, Y.-T.; Chen, Y.-L.; Jeng, U. S.; Lai, Y.-H.; Sun, Y.-S., Morphology and properties of Nafion membranes prepared by solution casting. Polymer
2009,
50 (7), 1764-1777.

Lee, S.-J.; Yu, T. L.; Lin, H.-L.; Liu, W.-H.; Lai, C.-L., Solution properties of nafion in methanol/water mixture solvent. Polymer
2004,
45 (8), 2853-2862.

Gebel, G.; Loppinet, B., Colloidal structure of ionomer solutions in polar solvents. J. Mol. Struct.
1996,
383 (1), 43-49.
(Invited) Catalyst Layer Interactions That Affect Coatability
Authors: Dixit Marm , Harkey Brice , Shen Fengyu , Hatzell Kelsey B 
Published: February 2020

Catalyst layers, unlike traditional barrier coatings, can be considered active coatings because they serve multiple functions related to transport (proton, electron, oxygen). Fundamentally, the distribution of the active and inactive materials in the electrode (or microstructure) is largely dependent on the processing step. Typically, catalyst layers are manufactured using scalable methods such as blade coating, slot-die, or spray coating1. These methods rely on dispersing the active material in a colloidal ink. Catalyst layer inks are examples of biphasic material systems composed of a solid material, a polymer, and a solvent. Nanoscale interactions between the individual constituents can alter macroscopic properties relevant for coating and manufacturing processes (i.e. viscosity, surface tension, aggregation, and rheology)1. Control over these macroscale properties is important for controlled electrode formation during scalable roll-to-roll manufacturing. Herein, we study a range of formulated inks composed of different solvents (methanol, isopropyl alcohol, octanol, and water), I:C ratios, and surface charges to build correlations between the feedstock material (inks) and electrode structure (coatings)2,3. We discuss the trade offs between thermodynamic and physics based modeling of ink-based systems to guide and inform ink design and formulation. Finally, this works focuses on drawing correlations between fundamental inks properties and downstream electrode properties (density, porosity, etc.) derived on a custom-made benchtop slot-die system.
[1] Hatzell, Kelsey B., et al. "Understanding inks for porous-electrode formation." Journal of Materials Chemistry A 5.39 (2017): 20527-20533.
[2] Dixit, Marm B., et al. "Catalyst Layer Ink Interactions That Affect Coatability." Journal of The Electrochemical Society165.5 (2018): F264-F271.
[3] Dixit, Marm, and Kelsey B. Hatzell. "Understanding Binary Interactions and Aging Effects in Catalyst Layer Inks for Controlled Manufacturing." ECS Transactions 80.8 (2017): 301-307.
Using RH Sensitivity to Estimate Carbon Support Loss in PEMFC Electrodes
Authors: Fairweather Joseph D. , Yu Paul Taichiang , Lakshmanan Balsu 
Published: February 2020

The carbon blacks typically used for catalyst supports in proton exchange membrane fuel cells (PEMFCs) are vulnerable to oxidation at high cell potential. Carbon lost to corrosion will lead to performance degradation from the reduced electrochemical surface area (ECSA) and an eventual collapse of electrode structure and porosity. Therefore, PEMFC stacks must be protected from potential excursions by a range of operational strategies. During the development of fuel cell systems, carbon support loss is often evaluated after cell failure has already occurred, using destructive methods such as cross sectioning and SEM imaging of the electrode thickness. The goal of the present work is to advance a non-destructive in situ test method for early estimate of moderate carbon loss. Such measurement allows the effectiveness of mitigation to be compared in a shorter time before running a stack to failure.
For the present tests, carbon oxidation in membrane electrode assemblies (MEAs) is quantified by measuring CO2 concentration in the exhaust gas during high potential excursions. Carbon loss is compared with the performance (current density at constant cell potential) as a function of inlet gas relative humidity - an RH sensitivity curve. The RH sensitivity at low power (Figure 1) is found to be highly responsive to moderate amounts of carbon corrosion. The current at high humidity decreases along with total ECSA, but the current at low humidity increases. The performance difference below 60% RH is sufficiently repeatable to be used for a calibrated indicator of carbon mass loss. An experimental design was executed to optimize test conditions to produce a linear response with respect to carbon loss (Figure 2). Other details of applying this method are discussed.
A brief investigation of the mechanism for shifting RH sensitivity is also included. Oxygen reduction reaction (ORR) mass activity under dry conditions is found to increase after moderate corrosion of carbon. CO stripping measurements indicate that a greater portion of the catalyst area stays active at low humidity following corrosion. Finally, the behavior of electrodes with different carbon supports was compared. A porous high surface area carbon (HSAC) support showed the increase in dry performance as described above, while a relatively non-porous Vulcan-style support showed little change in RH sensitivity as a function of carbon loss. It is hypothesized that the HSAC pores become more hydrophilic as the carbon surface oxidizes. The hydrophilic pores would then help to maintain ionic conductivity to a greater fraction of catalyst particles under lower RH conditions.

Figure 1
Effect of Carbon Surface on Nafion Thin Film Hygro-Expansion and Thermal-Expansion
Authors: Khattar Dhwaj , Cleland Keith James , Shrivastava Udit , Singh Ashutosh Kumar , Karan Kunal , Roberts Edward 
Published: February 2020

Polymer electrolyte fuel cell (PEFC) catalyst layers consist of carbon, platinum, and ionomer. Carbon is necessary to provide a high surface area to support catalytic platinum nanoparticles and facilitate electron transport to the reaction sites whereas ionomer is required to supply protons to the reaction site. In addition, together they contribute to the structural strength of a catalyst layer. Since ionomer and carbon make up a majority of the catalyst layer volume, the ionomer in catalyst layer mostly interfaces with carbon support. Studies have shown the suppression of ionomer properties in thin film form especially below 50 nm and is also highly dependent on the substrate. For example, Key et. al measured higher water content in 19 nm thick Nafion coated on Pt than ionomer on SiO2 [1]. Recently, Orfanidi et. al, showed that the functionalization of carbon with NHx group assists in better distribution of ionomer within catalyst layer and restructure the ionomer in such a way that oxygen transport resistance across the ionomer drops [2]. Hence, from the fuel cell application perspective, it is important to study the effect of different carbon substrates on ionomer properties.
There is lack of data available on fundamental properties such as hygro-expansion and thermal-expansion of nanometer thin film Nafion on carbon in general and the effect of carbon surface characteristics, in particular on these properties. This presentation will share the effect of hydrophobic carbon and functionalized hydrophilic surfaces on the hygro- and thermal-expansion of 20 and 70 nm thick Nafion films.

References:

[1] H.K. Shim, D.K. Paul, and K. Karan. Macromolecules
48, 2015, 8394.
[2] A. Orfanidi, P. Madkikar, H. A. El-Sayed, G. S. Harzer, , T. Kratky and H. A. Gasteiger. The J. of Electrochemical Society, 164, 2017, F418.
Evaluation of PEMFC Impedance Spectra By Using the Distribution of Relaxation Times
Authors: Heinzmann Marcel , Weber André , Ivers-Tiffée Ellen 
Published: February 2020

Electrochemical impedance spectroscopy (EIS) is one of the most valuable characterization methods for complex electrochemical systems such as fuel cells.
The measured impedance spectra are commonly analyzed by a complex nonlinear least square (CNLS) fit, delivering a model function represented by an equivalent circuit model (ECM). In this case the ECM has to be defined a priori, without knowing number, size and time constants of the contributing polarization processes. The assessment of a physico-chemically motivated ECM remains challenging, especially if polarization processes with close time constants occur. This leads to an overlap of processes in the frequency domain and thus makes it difficult to separate them, which may result in wrong model assumptions and instable and ambivalent fitting results.
To overcome this issue we will present an alternate approach, where ECM and starting parameters for the CNLS fit are obtained by a pre-identification of the impedance response by the distribution of relaxation times (DRT) method [1],[2]. This approach was established in the framework of our solid oxide fuel cells research [3], later on transferred to lithium-ion batteries [4] and recently to high temperature polymer electrolyte fuel cells (HT-PEMFC) [5].
A typical result of our approach on a low-temperature PEM fuel cell is displayed in Figure 1: Whereas in the imaginary part of the spectrum only one broad peak is visible, the DRT facilitates a deconvolution of up to five clearly separable peaks (P1 - P5). In order to assign each peak to a physicochemical mechanism, systematic and comprehensive variations of operating parameters as current density, humidity and gas composition at anode and cathode have been conducted. By that we are able to distinguish between (i) charge transfer kinetics at the Pt-catalyst, (ii) the proton transport coupled therewith in the ionomer of the catalyst layer and (iii) the gas transport mechanisms in the porous media of the electrode and gas diffusion layer (GDL). Furthermore, our analysis enables us to assign the polarization processes to the respective electrode and to quantify their share to the overall polarization.

References

[1] H. Schichlein, A. C. Müller, M. Voigts, A. Krügel, and E. Ivers-Tiffée, J. Appl.
Electrochem., 32, 875–882 (2002).
[2] E. Ivers-Tiffée and A. Weber, J. Ceram. Soc. Japan, 125, 193–201 (2017).
[3] A. Leonide, V. Sonn, A. Weber, and E. Ivers-Tiffée, J. Electrochem. Soc., 155, B36–B41 (2008).
[4] J. Illig, M. Ender, T. Chrobak, J. P. Schmidt, D. Klotz, and E. IVers-Tiffée, J. Electrochem. Soc., 159, A952–A960 (2012).
[5] A. Weiß, S. Schindler, S. Galbiati, M. A. Danzer, and R. Zeis, Electrochim. Acta, 230, 391–398 (2017).

Figure 1
In Situ and Ex Situ Spectroscopic Studies of the Inhibition of Active Sites in Iron-Nitrogen-Carbon Electrocatalyst for Oxygen Reduction Reaction
Authors: Artyushkova Kateryna , Chen Yechuan , Asset Tristan , Matanovic Ivana , Atanassov Plamen 
Published: February 2020

One of the most promising classes of PGM-free materials for oxygen reduction reaction (ORR) is based on graphene-like carbon containing nitrogen and transition metal (metal-nitrogen-carbon, MNC) 1, which show promise as replacement of Pt in both alkaline exchange membrane (AEM) and proton exchange membrane (PEM) fuel cells. Understanding the specific roles of nitrogen and metal in the activity and durability of MNC-based catalytic materials is a prerequisite for the rational design of ORR electrocatalysts with improved performance.
The mechanism of ORR in MNC catalysts has been studied previously by a combination of spectroscopic and theoretical structure-to-activity studies 2-4. Using inhibitors that have unique spectral signatures and have strong binding to the active sites allows elucidating the relationship between the chemistry of active sites and activity. We report results of synchrotron near ambient pressure X-ray photoelectron spectroscopic (NAP-XPS) analysis performed at synchrotron beamlines for series of electrocatalysts belonging to iron-nitrogen-carbon (FeNC) family. In-situ monitoring of oxygen binding to different nitrogen and metal moieties existing at the surface of these materials is performed with and without complexing inhibiting agent based on phosphonate (etidronic acid HEDP).
From the spectroscopic analysis of catalyst with and without adsorbed HEDP we observe that major sites blocked by HEDP are hydrogenated and protonated nitrogens. Using near-ambient pressure XPS we have studied how oxygen adsorption in humidified atmosphere is affected by presence of the HEDP potentially blocking N-H/N+ active sites. These spectroscopic observations of inhibited active sites is correlated to an electrocatalytic performance from rotating ring disk electrode (RRDE) tests.
References:

J. Stacy, Y. N. Regmi, B. Leonard and M. Fan, Renewable and Sustainable Energy Reviews, 2017, 69, 401-414.

D. Malko, A. Kucernak and T. Lopes, Journal of the American Chemical Society, 2016, 138, 16056-16068.

K. Mamtani, D. Jain, D. Zemlyanov, G. Celik, J. Luthman, G. Renkes, A. C. Co and U. S. Ozkan, ACS Catalysis, 2016, 6, 7249-7259.

J. L. Kneebone, S. L. Daifuku, J. A. Kehl, G. Wu, H. T. Chung, M. Y. Hu, E. E. Alp, K. L. More, P. Zelenay, E. F. Holby and M. L. Neidig, The Journal of Physical Chemistry C, 2017, 121, 16283-16290.
Coarse-Grained Molecular Dynamics Study of Ionomer Aggregation and Network Formation in Dilute Solution
Authors: Mokhtari Mehrdad , Eikerling Michael Hermann 
Published: February 2020

The presented work comprises a computational study of self-assembly in dilute solution of Nafion-type perfluorosulfonic acid (PFSA) ionomers. We employ coarse-grained molecular dynamics (CGMD) to investigate the formation of ionomer bundles [1] and study the assembly of ionomer bundles into a bundle network upon increasing ionomer concentration. Formation of this supramolecular network is experimentally indicated by a markedly increased viscosity [2]. Evolution of a gel-like structure in the aqueous solutions also studied experimentally by Cirkel et al. [3] and Rubatat et al. [4], revealing more details about transport properties, stability, and water sorption properties of the network structure of interconnected ionomer bundles in Nafion membranes. Simulation of the interconnected, gel-like ionomer state provides opportunities to scrutinize different proposed structural models of ionomer membranes and assess changes in bundle size and network connectivity as functions of backbone hydrophobicity, side chain density, counterion valence, and strength of electrostatic interaction between anionic head groups at ionomer sidechains.

References

[1] M. Ghelichi, K. Malek and M. Eikerling, Ionomer Self-Assembly in Dilute Solution Studied by Coarse-Grained Molecular Dynamics, Macromolecules 49, 1479-1489 (2016).
[2] Private communication.
[3] Peter A. Cirkel, Tatsuhiro Okada, A Comparison of Mechanical and Electrical Percolation during the Gelling of Nafion Solutions, Macromolecules 33, 4921-4925 (2000).
[4] L. Rubatat, G. Gebel, O. Diat, Fibrillar Structure of Nafion: Matching Fourier and Real Space Studies of Corresponding Films and Solutions, Macromolecules 37, 77727783 (2004).