bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Water Management and Carbon-Dioxide Contamination Effects in Anion-Exchange Membrane Fuel Cells
Authors: Gerhardt Michael R. , Pant Lalit M. , Shiau Huai-Suen , Weber Adam Z.
Published: February 2020

Anion-exchange membrane fuel cells (AEMFCs) offer a potential advantage over their traditional proton-exchange membrane counterparts in that AEMFCs can operate with non-precious metal catalysts [1]. Recently, high-power operation of AEMFCs has been demonstrated in laboratory-scale cells [2]. The performance of AEMFCs, however, can be highly sensitive to small changes in relative humidity due to the critical role of water in both the alkaline oxygen reduction reaction and in hydrating the membrane. Additionally, carbon-dioxide absorption and conversion to carbonate anions reduces membrane conductivity and worsens fuel-cell performance.

In this work, we use our previously developed two-dimensional model [3] to illustrate and explore the effects of membrane and ionomer properties, relative-humidity changes, and absorption of carbon dioxide on cell performance. We model local current density changes in large-area cells by stepping the two-dimensional model along the flow channel, updating it at each step to account for changes in gas concentration and relative humidity. Finally, we show how performance limitations from carbon-dioxide absorption, flooding, and dry-out could be alleviated through changes in operating parameters or ionomer properties.

Acknowledgements

The work was funded by the Assistant Secretary for Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U.S. Department of Energy under contract number DE-AC02-05CH11231. We thank Bryan Pivovar and the members of the Fuel Cells group of the National Renewable Energy Laboratory for helpful discussion and model validation data.

References

[1] J. R. Varcoe et al., “Anion-exchange membranes in electrochemical energy systems,” Energy Environ. Sci., vol. 7, pp. 3135–3191, 2014.

[2] D. R. Dekel, “Review of cell performance in anion exchange membrane fuel cells,” J. Power Sources, vol. 375, pp. 158–169, Jan. 2018.

[3] H.-S. Shiau, I. V. Zenyuk, and A. Z. Weber, “Elucidating Performance Limitations in Alkaline-Exchange- Membrane Fuel Cells,” J. Electrochem. Soc., vol. 164, no. 11, pp. E3583–E3591, 2017.
Fuel Cell Management System: PEMFC Lifetime Optimization by Model Based Approach
Authors: Piffard Maxime , Naiff da Fonseca Ramon , Massioni Paolo , Bideaux Eric , Gerard Mathias
Published: February 2020

The estimation and increase of the lifetime of PEMFC fuel cell under dynamic conditions is one of a major challenge about PEMFC. Increasing the durability of the fuel cell must be treated by both the development of new material and design but also by optimal strategies and management of the operating conditions of the fuel cell. Indeed, the different irreversible degradation mechanisms in the MEA (Membrane Electrode Assembly), as the platinum dissolution, Ostwald ripening, carbon support corrosion and chemical membrane degradation, and reversible degradation mechanisms (platinum oxidation, nitrogen stratification, liquid water management) are strongly coupled to the local conditions into the MEA. Moreover, the local conditions into the MEA depend on the material properties but also on the dynamic operating conditions of the fuel cell stack. The strong coupling of the different phenomena can be solved by numerical simulations and an optimum can be found for performance and durability.

In this approach, the lifetime of the fuel cell is optimized by a dynamic management of the operating conditions of the fuel cell stack. Indeed, for a same desired power, different set of operating conditions (pressure, temperature, current and stoichiometry) can deliver the same power. Constraints to manage the liquid water inside the fuel cell is also added. A unique cost function, based on a model approach, is built to optimize the fuel cell performance (including compressor consumption and cooling) and the durability of the MEA (irreversible degradations with platinum dissolution and chemical degradation of the membrane and reversible degradation with water management).

The different laws used are based on physical models. Their expressions are reduced to be analytical and directly solved. The operating conditions management algorithm is built off-line. It defines the optimum operating conditions of the fuel cell stack (anodic pressure, cathodic pressure, stack temperature, current, air stoichiometry and hydrogen stoichiometry) as a function of the desired power and some fuel cell internal states (water content inside the membrane, water vapor, State of Health SoH). These internal states can be estimated by state observers. The operating conditions management algorithm is validated within a multi-physics fuel cell model. The simulations on a dynamic power cycle show that the degradation rate can be divided by two and compressor consumption also reduced. Moreover, the constraints on the water inside the fuel cell guarantee a correct behavior of the fuel cell stack. The algorithm can also be easily adapted to the fuel cell SoH (State of Health).

Figure 1
The Effect of a Turbulence Grid on the Temperature Distribution in an Air-Cooled Proton Exchange Membrane Fuel Cell – a Modelling Study
Authors: Pløger Line Justesen , Fallah Rasheed , Al Shakhshir Saher , Berning Torsten , Gao Xin
Published: February 2020

Air-cooled proton exchange membrane fuel cells are becoming increasingly attractive as an alternative power source for a large number of applications including material handling, telecom back-up power and more recently unmanned aerial vehicles. A salient advantage is their simplicity of operation because they do not require a secondary coolant loop, which greatly simplifies their control. A recognized problem is the thermal management of the electrochemical reaction has the tendency to overheat the stack at low current densities around 0.4 A/cm2 e.g. in case of a Ballard 1020 ACS stack. Our research group has recently found out that, the biggest problem in the thermal management is the heat transfer into the air inside the cathode channels, and we have proposed to place a turbulence grid before the air inlet with the goal to induce a mixing effect in this otherwise laminar flow and thereby improve the heat transfer resulting in better thermal management of the electrochemical reaction. First experiments have resulted in an increase in the limiting current density by 20 % along with an increase in power density by more than 30% and a decrease in hydrogen consumption by more than 20 % at the desired operating point.

The work presented here summarizes a modeling analysis employing computational fluid dynamics with the commercial solver Fluent 18. The goal of this work was to gain additional understanding as to the effect of such a turbulence grid placed before the cathode inlet and ideally to optimize the key parameters such as the detailed grid geometry, the distance between the turbulence grid and the flow channel, and the cathode flow channels themselves. In our model, different types of grids were placed in varying distances before the cathode inlet. Only a single channel on the cathode side is modeled, and the airflow rate was calculated out of the desired stoichiometric flow ratio of 50 and a current density of 0.4 A/cm2. Inside the cathode flow channel a heating term that accounts for the waste heat generated by the electrochemical reaction was implemented. The numerical results summarize the distribution of the turbulence intensity induced by the grid, the turbulence dissipation rate, the velocity distribution and, most importantly, the predicted temperature distribution inside the cathode flow channel and the bipolar plate. The single most important result was the predicted maximum temperature inside the fuel cell, and the goal was to improve the heat transfer rate and reduce this temperature so that the fuel cell may be operated at a higher current density. The modeling results will be verified with experiments where the fuel cell performance and the temperature in a pre-determined position will be measured for a variety of turbulence grids printed with the 3D printer.

Figure 1
Heuristic and Nonheuristic Methods for the Design of Proton Exchange Membrane Fuel Cells
Authors: Lamb James , Andrei Petru
Published: February 2020

There has been much work on the numerical optimization of proton exchange membrane fuel cells (PEMFCs). The optimization techniques can be divided in heuristic and non-heuristic techniques.

Heuristic techniques (such as genetic algorithm, particle swarm optimization, differential evolution, simulating annealing, harmony search, memetic algorithms, bird mating optimization, and artificial immune system) usually use stochastic methods to identify an optimal solution, which require a large number of device simulations and compromise the accuracy of the solution. The computational cost of heuristic techniques limit their application to a small number of variables (usually under ten), and can generally be applied to simplified models.

In contrast, non-heuristic techniques (such as line search and trust-region methods, the Nelder-Mead method, the Powell algorithm, steepest descents, conjugate gradient methods, Newton and quasi-Newton methods, and linear and quadratic programming) are deterministic and often require computing or approximating the gradient of the objective function [1-4]. Usually these techniques have local convergence and their rate of convergence can be improved by using the Hessian matrix or other second-order derivatives, evaluating the gradient more accurately, or taking advantage of the particular functional form of the objective function. Depending on whether the gradient function can be evaluated or not, as well as on the accuracy with which the first and higher order derivatives can be computed, non-heuristic techniques usually require between a few and 100 iterations to optimize the objective function, while the total number of variables to be optimized could be larger than 105.

In this work we compare heuristic and nonheuristic methods and present a gradient-based technique for the optimization of the catalyst distribution in PEMFCs using finite element models. We demonstrate a non-heuristic technique to determine optimum platinum distribution in the catalyst layer (CL) by allowing the catalyst amount to vary independently at each not inside the CL. Therefore, the total number of finite elements in the CL, in this work, is larger than 104; however, the technique could be extended to systems with even more elements. Optimization is performed by first computing a catalyst sensitivity function, which is the gradient of the objective function with respect to the mass of catalyst at each location in the CL; then an adjoint space technique is employed to evaluate the catalyst sensitivity functions at each node in the finite element discretization. Cell performance is evaluated and compared for the optimized and non-optimized PEMFCs.

References

[1] F. C. Cetinbas, S. G. Advani and A. K. Prasad, Journal of Power Sources, 250, 110 (2014).

[2] J. Lamb, G. Mixon and P. Andrei, Jour of the ECS, 164, E3232 (2017).

[3] P. Andrei and L. Oniciuc, Jour of Appl. Physics, 104, Art. No. 104508 (2008).

[4] P. Andrei and L. Oniciuc, Jour of Comp. Elec., 7, 111 (2008).

Figure 1
Change of Preferential Liquid Breakthrough Pathways in PEMFC Gas Diffusion Layers: Evidence of Pressure-Induced Dynamic Transport
Authors: Chevalier Stephane , Josset Christophe , Auvity Bruno
Published: February 2020

Polymer Electrolyte Membrane (PEM) fuel cells are considered as promising clean sources for automotive applications. A key challenge to reduce the cost of this technology is to increase the power density by operating PEM fuel cells at high current densities. One strategy is to improve the 3D structure of the gas diffusion layer (GDL) located between the channel and the catalyst layer (CL). At the cathode side, this GDL is used to evacuate the liquid water toward the channel while providing access to the oxygen to the CL [1]. Although innovative GDL structures have been proposed, a better understanding of the liquid water would help to design better GDL. In particular, few works have investigated the liquid water transport after several hours of steady state fuel cell operating conditions although changes in liquid water preferential pathway have been observed [2]. Such changes are not predicted in theory, and a physical explanation of these mechanisms is still required.

In this presentation, we investigate ex situ the change of liquid water preferential pathways through PEM fuel cell GDLs. Liquid water breakthough from the GDL to the fuel cell channels is mimicked using a microfluidic PDMS device with embedded GDLs. Liquid water is injected through the GDL to the microchannel, and changes in liquid water pathways are observed after several hours of operations. These changes in liquid water pathway are attributed to the dynamic of droplet eruption in fuel cell microchannel. To validate this assumption, a small capillary network with is built. It is shown that after the liquid water breakthrough, the pressure variation due to the growth of the water droplets in the microchannel enables the liquid water to invade smaller capillaries which at the end can change the preferential path. The experimental observations reported in this work show that the invasion percolation theory can be used to predict the preferential pathway at the onset of the liquid water breakthrough, but pressure-induced dynamic transport [3] due the water droplet eruption in the channel has also to be taken into account to predict the preferential pathway after long time of fuel cell operation.

References

[1] T. Yoshida, K. Kojima, Toyota MIRAI Fuel Cell Vehicle and Progress Toward a Future Hydrogen Society, Interface Mag. 24 (2015) 45–49.

[2] Z. Lu, M.M. Daino, C. Rath, S.G. Kandlikar, Water management studies in PEM fuel cells, part III: Dynamic breakthrough and intermittent drainage characteristics from GDLs with and without MPLs, Int. J. Hydrogen Energy. 35 (2010) 4222–4233.

[3] S. Chevalier, C. Josset, B. Auvity, Fluid dynamic breakthrough in two connected capillaries: From stationary to oscillating state, Phys. Fluids. 29 (2017) 102102.
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
(Invited) Neutron Imaging of Fuel Cells: An Overview of Past, Current and Future Research
Authors: Boillat Pierre
Published: February 2020

Neutron Imaging has been used as a characterization method for water management of polymer electrolyte fuel cells since nearly two decades. Its attractiveness stems from a unique combination of characteristics: an excellent penetration through dense structural materials such as steel and aluminum combined to a high contrast for certain light elements such as the hydrogen in water. Owing to this, neutron imaging has been used extensively to understand the limitations introduced by liquid water in fuel cell operation. In this talk, I will first present an exemplary selection of results obtained at PSI and other research institutions, illustrating the major findings on fuel cell water management brought by neutron imaging in the past 15 years. I will then elaborate on how neutron imaging is currently used at PSI for supporting our research on novel materials and designs for fuel cells. Finally, I will give and outlook about what can be expected from neutron imaging of fuel cells in the future. In particular, the possibilities of ultra-high resolution imaging and the potential of the new generation of neutron sources will be discussed.
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.
Membrane-Electrode-Assemblies with Electrospun Fiber Mat Electrodes for Hydrogen/Air Fuel Cells
Authors: Slack John , Waldrop Krysta , Wycisk Ryszard , Gumeci Cenk , Dale Nilesh , Pintauro Peter N.
Published: February 2020

When MEAs are made by a decal, catalyst-coated-membrane, or catalyst-coated GDL method, there is little or no control over the macro-scale organization of the catalyst and binder. Thus, the high ORR catalytic activity of Pt-based catalysts seen in rotating disk experiments is rarely observed in an operating fuel cell MEA. Features such as particle and binder interconnectivity, macroporosity, and microporosity become more critical when high-performance nanomaterial catalysts are employed in fuel cell electrodes. Consequently, new electrode fabrication techniques are needed for next-generation MEAs. Nanofiber electrospinning is just such a method, which can address fuel cell electrode manufacturing and structure/performance issues. As a fabrication method, electrospinning is scalable, robust, and cost-effective, especially for the creation of non-woven mats of sub-micron diameter polymer fibers. Although not as well studied, the method can also be used to prepare particle/polymer fiber networks with high particle loading and high intra- and inter-fiber porosity. Mats from such fibrous materials can be used as electrodes in fuel cells [1-4], batteries [5,6], and capacitors [7], where high interfacial electrode area is of prime importance. In this talk, recent experimental work on nanofiber mat cathodes for hydrogen/air fuel cells will be described. Procedures for fabricating high particle-loaded nanofibers containing various Platinum and platinum-alloy catalysts with different polymer binders will be presented. The effects of catalyst type/loading and binder type on cathode mass activity and electrochemical surface area, cathode durability, and fuel cell power output at high and low relative humidity conditions will be discussed.

Acknowledgments

This work was funded by the Fuel Cell Consortium for Performance and Durability, DOE-EERE FC-PAD Project DE-EE0007653.

References

Zhang and P. N. Pintauro, ChemSusChem, 4, 1753-1757 (2011).

Brodt, R. Wycisk, and P. N. Pintauro, J. Electrochem. Soc., 160, F744-F749 (2013).

Brodt, T. Han, N. Dale, E. Niangar, R. Wycisk, and P. Pintauro, J. Electrochem. Soc., 162, F84-F91 (2015).

Brodt, R. Wycisk, N. Dale, and P. Pintauro, J. Electrochem. Soc., 163, F401-F410 (2016).

C. Self, R. Wycisk, and P. N. Pintauro, J. Power Sources, 282, 187-193 (2015).

Self, E. McRen, P. N. Pintauro, ChemSusChem,
9, 208-215 (2016).

Gao, Z. Shao, J. Li, X. Wang, X. Peng, W. Wang and F. Wang, J. Mater. Chem. A, 1, 63-67 (2013).
Reinforced Microcomposite Polymer Electrolyte Membrane and Its Characterization Fabricated By a Concise Process for PEMFC
Authors: Choi Young-Woo , Jang Seol , Yoon Young-Gi , Kim Tae-Young
Published: February 2020

In a different way from the conventional method, reinforced composite membranes were fabricated by using electrospinning and spraying with an accord. The hydrophobic polymer, polysulfone (PSf), was used as a substrate and the hydrophilic polymer, sulfonated poly(arylene ether sulfone) (sPAES), was used as an electrolyte. The ratio of PSf to sPAES was 1.7 : 8.3. The membrane properties and performance of the PSf electrospun / sPAES sprayed reinforced microcomposite membrane, PSf(ES)+sPAES(SP) was compared with i) pristine sPAES membrane, ii) PSf sprayed / sPAES electrospun reinforced microcomposite membrane, PSf(SP)+sPAES(ES), and iii) PSf, sPAES blend membrane. Although the PSf(ES)+sPAES(SP) membrane contained the substrate, its cell performance was not significantly different from the pristine sPAES membrane, and its durability was 2 times higher than that of pristine sPAES membrane. An article with the core results of this work was submitted to J. Membr. Sci. on March 18, 2018.
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).
Characterization of New Biological Membranes for Their Possible Application in Electrolytic and FUEL CELLS at Low Temperature
Authors: Arredondo-Baeza Cristian Humberto , Hernandez Prisciliano , perez-Silva Irma , Aguilar-Lira Guadalupe Yoselin , Rodriguez Jose Antonio , Dominguez Julia Maria
Published: February 2020

The present work describes the characterization of new protonic exchange biological membranes, using “maguey” as raw material, with the aim of providing a new alternative due to the fact that, over the past few years, Nafion (perfluorinated polymer) has been the most commonly utilized as polymer membrane in various application: Direct Alcohol Fuel Cell, Methanol and hydrogen [1], as well as electrolysers. In this sense, has been development different modifications to the Nafion [2] membrane without replacing it completely.

The organic membrane was based on the use of the “penca” cuticle. The cutine, the main component of the cuticle, is a polymer that consists of long chain fatty acids by ester-type bonds [3]. The epidermis of the plant is mainly responsible for gas exchanging through stomata which allows the cuticle to act as an interface between the cell and the external environment, thus allowing the proton exchange in the electrochemical process.

There were various types of treatments to the organic membranes, such as: mechanical activations, acidic, alkaline, polymeric coatings, electrical and thermal. With the purpose of obtaining hydrogen and oxygen in an electrolyzer. It was noted that the viable treatments for activation are both the mechanical and thermal, highlighting the thermal treatment as ideal due to the higher average life span and obtaining current intensity, in comparison with the mechanical treatment, which represents a lower average life span. In addition, the bio-membrane is coupling in a methanol fuel cell results competitive with commercial Nafion membrane, as shown in Table 1.

There were different techniques to know the morphology of the membrane, as well as their functional groups (SEM, Infrared, Raman), so the incorporation in an electrolytic cell and fuel show similar results to the Nafion membrane, which is a viable alternative to replace the Nafion.

References

[1] Ping Li, Wenjia Wu, Jindun Liu, Benbing Shi, Yaqian Du, Yifan Li, Jingtao Wang. Investigating the nanostructures and proton transfer properties of Nafion-Go hybrid membranes. Journal of Membrane Science. In Press, Accepted Manuscript, (2018) xxx.

[2] F. Ahmad Zakil, S.K. Kamarudin, S. Basri, Modified nafion membranes for direct alcohol fuel cells: An overview, renewable and Sustainable Energy Reviews 65 (2016) 841-852.

[3] Denise Castro-Ochoa, Carolina Peña-Montes y Amelia Farrés, Producción y características de cutinasas: Una alternativa interesante para biocatálisis a nivel industrial, TIP Revista Especializada en Ciencias Químico-Biológicas, 13 (2010) 16-25.

Figure 1
Impact of Co-Alloy Leaching and Cation in Ionomer Thin-Films
Authors: Tesfaye Meron , Kusoglu Ahmet
Published: February 2020

Strong R&D progress and increased demand for hydrogen powered fuel-cell cars, is shifting Polymer Electrolyte Fuel Cells (PEFCs) to lower Platinum electrocatalyst loading and to Platinum-cobalt (Pt-Co) alloys that have demonstrated double the kinetic activity improvement [1]. Implementation of these catalysts can lower catalyst cost to $7/kW (from $18/kW of standard Pt/C catalyst), surpassing the automotive requirement target of $10/kW and expediting commercialization [2]. Key challenge in integrating Pt-Co alloy catalyst as well as other Pt-Metal alloyed catalysts into the electrode assembly of PEFC has been durability and stability in the highly acidic environment. Co-alloy dissolution, leaching, surface oxide over layer formation upon heating, hollowing and particle facet loss have been demonstrated for Pt-Metal alloys via short and long lifetime tests and imaging techniques [3]. Amplifying this detrimental impact is the contamination of the membrane and the ionomer thin-film in the catalyst layer distressing conductivity, water uptake, and even gas transport [4]. In this talk, the direct impact of co-alloy and cation contamination in thin ionomer films of thickness < 200 nm is investigated in an effort to illuminate the direct effect of cations on structure and performance. Different levels of neutralization and leaching is mimicked by varying cation concentration and different counter ion types (Co2+, Ni2+, Na+, Cs+), which can elucidate impact of strength of ionic crosslinking and interactions on the polymer film’s nano-structure and water uptake behavior, characterized by grazing-incidence X-ray scattering and ellipsometry, respectively. Significant impact of confinement on structure and property will also be explored as a function of ionomer thickness to understand the performance of ionomer thin-films employed in the electrode assembly.

Acknowledgement

This work made use of facilities at the Joint Center for Artificial Photosynthesis at Lawrence Berkeley National Laboratory. This work was funded in part by the National Science Foundation Graduate Fellowship and the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy (under Contract No. DE-AC02-05CH11231).

References

[1] H. A. Gasteiger et al. Appl. Catal. B Environ., vol. 56, no. 1–2 SPEC. ISS., pp. 9–35, 2005.

[2] M. F. Mathias et al. Electrochem. Soc. Interface, vol. 14, pp. 24–35, 2005.

[3] E. Antolini et al. J. Power Sources, vol. 160, pp. 957–968, 2006.

[4] J. H. Dumont et al. ECS Trans., vol. 80, no. 8, pp. 861–867, 2017.