bluuebunny/crossref_metadata_2025 huggingface dataset:
Illuminating Oxygen Reduction Reaction Kinetics in High Temperature Polymer Electrolyte Membrane Fuel Cells Using EIS
Authors: Giotakos Panagiotis I. , Neophytides Stylianos G.
Published: February 2024

Owing to their notable power efficiency and zero greenhouse emissions, High Temperature Polymer Electrolyte Membrane Fuel Cells (HTPEMFCs) hold immense promise as a prospective candidate for generating clean energy. However, their commercialization is still impeded by the cathodic Oxygen Reduction Reaction (ORR) kinetics, which after almost half a century not only remain elusive, but constitute the most energy-intensive process, requiring large amounts of the expensive Pt catalyst to mitigate.

In this work we provide solid experimental evidence, that the simple three elementary step Dissociative Adsorption Pathway (DAP) with two intermediate species (Oad and OHad), can accurately capture both the steady state (IV) and the Electrochemical Impedance Spectra (EIS) as well.

Detailed EIS and IV experimental data were recorded at 180 °C under differential conditions, using a single serpentine HTPEMFC with a 4 cm2 active area. The fuel cell operated at the activation regime, where ORR potential losses dominate but mass transport limitations are negligible. The experimental data were successfully fitted with the derived analytic IV and EIS microkinetic model.

The use of the DAP in accordance with the Transitions State Theory (TST), allowed the extraction and analysis of ORR kinetics and energetics. The deconvoluted EIS outlined the important role of the
intrinsic kinetic inertia

, i.e. the outcome of the competitive nature of the elementary reaction steps on the adsorbed intermediate species. Kinetic inertia not only dominated EIS and the polarization resistance, but demonstrated that the commonly used Butler Volmer and apparent Tafel slope kinetic approach is incapable of describing the multistep ORR kinetics. With the help of the Degree of Rate Control (DRC) analysis, we successfully identified the O2(g) dissociative adsorption as the rate limiting step.

Finally, from an energetics perspective, by employing the TST kinetics formulation, we were able to calculate the free Gibbs’ transition states activation (kinetics) and reaction steps’ energies (thermodynamics). These results clarified that, the high ORR overpotential losses stem from the combined strength of both kinetically and thermodynamically imposed barriers, which originate from the high bonding strength of Oad on the Pt surface and the rather high activation energy of the O2(g) adsorption step.
A Lumped Model of Water and Heat Transport in a PEMFC Fuel Cell and the Associated Methods for Estimating the Effective Transport Parameters
Authors: Bligny Rémi , Leduc Valentin , Sdanghi Giuseppe , Dillet Jérôme , Xu Feina , Didierjean Sophie , Schmitt Tobias , Hanauer Matthias , Sauter Ulrich , Maranzana Gael
Published: February 2024

The fine and quantitative modelling of the coupled phenomena of water and oxygen transport and heat and charge transfer in PEMFCs is difficult from a practical point of view because the interfaces between the different layers are heterogeneous and difficult to characterize. They depend in particular on the mechanical stress field. Moreover, the two-phase flows in the porous layers and feeding channels are by nature stochastic and very difficult to predict. This fine modelling requires a perfect knowledge of the geometry, mechanical and thermal properties, wettability, etc... of the materials, their interfaces and their heterogeneity in space and time. Most of these parameters are unknown and so numerous that it is impossible to estimate them independently of each other by simple experiments. Based on this observation, our philosophy is to develop simple models whose effective transport parameters can be estimated by experiments carried out in situ, for real operating conditions [1]. These models are lumped models that depend on few parameters which integrate the properties of the interfaces. In this presentation, we propose a one-dimensional coupled water and heat transport model (adapted to a differential cell), associated with methods for estimating the unknown water transport and heat transfer parameters. The estimation of the parameters is performed in situ, for an imposed flow field geometry and clamping force. Original experiments are developed to decorrelate the effective diffusion coefficients in the gas phase, adsorbed phase and heat transport properties. The estimation of the parameters is based on simple water balances, i.e. a measurement of the quantities of water leaving the anode and cathode. The model and the experimental set-up are presented. The inverse technique of parameter estimation is detailed. Different materials are implemented in order to observe the resulting impact on the estimated effective transport coefficients.

Acknowledgements

The authors gratefully acknowledge the financial support of the Lorraine Université d’Excellence program.

References

[1] Rémi Bligny, Tobias Schmitt, Jérôme Dillet, Feina Xu, Sophie Didierjean, Matthias Hanauer, Ulrich Sauter, Gaël Maranzana, In-situ estimation of water transfer parameters in a proton exchange membrane fuel cell, Journal of Power Sources, Volume 560, 15 March 2023, 232719

Figure 1
On the Importance of MPL Structural Characteristics for PEM Fuel Cell Performance
Authors: Schweiss Ruediger , Herb Magnus , Earla Raj , Meiser Christian
Published: February 2024

Gas diffusions layers (GDLs) constitute vital subcomponents of proton exchange membrane fuel cells (PEMFCs) since they participate in all relevant transport processes (gases, vapor, liquid water, electricity and heat).Meanwhile, state-of-the-art GDLs are produced on commercial scale using high volume reel-to-reel (R2R) processes. In almost any case, GDLs are designed as dual-layer structures with a macro-porous carbon fiber-based substrate (backing) and a micro-porous layer (MPL) consisting of carbon particulates bonded with polytetrafluoroethylene (PTFE) binder. A body of scientific work has verified that different aspects of the MPL microstructure and the MPL/macroporous substrate interface play a substantial role in the water management of PEMFCs [1-6].

A systematic study was performed based on a singular backing using different MPL types and penetration levels.A simple method to estimate the micro-porous layer penetration in gas diffusion layers based on data obtained from force-deflection behavior of backings and MPL-coated GDLs is proposed. Comparison with SEM and previously published tomographic studies shows that a good estimate for the extent of MPL intrusion into the backing is obtained.

MPL loading and penetration is shown to affect different ex-situ GDL properties (in-plane gas permeability, electrical and thermal conductivity) as well as the GDL single cell performance characteristics with respect to humification and high current density operation.

Keywords: Gas diffusion layers, Microporous Layer, PEMFC fuel cells

Weber, and J. Newman, “Effects of microporous layers in polymer electrolyte fuel cells”, J. Electrochem. Soc. 152, A677-A688 (2005).

Lee, R. Yip, P. Antonacci, N. Ge, T. Kotaka, Y. Tabuchi, and A. Bazylak, Synchrotron investigation of microporous layer thickness on liquid water distribution in a PEM fuel cell, J. Electrochem. Soc. 162, F669-F676 (2015).

Zhou, S. Shukla, A. Putz, and M. Secanell, “Analysis of the role of the microporous layer in improving polymer electrolyte fuel cell performance”, Electrochim. Acta. 268, 366-382 (2018).

Cho, J. Park, H. Oh, K. Min, E. Lee, and J.Y. Jyoung, “Analysis of the transient response and durability characteristics of a proton exchange membrane fuel cell with different micro-porous layer penetration thicknesses”, Appl. Energy 111, 300-309 (2013).

T. Gostick, M. A. Ioannidis, M. W. Fowler, and M. D. Pritzker, “On the role of the microporous layer in PEMFC operation.”, Electrochem. Comm. 11, 576-579 (2009).

P. Ramasamy, E. C. Kumbur, M. M. Mench, W. Liu, D. Moore, and M. Murthy, “Investigation of macro- and micro-porous layer interaction in polymer electrolyte fuel cells”, Int. J. Hydrogen Energy 33, 3351-3367 (2008).
(Invited) Fuel Cell Component Durability for Million Mile Fuel Cell Trucks
Authors: Borup Rod L. , Weber Adam Z. , Myers Deborah J. , Neyerlin K.C. , Kusoglu Ahmet , Ahluwalia Rajesh , Mukundan Rangachary , Cullen David A. , Spendelow Jacob S. , Kleen Gregory
Published: February 2024

While significant advances have been made and early commercial fuel cell light-duty vehicles (LDVs) are starting to be produced, fuel cells in the heavy-duty-vehicle (HDV) transportation sector (including trucks, long-haul semitrailers, maritime, trains, etc.) are nascent, despite the fact that advantages of fuel cells compared to both diesel and electric powertrains are very compelling in terms of emissions, charging time, efficiency, power-to-weight ratio, among others. However, the fuel-cell technology for HDVs requires a paradigm shift in fuel-cell research and development compared to LDVs, where the emphasis becomes efficiency and improvements in durability instead of a focus on increased power densities and lower cell costs.

Heavy-duty applications require significantly longer vehicle lifetimes (>25,000 hours/1,000,000 miles for heavy-duty trucks), and therefore require improved fuel cell durability compared to light-duty vehicles. In 2020, HFTO formed the Million Mile Fuel Cell Truck Consortium (M2FCT) that includes a core team of five national laboratories to overcome durability and efficiency challenges in PEMFCs for heavy-duty applications with an initial focus on long-haul trucks.

While targets and testing protocols have been developed for light-duty vehicles, the same level of targets and testing protocols have not been established for heavy-duty transportation. With operational times of greater than > 25,000 hours required, the need for well-developed accelerated stress tests (ASTs) is amplified. Results from these ASTs demonstrate the need for more durable electrode layers and well-controlled potential variations. This presentation will provide an overview of the DOE’s Fuel Cell R&D approach, highlighting past and current activities, as well as strategies to enable fuel cell competiveness for heavy-duty applications.

Acknowledgments

This work was funded through the DOE M2FCT Consortium with thanks to DOE EERE HFTO, Fuel Cell Technologies Office. Team Leader: Dimitrios Papageoropoulos and Technical Development Manager: Greg Kleen.
Nanoscale in-Situ Characterization of Polymer Electrolyte Membrane Fuel Cell Catalyst Layers for Improved Water Management
Authors: Lytle Spencer , Parmar Harsharaj Birendrasingh , Seip Tess , Zhu Lijun , Wang Jian , Bazylak Aimy
Published: February 2024

Polymer electrolyte membrane fuel cells (PEMFCs) facilitate a sustainable energy infrastructure by offering emission-free electricity generation using renewably sourced hydrogen gas. The electrochemical reactions in a fuel cell occur at platinum-loaded catalyst layers (CLs), which are susceptible to degradation. Obstructing catalyst sites (triple phase boundaries1) with reaction by-products, such as water2,3, is the primary degradation mechanism in PEMFCs. Although various CL designs have been tested for improved electrochemical performance, in situ nanoscale visualization of platinum degradation and water accumulation in the CL at controlled temperature and relative humidity (RH) values are required to understand fundamental water mechanics through platinum and carbon nanostructures.

In this work, we employed scanning transmission X-ray microscopy (STXM) and X-ray absorption fine structure spectroscopy (XANES) to evaluate the effect of temperature on pristine and broken-in fuel cell CLs. We developed a novel CL in-situ sample cell to enable nanostructured characterization of catalyst layers using STXM in a controlled temperature environment. Carbon 1s, Fluorine 1s, and Oxygen 1s spectral edges were probed utilizing near-edge X-ray absorption fine structure spectroscopy (NEXAFS) to reveal chemical degradation mechanisms and differentiate material structure. Through our custom in-situ cell, we demonstrate that the chemical composition and water accumulation throughout the PEMFC CLs at low, intermediate, and high operating temperatures (25°C, 40°C, and 60°C, respectively) can be quantified, along with thermal expansion analyses of the CL and ionomer membrane. Moreover, we reveal realistic structural and chemical characteristics of nanoscale catalysts by distinguishing regions of Nafion® Ionomer, catalyst carbon support, and platinum throughout the PEMFC’s membrane electrode assembly at industrially relevant fuel cell temperatures. The insights from this work will inform strategies to mitigate water flooding from a nanoscale perspective in addition to the novel in-situ spectromicroscopy characterization of current CL features.

1. Fouzaï, I., Gentil, S., Bassetto, V. C., Silva, W. O., Maher, R., & Girault, H. H. (2021). 9(18), 11096-11123.

2. Li, H., Tang, Y., Wang, Z., Shi, Z., Wu, S., Song, D., ... & Mazza, A. (2008). 178(1), 103-117.

3. Kumsa, D. W., Bhadra, N., Hudak, E. M., Kelley, S. C., Untereker, D. F., & Mortimer, J. T. (2016). 13(5), 052001.
Impact of Clamping Force Distribution on Loss Processes in a Segmented PEMFC
Authors: Oppek Philipp , Goosmann Tobias , Weber Andre
Published: February 2024

The operation of large-scale polymer electrolyte membrane fuel cells (PEMFC) inevitably leads to significant spatial gradients along the gas channels. Depending on the local operating conditions, the physicochemical processes and thus also the resistances in the cell vary, which in turn determine the local performance. In addition, design parameters such as the spatial clamping force distribution have a significant influence on the ohmic contact resistance and the compression of the porous layers and thus the diffusion resistance. Thereby, the influences of these factors on the corresponding resistances are opposite to each other, resulting in conflicting objectives.

To enable an optimization of the operating strategy and the component design, a quantification of the local resistances and their dependencies is essential.

This requires a measurement setup that allows the precise adjustment of the operating conditions and contact pressure along the gas channel, as well as a measurement and analysis method that identifies and quantifies the locally occurring processes.

For this purpose, we are applying electrochemical impedance spectroscopy (EIS) on a segmented cell. In this cell the local clamping force is individually adjusted and continuously measured for each segment enabling measurements at constant clamping force as well as selectable clamping force distributions. The local performance limiting loss processes within the cell are separated by the distribution of relaxation times (DRT) and quantified by a physico-chemical meaningful transmission line model (TLM) as a function of local operating conditions and clamping force [1, 2, 3].

In this contribution an experimental analysis of the ohmic, charge transfer and diffusion resistances will be presented. The impact of contact pressure distribution and operating conditions on resistances and their distribution along the gas channels will be discussed. Furthermore, it is demonstrated how the performance can be optimized by adjusting the contact pressure distribution along the gas channel.

1. H. Schichlein et al., J. Appl. Electrochem. 32, pp. 875-882 (2002).

2. E. Ivers-Tiffée et al., J. Ceram. Soc. Japan 125, pp. 193-201 (2017).

3. M. Heinzmann et al., J. Power Sources 558, 232540 (2023).
Fault Detection and Identification for Polymer Electrolyte Membrane Fuel Cell Stack by External Magnetic Field
Authors: Freisem Leonard , Chadebec Olivier , Cauffet Gilles , Bultel Yann , Rosini Sébastien
Published: February 2024

Many technological locks prevent the deployment of Proton Exchange Membrane Fuel Cell (PEMFC). Particularly for vehicle applications, cost and durability represent two of the most significant challenges to achieve clean, reliable, and cost-effective PEMFC systems. Solving these shortcomings will be a great opportunity for a decisive breakthrough towards mass-diffusion of the current PEMFC technology. The long-term electrical performance losses are associated to either the degradation of the MEA constitutive materials or due to specific operating conditions (flooding, drying, etc.). In perspective, local current density distribution may support stack-level degradation analyzes as well as effective stack control to mitigate the consequences of degradation due to load cycles (electrochemical, thermal, mechanical and humidity effects) or faults.

External magnetic field measurement (MFM) shows a high potential in PEMFC non-invasive diagnosis. Thus, 2D and 3D current distributions and their anomalies in the fuel cell can be identified independent of the size of the causing fault.

To perform this local characterization, the external magnetic field measurement will enable to model the current density in stationary conditions over the cell surface and for the different cells of the stack. This methodology requires the complementary development of magnetic field techniques and inverse models.

In this work, this challenge is tackled by using tailored defective MEAs and specific operating conditions (flooding, drying, ...) to characterize, how local and overall performances of the MEA are affected and to identify the signatures of the various anomalies.

Figure 1
A Fuel Cell’s Big Brother: Artificial Intelligence for Monitoring Fuel Cells
Authors: Klass Lukas , Kabza Alexander , Sehnke Frank , Strecker Katharina , Hölzle Markus
Published: February 2024

The operation of fuel cell stacks on test benches today is typically monitored by constant

alarm threshold values for selected operating conditions. However, due to the wide range of

operating conditions of the stacks, this type of monitoring only works for extreme maximum

and minimum operating conditions. Wide setting ranges for thresholds prevent the detection

of minor faults, whereas too narrow limits will interrupt the tests unnecessarily. A particular

challenge is the monitoring of faults that either do not result in a directly measured response

from the fuel-cell stack or that only become noticeable with a time delay. The continuous

improvement of fuel cell stacks over the last years necessarily requires much-improved

monitoring methods, especially for durability tests with an operating time of thousands of

hours. For this reason, a novel monitoring concept using AI-based methods for the operation

of PEM fuel cells on test benches was developed and is being presented.

Firstly, machine-learning based mechanisms for monitoring the operating conditions as set

and controlled by the test bench are shown. Due to the cyclic operation during durability

tests, the operating conditions set at a load point can be compared to the past operating

conditions at the same load point. This proceeding allows the early and accurate detection of

faults caused by the test bench and thereby ensures the usability of the measured data as

well as an early alarm in case of problems.

In addition, a digital twin based method for monitoring the condition of the fuel cell stack is

presented. The deep-learning based digital twin calculates a probabilistic prediction of the

expected voltage of the fuel cell stack based on the current and past operating conditions.

The comparison of expected and measured cell voltage taking the model’s confidence into

account enables the early and precise detection of unforeseen events such as contamination

and thus averts consequential damage to the fuel cell stack. In contrast to physical models,

the digital twin represents a data driven model-ling approach for fuel cells.

The presented methods are applied to real testing data to demonstrate the detection of faults

during the operation of fuel cell stacks on test benches that would have remained

undiscovered by today’s monitoring mechanisms. It shows that the data driven digital twin is

able to predict the fuel cell’s stack voltage with an accuracy of 2.5 mV over 1000 h of unseen

data.

Figure 1
Bifunctional Electrocatalyst Materials for Improved Cell Reversal Tolerance in PEM Fuel Cell
Authors: Yoon Sooyoung , Oezaslan Mehtap , Hasché Frédéric
Published: February 2024

For several decades, proton exchange membrane fuel cells (PEMFCs) have been a topic of zero-emission energy conversion technology research, spanning from material development to system control. Most of the PEMFC research is focused on the cost reduction of catalyst and membrane as well as the improvement of the long-term durability. Harsh and dynamic operating conditions such as rapid load changes, cold start temperatures, insufficient gas supply or flooding of the anode with water lead to a fatal damage of the very thin anode catalyst layer. [1-2] During the hydrogen starvation, the carbon corrosion occurs to supply further protons and electrons to the cathode, resulting in an increase of the anode potential. This event is well-known as cell reserval and results in a decrease of the overall PEMFC performance.

In this study, we evaluated a new catalyst concept by combining both functionalities (hydrogen oxidation reaction (HOR) and oxygen evolution reaction (OER)) in single nanoparticles. The potential of this bifunctional catalyst concept will be compared with the mostly used catalyst system prepared by a physical mixture of Pt/C and IrOx as co-catalyst. Controlling the chemical composition and structure of the bifunctional nanoparticle catalyst system allows to improve the cell reversal tolerance.

References

[1] Moore, C. E., Eastcott, J., Cimenti, M., Kremliakova, N., & Gyenge, E. L. (2019). Novel methodology for ex situ characterization of iridium oxide catalysts in voltage reversal tolerant proton exchange membrane fuel cell anodes. Journal of Power Sources, 417, 53-60. DOI: https://doi.org/10.1016/j.jpowsour.2019.02.006

[2] Marić, R., Gebauer, C., Nesselberger, M., Hasché, F., & Strasser, P. (2020). Towards a Harmonized Accelerated Stress Test Protocol for Fuel Starvation Induced Cell Reversal Events in PEM Fuel Cells: The Effect of Pulse Duration. Journal of The Electrochemical Society, 167(12), 124520. DOI: https://doi.org/10.1149/1945-7111/abad68
Towards Reliable Stability Measurements of OER Catalysts
Authors: Bornet Aline , Pitscheider Simon , Bertheussen Erlend , Pedersen Christoffer Mølleskov , Maletzko Annabelle , Seselj Nedjeljko , Wiberg Gustav Karl Henrik , Kallesøe Christian , Melke Julia , Cremers Carsten , Arenz Matthias
Published: February 2024

Currently, significant efforts are taken to find the most active and stable electrochemical oxygen evolution reaction (OER) catalyst diverting from critical raw material. However, one also needs to consider new catalyst screening methods, especially with respect to stability investigations where rotating disk electrode (RDE) studies are not suitable.1 Recently, we introduced a gas diffusion electrode (GDE) setup as a new testing platform for OER catalysts.2 This methodology stems from fuel cell studies where carbon gas diffusion layer (GDL) is used as a transport layer to bring the reactant to the catalyst. Since carbon is not stable under the harsh OER conditions, water electrolyser uses titanium-based porous transport layers (PTLs). In the current work, we utilized the GDE setup to test the influence of the transport layer on the stability of a highly active Ir0.7Ru0.3Ox nanoparticle catalyst immobilized on homemade antimony-doped tin oxide (ATO) support. The test was conducted potentiostatically (@ 1.6 V vs RHE) for 2 h at 60 °C. The stability of the catalyst was then compared when deposited on GDL vs PTL. Rapid decline of the GDL-deposited catalyst activity was observed, while the PTL-deposited catalyst demonstrates a rather stable behavior (Fig. 1). We attribute this fast activity drop to the carbon oxidation of the GDL. Moreover, the activity at 30 °C of the PTL-deposited catalyst was compared to literature data on RDE setup [1]. In the RDE setup, a breakdown is observed after only 30 min when applying a constant current density. In contrast, PTL-deposited catalyst exhibits no activity loss during 2 h under similar conditions.

[1] H. A. El-Sayed. Journal of The Electrochemical Society, 166 (8), F458-F464 (2019)

[2] J. Schröder. JACS Au, 1, 247-251 (2021)

Figure
1
. Potentiostatic stability transients at 1.6 V vs RHE of Ir0.7Ru0.3Ox/ATO deposited on C-based GDL (green full) and on Ti-based PTL at 60 °C (black full) and 30 °C (blue dashed).

Figure 1
Effect of Superhydrophobic Catalyst Layers on PEMFC Durability
Authors: Folgado M. Antonia , Duque Luis , Diaz-Alvarez Ester , Chaparro Antonio M , Merino Susana , Plaza Daniel , de Diego Gonzalo , Hernández Rebeca , Serrano Marta
Published: February 2024

High durability of proton exchange membrane fuel cells (PEMFCs) is one main objective of this technology nowadays. Among different ways, the use of a superhydrophobic catalyst layer in the cathode may help to increase the stability of the cell under operation. Superhydrophobic cathodic layers improve water management in the cell by enhancing the back-diffusion transport from cathode to anode. As a consequence, anode humidification is favored whereas flooding of the cathode is avoided, leading to higher cell response at intermediate and high current densities [1]. Superhydrophobic catalyst layers can be obtained by adding specific agents to the precursor ink that is later deposited together with the catalyst and the ionomer. Another possibility is the use of electrospray deposition, which does not require additives. Electrospray is a dry deposition method where the ink is deposited under an electric field, yielding particular ionomer distribution inside the pores of the layer as a consequence of electrostatic interactions.

Accelerated stress tests (AST) are well stablished protocols to analyze durability of PEMFCs in a systematic and reduced time frame [2]. Protocols for stressing different components of the cell have been proposed. In this work, different cell configurations have been mounted, using electrosprayed catalyst layers in cathode, anode, and both. The cells have been submitted to an AST that affects mainly the cathodic catalyst layer. The study is complemented with microscopy analysis (cross-sectional) and local mechanical properties (small-punch) (Fig. 1).

The results show the effect of superhydrophobic cathodic catalyst layers on the durability of a PEMFC.

Acknowledgements

Funding by PORHYDRO2 project (TED2021-131620B-C22, ‘Preparation and characterisation of catalyst layers fabricated by electrospray for proton exchange fuel cells with passive gas feed’) by the Spanish Ministry of Science and Innovation.

[1] M.A. Folgado, J.J. Conde, P. Ferreira-Aparicio, A.M. Chaparro, Single Cell Study of Water Transport in PEMFCs with Electrosprayed Catalyst Layers, Fuel Cells. 18 (2018) 602–612. https://doi.org/10.1002/fuce.201700217.

[2] S. Stariha, N. Macauley, B.T. Sneed, D. Langlois, K.L. More, R. Mukundan, R.L. Borup, Recent Advances in Catalyst Accelerated Stress Tests for Polymer Electrolyte Membrane Fuel Cells, J. Electrochem. Soc. 165 (2018) F492–F501. https://doi.org/10.1149/2.0881807jes.

[3] R. Hernández, S. Merino, D. Plaza, L. Duque, M.A. Folgado, A.M. Chaparro, M. Serrano, G. de Diego, Study of Mechanical Properties of Membrane-Electrode Assemblies for Proton Exchange Membrane Fuel Cells By the Small-Punch Technique, ECS Meet. Abstr. MA2022-02 (2022) 1426–1426. https://doi.org/10.1149/ma2022-02391426mtgabs.

Figure 1
Design and Operation of PEM-Electrolyzers Considering Cost and Efficiency
Authors: Scheepers Fabian , Staehler Markus , Burdzik Andrea , Müller Martin
Published: February 2024

The design and operation of electrolyzers are always a trade-off between parameters that contrarily affect performance and operational goals. This talk will discuss some of those.

Compression of the product gases within an electrochemical process is often discussed as an alternative to subsequent mechanical compression. On the one hand, the electrochemical compression is advantageous in terms of energy efficiency; on the other hand, elevated gas pressure is responsible for increased gas loss due to permeation across the membrane. This can be prevented by using thicker membranes; in return, it impairs the proton transport in the electrolyzer and ultimately reduces its performance. It is therefore advisable to discuss an energetically sensible gas pressure level. As gas permeation is a crucial impact on this trade-off, it needs to be discussed how it is affected through operating conditions. Aside from the gas pressure difference between anode and cathode, the diffusion rate increases exponentially with temperature. However, lowering the stack temperature diminishes the electrochemical reaction kinetics as well as the ion conductivity of the ionomer. Hence, the influence of gas pressure, stack temperature and polarization curves on the plant efficiency are inextricably linked. Simulation results indicate that the energetically optimal design and operating conditions are functions of the applied cell voltage. As the design of the electrolysis plant is determined by its installation, only the operating conditions can be chosen flexibly. Economically, investment costs are best allocated to the cost of hydrogen when using high current density in order to have a high production capacity. On the contrary, a high current density also means a high cell voltage, which in turn results in a low plant efficiency and is responsible for high operating costs. Considering all these effects, the complexity of dependencies between parameters will be illustrated in this talk and how modeling can be used to access them. The results will outline challenges as well as directions how the technology can be further developed in future.

Figure 1
Development and Evaluation of Accelerated Durability Tests Under Realistic Operating Conditions for PEMFC Stacks – a Systematic Approach
Authors: Koprek Miriam , Schlumberger Robert , Wachtel Christian , Wilhelm Florian , Scholta Joachim , Hölzle Markus
Published: February 2024

Over the last decade, significant progress has been achieved in the commercialization of Polymer Electrolyte Membrane (PEM) fuel cells for mobile applications. However, long-term durability and stability of such systems still needs further improvement. To overcome today’s time-consuming long-term durability tests, the development of so-called accelerated durability tests (ADT) is urgently necessary. In this work, we present our recent results on such ADT test-protocols based on research promoting a detailed understanding of the individual aging mechanisms in PEM fuel cells.

Various stressors had been investigated separately to understand their impact on overall fuel cell ageing. Certain levels of cell potential, temperature and humidity could be identified as major stressors and were successively added to the test protocol. In addition to the electrochemical test results, additional focus was put on different in-situ and ex-situ characterization methods. This combination enables a detailed understanding of individual stressors and their interply. The PEM-stack used in this study is an automotive high-performance stack developed within the publically funded Auto Stack Industry (ASI) project. An extensive long-term test over 5,500 operating hours was carried out as baseline test using the New European Driving Cycle, but with additional features to mimic realistic automotive load-profiles. Based on the results of this reference protocol, four different ADT protocols of only 1,200 hours test duration were derived. All tests were performed using short stacks with automotive-size active area. In-situ measurements include spatially resolved current measurement, cyclic voltammetry and impedance spectroscopy. After each test, selected cells were additionally analyzed ex-situ using layer thickness measurement via SEM, IR-thermography and contact angle measurements.

The results from ex-situ investigations underline the degradation models postulated from in-site measurements. The overall data show that detailed understanding of individual stressors is necessary to successfully develop reliable accelerated ageing tests for PEM fuel cells.
Miniature Fuel Cells for Long-Term Unattended Power Needs
Authors: Kreller Cortney R. , Hettinga Wakeiyo , Jernigen Jeremy , Borup Rod L. , Brosha Eric L. , Rockward Tommy , Wilson Mahlon
Published: February 2024

For some niche applications, PEM fuel cells have the potential to improve safety and provide enhanced flexibility over conventional battery technology. This presentation will discuss the design and performance of two stacks where the application requires passive operation with pure H2 and O2 to provide continuous power with uncontrolled fluctuating ambient conditions. One application requires microwatts of power over decades and the other requires milliwatts of power for several years. The stacks are designed to operate with dead ended gas flows where passive membrane to vapor transport occurs through crenelations in the bipolar plates and membranes. Gas sealing over a -40 to 85˚C temperature range is another design challenge that has been addressed by utilizing a spring-loaded design that provides dynamic compression as the stack expands and contracts with temperature. This work will summarize the long-term performance and postmortem characterization of these miniature fuel cells as alternative power sources.
Investigation of the Effect of Graphite Bipolar Plate Flow Channel Inhomogeneities and Faults on HT-PEM Fuel Cell Stack Performance
Authors: Özel Tansu , Kraft Samuel , Cremers Carsten
Published: February 2024

Bipolar plates are a key component of fuel cell stacks. Bipolar plates have multiple functions. They connect the single cells of the stack electrically and must be therefore electrically conductive. They separate oxidant and fuel gases and distribute them on each side over the membrane-electrode-assembly (MEA). Bipolar plates separate coolant liquid too. Fuel cell stack is cooled by coolant liquid which is flowing through the cooling flow channels in the middle of bipolar plates.

Especially the bipolar plates for HT-PEM must endure a low pH environment, continuous electrical potential, and higher temperatures up to 200°C. The focus here is on investigations of anode and cathode side flow channels of graphite bipolar plates. Inhomogeneities and faults of flow channels are examined and their effects on fuel cell stack performance are analyzed. The analyses are based on optical scan data of flow channel geometry and measurement data of a HT-PEM fuel cell full stack consisting of 120 cells operated on a testbed under different variations. Inlet pressure and stoichiometry of both anode and cathode were varied, anode was fed with pure hydrogen and with different reformate gas compositions consisting of hydrogen, nitrogen, carbon dioxide and carbon monoxide. For each variation point, polarization curves between 0 A/cm2 – 0,55 A/cm2 in step of 0,05 A/cm2 were recorded.

With an on testbed installed cell voltage monitoring (CVM) system voltages of every cell were measured and logged. Enormous amount of optical scan data consisting of width and depth information of flow channels was merged to certain statistical data for anode and cathode bipolar plates. Correlations between statistical data and cell voltages are still being investigated. It is planned to repeat the measurements with another 120 cells HT-PEM fuel cell full stack and compare the results.
Modeling Electrical Conductivity of Injection-Molded Polymer Composite Bipolar Plates
Authors: Myers Maxwell T , Trimpey Jonathan K , Beevers David B , Bakis Charles E , Hollinger Adam S
Published: February 2024

Bipolar plates can be responsible for up to 40% of the total stack cost and 80% of the weight of a polymer electrolyte membrane fuel cell [1]. To reduce these cost and weight limitations, this work explores injection molding of polymer composites. Injection molding is well-suited for mass production and polymeric materials can significantly reduce the weight of traditional metallic bipolar plates. While polymers lack electrical conductivity, fillers can be added to fabricate conductive polymer composites. The main objective of this research is to model and injection mold polymer composites that will meet the United States Department of Energy technical target for bipolar plate electrical conductivity (> 100 S/cm).

A fiber contact model was developed to predict electrical conductivity based upon direction in the material, fiber alignment, fiber length and diameter, fiber concentration, and fiber conductivity [2]. Fiber alignment was measured experimentally by imaging cross sections of injection-molded nylon/carbon fiber composites. Imaging was performed on samples with different weight percentages of carbon fiber and from different mold designs to compare how fiber angles change based on mold geometry. To reduce the significant time required to measure fiber angles experimentally, computer recognition and processing of fiber alignment was developed. Nylon composites were injection molded with carbon fiber loadings ranging from 10 to 40 wt%. Modeling predictions show good correlation within 20% of experimental conductivity measurements. Samples with at least 20 wt% carbon fiber exceeded the US DOE technical target for bipolar plate conductivity, reaching 250 S/cm. In addition to modeling electrical conductivity, the Halpin-Tsai equations are used to model the elastic modulus and ultimate strain of the polymer composite. Tensile testing showed that the modulus of elasticity increases with carbon fiber loadings up to 30 wt%, reaching 7.3 GPa. At loadings above 30 wt%, the higher filler content can create voids which decrease the modulus of elasticity.

De Las Heras, A.; Vivas, F. J.; Segura, F.; Andujar, J. M., From the cell to the stack. A chronological walk through the techniques to manufacture the PEFCs core. Renewable & Sustainable Energy Reviews 2018, 96, 29-45.

Weber, M.; Kamal, M. R., Estimation of the volume resistivity of electrically conductive composites. Polymer Composites 1997, 18 (6), 711-725.

Figure 1
Embrittlement of PFSA Reinforced Membrane Interfaces after Ex-Situ Chemical-Mechanical Aging
Authors: Bas Corine , Crouillere Marie , Dubelley Florence , Robert Mylène , El Kaddouri Assma , Lottin Olivier , Dillet Jérôme , Mozet Kévin , Perrin Jean Christophe
Published: February 2024

Perfluorosulfonic acid (PFSA) membrane degradation has been identified as one of the main factors responsible for the short lifetime of PEMFCs [1,2]. The aging mechanisms of these membranes are complex due to mechanical fatigue combined to chemical aggressions. Mechanical fatigue results from the wetting/drying cycles while the chemical aggressions are induced by radicals formed during fuel cell operation. Although it is commonly accepted that chemical and mechanical stresses can interact to accelerate membrane degradation [3], coupled studies are rarely conducted. Thus, an original experimental set-up to perform ex-situ aging tests combining membrane exposure to cyclic mechanical stresses to a free radical environment under conditions close to those observed during cell operation has been developed [4]. Ex-situ aging was performed on PFSA membranes reinforced (Nafion™ XL) with a cyclic compression oscillating between 0 - 10 MPa (0.1 Hz frequency) and a Fenton solution containing 1 ppm Fe2+ and 3 %vol H2O2. Such stresses revealed a significant morphological alteration with the appearance of “bubbles” close to the surface membrane (Figure 1, left). No chemical structure modification was detected within the three different layers. Nevertheless, SEM-EDX, FTIR and Raman microscopic analyses highlight delamination close to the reinforcement/PFSA interface (Figure 1, rigth). Additional peeling tests argued this failure point in the Nafion™ XL membrane.

Figure 1
Water Dissociation Interfaces in Bipolar Membranes for H2 Electrolysers
Authors: Garcia-Osorio Dora Alicia , Jang Hansaem , Siritanaratkul Bhavin , Cowan Alexander
Published: February 2024

In order to meet large scale energy demands in a more sustainable way, water electrolysers could be coupled with the well-developed photovoltaic solar cell technology to provide the energy input for green H2 production. Commercial PEM (proton exchange membranes) electrolysers operate in acidic pH which favours H2 production at the cost of using IrO2 as catalyst for oxygen production at the anode representing a significant drawback for this technology. Contrary, an AEM (anionic exchange membranes) operates in alkaline electrolytes which enables the use of low cost and highly active OER catalyst such as NiCoFeOx,1 however at the expense of including an extra overpotential to drive the H2 production in the electrolyser.2

Using bipolar membranes (BPM), where a cationic exchange membrane CEM is used alongside an anionic exchange membrane, allows the electrolyser to operate at different pHs: at the cathode in an acidic environment to favour H2 production, and alkaline for O2 production at the anode. However, a BPM induces a significant increase in resistance across the electrolyser.2 Recently, it has been demonstrated that by adding metal oxides as water dissociation catalysts, the electrolyser overpotential significantly decreased passing from 8 V to 2.2 V at 500 mA cm-2.3 This milestone in the field was accomplished by using two metal oxides with different point of zero charge (PZC) 3 and 11 for IrO2 and NiO respectively. Interestingly, a similar performance was observed when only TiO2 was used as water dissociation catalyst which PZC sits between IrO2 and NiO.4 Indeed demonstrating the necessity of better understanding of the physicochemical phenomena that governs water dissociation interfaces.

Using TiO2 as water dissociation catalyst provides a suitable platform to understand how properties such as conductivity or different doping content affect water dissociation during H2 production in the electrolyser. Therefore, in this work modifications of TiO2 were investigated and its impact on the cell voltage when used between Nafion 212 and Sustainion membranes as CEM and AEM respectively, in a commercial 5 cm2 electrolyser at 60 ⁰C that operates only with DI water. To only benchmark the performance of the BPM, Pt and IrO2 were chosen as H2 and O2 catalysts respectively.

References

[1] ACS Catal. 9 (2019) 7–15

[2] ACS Energy Lett. 7 (2022) 3447–3457

[3] Science 369, (2020) 1099–1103

[4] Nat. Commun. 13 (2022) 1–10
Advances in Reinforced Polymer Electrolyte Membrane Designs for Improved Direct Coated Electrodes
Authors: Kobaisy Amr , Kurokawa Akinari , Oshiro Kazushi , Tani Masaki , Maruyama Masashi , Miyake Rie , Namba Takafumi , Ueda Yurika
Published: February 2024

In recent years, hydrogen fuel cells have become a key clean technology for the decarbonization of the transport sector. Significant investments are directed towards scaling the hydrogen infrastructure and the production of fuel cell vehicles to meet cost and climate targets set by governments across the globe. To achieve the required scale at cost, manufacturers of fuel cell components such as membrane electrode assembly (MEA) need to adopt high throughput processes while maintaining quality and performance of MEAs to meet heavy duty vehicle requirements.

Roll to roll direct coating (DC) process using slot die coating technique is proposed to deliver the lowest cost/highest throughput method for production of MEAs. Electrode ink containing catalyst, ionomer and solvents are applied directly on the membrane before drying to remove the solvents from the coating. The direct contact of solvents with PEM ionomer can create challenges resulting from ionomer swelling and shrinking to produce poor electrode quality and MEA performance.

This talk will discuss different design approaches to produce direct coated MEAs and present a novel approach in membrane design to address DC challenges to meet performance and quality targets that would enable the use of DC for scaling the fuel cell production.

Applying Gore’s knowledge in expanded poly-tetra-flour-ethylene (ePTFE) reinforcement properties and fuel cells research we developed a membrane that would reinforce the polymer electrolyte and electrode layers simultaneously while minimizing the impact of solvents used in DC processes. This results in improved MEA quality and performance compared to a traditional reinforced membrane design and enables the use of DC for high throughput/low-cost MEA manufacturing.

Figure 1
Cross-Aligned PTFE Nanofiber Reinforced Composite Membrane for PEM Fuel Cells
Authors: Yoon Ki Ro
Published: February 2024

Polymer electrolyte membrane fuel cells (PEMFCs) have widely been considered environmental friendly alternative energy technologies due to their high energy conversion efficiency and zero emission. In the recent, the importance of performance and durability of electrolyte membrane, interfacial layer separating two electrodes, prohibiting fuel cross-over, while transporting only protons, has become much crucial for utilizing PEMFCs to the automobile applications such as fuel cell electric vehicles (FCEVs) and drones.

Unfortunately, the current state membranes, mainly composed of perfluorosulfonic acid (PFSA) ionomers, have suffered from the high cost and low proton conductivity, and low dimensional stability during dynamic humidity changes during fuel cell operation. In order to deal with these issues, recently, a reinforced composite membranes (RCMs) have been developed in which a PFSA ionomer is impregnated into a porous support matrix consisted with nanofibrous polymer materials such as polytetrafluoroethylene (PTFE) due to their thermal/mechanical robustness. The PTFE based RCMs could provide enhanced mechanical stability and electrochemical performance with a reduced use of PFSA ionomer, but low impregnation of ionomers into nanosized hydrophobic PTFE networks, resulting in phase separation and irreversible creep deformation.

Herein, we report a novel preparation of vertically alined PTFE aggregated fibers (PTFE AFs) as a reinforcement by using facile electrospinning hetero-polymer solutions containing PTFE nanoparticles and PEO (Polyethylene oxide) carrier polymer and subsequent thermal removal of PEO. Developed PTFE AF were effectively soaked by PFSA ionomers, and PTFE AF based RCMs delivered outstanding dimensional stability and proton conductivity compared to commercial RCMs. Furthermore, PTFE AF based RCMs used MEA exhibited exceptional single-cell performance and long-term stability. The enhanced performance was attributed to the facile proton conduction through the one dimensional channels between aligned fibers without fiber scattering, and effective suppression of volume expansion of hydrated PFSA ionomer by rectangular shaped PTFE fiber network. We believe the widespread use of novel PTFE fiber based membranes with an unique pattern in a variety of membrane applications where porous supports are used.

Figure 1