bluuebunny/crossref_metadata_2025 huggingface dataset:
Recycling of Platinum Group Metals
Authors: Ashfield Laura
Published: February 2024

The platinum group metals (Pt, Pd, Rh, Ir, and Ru) are cited as critical minerals by the US Geological Survey and appear on the EU Critical Raw Materials list due to their low natural abundance and economic importance. Platinum has many uses including jewellery, medical devices and pharmaceuticals, coatings, automotive catalysts, nitric acid manufacture and other industrial catalysts, electronics, and plays a crucial role in the growing area of fuel cell and water electrolyzers.

Early recognition of the need to recycle these valuable elements has led to the development of a circular economy using highly advanced processes for extracting and separating them from complex materials, returning the metals to use in a highly pure form. This presentation will give an overview of the industry up to the present day, including examples of the application of separation techniques, and will explore the potential for reduced environmental impact from recycling platinum group metals and the benefits of consideration of design for recycle in product development.
Influence of Contact Pressure and Flow Rate on the Performance of Anion Exchange Membrane Electrolysis
Authors: Lemcke Michelle Sophie , Münchgesang Wolfram , Menzel Nadine , Bron Michael
Published: February 2024

Hydrogen production by electrolysis is a key aspect of a climate-neutral economy. However, there are still weak points in the established low-temperature technologies such as high material costs in case of PEM electrolysis and poor dynamic operations in case of alkaline electrolysis. The emerging electrolysis technology, the anion exchange membrane (AEM) electrolysis, addresses these weaknesses and combines their advantages. Due to the solid polymer electrolyte and the alkaline environment, AEM water electrolysis is featured by a compact zero-gap cell design and inexpensive materials like non-noble metal catalysts. Hence, it offers the potential to a cost-effective and efficient electrolysis technology.

To enable the breakthrough of this technology, we contribute by conducting performance evaluations of membrane electrode assemblies (MEAs) under application-oriented conditions. One focus is on non-noble metal MEAs with an active area of 25 cm2 operated with pure water and low concentrated potassium hydroxide solution.

To ensure comparability of different MEAs, it is crucial to compare them at their performance optimum. This is achieved by determining the optimal set-up parameters like contact pressure and operation parameters like flow rate for each MEA type. Otherwise, deviation from the optimal operating point by up to 50 % may occur.

The influence of the parameters contact pressure and flow rate on the MEA performance is discussed in this presentation. To investigate their impact, we analysed the MEAs in an electrolyser test station using polarisation curves, electrochemical impedance spectroscopy and load tests at constant current and constant voltage.

Some of the results presented are obtained within the project “REVAL – reversible anion exchange membrane electrolysis” (funding code 03ZZ0732D) funded by the German Federal Ministry of Education and Research (BMBF).
Microwave Drying of Catalyst Layers for Fuel Cells and Electrolysers
Authors: Heider Emanuel Albert , Bader Julian , Kiesel Simone , Kühn Steffen , Tran Hai-Anh , Oesterlein Moritz , Joerissen Ludwig
Published: February 2024

Due to an increasing demand for sustainable energy, the polymer electrolyte membrane fuel cell (PEMFC) is considered a key technology in energy conversion with hydrogen as an energy carrier. The performance characteristics of a PEMFC is significantly influenced by the morphology of the catalyst layer[1], which is formed predominantly during the drying step in the manufacturing process.

In order to improve the performance of PEMFC and hence reducing production costs, research effort as well as industrial interest has focused on the drying process. Moreover, energy efficiency of the drying step in the production of thin-film catalyst layers is considered a key driver of cost perspective for the mass-market introduction of PEM fuel cells and electrolyzers due to increasing energy costs and the need for reduction of environmental impact.

In the presented work, an innovative drying approach for thin-film catalyst layers, used in PEMFC and electrolyzer applications, is investigated. The thin-film is either coated on a substrate and transferred onto a polymer electrolyte membrane in a second process step or is directly coated onto the polymer electrolyte membrane by doctor blade coating. Drying is performed by coupling of microwave radiation into the wet film, leading to a homogeneous and energy-efficient heating of the coated film. Energy losses of the microwave drying process are significantly reduced compared to conventional convective drying. Additionally, the microwave induced drying step offers maximum control during the process.

Dried thin-films, produced in the lab scale, are transferred to a polymer electrolyte membrane by a hot-pressing step and are completed with gas diffusion layers to membrane electrode assemblies (MEA). Electrochemical performance of the MEA is characterized on a fuel cell test bench in single cell configuration. The morphology of the structure obtained from microwave drying is analyzed and compared to CCM samples dried in a conventional convective oven.

The effect of a microwave-based drying process is discussed with regard to fuel cell performance and structure-property relations of the electrodes.

References

[1] M. Breitwieser, M. Klingele, S. Vierrath, R. Zengerle, S. Thiele, Adv. Energy Mater. 8, 1701257 (2018).
Understanding the Break-in of PEM Fuel Cells: A Comprehensive Study of Break-in Methods and Underlying Mechanisms
Authors: Haimerl Felix , Avellone Emilio , Bandarenka Aliaksandr S.
Published: February 2024

The break-in process of Proton Exchange Membrane (PEM) fuel cells is critical for their performance and durability. While there is a rising number of publications on break-in procedures, a comprehensive comparison of break-in procedures is missing. In this study, we investigate the impact of several break-in procedures, including potentiostatic holds, potential cycling, air starvation, and hydrogen pumping, on the performance of PEM fuel cells using electrochemical impedance spectroscopy and polarization curves. The measurements provide valuable insights into the underlying break-in mechanisms that contribute to the activation of the catalyst layers, the membrane and the interface of both. The results can guide the optimization of break-in protocols and reduce the break-in time and, therefore, the production costs of PEM fuel cells.
Production of Novel Tubular Electrochemical Hydrogen Compressor
Authors: Zängler Wibke , Keller Robert , Wessling Matthias
Published: February 2024

For most applications, especially transport, hydrogen needs to be compressed due to its low volumetric density. Conventionally, mechanical compressors are used for hydrogen compression, but they possess disadvantages such as high maintenance due to moving parts and a limited one-stage compression ratio. A promising technology to overcome those obstacles is electrochemical hydrogen compression, in which hydrogen is compressed in an electrochemical membrane reactor.

To date, only planar electrochemical reactors for hydrogen compression have been investigated although tubular designs offer advantages in membrane area to reactor volume ratio, sealing options, pressure stability and reactor complexity. However, high contact and membrane resistances and scalable manufacturing processes are still challenges to be addressed for the advent of tubular electrochemical compressors in application.

Herein we introduce a manufacturing process for tubular electrochemical hydrogen compression reactors. The developed cell comprises a catalyst coated porous tubular anode covered by a tubular proton exchange membrane, which was subsequently coated with the cathode catalyst layer. The porous anode was prepared via metal 3D printing. 3D printing enables tailored porosity and geometry by which mass transport is enhanced. The catalyst layer was applied by manual spray coating. Constant current experiments and electrochemical impedance spectroscopy were performed to characterize the as prepared tubular electrochemical compressor. The results revealed the importance of tailored contacting concepts and the optimization of components regarding water transport, as the efficiency of the process is dominated by contact and membrane resistances.
Design and Construction of a LT-PEM Fuel Cell System for Aviation Application
Authors: Bürger Stefan , Cremers Carsten , Urban Niels
Published: February 2024

Fuel cell technology has gained considerable attention as an alternative power source for mobility applications. Fuel cell systems are already integrated in ground applications like trucks, cars, and busses. One reason is, that they have the potential to provide an environmentally friendly power supply solution compared to traditional combustion engines. Moreover, fuel cell drive trains offer several potential benefits, such as improved energy efficiency, noise reduction and no local emissions and even zero CO2 emission if they are fueled with green hydrogen. On the other hand, there are several key challenges associated with the integration of fuel cell technology into mobility applications, such as safety, durability, weight, and cost. These challenges become even more difficult when flight applications are considered, due to the higher .

We present our research of a fuel cell system design, which is constructed to power a one seat airplane, the Antares E2. This system will utilize compressed Hydrogen as fuel to power up to six electronic motors via an electric bus. The airplane needs 90 kW of power mainly for its electric propulsion and can be operated up to a ceiling altitude of 6500 m (21,300 ft). For redundancy and safety, it is necessary to split the power output to at least two systems. Therefore, each system must have a power output of 45 kW. The fuel cell system's design takes various factors into account, such as lightweight and compact components as well as safety analysis to ensure the operation in flight. To reach aviation standards a full FMEA analysis is conducted, to calculate the risks of operating the systems on an airplane. The goal is to have a fuel cell system which is eligible for operating an aircraft. We want to present first results of our research, consisting of first design to ground operation and include some simulations for flight conditions.

A successful development and certification of this fuel cell system would represent a significant milestone in the pursuit of sustainable aviation technologies, since it would be one of the first system which features approved airworthiness. This technology has the potential to reduce emissions and noise pollution associated with traditional combustion engines. Further research and development efforts are required to optimize the performance and reduce the cost of this fuel cell system.

This work is funded by the Federal Ministry for Digital and Transport (BMDV) in the project “H2GA” under the grant 03B10707. The authors declare that the opinions expressed in this submission are their own and are based on a thorough review of existing scientific literature.
Modeling of Proton Exchange Membrane Fuel Cell Stack and Start Strategy Optimization with a Multi-Objective Genetic Algorithm
Authors: Liu Zhao , Chen Hui Cui , Zhang Tong , Unwerth Thomas von , Meuser Carmen
Published: February 2024

This paper proposes a non-dominated ranking genetic algorithm (NSGA-II) method for fast optimizing the loading strategy at the start of a proton exchange membrane fuel cell (PEMFC) stack to optimize the dynamic response capability, power density and system efficiency. First, a Simulink model of the PEMFC stack including anode module, cathode module, water transfer module and output voltage module is established as the base model for optimization, and the accuracy of the stack model is verified through experiments. The power consumption of the air compressor is the main parasitic power considered, and it is modelled using the air compressor map by taking a table look-up method directly. The three performance indicators of dynamic response capability, power density and system efficiency are then optimized simultaneously based on NSGA-II. The results show that the optimized start-up loading strategy results in a PEMFC stack that outperforms the base model in all three indicators, demonstrating the success of the method in solving time-consuming multiple optimization problems. This study presents an effective and rapid approach for the multi-objective optimization of PEMFC stack, which is of guidance for engineering practice.
Tailoring Parallel Channel Flow Fields for Efficient Mass Transport and Compression in Proton Exchange Membrane Fuel Cells
Authors: Parmar Harsharaj Birendrasingh , Chadwick Eric Alexander , Shrestha Pranay , Lytle Spencer , Bazylak Aimy
Published: February 2024

The adverse effects of global warming have made it critical to transition our reliance on fossil fuels to more sustainable energy sources. Renewable energy can be stored in the form of hydrogen to continuously produce clean energy using a proton exchange membrane (PEM) fuel cell. However, to accelerate commercialization, especially in heavy-duty applications, the performance and durability of the fuel cell needs to be improved. Particularly, PEM fuel cell performance is strongly dependent on the flow fields which should be designed to optimize the transport of reactants and byproducts while maintaining uniform compression of the fuel cell materials. An important flow field design parameter is the channel aspect ratio (channel width by height) which directly influences compression and the transport of reactants and products. Although novel flow field configurations have been studied previously, an investigation on the effects of channel aspect ratio on cell performance using electrochemical testing and operando X-ray imaging has yet to be performed. In this study, we compared the water saturation and electrochemical performance across varying flow field channel aspect ratios from 0.5-2.0 with a fixed active area. The ohmic and mass transport resistances were quantified using electrochemical impedance spectroscopy. Operando X-ray imaging was performed to spatially resolve water saturation under the land and channel regions of the flow fields. We observed that lower channel aspect ratios (or higher number of channels for the given active area) led to lower ohmic resistances but resulted in significant water saturation at higher current densities due to ineffective water removal from the smaller channels. Notably, from these results we elucidated that there exists an ideal channel to rib width ratio to facilitate an effective balance of enhanced water removal using the channels and contact between the porous microstructures under the lands of the flow fields.
Hydrophobic Conductive Coatings for Fuel Cell Gas Diffusion Layers
Authors: Bodner Merit , Blaschke Fabio , Tritscher Florian
Published: February 2024

Mass transfer of the reactant gases, water management, thermal and electrical conductivity are all highly depending on the properties of the gas diffusion layer (GDL) in polymer electrolyte fuel cells (PEFCs). GDLs are produced in complex and energy demanding processes including high temperature graphitization and are modified using polytetrafluoroethylene (PTFE) to introduce the hydrophobicity needed to efficiently remove water [1]. PTFE is, however, negatively impacts the required electrical conductivity and is facing an uncertain future with the pending restrictions on the use of perfluoroalkyl substances (PFAS) [2], [3]. Therefore, we have investigated the use of electrically conductive polyaniline (PANI) coatings on carbon fiber substrates with modifications to increase hydrophobicity. As substrate, AvCarb carbon paper EP40 was used and PTFE treated EP40T was used as state-of-the-art reference. EP40 was coated through dip-coating or electro-coating using PANI modified with sodium dodecylbenzenesulphonate as additive to adjust hydrophobicity [4]. With this approach, we have been able to show comparable pore volumes and pore surface areas (Figure 1) through mercury porosimetry as well as comparable hydrophobic properties.

References

[1] A. Ozden, S. Shahgaldi, X. Li, and F. Hamdullahpur, “A review of gas diffusion layers for proton exchange membrane fuel cells—With a focus on characteristics, characterization techniques, materials and designs,” Prog. Energy Combust. Sci., vol. 74, pp. 50–102, 2019, doi: 10.1016/j.pecs.2019.05.002.

[2] E. Dhanumalayan and G. M. Joshi, “Performance properties and applications of polytetrafluoroethylene (PTFE)—a review,” Adv. Compos. Hybrid Mater., vol. 1, no. 2, pp. 247–268, Jun. 2018, doi: 10.1007/s42114-018-0023-8.

[3] ECHA/NR/23/04, “ECHA publishes PFAS restriction proposal,” 2023. https://echa.europa.eu/-/echa-publishes-pfas-restriction-proposal (accessed Mar. 27, 2023).

[4] F. Tritscher, A. Mularczyk, A. Forner-Cuenca, V. Hacker, and M. Bodner, “Surfactant doped polyaniline coatings for functionalized gas diffusion layers in low temperature fuel cells.”, under review

Figure 1: Mercury porosimetry measurements for the bare substrate, the state-of-the-art PTFE treated substrate, as well as hydrophobic PANI coated samples, prepared using dip-coating and electro-coating.

Figure 1
Investigation of Gas Diffusion Layer Degradation in Polymer Electrolyte Fuel Cell Via Chemical Oxidation
Authors: Edjokola Joel Mata , Hacker Viktor , Bodner Merit
Published: February 2024

The gas diffusion layer (GDL) is a key part of the membrane electrolyte assembly and is critical for the transport of fuel, oxygen and water. The GDL is made up of two layers: macroporous substrate (MPS) and microporous layer (MPL) (1). To achieve the hydrophobicity required for water management, the two layers are typically treated with polytetrafluoroethylene (PTFE) (2). In many long-term experiments, it has been observed that GDL degradation, such as carbon corrosion and PTFE loss, leads to a deterioration of water management, conductivity and mass transport (3).To solve this durability problem, a thorough and in-depth understanding of the GDL degradation mechanism is required. In this study, GDLs are subjected to an accelerated stress test to investigate degradation by chemical oxidation. GDLs are soaked in Fenton's reagent for 24 hours. The hydrophobic properties of pristine and soaked GDLs are compared based on contact angle measurements, thermogravimetry and scanning electron microscopy. In addition, the chemical composition of the solutions before and after the immersion test is analyzed using a total organic carbon analyzer and an ion chromatograph. The results show that the hydrophobicity of GDL exposed to Fenton reagent is decreased by 5 and 4 degrees for the MPL and the MPS respectively. Fig 1. depicts a decrease in surface contact angle, which is associated with surface oxidation and PTFE deterioration.

Acknowledgement

This research work is performed under the project AlpeDHues (AlpeDHues / FFG 889328) which is supported by the Austrian Research Promotion Agency (FFG).

References

C. Csoklich, R. Steim, F. Marone, T. Schmidt and F. Büchi, ACS Applied Materials & Interfaces,
13, 9908–9918 (2021).

A. Ozden, S. Shahgaldi, X. Li and F. Hamdullahpur, Progress in Energy and Combustion Science,
74, 50–102 (2019).

Y. Yang, X. Zhou, B. Li and C. Zhang, Applied Energy,
303, 117688 (2021).

Figure 1
Capillary Pressure Controlled Water Pathways in Gas Diffusion Layers for Polymer Electrolyte Fuel Cells Designed By Additive Manufacturing
Authors: Doerenkamp Tim , Buechi Felix N. , Schmidt Thomas J. , Eller Jens
Published: February 2024

Polymer electrolyte fuel cells (PEFC) are considered to make a significant contribution to the transition towards carbon free energy conversion, as they produce electric power from hydrogen and oxygen with water as the only by-product [1]. On its way to widespread commercialization, in particular the water management in PEFC is challenging. On one hand, the electrolyte membrane needs to be humidified to be highly conductive for the hydrogen protons. On the other hand, accumulation of the product water in the gas diffusion layer (GDL) on the cathode side mitigates the oxygen transport towards the catalytic surface, which leads to severe performance limitations [2-3]. Previous work has shown that structured GDLs can enhance PEFC performance [5] and additive manufacturing (AM) has been identified as a viable method to fabricate just such [4,6].

Currently available AM technologies are struggling to fulfill the needs in terms of minimal feature size (~8 um fiber diameter) and sample size (at least some cm2). Initial AM prepared GDLs were coarse with finest structures of about 120 um [6] which is in the range of typical GDL thickness. Here, we present AM prepared GDL like structures with 20 um printed features that can reach sizes of some tens of mm2.

The 3D printed structures are designed to guide the product water through the GDL by adjusting the throat size [7] and therefore the capillary pressure, which is required in the water phase to percolate through the throats to the neighboring pore as described by Young-Laplace law. Figure 1 shows tomographic data of a test lattice structure manufactured by high-resolution projection micro stereolithography (PµSL). The concept is validated by measuring the pressure in the water phase as a function of the throat size under ex-situ conditions. The desired percolation path of the water is monitored by 2D as well as 3D image data acquired by X-ray radiography and X-ray tomographic microscopy (XTM), respectively.

Figure caption:

XTM scan of a lattice structure manufactured by P
µ
SL: a) 3D rendering, b) x-z-plane cross section, c) x-y-plane cross section. Slight deformation in the base layers of the lattice structure is observed.

References

[1] O. Z. Sharaf et. al., Renewable and Sustainable Energy Reviews, 2014, 32, pp. 810-853

[2] M. F. Mathias et. al., Handbook of Fuel Cells, 2010

[3] J. Ihonen et. al., Journal of the Electrochemical Society, 2004, 151, pp. A1152-A1161

[4] D. Niblett et. al., Journal of the Electrochemical Society, 2020, 167, 013520

[5] C. Csoklich et. al., Energy & Environmental Science, 2022, 15, 1293-1306

[6] D. Niblett et. al., International Journal of Hydrogen Energy, 2022, 47, pp. 23393-23410

[7] D. Niblett et. al., Journal of Power Sources, 2020, 471, 228427

Figure 1
An Experimental Study on the Correlation between Characteristics of Gas Diffusion Layer and Performance Depending on Relative Humidity Variation in Proton Exchange Membrane Fuel Cell
Authors: Lee So Yeon , Ahn Chi-Yeong , Shim Hyungwon
Published: February 2024

As it is well known, Gas diffusion Layer(GDL) is a fundamental element to provide more efficient water transport in Proton Exchange Membrane Fuel Cell(PEMFC). Numerous previous studies showed how important and critical GDL is in PEMFC. There have been many efforts to improve the performance of GDL, such as studies on properties, structural improvement, and hydrophobic coating on substrate and micro porous layer. Through these efforts, PEMFC has been developed and also the relationship between GDL and each component was investigated well.

Relative Humidity(RH) is an important factor that affects proton conductivity and mass transport and is also an factor to be considered for water management. Although it should be relatively clear, it is necessary to compare and verify between the numerical study and experimental study since they does not always matches.

In this study, the results were compared with the physical properties of each GDL based on experimental data applying GDL with different characteristics. We studied to reveal the correlation between data such as thickness, porosity, and pore distribution of GDL and I-V Polarization curve conducted by changing RH conditions to investigate performance.
Water Transport Modeling in a Microporous Layer for a Polymer Electrolyte Membrane Water Electrolyzer Having a Gas-Liquid Separating Interdigitated Flow Field
Authors: Nakajima Hironori , Ekström Henrik , Shima Asuka , Sone Yoshitsugu , Lindbergh Göran
Published: February 2024

A novel interdigitated flow field design for polymer electrolyte membrane electrolyzers (proton exchange membrane water electrolysis cells), which has oxygen exhaust channels separated from pressurized liquid water feeding channels, has been developed for ground and space applications 1), 2). This structure separates oxygen and liquid water inside the anode of the cell. Thereby it dispenses with water circulators for bubble removal from the cell and external separators by natural or centrifugal buoyancy. We thus aim to develop a numerical model for further optimization of the cell design.

Finite element modeling (COMSOL Multiphysics) of water transport is three-dimensionally conducted for the anode porous transport layer coated with a hydrophobic microporous layer (MPL) (SIGRACET 29BC, SGL Carbon Inc.) assembled with the interdigitated flow field. The MPL works to separate evolved oxygen gas exhausted in the through-plane direction and pressurized liquid water injected in the in-plane direction owing to the capillary pressure 2), 3). Prominent leakage of the liquid water to the oxygen channels has not been detected.

Electrochemical kinetic parameters for the model are determined by electrochemical impedance spectra. Current-voltage measurement of the cell is also performed to validate the numerical modeling.

We model the current densities and the current ratio between the reactant liquid water and water vapor at the interface between the MPL and catalyst layer (CL). The model involves fractional bubble coverage of the CL with produced oxygen gas and liquid water saturation in the MPL. The vapor evaporating from the liquid water in the MPL is assumed to be mixed with the evolved oxygen for diffusive water transport. The volumetric evaporation rate is assumed as a function of the liquid water saturation in the MPL.

References

1) Y. SONE, O.S. HERNANDEZ-MENDOZA, A. SHIMA, M. SATO, H. NAKAJIMA, H. MATSUMOTO, Water Electrolysis by the Direct Water Supply to the Solid Polymer Electrolyte through the Interdigitated Structure of the Electrode, Electrochemistry. 89 (2021) 138–140. https://doi.org/10.5796/electrochemistry.20-00145.

2) H. NAKAJIMA, V. VEDIYAPPAN, H. MATSUMOTO, M. SATO, O.S. MENDOZA-HERNANDEZ, A. SHIMA, Y. SONE, Water Transport Analysis in a Polymer Electrolyte Electrolysis Cell Comprised of Gas/Liquid Separating Interdigitated Flow Fields, Electrochemistry. 90 (2022) 017002. https://doi.org/10.5796/electrochemistry.21-00097.

3) H. Nakajima, S. Iwasaki, T. Kitahara, Pore network modeling of a microporous layer for polymer electrolyte fuel cells under wet conditions, J. Power Sources. 560 (2023) 232677. https://doi.org/10.1016/j.jpowsour.2023.232677.

Acknowledgments

This study is based on results obtained from a project, JPNP21014, commissioned by the New Energy and Industrial Technology Development (NEDO).
(Poster Award - Honorable Mention) Durable Polybenzimidazole Anion Exchange Membranes for Alkaline Water Electrolyzers
Authors: Boström Oskar , Choi Seung-Young , Xia Lu , Lohmann-Richters Felix , Jannasch Patric
Published: February 2024

Water electrolysis under alkaline conditions allows the use of inexpensive non-platinum-group catalysts such as nickel.1, 2 Conventional alkaline electrolyzers usually employ a highly concentrated aq. KOH solution as electrolyte (5-7 M) with a porous diaphragm as separator. Alternatively, protolysable polymers such as polybenzimidazole (PBI) may be swollen with electrolyte and used as ion-solvating membranes.2, 3 However, the chemical stability of the polymers can become a serious issue under these harsh conditions. Operation under more dilute conditions, e.g., up to 2 M KOH, may bring the benefits of the alkaline conditions combined with a longer cell lifetime. Under these conditions, aliphatic cyclic quaternary ammonium (QA) cations, such as piperidinium, have shown excellent stability.

In the present work, performed as part of the EU project “NEXTAEC”, we have designed and synthesized m-PBI grafted with mono- and bis-piperidinium functionalized side chains, respectively (Figure 1a-b). AEMs were prepared from polymers with varying ion exchange capacities and studied at 80 °C containing KOH solutions in the concentration range 0.5-2 M KOH. The membranes were characterized with respect to, e.g., electrolyte solution uptake, alkaline stability, and electrolyser performance (Figure 1c). The uptake showed a strong inverse correlation with KOH concentration, which also affected the electrochemical performance. The stability as evaluated by 1HNMR spectroscopy was excellent showing, in the worst case, less than 8 % ionic loss after 6 months storage in 2 M KOH at 80 °C.

Li, D.; Park, E. J.; Zhu, W.; Shi, Q.; Zhou, Y.; Tian, H.; Lin, Y.; Serov, A.; Zulevi, B.; Baca, E. D.; Fujimoto, C.; Chung, H. T.; Kim, Y. S., Highly quaternized polystyrene ionomers for high performance anion exchange membrane water electrolysers. Nature Energy
2020,
5 (5), 378-385.

Aili, D.; Kraglund, M. R.; Rajappan, S. C.; Serhiichuk, D.; Xia, Y.; Deimede, V.; Kallitsis, J.; Bae, C.; Jannasch, P.; Henkensmeier, D.; Jensen, J. O., Electrode Separators for the Next-Generation Alkaline Water Electrolyzers. ACS Energy Letters
2023, 8 (4),1900-1910.

Aili, D.; Yang, J.; Jankova, K.; Henkensmeier, D.; Li, Q., From polybenzimidazoles to polybenzimidazoliums and polybenzimidazolides. Journal of Materials Chemistry A
2020,
8 (26), 12854-12886.

Marino, M. G.; Kreuer, K. D., Alkaline stability of quaternary ammonium cations for alkaline fuel cell membranes and ionic liquids. ChemSusChem
2015,
8 (3), 513-23.

Figure 1
(Invited) Monopolar and Bipolar Membranes Based on Nanofiber Electrospinning
Authors: Pintauro Peter N.
Published: February 2024

Cation-exchange, anion-exchange, and bipolar membranes play crucial roles in a variety of electrochemical processes and devices, including chloralkali cells, electrodialysis separations for water purification, proton-exchange membrane and hydroxide-exchange membrane (alkaline) fuel cells, redox flow batteries, and processes for direct air capture of CO2. The incorporation of polymeric nanofibers into such membranes provides an attractive and tunable method of creating materials with new nano-morphologies and highly desirable properties.

The impregnation of an ionomer solution into a pre-formed nonwoven porous mat of electrospun polymer fibers is a well-known method of making reinforced proton-exchange membranes. The use of simultaneous dual-fiber electrospinning or the electrospinning of polymer blends can be used to intermix/incorporate/co-locate dissimilar and incompatible polymers on the nanoscale. Although less studied in the literature, these methods offer many interesting possibilities for new membrane structures with targeted and unique transport and mechanical properties.

In this review talk, the use of dual fiber and blended polymer fiber electrospinning for membrane fabrication will be presented for the following: (1) Nanofiber reinforced cation (proton) exchange membranes, (2) Electrospun NafionTM/PVDF dual fiber and single-fiber membranes for H2/Br2 redox flow batteries, (3) Composite anion exchange membranes, and (4) Bipolar membranes with a 3D nanofiber junction. Materials and methods for membrane fabrication will be described and the properties of the membranes will be discussed.
Advanced PEM Electrolyzer Membrane for Hydrogen Crossover Mitigation
Authors: Yang Fan , Sun Qiang , Mittelsteadt Cortney
Published: February 2024

Proton Exchange Membrane (PEM) electrolyzers are a promising technology to produce hydrogen as a clean energy carrier. However, a significant challenge is hydrogen crossover, especially at high pressures (>40 bar) and when utilizing thin (<100 um) membranes. This poses significant safety hazard due to the mixing of H2 with oxygen, especially in the balance of plant due to higher void volumes.

Mitigating membrane crossover is therefore critical to the safety of the entire PEM electrolyzer system. Several research groups have demonstrated preliminary works on the H2 crossover mitigated membrane for PEM electrolyzers. Klose et al. [1] implemented a Pt interlayer between one piece of NR212 membrane and a piece of N115 membrane. The work showed significant reduction of H2 crossover in their design compared to the regular PFSA membrane. However, the work only demonstrated the effectiveness of crossover reduction under ambient pressure. Moreover, the spraying method they proposed is not readily scalable. Stahler et al. [2] demonstrated that applying an interlayer between the anode catalyst layer and recombination layer will help to reduce the H2 crossover. However, this work also failed to demonstrate mitigation at high H2 pressure. Additionally, each of these methods used Pt/C in the recombination layer. Carbon, though robust in the fuel cell applications may readily oxidize at the higher electrolyzer potentials. This could have consequences on membrane durability.

Preliminary data has demonstrated that our proposed mitigate strategy can significantly reduce the H2 crossover. The MEA with regular NR212 membrane cannot be operated safely under 70 oC under even mild pressure. However, with our addition of the highly efficient recombination layer, the crossover can be dropped to 6% LEL even at 40 bar. This discovery will help to improve the PEM electrolyzer safety dramatically.

References:

C. Klose et al 2018 J. Electrochem. Soc. 165 F1271

A. Stähler et al 2022 J. Electrochem. Soc. 169 034522
Investigating the Electro-Osmotic Coefficients of PFSA and Anion-Exchange Ionomers Using Microelectrodes
Authors: Petrovick John G. , Kushner Douglas I. , Goyal Priyamvada , Radke Clayton J. , Weber Adam Z.
Published: February 2024

The electro-osmotic coefficient of ionomer membranes is a significant water management property that quantifies the number of water molecules dragged with the mobile ion (typically a proton) when that ion moves due to the operation of an electrochemical cell or an electric field. This coefficient becomes critical when attempting to model water distribution and movement in fuel cells and electrolyzers, where water is an important factor influencing device performance. However, there is disagreement on the value of the electro-osmotic coefficient for PFSA membranes and little significant study of the coefficient in anion exchange membranes (AEMs). Here we present an electrochemical, two-electrode method of determining the electro-osmotic coefficient of ionomers using differential relative humidity (RH) measurements. This approach allows for more accurate determination of the electro-osmotic coefficient. We present the electro-osmotic coefficient as a function of temperature and mobile ion for a variety of ionomers, including Nafion, sulfonated polystyrene, Versogen,, and Sustainion. In addition, a model based on the Maxwell-Stefan-Onsager framework is developed for the AEMs, enabling calculation of the membrane water permeability via fitting of the electro-osmotic coefficient. These coefficients will allow for more accurate models of water transport in electrochemical systems, leading to a greater understanding of the inefficiencies in these systems and, hopefully, insight into how to improve them. This work was supported by the HydroGEN Advanced Water Splitting Materials consortium, which is supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office, under contract number DE-AC02-05CH11231.
Understanding of Ionic Structure Change Under Hydration Levels by Using CSAFM
Authors: Kwon Osung , Park Jaehyung
Published: February 2024

Proton exchange membranes (PEMs) are a key component of proton exchange membrane fuel cells. They work as gas separator, insulator, and proton conductor. Thus, characterization of the membrane is a crucial process for developing PEM. However, this work is not easy because its complicated phase separated morphological structure and widely varying ionic structure under hydration. Current sensing atomic force microscopy (CSAFM) measures nano current flow between a tip and the sample surface and can map the nano current flow distribution of scanned area. In this study, the ionic structure of Nafion under different hydration condition is studied by using CSAFM. Specifically, the area variation of ionic domain on the membrane surface under different relative humidity is characterized by quantitative method based on CSAFM measurement. The study is done by several steps. First, the Nafion 212 is scanned in the environmental chamber by varying 15% to 65% relative humidity. In this process, the current distribution and the morphology are simultaneously mapped at each RH. Second, the local net charge value of protons, which is connected with area of ionic domain on the membrane surface, are calculated based on current distribution. In this process, the area of ionic domain on the membrane surface under different RH is estimated. The study shows several remarkable results. First of all, the non-uniform ionic domain increasing is observed from sequentially mapped current distribution on the surface under different RH. Second, the reliable estimation method of ionic domain variation is introduced by this study.
Electrospun High Performance Polymer Reinforced Membranes for Exceptional Durability Fuel Cell Membrane Electrode Assemblies
Authors: Zaton Marta , Donzel Nicolas , Cavaliere Sara , Rozière Jacques , Jones Deborah J. , Nesling Emily , Bobolecki Josef , Buche Silvain
Published: February 2024

Adequate material selection is one of the most important aspects in component design. Therefore, high-performance polymers have garnered significant interest for Proton Exchange Membrane Fuel Cell (PEMFC) and Water Electrolysis (WE) applications due to their exceptional mechanical, thermal, and chemical properties. This 'beginning by design' strategy requires a deep knowledge of environmental stressors and degradation mechanisms and focuses on proposing next-generation advanced materials able to withstand defined stress conditions for lightweight and heavy-duty transport applications. This presentation presents recent advances and challenges encountered in the preparation of high-performance polymer-reinforced membranes and highlights their specific properties resulting in exceptional durability of nearly 120,000 cycles when tested under combined Open Circuit Voltage (OCV) with Relative Humidity (RH) cycling.

This work was supported by the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 101006641 IMMORTAL. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme, Hydrogen Europe and Hydrogen Europe Research.
Insight into the Chemical Stability of N-Heterocyclic Ammonium Groups for Anion-Exchange Polyelectrolytes
Authors: Jin Yiqi , Chen Nanjun , Li Hui , Liu Haijun , Fan Jiantao
Published: February 2024

The chemical stability of cationic groups, not only related to alkaline degradation but also to electrochemical degradation at high potentials, is the key factor that limits the durability of anion exchange membranes (AEMs) and anion exchange ionomers (AEIs) [1]. In recent years, quaternary ammonium (QA) groups represented by N-heterocyclic ammonium (NHA) groups display excellent ionic conductivity and superior alkaline stability, which makes NHA groups promising candidates to be applied in AEMs and AEIs [2]. However, electrochemical degradation of NHA groups has been neglected in previous research, even though the electrochemical oxidation of phenyl QAs was found in the ionomer at the oxygen evolution potentials [3]. In short, the mechanism by which effect of substituents affects the durability of NHAs cations, including alkaline stability and electrochemical stability, is unclear yet, and NHA groups must be attached to the polymer backbones by substituents to achieve their applications.

In this work, the chemical stability of NHA is comprehensively studied. To investigate the relationship between alkaline durability and structure, we report a systematic study on the alkaline stability of 24 representative NHA groups at different hydration numbers (λ). The electronic effect of substituents on NHA groups and degradation mechanisms of NHA groups are systematically investigated by 1H nuclear magnetic resonance (1H NMR) and density functional theory (DFT) calculations, showing that the NHA groups with electron-donating substituents exhibit outstanding alkaline stability and linking NHA groups with the polymer backbone via γ-position could be a rational design for highly alkaline stable AEMs and AEIs. Furthermore, a constant voltage is applied to the QAs electrolyte solution to measure the electrochemical stability by simulating the real operating environment of and AEM water electrolyzers. Compared to structural changes before and after voltage application, NHA exhibits worse stability than alkyl QAs, involving the radical degradation and electrochemical degradation. These results above give us a clearer picture while designing the polymer used for electrochemical devices, which is that a careful balance needs to be established between alkaline and electrochemical durability, especially under the high potential and harsh alkaline environment.

References

[1] D. Li et al., “Durability of Anion Exchange Membrane Water Electrolyzers,” Energy Environ. Sci., vol. 14, no. 6, pp. 3393-3419, Jan. 2021.

[2] M. G. Marino et al., “Alkaline Stability of Quaternary Ammonium Cations for Alkaline Fuel Cell Membranes and Ionic Liquids,” ChemSusChem, vol. 8, no. 3, pp. 513-523, Feb. 2015.

[3] D. Li et al., “Phenyl Oxidation Impacts the Durability of Alkaline Membrane Water Electrolyzer,” ACS Appl. Mater. Interfaces, vol. 11, no. 10, pp. 9696-9701, Feb. 2019.

Figure 1
Exploring Proton Activity at the Membrane/Electrode Interface with Microelectrodes
Authors: Anderson Grace C. , Rajupet Siddharth , Petrovick John G. , Kushner Douglas I. , Bell Alexis T. , Weber Adam Z.
Published: February 2024

Polymer electrolyte membrane (PEM) technology is a key component in low-temperature, high efficiency fuel cells and electrolyzers. Hydrogen fuel cells convert chemical energy from hydrogen into electrical energy, while water electrolyzers do the opposite, using electrical energy to generate hydrogen and oxygen from water. Polymer electrolyte membrane fuel cells (PEMFCs) and water electrolyzers (PEMWEs) are attractive technologies for clean and efficient energy conversion, with wide-ranging applications, including transportation, stationary power generation, and energy storage. These technologies have significant potential to reduce greenhouse gas emissions and dependence on fossil fuels, making them a crucial component of the transition towards a low-carbon economy. The most commonly used PEMs are perfluorinated sulfonic-acid (PFSA) membranes, and they have been extensively studied. However, the proton activity at the membrane-electrode interface under solid-state operating conditions is very challenging to measure and remains unclear. The interfacial proton activity plays a critical role in the kinetic performance, therefore understanding how different polymer properties and operating conditions impact the proton activity will give new insights to improve performance. The proton activity is calculated for equilibrium and reaction conditions through ocv measurements and kinetic fitting to HOR/HER measurements in a three-electrode microelectrode system. Additionally, investigating the impacts of water activity, proton concentration, and equivalent weight offers new insights into the properties and behavior of the local environment.
Nanostructured Fe-N-C Electrocatalysts with CeO2 Additives for PEM Fuel Cells
Authors: Kırlıoğlu Ahmet Can , Buldu-Akturk Merve , Rahbarshendi Faezeh , Yurum Alp , Alkan Gursel Selmiye , Yarar Kaplan Begum
Published: February 2024

The development of cost-effective electrocatalysts for polymer electrolyte membrane fuel cells (PEM fuel cells) is essential for the widespread use of this technology. The high cost and limited availability of Pt-group metals (PGMs) used as catalyst materials are the main barriers to the widespread commercialization and development of PEM fuel cells. [1] Therefore, the use of high surface area and effective catalysts without Pt have gained great importance in PEM fuel cells. This study introduces high surface area electrocatalysts that are free of platinum group metals (non-PGM) consisting of iron-nitrogen-carbon (Fe-N-C). Here, the uniform distribution of Fe was achieved using graphene oxide (GO) nanoparticles to enhance the catalyst's performance for oxygen reduction reaction (ORR). [2] Furthermore, the addition of a small amount of cerium oxide (CeO2) nanoparticles to the catalyst layer helps to prevent the degradation of the catalyst and ionomer by preventing H2O2 formation as well as increasing the ORR activity due to high oxygen storage capacity. [3] Initially, GO is synthesized by improved Hummer’s method. The GO nanoparticles are obtained through a process involving ball-milling and acid treatment. These nanoparticles are then thermally reduced and nitrogen-doped to form nitrogen-doped reduced graphene oxide nanoparticles. Fe-N-C complexes are synthesized by reacting these nanoparticles with FeCl2 precursor, which are then hydrothermally treated to introduce CeO2 additives. The resulting catalysts are analyzed using various techniques (FT-IR, XPS, SEM, TEM, EDX) and display excellent electrochemical performance. The ORR activity of the Fe-N-C catalysts was investigated and compared with the electrocatalysts prepared with larger graphene oxide particles. A similar comparison is also made with and without CeO2 additives.

The authors gratefully acknowledge the financial support of The Scientific and Technological Research Council of Turkey (TÜBİTAK) (Grant Number: 122M429)

References

[1] He, C., Desai, S., Brown, G., & Bolleplli, S. (2005). PEM fuel cell catalysts: Cost, performance, and durability. The electrochemical society Interface, 14(3), 41.

[2] Weiss, J., Zhang, H., & Zelenay, P. (2020). Recent progress in the durability of Fe-NC oxygen reduction electrocatalysts for polymer electrolyte fuel cells. Journal of Electroanalytical Chemistry, 875, 114696.

[3] Taşdemir, A., Iskandarani, B., Yürüm, A., Gürsel, S. A., & Kaplan, B. Y. (2021). CeO2 nanorod decorated NrGO additives for boosting PEMFC performance. International Journal of Hydrogen Energy, 46(63), 32250-32260.