Low Temperature Polymer Electrolyte Research Articles

Thermal stability and microstructure of fluorine-free hydrophobic coatings of gas diffusion layers for fuel cell applications

Polytetrafluoroethylene (PTFE) is used as commercial hydrophobic treatment for gas diffusion layers (GDL) in polymer electrolyte fuel cells. This commercial hydrophobic treatment can reduce the electrical conductivity of GDLs and is facing an uncertain future due to the pending restriction of perfluoroalkyl substances (PFAS). Previously, we proposed surfactant doped polyaniline (PANI) coatings as a fluorine-free alternative hydrophobic treatment. Due to their anti-corrosion properties as well as the electrical conductivity, these coatings offer additional benefits for the GDL compared to PTFE. Prior work demonstrated improved maximum power of a low temperature polymer electrolyte fuel cell (LT-PEFC) using the PANI coated GDL compared to the commercial PTFE treated reference. Based on these findings, additional investigations are needed to optimize the coating and assess possible areas of applications. With this study, we propose the use of the coating in high temperature PEFCs due to its thermal stability determined via thermogravimetric analysis of polyaniline doped with different types of surfactants. A main focus of this work is the investigation of the uniformity and overall porosity of the polyaniline coatings on GDLs via µCT supported by deep learning. This analysis is complemented with fluid dynamics simulations to determine the tortuosity and the gas flow through the GDL. In the future, this approach could enable the optimization of the fluorine-free hydrophobic coatings in combination with the different layers of the membrane electrode assembly (MEA) such as the GDL and the catalyst layer to prevent mass transport limitations.

Prototype Demonstration of Innovative and Sustainable Recycling of Materials in Polymer Electrolyte Membrane Fuel Cells and Electrolyzers

Low-temperature (LT) polymer electrolyte membrane (PEM) fuel cells (FCs) and electrolysis cells (ECs) contain valuable materials such as platinum-group metals (PGMs) and perfluorosulphonic acid (PFSA) polymer. The Danish companies IRD Fuel Cells A/S and CriMaRec ApS together with the University of Southern Denmark are developing and scaling up efficient and environmentally friendly processes to recycle PGMs, mainly platinum (Pt) and iridium (Ir), with the aim of establishing production alternatives to the costly, energy-intensive, and pollutive conventional processes. The approach is based on patented electrochemical methods involving potential cycling [1,2]. The efforts also comprise recycling or reuse of PFSA polymer as an alternative to incineration. The established outcomes are excellently performing LT-PEMFC&EC membrane–electrode assemblies (MEAs) containing PFSA material recovered from spent MEAs and PGMs recycled from MEAs [3,4] as well as from existing scrap resources such as spent catalysts from exhaust systems of automobiles [5].In this presentation we shall provide the main results proving our PGM-recycling concepts for Pt and Ir catalysts. Pt and Ir compounds (such as (NH4)2[PtCl6], Pt(NO3)2, and IrCl3) obtained from the processing of spent MEAs and spent autocatalysts were found to have the same qualities as those of commercial equivalents, and new electrocatalyst products (Pt/C and IrO x nanoparticles) made from these recycling compounds show properties and performances that are similar to or better than those produced from fresh precursors. Our development of the PGM-recovery processes into pilot-scale production is also presented. Two reactors with volumes of 18 dm3 and 50 dm3, respectively, have been designed, constructed, and optimized for extraction of PGMs from autocatalyst material and MEAs, respectively. In preliminary runs validating the recovery processes in these prototype reactors, 7.3 g of PGM (mainly Pt and palladium (Pd)) were recovered from a 4.5-kg batch of autocatalyst material with an estimated efficiency of 91 %, while 15.4 g of PGM (Pt and ruthenium (Ru)) were recovered from a 0.7-kg batch of LT-PEMFC MEAs with an efficiency of around 93 %. The reactor processes involve low energy consumption, low emissions, and a cycle time less than 2 h – in very great contrast to the conventional recovery processes – and the associated costs are in the order of 10 % of the PGM market price. Furthermore, we present our optimization of the recovery and regeneration of PFSA from the membranes of spent MEAs and the successful reapplication of this material as ionomer in new LT-PEMFC&EC MEAs. The feasibility of the PFSA recycling has been demonstrated as the performances of these new MEAs are similar to or better than those of MEAs prepared using fresh commercial ionomer. On top of these results, we present strong performances of LT-PEMFC&EC MEAs with recycled Pt/C cathode and IrO x anode electrocatalysts, respectively.The perspectives of this work are that a highly competitive large-scale production of LT-PEMFC&EC MEAs containing recycled PGM and PFSA will allow the MEA manufacturer to offer its customers the cost-reducing possibility of returning the spent MEAs for recycling. It can also ensure adequate reuse and/or recycling of production process waste, thus reducing the amount of scrap material. Moreover, it will facilitate the flow of secondary (recycled) PGMs from declining industrial sectors into the hydrogen-energy sector, securing for the latter the supply of these critical raw materials and decreasing the dependence on primary (mined) PGM. The green transition from fossil-fuel-based energy to renewable energy is thus accelerated, with the cost of the PEMFC&EC technology being considerably reduced and its deployment accordingly promoted. Acknowledgement The work is supported by the Energy Technology Development and Demonstration Programme (EUDP) of the Danish Energy Agency through the project 64019-0551 3R – Recycle, Reuse, Reduce.

Development of Co-, Fe- and N-Doped Mesoporous Carbon Catalysts for Anion-Exchange Membrane Fuel Cell Cathode

Hydrogen has a lot of promise to be utilized in sustainable transportation and energy production using low-temperature polymer electrolyte membrane fuel cells. While proton-exchange membrane fuel cells are already commercialized, they still have issues with needed substantial amount of platinum as electrocatalyst. By switching to alkaline electrolyte, cheaper and more sustainable electrocatalysts can be used for cathodic oxygen reduction reaction (ORR). For instance, transition metal and nitrogen doped nanocarbons (M-N-C, M = Fe, Co, Mn, etc.) have shown very good ORR activity in alkaline media. Anion-exchange membrane fuel cell (AEMFC) technology, however, is still in research phase, and any further developments in electrocatalysts is necessary.1-3 Herein the focus is on developing mesoporous M-N-C electrocatalysts for the ORR and studying the effect of carbon support porous structure on the AEMFC performance. Mesoporous carbons (MCs) are prepared by combining phloroglucinol with glyoxal/glyoxylic acid. In the first part, soft-templating approach by Pluronic F127 is taken,4 in the second part of the work, effect of additional hard template (MgO) is investigated through dual-templating. We have limited the amount of harsh and environmentally unfriendly chemicals, offering more sustainable approaches beyond the silica-templating for synthesizing mesoporous carbons. The prepared MCs have high specific surface area (up to 900 m2 g-1) and have high content of mesopores in 5-8 nm range. To further study the effect of porous structure of carbon support on the AEMFC performance, nanocarbon composites with MC (prepared in first part) and either highly microporous carbide-derived carbon (CDC) or carbon nanotubes (CNTs) are also prepared (Figure 1a).Our previous works have shown that bimetallic materials, containing iron and cobalt, perform the best in AEMFC.5-6 Thus herein, all prepared nanocarbon supports are doped with nitrogen (1,10-phenanthroline as source), cobalt and iron (Co- and Fe-acetate) via high-temperature pyrolysis, which yields electrocatalyst with atomically dispersed metal centers (Figure 1b). Rotating disc electrode (RDE) method is employed for preliminary ORR-activity testing with the prepared CoFe-N-C materials showing high electrocatalytic activity in 0.1 M KOH (E 1/2 up to 0.84 V vs RHE) and good stability after 10,000 potential cycles. In the first part, using nanocarbon composites with varying porous structure yielded electrocatalysts with almost identical performance in the RDE test. However, the effect of porous structure came evident during AEMFC testing, wherein presence of more mesoporous structure was beneficial.4 In the second part using dual-templating approach, the most optimal ratio of two templates (F127 and MgO) was found, together with promising AEMFC performance.In conclusion, we have employed three different mesoporous carbon synthesis routes (soft- or dual-templating), optimized the conditions, and after doping obtained highly active ORR electrocatalysts with great promise for the AEMFC application.

Humidification-Thermal Cycling-Based Mechanical Degradation Analysis of Low-Temperature PEMFC Using a Full-Scale Transient Physics-Based Model

Low-Temperature Polymer electrolyte membrane fuel cells (LT-PEMFCs) have garnered huge attention as green energy technology due to low environmental impact and high efficiency. However, the long-term durability of these systems remains a critical concern, particularly regarding mechanical degradation of the proton exchange membrane. It is one of the most critical PEMFC components, facilitating ionic conduction and restricting the reactant gas cross-over. An examination of aged membranes through ex-situ analysis has uncovered various degradation features, including the emergence of crazes, cracks, pinholes, membrane thinning, and elongation1. Partly these defects appear due to cyclic stress arising from the repetitive expansion/compression of the membrane under water absorption/desorption2,3. Consequently, these defects reduce the open circuit voltage and increase the ohmic loss in the cell4. The crossover of reactants beyond a certain limit can instigate the formation of localized hotspots, further accelerating membrane degradation and eventually catastrophic failure of the cell. Multiple investigations have highlighted the influence of clamping force and humidity-temperature cycling on LT-PEMFC performance5,6. Nevertheless, most of these studies have primarily focused on structural mechanics, overlooking other critical aspects such as electrochemical reactions, fluid flow, heat transfer, and species transport. This type of decoupled approach does not provide real-time stress evolution inside the membrane with the cell operation. Moreover, existing models are often either two-dimensional or simplified single-channel 3D representations, with simplifications like isothermal operation, simplified reaction kinetics and more5,7,8. These models lack spatiotemporal resolution of the membrane deformation or stress distribution under diverse operating conditions.In this study, we present a comprehensive analysis of mechanical degradation in the LT-PEMFC membranes through the implementation of a transient physics-based model. The research focuses on understanding the intricate interplay between mechanical stress, environmental factors, and the resulting degradation mechanisms within the membrane. A transient model is developed using COMSOL Multiphysics to simulate the mechanical behaviour of the membrane under various operational conditions and stress scenarios encountered during the fuel cell's lifespan. It is a full-scale Multiphysics model that comprises charge transfer, species transport, porous media flow, electrochemical reactions, heat generation, ionomer water transport, liquid water transport, and solid mechanics. The model accuracy is confirmed with the lab experiment on 32 cm2 cell with multi-serpentine channels at 80% RH & 75 °C. This model incorporates factors such as humidity, temperature variations, and clamping pressure. By analyzing stress accumulation and its effects on the Nafion membrane, we aim to identify critical locations that lead to mechanical degradation and permanent deformation. Furthermore, the transient response of the cell parameters like liquid water dynamics, stress accumulation and membrane water content dynamics are studied under the urban dynamometer driving schedule (UDDS), which has not been reported earlier. Preliminary results of the liquid water dynamics in Figure 1 (a) suggest that the liquid water accumulates during the higher current density operations between 1500 and 1800 seconds. Also, the liquid water saturation is unable to reach its initial state of 0.12 during a sudden change in the power demand that leads to the cumulative accumulation of liquid water inside diffusion media. Though It improves the water content and ionic conductivity of the membrane, it increases the chance of cell flooding and stress accumulation due to membrane swelling. Figure 1 (b) shows the cell deformation under the clamping pressure of 1 and 2 MPa, reducing the species transport inside the diffusion media. The outcomes of this study aim to provide deeper insights into the stress accumulation and permanent deformation mechanisms affecting membrane degradation. Understanding these degradation pathways is crucial for the development of improved materials and design strategies that enhance the durability and long-term performance of PEMFCs, ultimately contributing to the advancement and widespread adoption of clean energy technologies.

Durability Investigation of Low Pt-Loaded PEM Fuel Cells with Different Catalyst Layer Morphologies

Low-temperature Polymer Electrolyte Membrane Fuel Cells (PEMFCs) emerge as the most promising fuel cell technology for transportation. Despite the growing interest in fuel cell electric vehicles (FCEVs) motivated by their rapid refueling, high power density, and long-range, their commercialization lags behind that of battery electric vehicles (BEVs) and internal combustion engine vehicles (ICVs). Apart from the lack of hydrogen infrastructure, other primary bottleneck lies in the cost-intensive production of essential components, particularly the dependence on noble metals such as platinum (Pt) to achieve high catalytic activity in the catalyst layer (CL). Simultaneously, meeting durability requirements for long-term performance and stability proposes another challenge. Therefore, enhancing the durability of PEM fuel cell systems without compromising performance and cost presents a significant challenge which stems from the trade-off relationships among these factors. The current target set by the U.S. Department of Energy (DOE) is achieving a durability of 8,000 hours of operation time, meaning 15,000 miles of driving, with less than 10% performance degradation using a 0.1 mg/cm2 Pt-loaded catalyst.The CL is a complex, heterogeneous structure composed of multiple components with different functionalities, and the electrochemical reaction takes place at the interfaces of the components. Several requirements are essential for the CL, including the presence of highly-dispersed Pt sites with high catalytic activity, a continuous path for efficient proton transport and electron conduction, and a through-connected pore network facilitating gas transport and water removal. Extensive research has been directed toward reducing Pt loading in the CL , motivated by the high cost and limited availability of Pt. At low Pt-loadings, researchers detailed the increased oxygen transport resistance within the CL, which is attributed to the reduction of active sites, as well as the heightened flux of reactants near each active site [1]. Therefore, optimizing the CL, both in terms of mass transport and reaction rate, as well as meeting economic and technical requirements, poses a significant challenge. While the impact of CL compositions on the cell performance is studied previously [2][3], systematic investigations are necessary to reveal the effect of CL characteristics on the electrode degradation. The understanding of performance losses during degradation processes is necessary for optimizing the CL for long-term operation and reducing Pt-loading in the cathode without compromising cell durability.This work aims on tailoring the impact of CL characteristics on electrode degradation for low Pt-loaded cells. To achieve this, five different samples with distinct CL features including Pt-loading, CL thickness, Pt/C ratio, and dilution ratio are fabricated. The samples are fabricated using the catalyst-coated membrane approach to suppress interfacial resistances between the membrane and the ionomer in the CL. In addition, a novel ultrasonic deposition method is employed to develop uniform and ultra-thin CLs enabling precise control of the CL thickness. With the use of an accelerated stress test (AST) ranging within 0.6-1 V in an air/H2 environment, the performance loss of the samples at the beginning-of-life (BOL), end-of-life (EOL) and at different stages during the applied AST is investigated. This experimental study serves as a foundational exploration into comprehending the individual impacts of CL compositions on electrode degradation and establishes the framework for the design of durable low Pt-loaded PEM fuel cells.

Intrinsically Microporous Ion-Pair Membranes for HT-PEMFCs

Fuel cells are electrochemical devices with high energy efficiency expected to be applied economically and eco-friendly across various energy sectors. Low-temperature polymer electrolyte membrane fuel cells (LT-PEMFCs) using Nafion operates at a relatively low operating temperature (60-80°C) and fully hydration condition. HT-PEMFC is operable at high temperatures (140-180°C), but requires anhydrous conditions to avoid loss of doped phosphoric acid (PA). In this presentation, polymer membranes designed through with intrinsic microporosity were synthesized through super acid polycondensation. We demonstrated that high proton conductivity (106.33 mS cm-1 at 180℃) is obtained by forming phosphoric acid filled ion-channels within the interconnected microporous structure. Moreover, ion-pair coordinated PIMs are fabricated by methylation of PIMs to improve PA retention even under humidified conditions. It is suggested that the water tolerance of ion-pair coordinated PIMs is improved and can be operated under various conditions regardless of humidification and operating temperature and exceptional membrane electrode assembly performance and durability achieved even under humidified reformate gas conditions.

A Scalable and Robust Water Management Strategy for PEMFCs: Operando Electrothermal Mapping and Neutron Imaging Study.

Effective water management is crucial for the optimal operation of low-temperature polymer electrolyte membrane fuel cells (PEMFCs). Excessive liquid water production can cause flooding in the gas diffusion electrodes and flow channels, limiting mass transfer and reducing PEMFC performance. To tackle this issue, a nature-inspired chemical engineering (NICE) approach has been adopted that takes cues from the integument structure of desert-dwelling lizards for passive water transport. By incorporating engraved, capillary microchannels into conventional flow fields, PEMFC performance improves significantly, including a 15% increase in maximum power density for a 25 cm2 cell and 13% for a 100 cm2 cell. Electro-thermal maps of the lizard-inspired flow field demonstrate a more uniform spatial distribution of current density and temperature than the conventional design. Neutron radiography provides evidence that capillary microchannels in the lizard-inspired flow field facilitate the efficient transport and removal of generated liquid water, thereby preventing blockages in the reactant channels. These findings present a universally applicable and highly efficient water management strategy for PEMFCs, with the potential for widespread practical implementation for other electrochemical devices.

In-situ formation of quasi-solid polymer electrolyte for wide-temperature applicable Li-metal batteries

As next-generation rechargeable batteries, the development of solid-state lithium-metal batteries (LMBs) in a multitude of applications is confronted with a trade-off between high energy density, safety, and wide-temperature tolerance. Especially in cold climates, their applications are challenged by insufficient dynamics in bulk electrolyte and at electrode/electrolyte interface. Herein, a flexible, highly ionic conductive, and low-temperature applicable quasi-solid polymer electrolyte (QSPE) is designed and fabricated, which achieves a stable Li-metal anode over a wide-temperature range (−20 ∼ 60 °C). The QSPEs prepared via in-situ polymerization of polyethylene glycol (PEO)-based monomers in low-melting solvent (1,3-dioxolane (DOL) or ethyl difluoroacetate (EDFA)) endow low-temperature tolerance, prominent ionic conductivity (4.5 × 10−4 S cm−1 at −20 °C) and exceptional electrochemical performance over a wide-temperature range. Consequently, with the DOL-based QSPE (D-QSPE), the Li/D-QSPE/LiFePO4 cell presents stable, long-term cycling at −20 °C (minimal capacity degradation over 550 cycles) and excellent fast-charging capacity (capacity retention of 81 % over 1300 cycles at 5 C). Even utilizing a thin lithium foil (25 μm) and a high mass loading LiFePO4 cathode (2.5 mAh cm−2), the assembled Li/LFP cell with a N/P ratio of 1.96 still exhibits good cycling performance at −20 °C. Additionally, the EDFA-based QSPE (E-QSPE) allows LMBs with NCM811 cathodes cycling over 140 cycles (capacity retention > 95 %) at −20 °C. With the capability of circumventing sluggish ion transport kinetics of quasi-solid polymer LMBs in cold climates, the developed polymer electrolyte provides new pathways for safe, high-capability, and wide-temperature operable batteries.

Design of bio-based adhesives for fuel cell applications

ABSTRACT Fuel cells contribute to decentralized and individually controllable energy supply. The low-temperature polymer electrolyte membrane fuel cell is ideal for both stationary and mobile use due to its low operating temperatures and superiority in discontinuous operation. Thermoplastics can be used as materials for bipolar halfplates, which have the advantage of low-cost manufacturing processes, as the components do not require cost-intensive post-processing due to their excellent corrosion resistance and electrical contacting. But the environmental conditions in operation pose a great challenge to the materials to be used: permanent humidity and sulphuric acid environment at 85°C, high required electrical conductivity and hydrogen impermeability. In order to demonstrate the potential of bio-based materials, adhesives for both sealing and conductive bonding of all joints within a fully bonded fuel cell are being developed and tested in an ongoing project. The epoxy resin systems developed can be both, one and two-component, and have different proportions of sustainable carbon. In addition, the fuel cell components, also consist of sustainable raw materials, so that bonding surfaces also pose a challenge. Results on the lap shear strength of the developed adhesives as well as on the durability of the adhesives under fuel cell environment are presented. Initial functional tests on bipolar plates bonded with proportionally bio-based raw materials show a functionality comparable to that of petroleum-based raw materials for epoxy adhesives.

A Novel Machine Concept for the Continuous Manufacturing of 7-layer Membrane Electrode Assemblies for PEM Fuel Cells

The main cost driver for the low temperature polymer electrolyte membrane fuel cell (LT-PEMFC) is the 7-layer membrane electrode assembly (MEA) consisting of one catalyst coated membrane (CCM), two subgaskets and two gas diffusion layers (GDL). To fulfil the auxiliary functions such as gas crossover prevention and electrical insulation, the subgasket area is also referred to as the non-active area, which doesn’t contribute to electricity generation. To avoid scraps of cost-intensive materials, the size of the CCM and GDL is often designed only slightly larger than the active area, corresponding to the central cut-outs of the subgasket. Over the last decade, numerous patents have been filed to contribute to the machine and process design to automatically manufacture the 7-layer MEA, which can be broadly divided into pick-and-place based sheet-to-roll processes and traditional roll-to-roll processes, however, with material waste. Pick-and-place operations for fragile and limp MEA components that require damage-free handling are challenging. Hence, a roll-to-roll process for the MEA assembly is still desired given the upcoming manufacturing scale-up. In this work, a novel machine concept based on a cut-and-place principle was proposed and developed, which combines the advantages of efficient material utilization from single-sheet handling and high productivity through adaptive roll-to-roll processing. The design focused on a multifunction-integrated handling system that couples the final manufacturing step with the assembly process to avoid changing the order state of the limp materials during transport and buffer storage. A complete process workflow focusing on the speed synchronization between machine components is also illustrated. Application scenarios and the system limitations of the developed machine concept are also discussed.

In-Situ Analysis of Electrodes Using Fine-Tuned Poly(Terphenyl Piperidinium) Ionomers in Anion Exchange Membrane Fuel Cells

In the field of low temperature polymer electrolyte fuel cells, anion exchange membrane fuel cells (AEMFCs) have been considered a promising alternative by circumventing the obstacles to commercialization faced by the established PEMFC technology. The application of platinum group metal-free catalysts for the oxygen reduction reaction, the potential to utilize cheaper and more sustainable polymers than the industry benchmark Nafion®, and the generally less corrosive alkaline operation conditions, have all been identified as inherent advantages of the AEMFC technology, potentially enabling more cost-effective and environmental-friendly mass production of AEMFC system.The first major challenge in developing AEMFC systems was the lack of stable and conductive anion exchange polymers to be used as membrane and ionomer materials. This challenge was at least partly overcome by the successful development of a variety of next-generation polymers. Among those, poly(arylene piperidinium) show great potential through the combination an ether-free aromatic backbone for increased mechanical stability with a piperidinium-based cationic groups displaying excellent resistance to hydroxide attack in highly alkaline environment [1]. Furthermore, the crucial parameters ion exchange capacity (IEC), water uptake and dimensional swelling can be finely controlled via copolymerization and partial substitution of the cationic functional group in the repeating unit [2].In a previous study using a series of poly(terphenyl piperidinium) membranes with different IECs, we established the importance of these three parameters, in particular for the ionomer used in the catalyst layer of the electrode [3]. Furthermore, it was established that water balance of AEMFC systems proved to be one of the greatest challenges in reaching and maintaining high cell performance. The asymmetrical nature of the simultaneous electrochemical production and consumption of water at the anode and cathode, respectively, necessitates fine-tuning the ionomer properties, as well as selecting operational parameters for each electrode individually in order to strike an optimal water balance [4].In this study, we expand on our previous work by analyzing a matrix of electrode combination based on three poly(terphenyl piperidinium)ionomers with different IEC values. Furthermore, we complemented our analysis by evaluating the effects of substituting a fraction of regular dissolvable ionomer with insoluble non-conformal particles of cross-linked poly(terphenyl piperidinium). The beneficial effects of insoluble non-conformal ionomer particles in the catalyst layer has been previously shown by Varcoe and coworkers utilizing radion-grafted anion exchange membranes [5], and by Holdcroft and coworkers utilizing phenylated poly(phenylene) ionomers for PEMFCs [6].Different electrode combinations were evaluated while varying operational parameters such as gas flow rates, gas relative humidities and back pressure. The recording of observed cell performances were complemented by in-situ analysis of in-let/out-let gas relative humidities, H2/O2 electrochemical impedance spectroscopy for kinetic analysis and information on ohmic losses, H2/Ar electrochemical impedance spectroscopy to measure ionic conductivity, cyclic voltammetry to measure electrochemically active surface area as well as ex-situ characterization of the electrodes before/after the test run.The study was carried out with the aim to establish a correlation between the properties of individually tuned ionomers and operational parameters, and to investigate reasons for performance losses due to mass transport limitations, drop in ionomer conductivity, loss of active area, and decreased kinetics caused by phenyl adsorption.Finally, we demonstrate how the application of individually optimized electrodes using fine-tuned poly(terphenyl piperidinium) based ionomers in conjunction with suitable operating conditions will lead to a drastic increase in fuel cell performance compared to symmetrical non-optimized electrodes.A selection of experimental data is shown in Figure 1.[1] J. S. Olsson, T. H. Pham, P. Jannasch, Adv. Funct. Mater. 2017, 28, 1702758.[2] J. S. Olsson, T. H. Pham, P. Jannasch, Tuning poly(arylene piperidinium) anion-exchange membranes by copolymerization, partial quaternization and crosslinking, J. Membrane Sci., 2019, 578, 183-195.[3] T. Novalin, D. Pan, G. Lindbergh, C. Lagergren, P. Jannasch, R.W. Lindström, Electrochemical performance of poly(arylene piperidinium) membranes and ionomers in anion exchange membrane fuel cells, J. Power Sources, 2021, 507, 230287. [4] D. P. Leonard, S. Maurya , E. J. Park , S. Noh , C. Bae , E. D. Baca , C. Fujimoto and Y. S. Kim , J. Mater. Chem. A, 2020, 8 , 14135-14144.[5] L. Q. Wang , J. J. Brink , Y. Liu , A. M. Herring , J. Ponce-Gonzalez , D. K. Whelligan and J. R. Varcoe, Energy Environ. Sci., 2017, 10 , 2154-2167.[6] E. Balogun, S. Cassegrain, P. Mardle, M. Adamski, T. Saatkamp, and S. Holdcroft, ACS Energy Lett. 2022, 7, 2070-2078. Figure 1

(Invited) The More Elements the Better? Studying Structure-Function Relations in High Entropy Alloy Nanoparticles As Fuel Cell Electrocatalysts

Low-temperature polymer electrolyte membrane fuel cells (PEMFCs), which convert chemical energy into electricity, are widely considered a suitable, sustainable technology to replace conventional combustion engines. However, fundamental issues such as fuel cell efficiency and durability still leave room for improvement, which could be achieved by finding more active and stable fuel cell electrocatalysts.[1] High entropy alloys (HEA) – solid solutions of five or more elements - are an emerging material class in the development of novel electrocatalysts. These multi-metallic compounds provide exciting new possibilities for catalyst design.[2] Recent theoretical analyses predict a great potential for HEAs as fuel cell catalysts due to the almost unlimited number of unique surface sites, which enables a wide distribution of adsorption energies. By changing the composition, the distribution of adsorption energies can be tailored toward the optimal binding energies of the catalytic intermediates.[3] The field of high entropy alloy catalysis enables a new, statistical approach to materials design. From an experimental viewpoint, however, HEAs come with new challenges regarding their synthesis and characterization.While HEA nanoparticles are essential for efficient catalysis to provide sufficiently large surfaces, their synthesis is only in its infancy. For a direct comparison between theoretically predicted properties and the performance of the prepared catalysts, single-phase HEA nanoparticles are essential.[4] Through studies of the synthesis pathways and in-depth structural characterization of the HEA nanoparticles with synchrotron X-ray techniques, it is possible to prepare model single-phase HEA nanoparticle catalysts. These well-mixed, multi-metallic materials allow us to study not only the different structure-activity properties of HEA nanoparticle fuel cell catalysts but to also explore the stability of these novel materials under reaction conditions. Studying the dissolution and degradation behaviour of model HEA catalysts in an acidic environment, the mechanisms that underly the degradation of multi-metallic PEMFC catalysts are explored. By relating structural characterization techniques with electrochemical analyses,[5] we can address the question of which role element mixing can play in the activation and stabilization of new fuel cell catalysts.[1] Schroeder, J.; Pittkowski, R. K.; Du, J.; Kirkensgaard, J. J. K.; Arenz, M. J. Electrochem. Soc. 2022, 169, 104504.[2] Löffler, T., Ludwig, A., Rossmeisl, J, Schuhmann, W. Angew. Chem. Int. Ed. 2021, 60, 2-12.[3] Batchelor, T. A. A, Pedersen, J. K., Winther, S.H., Castelli, I.E., Jacobsen, K. W., Rossmeisl, J. Joule 2019, 3, 834-845.[4] Pittkowski, R.; Clausen, C. M.; Chen, Q.; Stoian, D.; van Beek, W.; Bucher, J.; Welten, R. L.; Schlegel, N.; Mathiesen, J. K.; Nielsen, T. M.; Rosenkranz, A. W.; Bojesen, E. D.; Rossmeisl, J.; Jensen, K. M. Ø.; Arenz, M. ChemRxiv, 2022, https://doi.org/10.26434/chemrxiv-2022-khw4t.[5] Schroeder, J.; Pittkowski, R. K.; Martens, I.; Chattot, R.; Drnec, J.; Quinson, J.; Kirkensgaard, J. J. K.; Arenz, M. ACS Catalysis 2022, 12, 2077–2085

Editorial

The editorial of Thermal Engineering of this issue continues the discussion on scientific research needs in vital areas in which thermal engineering has important participation. The main goal is to motivate the readers, within their specialties, to identify possible subjects for their future research. The naval sector dominates global commerce totalizing more than 80% of volumes transported]. Heavy fuel oil and marine gas oil are the most utilized fuels and make up 2 to 3% of the human produced CO2 dumped in the atmosphere. Until the year 2050, the International Maritime Organization (IMO) is committed to a 50% reduction of ship greenhouse gases (GHG) emissions with predicted full elimination by 2100. However, military ships are expected to require ten times more electric power than current navy vessels. As a result, the all-electric military ship initiative depends heavily on scientific research and development of environmentally benign high density power generation systems. In that scenario, fuel cells bring a possible path to problem solution. The low-temperature Polymer Electrolyte Membrane Fuel Cell (PEMFC) is recognized to be the most popular FC. Although PEMFC has been used in transportation (e.g., vehicular, ships), PEMFC general use still brings several concerns, due to some shortcomings (e.g., water management, platinum content, Nafion membrane high cost, free energy demanding H2 availability). In parallel, there has been a demand to develop innovative and environmentally correct technologies for alternative energy sources to replace traditional fossil and nuclear sources, including the naval sector, for quite a while, and this need is current, and the main hurdles to overcome are the generation and storage of renewable energy in a technically and economically viable way. The mission of Thermal Engineering is to document the scientific progress in areas related to thermal engineering (e.g., energy, oil and renewable fuels). We are confident that we will continue to receive articles’ submissions that contribute to the progress of science.

Design of a novel Low-Temperature Polymer electrolyte Membrane fuel Cell: 3D modelling and experimental verification

The termination of fossil fuel usage and the associated environmental pollution poses critical challenges to human society. Fuel Cells (FCs) offer a promising solution due to their high efficiency, leading to reduced consumption of fossil fuels and lower environmental impact. Among various types, Polymer Electrolyte Membrane FCs (PEM-FCs) are particularly advantageous for transportation industries due to their solid membrane, high energy density, fast operation, system stability, efficiency, and minimal pollutant dispersion. The flow channels in PEM-FCs play a crucial role in their performance and efficiency, affecting parameters like cost, weight, and overall performance. Therefore, this research aims to explore the effect of flow channels on PEM-FCs' efficiency and performance using experimental and numerical methods. After analyzing various channel designs, the study suggests utilizing the Symmetric Spiral Channels (SSCs) for further investigation and fabrication. An SSC was fabricated and integrated into a mono-cell, and its performance was studied concerning relative moisture and temperature. Additionally, a 3D model of the FC was designed and validated, enabling the analysis of properties and thermos-physical quantities in different parts of the PEM-FC. The results revealed that while the polarization curve of the SSC may not differ significantly from the simple spiral channel, the FC's overall efficiency improves when considering the output power after accounting for parasitic drop power. This power is consumed for fuel and oxidant pumping. The SSC helps reduce the pressure difference within the PEM-FC, leading to enhanced efficiency. Furthermore, the proposed structure exhibits a temperature difference of less than 10 K, indicating an extended membrane life cycle. These findings highlight the potential benefits of using SSCs in PEM-FCs to enhance their performance and efficiency, contributing to the advancement of cleaner energy solutions for a sustainable future.

Novel Strategy for Engineering Ultra-Thin Proton Exchange Membranes for Advanced PEM Fuel Cells

The energy needs of the modern world currently relies heavily on fossil fuels and energy conversion technologies that emit greenhouse gases (GHGs). These GHGs have been shown to have a detrimental impact on global climate. Climate change has created a vital shift in the way society thinks about energy conversion and storage. Today we are seeing huge increase in the demand for utilization of renewable energy sources (solar, wind, and etc.) as well as in their integration with zero-carbon emission energy conversion and storage devices such as fuel cells, water electrolyzers, and batteries. The renewable energy sources are intermittent by nature since the wind does not always blow and the sun does not always shine. This creates a need for a way to store excess green energy that would otherwise be wasted when the demand does not meet the production. Development of advanced Proton Exchange Membrane (PEM) water electrolyzers and fuel cells that can be integrated with renewable energy sources to convert the excess electricity to hydrogen, is the most efficient approach for sustainable energy storage and utilization. Development of such sustainable energy systems is of primary importance for implementation and widespread application of the green energy technologies in our everyday life and elimination of the GHG emissions. Low temperature Polymer Electrolyte Membrane Fuel Cells (PEMFC) are the most promising type of fuel cells for application in the transportation sector. Currently, the commercialization of these devices is hindered by their high cost and limited durability. Further research is needed to increase their efficiency, power output, catalyst utilization, and durability. Fabrication of thinner proton conductive membranes, is one of the strategies that are of particular research interest. Successful development of thinner PFSA membranes will result in reduction of the ohmic resistance of the MEAs, cost reduction, and will improve their performance. Fabrication of thinner PEM membrane is a challenging task that requires innovative engineering approaches that will allow to fabricate ultra-thin, pinhole free membranes with the desired mechanical stability and hydrogen crossover suppression properties. This work aims on development of novel approaches for engineering ultra-thin PEM membranes with thicknesses below 10µm, and to perform a systematic study of the membrane thickness impact on the MEAs cost, activity, and durability performance. In addition, the effect of various reinforcement materials on the membrane properties have been studied, and their optimal concentrations and position in the volume of the membrane has been investigated. All PEM membranes of interest have been fabricated with a state-of-the-art ultrasonic spray deposition method, designed, and developed at UConn. This methodology allows for precise control of the thickness and composition of the thin membranes, as well as of the thickness, composition, and precious metal loading in the catalysts layers. The newly designed MEAs have been tested at real fuel cell operating conditions, and the results will be presented and discussed in detail at the 243rd ECS meeting in Boston, MA.

Optimizing the Design and Fabrication of Membrane Electrode Assemblies for High Performance CO2 Electrolyzers

The electrode layer is a critical component of low-temperature polymer electrolyte membrane electrochemical devices such as fuel cells and CO2 electrolyzers. The electrode has a major impact on the device’s efficiency, high current density performance and long-term durability. As such, the rational design and fabrication of electrode structures and interfaces with optimal component interactions, ionic and gas phase accessibility, as well as water management properties is crucial for advancing the performance, durability and economic viability of these electrochemical devices.Typically, membrane electrode assemblies are manufactured using fabrication techniques such as roll to roll, electrospinning or ultrasonic spray coating. These methods rely on homogenizing the catalysts, ionomers, solvents, and any other polymeric additives into a colloidal ink and depositing them onto a substrate. At the microscopic level, the combination of electrostatic repulsion and Van der Waals attraction between the individual constituents (solvent, catalyst, polymer) can alter the macroscopic properties (i.e. viscosity, surface tension, rheology) of the colloidal inks. These properties are relevant for coating and MEA manufacturing processes, as the net interparticle interaction potentials determine the tendency of particles to aggregate or disperse which impacts tortuosity, density and porosity of the deposited layer. .As such, optimizing component interactions is crucial for improving particle dispersion, drying behavior and stability of inks to fabricate high performance defect-free electrodes. Its imperative to expand our understanding of structure-property relationship between MEA composition and electrochemical characteristics (i.e. CO selectivity, HFR, mass/charge transport) to fabricate electrodes with high CO2 conversion efficiencies. Elucidating how composition (loading/thickness) morphology (porosity, surface roughness) and architecture (ionomer coverage, additives) of the catalyst layer and in turn its resulting impact on short term and long term performance will determine the commercial viability of CO2 electrolysis systems. This talk will highlight current R&D advancements in understanding of component interactions (i) for integrating high performance materials in electrodes for industrially relevant CO2 reduction applications, ii) improving electrode structure to maximize active site utilization and iii) mitigating mass transport limitations at catalyst-ionomer interface with a focus on understanding decay mechanisms.

Functional and Safety Challenges of Hydrogen Fuel Cell Systems for Application in Electrified Regional Aircraft

This paper identifies potential weaknesses and challenges of hydrogen fuel cell systems as main energy provider for electrified aircraft propulsion and presents potential solutions. The general design, operating principles and main characteristics of hydrogen-fuelled low-temperature polymer electrolyte membrane fuel cell systems (PEMFCSs) are described. The safety assessment process in aviation according to Aerospace Recommended Practices ARP4754A and selected methods according to ARP4761 are introduced. The functions of fuel cell systems in electrified aircraft powertrains are analysed in functional structure trees on aircraft, powertrain and fuel cell system level. By means of a Functional Hazard Analysis (FHA), potential malfunctions and their effects are investigated and their severity is evaluated. Critical failure modes are identified and requirements for acceptable failure probabilities are stipulated. Solution options to mitigate failure effects are stated. The results of the mentioned analyses reveal design challenges associated with the application of fuel cell systems in electrified aircraft propulsion, for instance, concerning functional independence as well as solutions for cold start conditions, heat transfer and lightweight design. Furthermore, safety challenges arise due to the utilisation of cryogenic hydrogen as fuel and the high amount of electric energy.

Power Output Optimisation via Arranging Gas Flow Channels for Low-Temperature Polymer Electrolyte Membrane Fuel Cell (PEMFC) for Hydrogen-Powered Vehicles

As we move away from internal combustion engines to tackle climate change, the importance of hydrogen-powered vehicles and polymer electrolyte membrane fuel cell (PEMFC) technology has dramatically increased. In the present study, we aimed to determine the optimal configuration for the power output of a PEMFC system using computational fluid dynamics (CFD) modelling to analyse variations of the primary serpentine design of gas flow channels. This helps improve efficiency and save on valuable materials used, reducing potential carbon emissions from the production of hydrogen vehicles. Different numbers of serpentine gas channels were represented with various spacing between them, within the defined CFD model, to optimise the gas channel geometry. The results show that the optimum configuration was found to have 11 serpentine channels with a spacing of 3.25 mm. In this optimum configuration, the ratio between the channel width, channel spacing, and serpentine channel length was found to be 1:2.6:38 for PEMFCs. Furthermore, the inclusion of fillets to the bends of the serpentine gas channels was found to have a negative effect on the overall power output of the fuel cell. Moreover, the optimisation procedures with respect to the number of gas channels and the spacing revealed an optimal power density exceeding 0.65 W/cm2.

Review of fuel cell technologies and evaluation of their potential and challenges for electrified propulsion systems in commercial aviation

This paper presents an overview of the most relevant fuel cell types and identifies the most promising options for application in propulsion systems for commercial electrified aviation. The general design, operating principles and main characteristics of polymer electrolyte membrane, alkaline, direct methanol, phosphoric acid, molten carbonate and solid oxide fuel cells are described. Evaluation criteria are derived from aviation-specific requirements for the application of fuel cells in electrified aircraft. Based on these criteria, the presented fuel cell types are evaluated by means of a weighted point rating. The results of this evaluation reveal the high potential for application of solid oxide, low-temperature and high-temperature polymer electrolyte membrane fuel cells. Design challenges of all fuel cell types are being emphasised, for instance, concerning cold start, cooling and supply of pressurised air.

Synergies of fuel cell system thermal management and cryogenic hydrogen exergy utilization

Low-temperature polymer electrolyte fuel cell systems (FCSs) need to reject large amounts of low temperature heat. Often a mobile FCS’s cooling capacity limits the FCS power output. Cryogenic hydrogen is typically utilized as a direct heat sink using heat exchangers (HXs), even though HXs destroy most hydrogen exergy. This paper investigates synergies between FCS thermal management and cryogenic hydrogen exergy utilization in terms of their benchmark performance: the FCS coolant circuit supplies heat at coolant temperature level to a so named reversible cryogenic exergy utilization system (rCEUS) comprised of thermodynamically ideal heat engine processes. The rCEUS converts this heat partly to electrical energy (the value of which equals the hydrogen exergy) and rejects remaining heat to hydrogen to heat it to coolant temperature. The rCEUS output power is used to support the FCS, so the FCS rejects less heat and a significant fraction of this heat is utilized by the rCEUS. As a result, significantly less heat has to be transferred to ambient and the fuel demand decreases. In this paper, three hydrogen storage options are compared: liquid hydrogen, subcooled liquid hydrogen and cryo-compressed hydrogen. Different para- and orthohydrogen compositions are evaluated. For typical FCS operating points, rejected FCS heat to ambient is reducible by 40–67%. FCS power demand is reducible by 14–31%. FCS rejected heat to ambient reduction is 4.5–8 times larger than that of conventional HXs. Calculations are based on hydrogen’s lower heating value.