Membrane Electrode Assembly Fabrication Research Articles

Influence and Improvement of Membrane Electrode Assembly Fabrication Methods for Proton Exchange Membrane Water Electrolysis

Influence and Improvement of Membrane Electrode Assembly Fabrication Methods for Proton Exchange Membrane Water Electrolysis

Recent advances in Pt catalysts and membrane electrode assemblies fabrication for proton exchange membrane fuel cells

Recent advances in Pt catalysts and membrane electrode assemblies fabrication for proton exchange membrane fuel cells

Hot air convection drying characteristics and microstructures of Pt/C catalyst layers in proton exchange membrane fuel cells

Large-scale fabrication of membrane electrode assemblies for proton exchange membrane fuel cells normally uses hot air convection drying of the catalyst layer (CL). The temperature, velocity, and relative humidity of the hot air affect the CL microstructure and, consequently, the power generation rate. This study experimentally investigated the impact of the hot air temperatures (30 °C, 50 °C, 70 °C and 90 °C), velocities (0.5, 1.0, 1.5 and 2 m/s) and relative humidities (5%, 10%, 20% and 30%) on the CL drying characteristics and microstructures. The mass loss was recorded by an electronic balance as the slurry coating dried with the CL microstructure then evaluated using a scanning electron microscope and nitrogen absorption-desorption measurements. The drying was almost completed for all cases within 90 s. A correlation was then developed for the CL hot air convection drying moisture ratio which was best fit by the two-term exponential model. The correlation accurately predicted the data for low relative humidities with average differences within 10%. The hot air temperature, velocity and relative humidity can significantly affect the CL pore size. High temperatures and velocities formed thicker CLs, while high relative humidities led to thinner CLs. These results indicate that the CL microstructure can be regulated by controlling the drying conditions.

3D-ordered catalytic nanoarrays interlocked on anion exchange membranes for water electrolysis

3D-ordered catalytic nanoarrays interlocked on anion exchange membranes for high-performance and long-life water electrolysis.

Automated Production of Catalyst Coated Membranes for PEM Water Electrolysis Using a Direct Ultra-Sonic Spray Coating Approach

The production of green hydrogen through polymer electrolyte water electrolysis (PEMWE) has attracted attention in recent years for its potential to enable the widespread use of green hydrogen [1, 2]. This technology particularly impacts important sectors of today’s society such as the agricultural and mobility sectors. Among the different components of an electrolysis cell, the membrane electrode assembly (MEA) is regarded as the most important component for its operation, since it is where the water-splitting reaction takes place. For this reason, the choice of materials and production approach play a highly important role to optimize its lifetime, performance, and cost [3]. Within this context, the MEA production via ultra-sonic spray coating has been lately gaining relevance due to its potential to yield high-activity electrode layers with a low catalyst loading.Conventionally, electrodes for PEMWE have been fabricated using other catalyst deposition techniques such as the doctor blade, airbrush spray coating or rod coating on a separate substrate, which is then transferred onto the membrane via hot pressing. However, the shortcomings of these approaches which include an additional hot press step were recently reported, particularly due to the complexity associated with electrodes with low catalyst loadings due to their sensitivity towards mechanical stress [1, 4]. On the other hand, effective approaches involving a direct ink deposition onto the membrane using ultra-sonic spray coating have been long reported for fuel cell applications [5, 6].In this work, we take the approach of direct ink deposition via ultra-sonic spray coating to produce iridium based MEAs for PEMWE. Furthermore, the dependency of the MEA electrochemical activity on the process and material choice are studied in an iterative manner. Of particular interest for this study is the material transfer rate from the catalyst ink to the membrane, the reproducibility of the developed spray coating process and the variation of materials used for the MEA fabrication. The spray process was performed with an ultra-sonic spray nozzle attached to an automized 3-axis rig and coupled with a syringe pump. The fabricated MEAs were characterized using a single cell setup with an active area of 4 cm2. The results of the first generation of the fabricated MEAs show that the material ratios in ink composition play an important role in the ink flowability through the piping which carries the ink to the ultra-sonic nozzle. Furthermore, this behavior has a direct and strong influence on the final composition of the catalyst layer, which consequently directly affects the cell performance.

Investigation of optimized spraying process for directly coated electrode in polymer electrolyte membrane fuel cell

Membrane electrode assembly (MEA) is a core component in polymer electrolyte membrane fuel cells (PEMFCs). A well-constructed catalyst layer is essential for achieving high-performance and reliable fuel cells. Among MEA fabrication processes, direct spray coating has advantages regarding cost-efficiency, processability, and controllability compared to direct sputtering and decal transfer method. In the spray process, the morphology of the catalyst layer depends on conditions in which ink droplets are sprayed and evaporated. Although quantitatively optimizing the spray process is crucial, there is still a lack of well-defined research for optimized spray process. Herein, we propose k-value that can indicate uniform coverage, expressed as a ratio of the area where ink droplets spread compared to the sprayed area. The k-1.0 MEA is fabricated under k-value conditions of one by adjusting nozzle moving speed, which is expected to have the most uniform coverage. Compared to k-0.3 MEA and k-3.0 MEA, the power density improves by 22.3 % and 11.1 %, respectively. This is attributed to the reduced ion transport resistance of the catalyst layer being reduced by 23.7 % and 8.5 % and the increased electrochemical active surface area by 16.1 % and 9.4 %, respectively. Furthermore, the morphology of catalyst layers and substrate temperature effect are investigated.

Enhancing durability of automotive fuel cells via selective electrical conductivity induced by tungsten oxide layer coated directly on membrane electrode assembly.

The poor durability, attributed to catalyst corrosion during start-up/shutdown (SU/SD), is a major obstacle to the commercialization of fuel cell electric vehicles (FCEVs). We recently achieved durability enhancement under SU/SD conditions by implementing a metal-insulator transition (MIT) using proton intercalation/deintercalation in WO3. However, such oxide-supported catalysts were unsuitable for direct application to the mass production stage of membrane electrode assembly (MEA) process due to their physical and chemical properties. Here, we report a unique approach that achieves the same durability enhancement in SU/SD situations while being directly applicable to the conventional MEA fabrication process. We coated WO3 on the bipolar plate, gas diffusion layer, and MEA to investigate whether the MIT phenomenon was realized. The WO3-coated MEA demonstrated 94% performance retention during SU/SD, the highest level to our knowledge. It can directly contribute to enhancing the durability of commercial FCEVs and be immediately applied to the MEA mass production process.

(Invited) Overall Research on Electrode Coating Processes (OREO) - the Role of Imaging and Spectroscopy in Scale-up Fabrication of Low Temperature Water Electrolyzers

With the recent trends in hydrogen technologies, scale-up fabrication of membrane electrode assemblies (MEAs) for the electrochemical systems such as fuel cells and electrolyzers is gaining significant attention. Companies and researchers are focusing on diverse large-scale electrode fabrication processes, such as roll-to-roll and screen-printing. However, optimizing such processes is not trivial, and a number of parameters, including but not limited to catalyst type, solvent, ink mixing, electrode coating and drying, play a role in the quality of the final product. Correlations between the fabrication parameters and resulting electrode microstructure, properties and performance are important to understand, in order to better control the processes. Imaging and spectroscopy techniques play an important role in this understanding, starting from catalysts, inks and all the way to the electrodes. Information about catalyst distribution, composition, and surface chemistry can be correlated to ink characteristics, and finally to electrode structure, component distribution and properties, and their effect on MEA performance can be investigated.In this talk, a collaborative work between four institutions, University of Connecticut, Colorado School of Mines, National Renewable Energy Lab and Fraunhofer ISE, within a project on Overall Research on Electrode Coating Processes (OREO), is discussed, with the focus on low temperature water electrolyzers scale-up fabrication and characterization. The talk will especially focus on the role of advanced microcopy and spectroscopy in the characterization of catalyst powders, inks and electrodes.

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.

(Invited) Modeling Two-Phase Transport in the Cathode Catalyst Layer of a PEM Fuel Cell with a Focus on the Ionomer Phase Structure and Its Effect on Oxygen Transport

A hydrophobic treatment was developed to reduce the liquid water saturation level and increase its removal rate from the cathode catalyst layer (CL) of a PEM fuel cell. If this was achieved, the transport rate of oxygen to the reactive sites would be expected to increase and the fuel cell performance would be improved, especially in the high current-density mass-transport controlled region. The performance of the fuel cells with the hydrophobically treated cathode CLs tested with humidified air at 70oC shows significant improvement (> 200% increase in peak power).[1,2] The polarization curves obtained show improvements over the entire curve from the kinetic-controlled region to the mass-transport affected and mass-transport limited regions instead of only the mass-transport limited region as originally expected. A mathematical model was developed to provide insight into the causes for the observed responses with a focus on the oxygen-water two-phase transport phenomena in the catalyst layer. It suggests the hydrophobic treatment affects the CL in two ways. First, the interface of the ionomer layer exposed to the gas pores becomes more hydrophobic and facilitates less coverage and faster water drainage from the CL resulting in better performance at high current densities. Second, it reduces the hydration level in the ionomer phase which results in higher oxygen concentration in the ionomer phase on top and in the catalyst agglomerates leading to higher performance over the whole polarization curve. This presentation will discuss the major features of the new model and the findings obtained in this study.[3] These efforts show that the modeling work is not just a simulation of the experimental results using established theories and equations. It requires researching, finding, and understanding the mechanisms and phenomena that govern the physical processes in the fuel cell and result in the measured fuel cell performance. The modeling work provides insights that could not be gained from fuel cell testing.References Regis P. Dowd Jr., Cynthia S. Day, and Trung Van Nguyen, “Engineering the Ionic Polymer Phase Surface Properties of a PEM Fuel Cell Catalyst Layer,” J. Electrochem. Soc., 164 (14), F138-F146 (2017). 10.1149/2.1081702jesRegis P. Dowd, Yuanchao Li, and Trung Van Nguyen, “Controlling the Ionic Polymer/Gas Interface Property of a PEM Fuel Cell Catalyst Layer During Membrane Electrode Assembly Fabrication,” J. Appl. Electrochem., 50 (10) 993-1006 (2020). 10.1007/s10800-020-01453-wYuanchao Li and Trung Van Nguyen, “A One-Dimensional Model of the Cathode Catalyst Layer of a PEM Fuel cell Hydrophobically Treated for Water Management,” J. Electrochem. Soc., 169 114505 (2022). 10.1149/1945-7111/ac9bdf

(Invited) Innovative Membrane Electrode Assemblies for the Next Generation Proton Exchange Membrane Water Electrolyzers

The Hydrogen Economy (HE) is the economy of the near future and is the only viable alternative to the current fossil fuel-based economy. This future green economy will eliminate the greenhouse gas emissions and stop the imminent global warming and climate change. The HE implementation relies on the development of zero-carbon emission technologies for Hydrogen (H2) production. “Green” hydrogen can be produced at large scale by integration of water electrolyzers (WEs) with renewable energy sources. Currently, the proton exchange membrane water electrolyzers (PEMWEs) are considered to be the most advanced WEs that can be integrated with solar panels and wind turbines to produce large quantities of green H2. The main challenges that the state-of-the-art membrane electrode assemblies (MEAs) for PEMWEs are currently facing are: (i) high cost because of the high platinum group metals (PGM) loadings in their catalysts layers (2-3 mgPGM/cm2 in each electrode), and time consuming and expensive multi-step fabrication processes associated with their manufacturing; (ii) limited durability caused by the instability of the catalysts and the other cell components, and (iii) safety concerns associated with the hydrogen gas crossover and the absence of technologies that can effectively keep it below the safety level of the lower flammability limit (LFL) [1, 2, 3].In this work, we demonstrate the capabilities of a unique methodology for fabrication of advanced catalysts, catalyst layers, and MEAs for PEMWEs, known as Reactive Spray Deposition Technology (RSDT). The RSDT is a flame assisted method [4, 5] that combines the catalysts synthesis and deposition directly on the PEM membrane in one-step, which results in fast and facile fabrication of large scale (up to 1000 cm2) MEAs for application in PEM fuel cells and water electrolyzers [5, 6]. This technology allows precise control of the composition, morphology, and particle size distribution of a wide range of nanoparticles, supported and unsupported on carbon, and ensures fine tuning of the catalysts’ activity and durability. MEAs with geometric areas of 86 cm2 and 680 cm2, both with one order of magnitude lower PGM loading in their catalyst layers in comparison to the state-of-the-art MEAs for PEM water electrolyzers [6,7], are fabricated by the RSDT and evaluated for up to 5000 hours at current density of 1.8 A cm-2, 50 oC, and 400 psi differential hydrogen pressure. Diagnostic tests that include polarization curves, electrochemical impedance spectroscopy, linear sweep voltammetry, and hydrogen crossover measurements are performed periodically in order to evaluate the cell performance change during the long-term durability test. After the test, the MEAs are disassembled and subjected to comprehensive post test analysis. A wide range of techniques, including high-resolution TEM, STEM, EDS, SEM, ICP, XCT, XPS, and digital optical microscopy, have been used to study the degradation mechanisms governing the performance loss in the MEAs during the long-term steady state operation. The results from these tests will be presented and discussed in detail in this talk.References https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_myrdd_fuel_cells.pdf https://www.energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdfKlose, P. Trinke, T. Böhm, B. Bensmann, S. Vierrath, R. Hanke-Rauschenbach, and S. Thiele, J. Electrochem. Soc., 165, F1271–F1277 (2018).Kim, S., Myles, Maric, R., et al. Electrochimica Acta, 177, 190-200 (2015).Yu, H., Baricci, A., Bisello, A., Bonville, L., Maric, R., et al. Electrochimica Acta, 247, 1155-1168 (2017).Mirshekari, G., Ouimet, R., Zeng, Z, Yu, H., Bliznakov, S., Bonville, L., Niedzwiecki, A., Errico, S., Capuano, C., Mani, P., Ayers, K., Maric, R. International Journal for Hydrogen Energy, 46(2), 2021, pp. 1526-1539 (2021).Ayers, K. Current Opinion in Electrochemistry, 18, 9–15 (2019).

Silver-Based Supportless Membrane Electrode Assemblies for Electrochemical CO2 Reduction

CO2 is one of the major contributors to the emission of greenhouse gases boosting climate change. Meanwhile, renewable energy production is fluctuating due to weather conditions, demanding for appropriate storage, e. g. by Power-to-X technology. The first step of these processes, the production of hydrogen via water electrolysis, is typically linked to a second step to obtain hydrocarbons [1]. Meanwhile, electrochemical CO2 reduction (eCO2R) is capable of generating chemical feedstocks by converting excess CO2, simultaneously using renewable energy sources during peak times. A promising pathway of eCO2R focuses on CO, as it can be produced with high selectivity at silver catalysts, concurrently generating hydrogen as the only byproduct [2]. To partly overcome the mass transport limitations resulting from the very limited solubility of CO2 in aqueous electrolytes, gas diffusion electrodes (GDEs) are typically used for eCO2R in a three-chamber setup with anolyte, catholyte and separate gas compartment [3].However, there are still considerable overpotentials in this setup, among others caused by ohmic losses such as the electrolyte resistance. Employing membrane electrode assemblies (MEAs), either both electrodes or one of them can be combined with the membrane to form a full- or half-MEA, respectively, resulting in a significant decrease in cell voltage. Although there have already been studies on the fabrication of MEAs employing silver catalysts for eCO2R [4, 5], they are still very limited in options and mostly based on carbon gas diffusion layers (GDLs).The manufacturing approach applied in this work is based on a catalyst ink recipe for sintered silver GDEs originally developed for chlor-alkali electrolysis by Moussallem et al. [6]. Instead of using Nickel mesh as a substrate, the suspension is spray-coated on a stainless steel plate to enable the required treatment at temperatures above 300 °C. Afterwards, the catalyst layer is hot-pressed on the prepared anion exchange membrane at more moderate temperatures, forming a supportless cathodic half-MEA.Resulting from variations in the manufacturing procedure, different MEAs are electrochemically characterized, examining Faradaic efficiencies as well as cell voltages, also in comparison to measurements performed in three-chamber setup. Addressing challenges in product efficiency and membrane degradation, it is shown that this type of MEA is capable of eCO2R to CO, already reducing the cell potential at elevated current densities by nearly 50 %, see fig. 1.[1] Tom Kober et al. Report: perspectives of power-to-X technologies in Switzerland: supplementary report to the white paper. en. Technical report. 2019. doi: 10.3929/ETHZ-B-000525806.[2] Yoshio Hori et al. “Electrocatalytic process of CO selectivity in electrochemical reduction of CO2 at metal electrodes in aqueous media”. Electrochimica Acta, 39 (11-12), (1994), 1833–1839.[3] Thomas Burdyny and Wilson A. Smith. “CO2 reduction on gas-diffusion electrodes and why catalytic performance must be assessed at commercially-relevant conditions”. Energy & Environmental Science, 12 (5), (2019), 1442–1453. doi: 10.1039/C8EE03134G.[4] Zengcai Liu et al. “CO2 electrolysis to CO and O2 at high selectivity, stability and efficiency using Sustainion membranes”. Journal of The Electrochemical Society, 165 (15), (2018), J3371–J3377. doi: 10.1149/2.0501815jes.[5] Jonghyeok Lee et al. “Electrochemical CO2 reduction using alkaline membrane electrode assembly on various metal electrodes”. Journal of CO2 Utilization, 31 (2019), 244–250. doi: 10.1016/j.jcou.2019.03.022.[6] Imad Moussallem et al. “Development of high-performance silver-based gas-diffusion electrodes for chlor-alkali electrolysis with oxygen depolarized cathodes”. Chemical Engineering and Processing: Process Intensification, 52 (2012), 125–131. doi: 10.1016/j.cep.2011.11.003. Figure 1

A Comparative Study of CCM and CCS Membrane Electrode Assemblies for High-Temperature Proton Exchange Membrane Fuel Cells with a CsH5(PO4)2-Doped Polybenzimidazole Membrane.

Membrane electrode assemblies (MEAs) are critical components in influencing the electrochemical performance of high-temperature proton exchange membrane fuel cells (HT-PEMFCs). MEA manufacturing processes are mainly divided into the catalyst-coated membrane (CCM) and the catalyst-coated substrate (CCS) methods. For conventional HT-PEMFCs based on phosphoric acid-doped polybenzimidazole (PBI) membranes, the wetting surface and extreme swelling of the PA-doped PBI membranes make the CCM method difficult to apply to the fabrication of MEAs. In this study, by taking advantage of the dry surface and low swelling of a CsH5(PO4)2-doped PBI membrane, an MEA fabricated by the CCM method was compared with an MEA made by the CCS method. Under each temperature condition, the peak power density of the CCM-MEA was higher than that of the CCS-MEA. Furthermore, under humidified gas conditions, an enhancement in the peak power densities was observed for both MEAs, which was attributed to the increase in the conductivity of the electrolyte membrane. The CCM-MEA exhibited a peak power density of 647 mW cm-2 at 200 °C, which was ~16% higher than that of the CCS-MEA. Electrochemical impedance spectroscopy results showed that the CCM-MEA had lower ohmic resistance, which implied that it had better contact between the membrane and catalyst layer.

Improving stability of reinforced composite membrane with hydrophilic interlayer coating

Coating a reinforced composite membrane with a hydrophilic Pt layer can substantially improve the durability of polymer membranes used in fuel cell applications. In this study, we investigated the performance and durability of Aquivion/expanded polytetrafluoroethylene (ePTFE)-reinforced composite membranes with varying Pt contents. We introduced a Pt coating onto ePTFE via magnetron sputtering and characterized the Pt layer using scanning electron microscopy and X-ray photoelectron spectroscopy. As the amount of Pt coating increased, the surface of ePTFE became more hydrophilic; thus, the Pt-impregnated composite membrane was better than the bare composite membrane. We evaluated the fuel cell performance through a single-cell test following membrane electrode assembly fabrication, and performed an accelerated degradation test by maintaining the cell at an open circuit voltage at 90 °C and low humidity (30% relative humidity) for 144 h. Compared to the pure composite membrane, the Pt-coated composite membrane showed less degradation and a lower fluorine emission rate. These results indicated that Pt-coated composite membranes are potentially suitable candidates for use in proton exchange membrane fuel cells.

Large–Scale, High-Performance, Durable and Low-Cost Membrane Electrode Assemblies for Proton Exchange Membrane Water Electrolyzers

Proton exchange membrane (PEM) water electrolyzers, designed to produce hydrogen from intermittent renewable energy, will play a key role in future sustainable energy systems.1 However, the widespread commercialization of PEM water electrolyzers is obstructed by their high cost, low durability, and safety concerns related to the hydrogen crossover. Currently, the production cost of green H2 is in the range of $3-8 kg-1. In order to boost the commercialization of this clean energy devices and lower the production cost of green H2, DOE implemented targets of $2 kg-1 by 2025 and $1 kg-1 hydrogen by 2030.2 In addition, the durability of all electrolyzer components has to be improved in order to increase the lifetime of a PEM water electrolyzer stack to the targeted 80,000 hours. These challenging targets inspired the researchers all over the world to work on development of novel catalyst and catalyst layers with decreased platinum group metal (PGM) loadings, invent new cost-effective methods for fabrication of membrane electrode assemblies (MEAs), develop innovative designs for the MEAs capable of decreasing the hydrogen crossover, and improve the corrosion resistance of the cell hardware and the other stack components to enhance their durability.In this work, the unique Reactive Spray Deposition Technology (RSDT) is used to fabricate a high-performance, durable, and low-cost MEAs with geometric area of 680 cm2. These large scale MEAs have one order of magnitude lower PGM loadings in their catalyst layers in comparison to the state-of-the-art (SOA) commercial MEAs. The RSDT is a flame-based method that combines the catalysts synthesis and electrodes deposition in one step and thus substantially reduces the time and cost for MEAs fabrication.3–5 As fabricated large-scale MEAs with 680 cm2 geometric area of their electrodes, have loadings of 0.2 mgPt/cm2 in the cathode and 0.3 mgIr/cm2 in the anode, which are 10 times lower than the loadings in the SOA MEAs. The MEAs of interest have been tested at steady-state conditions that are typical for an industrial hydrogen production system for over 1000 hours. The cell voltage transients, as well as the periodically measured polarization curves during the test, clearly show that as fabricated MEAs have excellent activity and durability performance. Furthermore, the RSDT fabricated MEAs have integrated dual recombination layers that effectively reduce the hydrogen crossover to below 10 % LFL at all measured current densities (from 0.58 to 1.8 A/cm2). In addition, the MEA was subjected to comprehensive post-test analysis to study the degradation mechanisms governing the performance loss during the long-term durability test, and the results obtained will be presented and discussed in this presentation.Reference1. C. Van Pham, D. Escalera-López, K. Mayrhofer, S. Cherevko, and S. Thiele, Adv. Energy Mater., 11 (2021).2. https://www.energy.gov/eere/fuelcells/hydrogen-shot-summit-proceedings-panel-session-1-electrolysis3. H. Yu, N. Danilovic, Y. Wang, W. Willis, A. Poozhikunnath, L. Bonville, C. Capuano, K. Ayers, and R. Maric, Appl. Catal. B Environ., 239, 133–146 (2018).4. G. Mirshekari, R. Ouimet, Z. Zeng, H. Yu, S. Bliznakov, L. Bonville, A. Niedzwiecki, C. Capuano, K. Ayers, and R. Mari, Int. J. Hydrogen Energy, 46, 1526–1539 (2021).5. H. Yu, L. Bonville, J. Jankovic, and R. Maric, Appl. Catal. B Environ., 260, 118194 (2020).

Optimization Strategies for Commercialization of High-Temperature Pemfcs

The increasing requirement for renewable energy places high-temperature proton exchange membrane fuel cells (HT-PEMFCs) on the forefront of “green” energy-generating power devices. Compared to certain PEMFC technologies, HT-PEMFCs possess faster electrode kinetics, high tolerance to fuel poisons and impurities, no humidification requirements, simplified cooling and system design.1 Herein we present optimization strategies of membrane electrode assemblies (MEAs) for HT-PEMFCs, focusing mainly on the (1) component characterization, (2) MEA fabrication, and (3) testing protocols. A selection of gas diffusion electrodes (GDEs) was tested, as well as the presence/absence of a microporous layer (MPL) on the cell performance. The catalyst layer (CL) has been modified in the terms of fabrication methods, catalyst type, platinum (Pt) content, as well as a variety of binders and additives. The PEM optimizations focused on varying and testing: (1) the molecular weight (Mw) of polybenzimidazole (PBI) for membrane casting, (2) PEM thickness, and its (3) acid doping levels (ADL). The MEAs were then fabricated at altering hot-pressing conditions and their performances were compared. The MEA testing focused on activation, humidity levels, high current operations, elevated temperature and pressure operations, as well as long-term stationary and dynamic durability protocol studies. The material fabrication optimizations resulted in higher onset and peak-of-life voltages, as well as longer cell durability. Together with optimized cell testing, we have achieved power densities of more than 0.8 W/cm2, with stationary durability of more than 13,000 hours at 0.3 A/cm2 current density, with the degradation rate of 4 μV/h. Originally the dynamic durability was demonstrated with more than 290 start-stop cycles showing the performance degradation of up to 100 µV/cycle, however, new tests show degradation rates of less than 46 µV/cycle. The performance and durability that we have demonstrated here position HT-PEMFCs as matured technology that can enter the mass market as a commercial and reliable electrochemical power device, to answer the ever-increasing societal energy demands in the age of climate change. Figure 1. Performance of Blue World Technologies MEAs: (A) from different production batches showing small performance scatter, and (B) i-V and power curves at elevated pressures.Reference:1. O. Jensen, D. Aili, H. A. Hjuler, Q. Li, High Temperature Polymer Electrolyte Membrane Fuel Cells - Approaches, Status and Perspective, ISBN 978-3-319-17081-7; DOI 10.1007/978-3-319-17082-4, Springer International Publishing, New York, 2015. Figure 1

Effective and Durable Recombination Layers for Hydrogen Crossover Mitigation in Proton Exchange Membrane Water Electrolyzers

The Hydrogen Economy (HE) is the economy of the near future and is the only viable alternative to the current fossil fuel-based economy. This future green economy will eliminate the greenhouse gas emissions and stop the imminent global warming and climate change. The HE implementation relies on the development of zero-carbon emission technologies for Hydrogen (H2) production. “Green” hydrogen can be produced in large scale by integration of water electrolyzers (WEs) with renewable energy sources. Currently, the proton exchange membrane water electrolyzers (PEMWEs) are considered as the most advanced WEs that can be integrated with solar panels and wind turbines to produce large quantities of green H2. The main challenges that the state-of-the-art membrane electrode assemblies (MEAs) for PEMWEs are currently facing are: (i) high cost because of the high platinum group metals (PGM) loadings in their catalysts layers (2-3 mgPGM/cm2 in each electrode) and time consuming and expensive multi-step fabrication processes associated with their manufacturing; (ii) limited durability caused by the instability of the catalysts and the materials, and (iii) safety concerns associated with the hydrogen gas crossover and the absence of technologies that can effectively mitigate and keep it below the safety level of the lower flammability limit (LFL) [1, 2, 3].In this paper, we demonstrate the capabilities of the reactive spray deposition technology (RSDT) to fabricate MEAs with one order of magnitude lower PGM catalyst loadings in their electrodes, and catalytic recombination layers integrated in the volume of the MEAs that effectively suppress the H2 crossover. The RSDT is a flame assisted method that combines the catalysts synthesis and deposition directly on the PEM membrane in one-step, which results in fast and facile fabrication of large scale MEAs [4, 5, 6]. RSDT-fabricated recombination layers (RLs) demonstrated effective reduction of H2 crossover from 30-50% of the LFL to less than 10% of the LFL when operating at current densities between 0.58 A/cm2 and 1.86 A/cm2. These recombination layers are with Pt loading of only 0.02 mgPt/cm2 and are incorporated in the volume of the membrane of the RSDT-fabricated MEAs. The MEAs with an active area of 86 cm2 and low catalyst loadings (0.3 mgIr/cm2 in the anode and 0.2 mgPt/cm2 in the cathode) have been tested for over 5000 hrs, and it was found that the H2 crossover increased to about 20 % of the LFL after 2000 hrs of operation. In order to improve the durability of the RLs, a new design comprised from two RLs separated with thin (10 um) Nafion membrane has been fabricated by the RSDT, and the results from the stability test of 3000 hrs will be presented and discussed in detail at the 242th ECS meeting. https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_myrdd_fuel_cells.pdf https://www.energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdf Klose, P. Trinke, T. Böhm, B. Bensmann, S. Vierrath, R. Hanke-Rauschenbach, and S. Thiele, J. Electrochem. Soc., 165, F1271–F1277 (2018).Yu, H., Baricci, A., Bisello, A., Bonville, L., Maric, R., et al. Electrochimica Acta, 247, 1155-1168 (2017).Roller, J., Maric, R., 24(8) December 2015 pp. 1529-1541 (2015).Mirshekari, G., Ouimet, R., Zeng, Z, Yu, H., Bliznakov, S., Bonville, L., Niedzwiecki, A., Errico, S., Capuano, C., Mani, P., Ayers, K., Maric, R. International Journal for Hydrogen Energy, 46(2), 2021, pp. 1526-1539 (2021).

Rationally Designed PGM-Free Catalyst MEA with Extraordinary Performance

Platinum group metal (PGM) catalysts are the major electrocatalysts for oxygen reduction reaction (ORR) in the polymer electrolyte membrane fuel cells (PEMFCs). However, the high cost of PGM catalysts is the major huddler for the widespread applications of fuel cell electric vehicles. To remove this cost obstacle of fuel cell commercialization, PGM-free catalysts have been considered as the replacement of PGM catalysts for ORR because of the low cost and relatively comparable performance with PGM catalyst. Fe-C-N complex is the one of the most active centers in PGM-Free catalyst groups. This type of catalyst shows excellent activity characterized using the rotation disk electrode (RDE), i.e., the half wave potential (E1/2 ) could reach 0.91 V versus standard hydrogen electrode (SHE). However, in a membrane electrode assembly (MEA), the performance of PGM-Free catalysts cannot achieve the comparable performance to PGM catalyst. Since there are so many differences between PGM-free, and PGM catalysts e.g., activity, stability, surface conditions, particle size etc. The fabrication of PGM-Free catalyst MEA cannot simply borrow the methods from that of making PGM MEA. In addition, the thicknesses of catalyst layers of PFM-free are significantly thicker than that of PGM, i.e., 10 times. Hereby, we proposed a novel method of fabricating PGM-Free catalyst MEA, so that the intrinsic catalyst activity from RDE can be translated into MEA performance. The method is based on the catalyst coated membrane (CCM) method using optimized ionomer to carbon (I/C) ratio and solvent mixture of catalyst ink. Such method pushes PGM-free MEA first ever achieved the current density of 50.8 mA cm-2 at 0.9 V iR-free in H2/O2 and over 150 mA cm-2 at 0.8 V in H2/air, which surpassed the 2025 performance targets of US Department of Energy (DOE) for PGM-Free catalyst MEA. Further, the property (solvent composition, dispersion of catalyst and ionomer in an ink), structure (pore structure) and the MEA performance have been characterized using mercury intrusion porosimetry (MIP), MEA testing. A property-structure-performance relationship has been established.

Crosslinked anion exchange membranes prepared from highly reactive polyethylene and polypropylene intermediates

To obtained polyolefin-based anion exchange membranes (AEMs) with high performance in high efficiency, reactive polyolefin intermediates were prepared via polymerization of ethylene or propylene with 1-iodo-10-undecene (IUD) by single-site rac-ethylenebis(indenyl)Zr(IV) dichloride and dimethyl (pyridylamido)Hf(IV) catalysts, respectively. The catalytic activity for synthesis of these reactive polyolefin intermediates was up to 2.94 × 106 for ethylene copolymers (PEI-x) and 7.20 × 106 gpolymer molcat.−1 h−1 for propylene copolymers (PPI-x), respectively. Moreover, incorporation ratio of IUD in copolymers was high up to 19.8 (PEI-x) and 29.7 mol% (PPI-x), respectively. These copolymers could be well dissolved in o-xylene, make them easily crosslinked and quaternized to give polyolefin-based AEMs. These AEMs with crosslinking structure exhibited high hydroxide conductivity (131 and 143 mS/cm for PEI-20-C100-QA and PPI-30-C70-QA at 80 °C, respectively) and excellent alkaline stability without visible loss in hydroxide conductivity after 1680 h. These AEMs exhibited evident microphase separation via microphase study, presented low swelling ratio even with high water uptake. A H2/O2 fuel cell with PEI-20-C100-QA presented a peak power density of 439 mW cm−2 without optimized membrane electrode assembly fabrication process.

Development of Poly(Arylene ether Sulfone)-Based blend membranes containing aliphatic moieties for the low-temperature decal transfer method

Several hydrocarbon-based polymer membranes have been developed for proton exchange membrane fuel cells; however, their commercialization is hindered by the inefficient fabrication of membrane electrode assemblies (MEAs). In this study, we developed novel sulfonated poly(arylene ether sulfone)s with aliphatic backbones for application in the low-temperature decal transfer method commonly employed in MEA fabrication. Furthermore, the polymer was blended with fully aromatic sulfonated poly(arylene ether sulfone)s with relatively high dimensional stability to enhance membrane durability. The blended membranes exhibited unique morphological structures that improve their performance and long-term stability. One polymer blend (Hex-BP-2) fabricated by low-temperature decal transfer without any additional treatments showed high durability over 1000 wet-dry cycles and high fuel cell performance (579 mW cm−2). Such polymer blend membranes are excellent alternatives to perfluorinated sulfonic acid polymers owing to both their high performance and long-term stability.