bluuebunny/crossref_metadata_2025 huggingface dataset:
One-Step Synthesis of Selective Nife-Layered Double Hydroxide Anode Catalyst for Highly Efficient and Stable Anion Exchange Membrane Water Electrolyzers, Operating with Seawater
Authors: Xing Jiale , Zeng Zhiqiao , Koni Arkid , Mirshekari Gholamreza , Best Wesley , Kumar Vikas , Sammes Lauren , Bonville Leonard J. , Maric Radenka , Bliznakov Stoyan
Published: November 2022

Seawater electrolysis faces unique and fundamental chemical challenges, such as the suppression of highly detrimental halogen chemistries [1], that poison the current state-of-the-art anode catalyst and accelerate the degradation of the membrane [2]. The technically favored solution path is to address these issues by developing a new selective catalyst and possibly by limiting operating conditions [3]. Therefore, developing a facile and cost-effective way to design highly active, selective, and and stable seawater-splitting catalysts is of great importance for research and industry [4]. In this work, hexagonal NiFe-layered double hydroxide (LDH) nanosheets were synthesized by one-step solvothermal reactions. As synthesized NiFe-LDH catalyst exhibits high activity, selectivity, and stability towards the oxygen evolution reaction (OER) in alkaline electrolyte, delivering current densities of 10 mA/cm2 at low overpotentials of 359 mV, with no significant degradation observed during RDE testing at constant voltage of 1.57 V for 72 hours in 1.0 M KOH electrolyte. In addition, in order to fabricate catalyst coated electrode (CCE), the nanostructured NiFe-LDH catalyst was homogeneously sprayed onto a platinized titanium porous transport layer (PTL) using an ultrasonic spray coating system. As prepared CCE is used as an anode and commercially available Raney nickel catalyst deposited on a nickel fiber frit is used as a cathode to assemble a MEA with Sustainion® X37-50 grade T anion exchange membrane (AEM) that was tested in alkaline seawater. Employing local seawater, the AEM electrolyzer cell demonstrated stable performance for over 1000 hours at a constant current density of 300 mA cm -2.

Reference:

[1] S.-C. Ke, R. Chen, G.-H. Chen, X.-L. Ma, Energy Fuels 2021, 35, 12948.

[2] S. Dresp, F. Luo, R. Schmack, S. Kühl, M. Gliech, P. Strasser, Energy Environ. Sci. 2016, 9, 2020.

[3] S. Dresp, F. Dionigi, S. Loos, J. Ferreira de Araujo, C. Spöri, M. Gliech, H. Dau, P. Strasser, Advanced Energy Materials 2018, 8, 1800338.

[4] H. Koshikawa, H. Murase, T. Hayashi, K. Nakajima, H. Mashiko, S. Shiraishi, Y. Tsuji, ACS Catal. 2020, 10, 1886.
Reverse Monte Carlo Modeling for Catalyst Nanoparticles in Polymer Electrolyte Fuel Cells By High-Energy X-Ray Diffraction Measurement
Authors: Mizuno Yuki , Tsuji Hirokazu , Uruga Tomoya , Kaneko Takuma , Ohara Koji , Uchimoto Yoshiharu , Imai Hideto , Tsuji Yoichiro , Sakurai Yoshiharu
Published: November 2022

Polymer electrolyte fuel cells (PEFCs) consist of a gas diffusion layer (GDL) and an electrode on each side, and a polymer electrolyte membrane (MEA) between the electrodes. The main components of the MEA are catalysts, electrolyte membranes and electrodes. In this study, the local atomic structures of catalytic nanoparticles in MEA were investigated by high-energy X-ray diffraction measurement and reverse Monte Carlo (RMC) modeling. The purpose of this study is to show guidelines for improving the performance of the PEFCs that contribute to industry by clarifying the differences in each catalyst structure and linking them with catalyst performance such as catalytic activity and catalyst durability.

In this conference, we report the structural work on the platinum nanoparticles-supported carbon catalyst TEC10V30E (manufactured by TANAKA KIKINZOKU KOGYO K.K.). Although this sample is a commercial product, it is important to investigate its structure because it can be used as a standard sample for evaluating various catalyst samples in the future.

RMC modeling based on the structure factor S(Q) obtained from high-energy X-ray diffraction measurement is suitable to determine the 3-dimensional (3D) atomic structures of nanoparticles. High-energy X-ray diffraction measurements were performed using a two-axis diffractometer at the beamline BL04B2 in SPring-8; the energy was used 61.4 keV corresponding to 0.202 Å in wavelength. RMC simulations were performed to obtain structure information from RMC-generated 3D configuration models using RMC_POT software in the case of non-periodic boundary conditions for experimental structure factor data. Figure 1 shows the experimental structure factor of the Pt nanoparticles in TEC10V30E and the RMC-simulated structure factor. For the Pt nanoparticle studied here, the initial configuration of the RMC simulations is a spherical shape with 3.8 nm in diameter based on the fcc bulk crystal structure. The agreement between the experiment and the RMC-simulated S(Q) is satisfactory. The 3D structure model of the Pt nanoparticle obtained by RMC simulations is shown in Fig. 1. It was found that the deviation from the lattice position was larger on the surface than on the inside in the obtained structure model.

This research approach is expected to accelerate the creation of new catalysts for fuel cells by providing local atomic-scale structural information. It is also important to create the database of atomic arrangement structure data that is the basis of material design and material research.

In the meeting, data recorded from actual catalyst samples will also be presented, including those from the MIRAI fuel cell (manufactured by Toyota Motor Corp.).

This work was performed under the NEDO FC-Platform project.

Figure 1
3D Visualization of Liquid Water in Catalyst Layer Using X-Ray CT
Authors: Sugahara Takaya , Sasabe Takashi , Naito Hiroshi , Kodama Manabu , Hirai Shuichiro
Published: November 2022

Polymer electrolyte fuel cells (PEFCs) play an important role in solving environmental and energy problems, and are required to perform at higher current density to achieve the cost reduction. Under a certain operating condition, however, water condenses and accumulates in the cathode catalyst layers (CLs) and the gas diffusion layers (GDLs). In such cases, the oxygen transport is prevented by liquid water accumulation, and therefore more precise water management methods are required to perform at higher current density. In this study, we perform 3D visualization of liquid water not only in GDLs but also in CLs in order to study the mechanism of generation-discharge mechanism of liquid water in the membrane electrode assembly (MEA) in more detail.

In this study, X-ray measurements were performed using laboratory-based X-ray imaging equipment Rigaku nano3DX. The fuel cell with an active area 1.0 × 1.0 mm2 was used. The GDLs used were Toray TGP-H-060 coated with micro porous layer (MPL). Considering X-ray transparency, CLs with relatively lower Pt loading (10wt%) was applied to the membrane. The images modification, which corrects displacements of membrane due to swelling, were performed to compare the wet case and the dry case. The present operation was performed under room temperature.

The figure shows liquid water of cathode CL integrated in the thickness direction at current density of 1.0 A/cm2. It is observed that liquid water in CL accumulates above the Rib. In addition, it was found that liquid water in CL accumulates in the regions close to the liquid water accumulating in the cracks of MPL.

Figure 1
Visualizing 4D Pore-Scale Gas Transport in Operating PEM Electrolyzers Using X-Ray Computed Tomography
Authors: Ham Chaeyoung Tina , Shrestha Pranay , Kober Leya Roshani , Bazylak Aimy
Published: November 2022

Mass transport losses in polymer electrolyte membrane (PEM) electrolyzers are predominantly caused by the accumulation of oxygen gas within the pores of the porous transport layer (PTL), hindering reactant water delivery to reaction sites (1). To enhance mass transport and optimize electrolyzer performance, a comprehensive understanding of the mechanisms driving oxygen gas transport in the PTL is required. Numerous studies have utilized various imaging techniques - including optical, neutron, and X-ray radiography to elucidate the evolution and transport of oxygen gas in the multiphase flow regime during PEM electrolyzer operation (2). However, these techniques only capture two-dimensional (2D) images, resolving average gas distributions rather than a holistic pore-scale quantification. Few studies have used three-dimensional (3D) imaging to resolve the dynamic microscale distributions of oxygen gas in the PTL. Understanding the impact of key parameters affecting 3D oxygen gas transport, such as PTL morphology, will allow for tailored pore-scale material optimization for enhanced gas transport and improved performance of PEM electrolyzers.

This study presents a non-destructive operando imaging approach using X-ray computed tomography (CT), enabling the visualization of transient 3D oxygen gas evolution and transport in the PTL of a PEM electrolyzer. Using state-of-the-art synchrotron X-rays, high temporal and spatial resolutions were achieved to capture the pore-scale formation and growth of oxygen gas pathways within the PTL at various operating conditions. Electrochemical performance of an in-house designed electrolyzer cell was also characterized while acquiring tomographic images to investigate the impact of observed transport mechanisms on performance. The methodology presented in this work showcases the capability of using X-ray CT to visualize the complex interfacial multiphase flow in PTLs. Findings from this study will provide valuable insight towards pore-scale material optimization of clean energy porous materials aimed at curtailing the costs of green hydrogen production.

References

1. M. Suermann, T. J. Schmidt, and F.N. Büchi, ECS Trans., 69(17), 1141-1148 (2015).

2. M. Maier, K. Smith, J. Dodwell, G. Hinds, P. R. Shearing, and D. J. L. Brett, Int. J. Hydrog. Energy.,
47(1), 30-56 (2022).
(Digital Presentation) Characterization of Molecular Aggregation State in Deteriorated Nafion Membrane on the Basis of X-Ray Diffraction Measurement
Authors: Hirai Tomoyasu , Seko Tamio , Higashiguchi Wataru , Fujii Syuji , Nakamura Yoshinobu
Published: November 2022

Nafion is widely utilized as key polymer for proton electrolyte fuel cells owing to their high chemical, mechanical, and proton-conducting properties. The molecular aggregation state in Nafion films strongly affects the performance in the fuel cells. During operation process in fuel cells, peroxide derivatives such as H2O2 is generated and the chemical species deteriorates Nafion membrane, leading to a decreasing of performance of the fuel cells. The detail deterioration process including local structure, however, does not well-understand. In this work, we evaluate the local molecular aggregation state in deteriorated Nafion using microbeam wide X-ray diffraction (WAXD) measurements.

Figure 1a shows WAXD line profile of before and after deterioration of Nafion membranes. The diffraction peaks were observed in ranging from 11 to 12 nm-1, which could be assigned to crystalline and amorphous structure in Nafion. The ratio of crystalline peak in deteriorated Nafion was more striking than that of initial Nafion membrane. This phenomenon might be explained following two mechanism. ① Polymer chains in amorphous domain were disconnected and were removed from the membrane. ② Polymer chains were disconnected and molecular motion of lower molecular weight is activated, leading to a formation of new crystalline domain caused by aggregation of lower molecular weight polymer chains. It is anticipated that above mechanisms occurs individually or at the same time. Though the dominant mechanism is still not clear, we can conclude that deterioration in Nafion starts from amorphous domain.

To evaluate local molecular aggregation state in deteriorated Nafion, microbeams with size of 50 μm and 7 μm were utilized for WAXD measurements. Figure 1b and c show variation of ratio in crystalline domain as function of strain. The ratio of the crystalline domain in deteriorated Nafion was more striking than that of untreated Nafion. The ratio was constant when 50 μm beam was used, but not the case in 7 μm beam. This indicates that deterioration of Nafion membrane occurs 7 to 50 μm scale. The detail will be discussed in my presentation.

Figure 1
Operando Measurement of Hydrogen Crossover in Proton Exchange Membrane Electrolysis Cells at Differential Pressures
Authors: Wrubel Jacob A , Zack Jason , Park Andrew M , Bender Guido
Published: November 2022

Low temperature water electrolysis (LTE) using proton exchange membrane electrolysis cells (PEMECs) is a promising approach for producing green H2 that can use electricity from renewable sources. In practice, H2 is stored and dispensed at high pressures. To alleviate efficiency losses associated with pressurizing the product hydrogen, PEMECs can be operated at high differential pressures, e.g., >30bar on the cathode side. However, high differential pressure operation can result in undesirable H2 crossover to the anode (O2) side. This not only reduces the Faradaic efficiency of the cell, but also can result in flammability hazards.

H2 crossover in PEMECs is a function of both materials properties such as membrane thickness, water uptake, and permeability, and operating conditions such as temperature, differential pressure, and current density. Example data are shown in Figure 1. While thinner membranes are susceptible to higher H2 crossover rates, they are a desirable material to use because they can result in significantly improved cell performance and lower material and production costs. To mitigate safety concerns related to H2 crossover, gas recombination catalyst (GRC) layers can be introduced into the membrane electrode assembly. The GRCs will react the crossover H2 with O2 to produce water, thereby minimizing the amount of H2 entering the O2 stream.

In this talk we will present data from operando crossover measurements of PEMECs employing a variety of membrane materials, both with and without GRCs. The experiments are complimented by modeling results that allow further insights into the processes at hand. Multiple temperatures, differential pressures, and current densities are studied. The results will investigate the tradeoff between performance and capturable H2 production that occurs when thinner membranes are used, and how this effect responds to differential pressure operation.

Figure 1
Atomic-Scale Strucural Analysis of Pt-Based Nanoparticles Using Scanning Transmission Electron Microscopy
Authors: Kuwabara Akihide , Omori Yuki , Huang Hsin-Hui , Kobayashi Shunsuke
Published: November 2022

Polymer electrolyte fuel cells (PEFCs) is proposed as an alternative to the power generation system in fuel cell vehicles. The performance of the PEFCs is significantly affected by the catalytic activity of the cathode, which contains platinum in general. Recent theoretical studies show that the Pt-Pt interatomic distance at the subsurface of the Pt-based catalysts might considerably influence the catalytic activity. However, experimental evidence remains a challenge due to the requirement of measurement accuracy in picometers at the subsurface. The present work attempts to achieve precise measurements on the Pt-Pt interatomic distance of Pt particles by high-angle annular dark-field (HAADF) imaging in scanning transmission electron microscopy (STEM). Further, we also aim to understand the effects of the change in Pt-Pt interatomic distance on the catalytic activity.

A catalyst of 10 wt.% Pt-loaded on graphitized carbon (Sigma-Aldrich) was used in this work. TEM specimen was prepared by dispersing the catalyst on a carbon film supported copper grid. Structural characterizations were examined by a spherical aberration corrected scanning transmission electron microscope (JEM-2100F, JEOL) operated at 200 kV.

In order to determine the Pt atomic coordinate accurately, images were first taken under the optimized conditions. Further, a series of images were taken and integrated to form one image with high signal-to-noise ratio and minimized drifting. Finally, the Pt atomic coordinates were extracted precisely on a picometer scale by fitting of the individual atomic columns to two-dimensional Gaussian functions using a custom code developed by MatLab software. To gain insight into the atomic changes in Pt particle, a map of Pt-Pt interatomic displacement vector was constructed and superimposed on the HAADF-STEM image. Intriguingly, a significant Pt-Pt interatomic displacement occurs at the surface of the Pt particle, corresponding to changes in surface morphology and particle size.

The state-of-the-art methodology demonstrated here could greatly advance our understanding of surface chemistry of Pt-based catalysts such as Pt3Co alloys. Further understanding of the correlation between the interatomic distances on the catalyst surface and the catalytic activity may give considerable interests and guidelines for future developments of PEFCs.
Investigation of Liquid Water Behavior and Performance of PEFC Catalyst Layers Using a Microdevice and in-Operando Infrared Microscopy
Authors: Suzuki Takahiro , Kobayashi Ryota , Kakinuma Katsuyoshi , Uchida Makoto , Iiyama Akihiro , Tsushima Shohji
Published: November 2022

Studies on water behavior in the vicinity of a catalyst layer (CL) and its effect on the cell performance are important challenges because water management is a key factor to achieve higher performance of polymer electrolyte fuel cells (PEFCs). In this study, a microdevice that contains a catalyst coated membrane (CCM) was developed (1) and in-operando infrared (IR) microscopy was conducted to visualize water behavior on the CL. Two types of CLs contain either carbon (2) or tin oxide (3) as supporting material to investigate the effects of materials on the water behavior and cell performance.

The microdevice, which was made of a silicon wafer, contains two microchannels (100 μm-width, 200 μm-pitch) and a current-collecting layer (30 μm-width) on a rib of the cathode plate. The CCM was sandwiched by two plates. The anode channel faced the rib of the cathode. The surface of a cathode catalyst layer was coated with thin Au by sputtering to enhance IR reflectance, which did not change the porous structure of the CL significantly. The surface of the cathode catalyst layer was observed by IR microscopy through the cathode plate.

Figure 1 shows liquid water generated during the constant current operation of the device. The catalyst layer contains carbon as the supporting material in this case. The effects of the materials and flow conditions on the water behavior and cell performance were investigated.

Acknowledgments

This work was supported by NEDO ECCEED’30.

References

(1) T. Suzuki et al., J. Therm. Sci. Technol., 11 (2016), 16-00370.

(2) T. Suzuki et al., Int. J. Hydrogen Energy, 41 (2016), 20326.

(3) Y. Chino et al., J. Electrochem. Soc., 162 (2015), F736.

Figure 1
Probing Heterogeneous Water Distributions within Fuel Cell Membranes Using Combined Neutron and X-Ray Tomography (NeXT)
Authors: Shrestha Pranay , LaManna Jacob Michael , Fahy Kieran , Kim Junseob , Lee ChungHyuk , Lee Keonhag Keonhag , Baltic Eli , Jacobson David , Hussey Daniel , Bazylak Aimy
Published: November 2022

Water management in a fuel cell is an essential prerequisite for achieving high cell performance, where sufficient water is required for membrane hydration while excess liquid water leads to undesired mass transport losses. Existing heterogeneity within the fuel cell, such as those created by flow-field lands and channels create three-dimensional (3-D) heterogeneity in water distribution within the fuel cell components, which may have long term effect on the durability of fuel cell components, such as the membrane (1). 3-D visualization techniques such as X-ray (1-4) and neutron (5) tomography are powerful in revealing the effect of the existing heterogeneity on water distributions in 3-D. However, there is an opportunity to combine neutron and X-ray tomography (6) to probe into the details of these heterogenous water distributions even further and clarify their impacts on 3-D membrane hydration.

In this study, we investigate the effect of heterogeneity in fuel cells (primarily land-channel heterogeneity) on 3-D membrane hydration and membrane morphology changes during fuel cell operation using simultaneous neutron and X-ray tomography (NeXT). The fuel cell is tested at varying gas humidity conditions in a serpentine flow-field configuration. A simultaneous coupling of neutron and X-ray imaging provides high contrast across various components of the fuel cell. Specifically, neutrons are highly attenuated by hydrogen atoms; hence neutron imaging is used to accurately locate and quantify operando water distribution. X-rays are sensitive to metals; hence simultaneous X-rays imaging is used to track metal-containing components (metal flow-field) and interfaces (such as interface between Pt-containing catalyst layer and membrane). This study demonstrates how heterogeneity in fuel cells plays a role in 3-D membrane hydration and needs to be tailored to enhance cell performance.

References

Y. Singh, R. T. White, M. Najm, T. Haddow, V. Pan, F. P. Orfino, M. Dutta, and E. Kjeang, J. Power Sources., 412 (2019): 224-237.

Y. Nagai, J. Eller, T. Hatanaka, S. Yamaguchi, S. Kato, A. Kato, F. Marone, H. Xu and F. N. Büchi, J. Power Sources., 435 (2019).

S. J. Normile, D. C. Sabarirajan, O. Calzada, V. De Andrade, X. Xiao, P. Mandal, D. Y. Parkinson, A. Serov, P. Atanassov and I. V. Zenyuk, Meter. Today Energy., 9 (2018).

S. S. Alrwashdeh, I. Manke, H. Markötter, M. Klages, M. Göbel, J. Haußmann, J. Scholta and J. Banhart, ACS Nano., 11, 6 (2017).

J. M. LaManna, Y. Yue, T. A. Trabold, J. D. Fairweather, D. S. Hussey, E. Baltic and D. L. Jacobson, Meet. Abstr. - Electrochem. Soc., 32 (2017).

J. M. LaManna, D. S. Hussey, E. Baltic and D. L. Jacobson, Rev. Sci. Instrum., 88, 11 (2017).
Suitability of Composite Feed-Stock Material for Bi-Polar Plates Using Low-Cost Additive Manufacturing
Authors: Alexander David , Ceballos Bianca Myraih , Yapell David , Ruiz Christian , Borup Rod L. , Rockward Tommy
Published: November 2022

Extrusion-based 3D printing processes have the lowest cost for equipment and materials used in additive manufacturing (AM). Recently, the AM technology has been extended beyond the typical polymer-based parts to include the capability of printing metal parts via Bound Metal Deposition (BMD). This technological advancement has, in turn, increased the potential application range of printed components particularly for Polymer Electrolyte Fuel Cells (PEFC). Although AM offers some design and cost advantages over traditional manufacturing, the finished part, post processing, must yield acceptable bi-polar plate properties outlined by the Hydrogen and Fuel Cell Technologies Office (HFTO). The post-processing techniques employed are de-binding, sintering, and surface treatment which are performed in a single step process. Here we focus on corrosion resistance, electrical conductivity, area specific resistance and porosity as the key parameters to qualify the candidate bi-polar plate material. The objective of this study is to investigate the effects of thermal processing parameters on the commercial metal composite filament via various characterization methods such as linear sweep voltammetry, area specific resistance, and x-ray computed tomography.
Simultaneous Generation of Clean Water and Electricity Via Desalination Fuel Cells
Authors: Suss Matthew , Abu Khalla Shada , Asokan Arunchander , Abdalla Salman
Published: November 2022

We will present a nascent technology which desalinates water and produces net electricity simultaneously from a single electrochemical cell, driven by the hydrogen/oxygen redox couple [1]. The cell combines hardware of PEM fuel cells, alkaline fuel cells and electrodialysis cells, and thus we term this device a "desalination fuel cell" [2]. We will describe both the operating principle and lab-scale cell results, as well as our development of the fundamental thermodynamics to predict the maximum available electricity production from our cell during its combined chemical reaction-separation process [2]. Our recent advances will be described, including the development of chloride-tolerant non-platinum group metal ORR catalysts [3], achievement of >95% thermodynamic energy efficiency [4], and establishment of system scaling rules. This technology promises to extend the concept of the hydrogen economy to water purification, and we will discuss the outlook on this technology and potential application areas.

References:

[1] Suss ME, Zhang Y, Atlas I, Gendel Y, Ruck EB, Presser V. Emerging, hydrogen-driven electrochemical water purification. Electrochemistry Communications. 2022

[2] Atlas I, Khalla SA, Suss ME. Thermodynamic energy efficiency of electrochemical systems performing simultaneous water desalination and electricity generation. Journal of The Electrochemical Society. 2020.

[3] Asokan A, Abu-Khalla S, Abdalla S, Suss ME. Chloride-Tolerant, Inexpensive Fe/N/C Catalysts for Desalination Fuel Cell Cathodes. ACS Applied Energy Materials. 2022.

[4] Abu Khalla S, Atlas I, Litster S, Suss ME. Desalination Fuel Cells with High Thermodynamic Energy Efficiency. Environmental science & technology. 2021.

Figure 1: Schematic of a desalination fuel cell, which utilizes chemical energy to desalinate water and produce electricity simultaneously. The cell is driven by the hydrogen-oxygen redox couple.

Figure 1
Superior Performance and Durability Water Electrolysis with a Highly Conductive and Stable Anion-Exchange Membrane
Authors: Kang sun Young , Cho Yong-Hun , Sung Yung-Eun
Published: November 2022

The commercialization of anion-exchange membrane water electrolysis (AEMWE) is important to produce low-cost and high-purity hydrogen. However, water electrolysis with an anion-exchange membrane (AEM) has limitations such as its poor stability and ionic conductivity, leading to low durability and performance of AEMWE. In this study, we developed superior-performance and stable AEMWE by employing an AEM without aryl-ether backbone structure. To achieve superior -performance and durable AEMWE, the effect of various parameters that is suitable for the adapted AEM was estimated. As a result, the AEM adapted in this work showed much better and was more durable than the conventional AEM (FAA-3). Moreover, it exhibited high efficiency under pure water feeding conditions. These results were contributed to high-efficient and durable AEM caused by its absence of aryl-ether backbone. This work suggests the potential use of polyphenylene structure as aryl-ether free backbone of AEM on AEMWE under alkaline solution and/or pure water condition.
Ti-Rich Mg1-X
Ti2+X
O5: A Highly Conductive and Acidic-Stable Ternary Oxides
Authors: Byeon Young-Woon , Mailoa Jonathan , Kornbluth Mordechai , Lee Gi-Hyeok , Cai Zijian , Sun Yingzhi , Yang Wanli , Johnston Christina , Christensen Jake , Kim Soo , Cheng Lei , Kim Haegyum
Published: November 2022

Searching for a material that simultaneously satisfies highly conductive and corrosion-stable properties is crucial for various energy conversion applications, particularly for catalyst-supporting materials in polymer electrolyte membrane fuel cells (PEMFC). Here, we suggest the Mg-Ti-O chemical space as promising ternary compounds with high electrical conductivity and corrosion stability in acidic conditions to be potentially used in such applications. A high electrical conductivity (6.09 × 10-1 S/cm) and a good corrosion stability (1.2 × 10-4 mA cm-2 at pH = 1) are achieved at room temperature, by tuning the chemical compositions of Mg1-x
Ti2+x
O5 (MTO). We found that the corrosion stability of suggested MTO is two orders of magnitude higher than that of conventional carbon supporters used for PEMFC while providing high electrical conductivity. Furthermore, our combined computational and experimental works elucidate that the reducing gas environment during the solid-state synthesis ensures the higher Ti solubility in MTO, i.e., a reduced valence state of Ti, thus promoted the electrical conduction.
Platinum Group Metal-Free ORR Catalysts for Anion Exchange Membrane Fuel Cells
Authors: Zhang Hanguang , Zelenay Piotr
Published: November 2022

Platinum group metal (PGM)-free catalysts for oxygen reduction reaction (ORR) have attracted significant attention in the last two decades. These catalysts typically perform better in alkaline aqueous electrolytes than in their acidic counterparts.1, 2 However, the performance of PGM-free ORR catalysts in anion exchange membrane fuels cells (AEMFCs) have been consistently lower than in the acidic polymer electrolyte fuel cells (PEFCs). The most likely reasons for the sub-par behavior of PGM-free catalysts in AEMFCs has been often linked to difficulties in preparing electrodes with anion exchange ionomers and assuring efficient water management. These challenges have been amplified by the high-loading requirement for PGM-free ORR catalysts, resulting in electrodes by as much as an order of magnitude thicker than the PGM-based ones.

In this presentation, we will demonstrate AEMFCs with much improved performance of the PGM-free cathode (Fe-N-C catalyst-based). The performance improvement has been achieved by optimizing the electrode fabrication process, including changes to the electrode configuration and catalyst ink preparation. These changes have allowed us to elevate the AEMFC performance, including the peak power density of > 0.8 W cm-2 in H2-O2 cells, to the level comparable to that of the corresponding PEFC, operating with a PGM-free cathode under the same operating conditions.

References:

1. Li, X.; Liu, G.; Popov, B. N., Activity and stability of non-precious metal catalysts for oxygen reduction in acid and alkaline electrolytes. Journal of Power Sources
2010,
195 (19), 6373-6378.

2. Choi, C. H.; Lim, H.-K.; Chung, M. W.; Chon, G.; Ranjbar Sahraie, N.; Altin, A.; Sougrati, M.-T.; Stievano, L.; Oh, H. S.; Park, E. S.; Luo, F.; Strasser, P.; Dražić, G.; Mayrhofer, K. J. J.; Kim, H.; Jaouen, F., The Achilles' heel of iron-based catalysts during oxygen reduction in an acidic medium. Energy & Environmental Science
2018,
11 (11), 3176-3182.
Rationally Designed PGM-Free Catalyst MEA with Extraordinary Performance
Authors: Li Chenzhao , Liu Shengwen , Zeng Yachao , Liu Yadong , Cullen David A. , Wu Gang , Xie Jian
Published: November 2022

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.
Self-Supporting Ag Nanowire Mat Electrodes on PTFE Gas Diffusion Layers for Electrochemical Conversion of CO2 to CO
Authors: Raciti David , Braun Trevor Michael , Tackett Brian , Xu Heng , Cruz Mutya , Wiley Benjamin , Moffat Thomas P
Published: November 2022

High surface area nanocatalysts combined with conductive carbon-based gas-diffusion layers (GDL) enable high CO2 flux and conversion, but can suffer from ineffective catalyst utilization and flooding of the GDL ultimately limiting the lifetime of electrolyzer operation. Herein we explore an alternative gas-diffusion electrode that incorporates a self-conducting network of Ag nanowires on a non-conductive PTFE GDL (Figure 1 a-b) as a gas-diffusion electrode (GDE) for CO2 conversion (Figure 1 c-d). Properties influenced by Ag nanowire mat thickness and durability of the Ag nanowires are explored. Furthermore a 1-D model of the electrode morphology and microstructure quantitatively captures the steady-state compositional gradients (Figure 1d) within the catalyst layer giving insight into the observed empirical differences in catalyst layer thickness. The self-conductive nanowire network and robust hydrophobic porous support structure provide an effective platform to further understanding of meso-scale properties and microenvironment present during CO2 electroreduction.

Figure Caption: (a) Top-down and (b) Cross-section electron micrographs of a Ag nanowire covered PTFE GDL. (c) Schematic depicting the utilization of the Ag NW covered PTFE GDL as an electrode for electrochemical CO2 reduction and (d) resulting relationships between catalyst layer thickness, mass activity and simulated local pH.

Figure 1
Nafion Composite Membrane Reinforced By Phosphonated Polypentafluorostyrene Nanofibers
Authors: Kerres Jochen Alfred , Solihul Muhammad Mu’min , Komma Miriam , Böhm Thomas , Wagner Maximilian , Krieger Anja , Thiele Simon
Published: November 2022

The membrane is one of the crucial components of fuel cells. Applying composite membranes for fuel cells is a promising option due to better mechanical properties compared to membranes without reinforcement. Composite membranes can be prepared by combining ionomer with a filler which can be selected from many types of materials, such as polymers, ceramics, carbons, and metals. Filler materials exist in different nanostructures which provide flexible designs for composite membranes. However, the main issue in composite membranes is a trade-off among properties when adjusting the ratio between ionomer and filler, especially between ionic conductivity and mechanical modulus. On the one hand, maintaining high protonic conductivity is possible when small concentrations of reinforcing fillers are incorporated. On the other hand, a high amount of reinforcement can improve the mechanical properties significantly but could result in low protonic conductivity as well. Our strategy to overcome this issue is by employing protonic conductive nanofibers as reinforcement. Electrospinning is a versatile method to transform polymer solutions into long and solid nanofibers. Electrospun fibermats possess a high porosity and contain voids which can be filled with an ionomer like Nafion by spraycoating to form a dense composite membrane.

We were successful in producing electrospun nanofibers from phosphonated polypentafluorostyrene (PWN70) and unmodified polypentafluorostyrene (PPFSt). PWN70/Nafion and PPFSt/Nafion composite membranes were prepared separately by spraycoating of a Nafion solution into PWN70 and PPFSt fibermats that have comparable thickness and fiber loading. From tensile tests, we found that composite membranes made from PWN70/Nafion and PPFSt/Nafion have much higher Youngs’ modulus (E) than pure Nafion (Figure 1A). Although PWN70/Nafion is a relatively brittle membrane, it has the best Youngs’ modulus and yield stress. Protonic conductivity is also a crucial membrane property which can be determined by electrochemical impedance spectroscopy. In Figure 1B, Nafion reinforced by PPFSt fibers has a reduced conductivity due to non-ion-conductive PPFSt. Surprisingly, the protonic conductivity of a PWN70/Nafion composite membrane is similar to spraycoated Nafion. Without reducing much the protonic conductivity, the PWN70/Nafion composite membrane shows comparable ohmic resistance to the spraycoated D2020 in fuel cell operation which has also been done in this work. Since the PWN70 nanofibers are ion-conductive and electro-spinnable, the nanofibers offer benefits when designing fiber-reinforced composite membrane possessing both good mechanical stability and protonic conductivity.

Figure 1
Electrode Ionomer Accelerated Stress Test Applied to High Oxygen Permeability Ionomer in Fuel Cells
Authors: Mesa Juan , Blackburn Scott , Plymill Austin , Brown Gerald , Park Andrew M , Paul Devproshad , Litster Shawn
Published: November 2022

Perfluorosulfonic acid (PFSA) polymer electrolytes are widely used in proton exchange membrane (PEM) fuel cell fabrication for the membrane separator and the electrode binder. The PEM serves to electrically insulate the cathode catalyst layer (CCL) from anode catalyst layer (ACL), provide proton conduction between both CCL and ACL, as well as prevent gas crossover. PFSA ionomers are also used in the CCL and ACL to mechanically bind the catalyst particles into thin-films, provide proton conduction between the PEM and catalyst surface, and produce a high proton reactant concentration at the oxygen reduction reaction catalyst. Despite their versatility to be used as a membrane and catalyst binder, the typical PFSA ionomers pose challenges due to the high oxygen transport resistance that is introduced by the thin ionomer films over the catalyst. In recent years, novel high oxygen permeability ionomers (HOPIs) have been developed as the successor to the traditional Nafion™ PFSA ionomers. Despite their remarkable results as a catalyst binder due to their increased oxygen transport rates, less is known regarding their degradation and functional lifetime. Although accelerated stress tests (ASTs) for platinum (Pt)/Pt-alloy catalysts, carbon supports, and membranes are well-established and commonly applied, there is no standard and easily implemented AST for electrode ionomers. One challenge is that membrane ASTs usually quantify the fluoride emission rate (FER) to assess chemical degradation, which is difficult to apply for electrode PFSA ionomer when also using a PFSA membrane because the FER is overwhelmed by membrane signal. In addition, changes in OCV and H2 crossover are not directly indicative of electrode ionomer degradation. Furthermore, concomitant degradation of the catalyst and support can interfere with interpreting electrode ionomer degradation. Here we present an effective and easily applied electrode ionomer chemical AST protocol that can be used to evaluate degradation in the functionality of the electrode ionomer. The approach borrows the chemical AST conditions of the chemical membrane AST’s open circuit voltage (OCV) hold and avoids excessive potential cycling to minimize catalyst and support degradation that will elicit changes in electrode properties separate from ionomer degradation. During the AST, we measure the cathode’s proton conduction resistance, oxygen permeability, and electrochemically surface area (ECSA) to evaluate the degradation of the ionomer’s functionality. Thus, this protocol can be used to assess if more complex and time consuming analyses of ionomer durability are needed as new chemistries emerge. Here we present results of this AST to both conventional PFSA ionomers and HOPIs.
(Invited) Novel Ionomers and Ionomer Membranes for Fuel Cells and Redox-Flow Batteries
Authors: Kerres Jochen Alfred
Published: November 2022

In this contribution the development of new nonfluorinated and partially fluorinated polymeric platsforms containing perfluoroaromatic building blocks, and their modification with phosphonic and/or sulfonic acid groups and/or anion-exchange groups and/or flexible alkane side chains by nucleophilic aromatic substitution of F or via other synthesis routes is described. The prepared polymers were, where appropriate, blended among each other or with basic high-performance commercial polymers such as polybenzimidazoles or self-synthesized novel basic aromatic polymers to further improve their membrane properties by ionic cross-linking. Moreover, composite membranes consisting of ion-conductive or non-conductive electrospun fiber mats which were filled with PFSA dispersions were synthesized and optimized. The synthesized ionomers and ionomer (blend) membranes were characterized in terms of composition via NMR and FTIR, molecular weight by size exclusion chromatography (SEC), thermal stability via TGA-FTIR-GC-MS coupling and via DSC, and mechanical properties via stress-strain tests and DMA, morphology via electron microscopy, and conductivity via impedance spectroscopy. The (blend) membranes were then applied in fuel cells (low-T and high-T, H2 and direct alcohol fuel cells), and in redox-flow batteries, yielding good performance in these applications.
Cross-Linking of Proton Exchange Membranes with Enhanced Stability and Reduced Fuel Crossover for Direct-Isopropanol Fuel Cells
Authors: Auffarth Sebastian , Kerres Jochen Alfred
Published: November 2022

Isopropanol fuel cells offer a promising way to provide electric energy from a liquid, non-toxic fuel. The secondary alcohol isopropanol is converted into acetone without producing significant amounts of CO2. The oxidation product acetone can be easily hydrogenated back to isopropanol to close the storage cycle, thereby avoiding fugitive molecular hydrogen with its low volumetric energy density at ambient conditions. Until now, electrodes and membranes for Direct Isopropanol Fuel Cells (DIFC) usually rely on various perfluorosulfonic acid derivates, like Nafion. Besides its high cost and unfavorable high fluorine content, the dissolution of Nafion in isopropanol mixtures has prevented the long time operation of DIFCs so far. Ionomer swelling during operation promotes efficiency-reducing crossover of isopropanol and acetone. This study introduces a new click-like covalent cross-linking strategy for fluoroaromatic ion-exchange polymers. Combined with ionic cross-linking of polymer blends, membranes with increased isopropanol stability were manufactured and compared to commercial Nafion membranes. The ionic and covalently cross-linked membrane resists a dissolution stress test up to 84 w-% and reduces the detected isopropanol/acetone crossover up to 75/100 % during fuel cell operation. Consequently, the cross-linking procedure and respective membrane material can be considered a significant step toward the technical implementation of DIFCs.
Evaluation of High Oxygen Permeability Ionomer (HOPI) Oxygen Permeability for Proton Exchange Membrane Fuel Cells (PEMFCs)
Authors: Liu Jiawei , Braaten Jonathan , Tiwari Nicholas , Wang Xiaoxiao , Blackburn Scott , Brown Gerald , Park Andrew M , Ulissi Zachary , Litster Shawn
Published: November 2022

The performance of proton exchange membrane fuel cells (PEMFCs) is sensitive to Pt loading in the cathode catalyst layer, with lower Pt loadings significantly increasing the oxygen transport resistance of the catalyst-ionomer interface when using perfluorosulfonic acid (PFSA) ionomers. The oxygen permeability is suspected to be locally decreased at Pt interfaces due to ionomer densification caused by the Pt-ionomer interactions. However, due to the high cost of Pt, it is important to be able to reduce Pt loadings without increasing oxygen transport resistance. With this goal in mind, new precommercial high oxygen permeability ionomers (HOPIs) with blocky backbone units are being studied. These HOPIs show significantly lower local oxygen transport resistance in fuel cells as well as greater efficiency and durability. However, there was a question of whether HOPI’s higher in-situ oxygen permeability is due solely to reduced densification or if it is also due to increased bulk permeability of the films. Here we evaluated this question using a unique oxygen permeability measurement apparatus that measures the oxygen permeability of thin-films supported on mesoporous substrates. This apparatus allows films to be characterized without the polarized Pt surfaces used in other oxygen permeability diagnostics, providing insights into the bulk permeability of cast thin-films with minimized substrate effects. This presentation will present our findings of the oxygen permeability of pristine thin-film HOPIs characterized against that of the baseline PFSA ionomer. Results show that the HOPI is significantly more oxygen permeable than the baseline. This finding is supported by our molecular dynamics simulations of these ionomer films. This increased bulk film oxygen permeability indicates that a significant portion of the decreased oxygen transport resistance in the cathodes is associated with the greater bulk permeability of these films and not just local Pt interface effects.

This material is based upon work supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office, Award Number DE-EE0008822.