bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of Ionomer Dispersion in the Design of Microstructure of Catalyst Layers: Oxygen and Hydrogen Evolution Reactions
Authors: Park Jong-Hyeok , Kim Beom-Seok , Park Jin Soo
Published: November 2022

Green hydrogen production is importance in the upcoming hydrogen economy era. Proton exchange membrane (PEM) water electrolysis is one of the most important technology to produce the green hydrogen that requires only water and extra electricity supplied from renewable energy. Main component, i.e., membrane electrode assembly (MEA), is a key part consisting of polymer electrolyte membrane and two electrodes which are oxygen evolution reaction (OER) electrode and hydrogen evolution (HER) electrode. Both electrode should be coated on the surface of membranes for better performance and mass production. Catalyst layers for OER and HER electrodes are composed of an electrocatalyst (Pt/C) and proton conducting ionomer. In the previous literature, proton conducting ionomer directly affects their performance and durability. Thus, the optimized design of the microstructure of the catalyst layers is essential. In this study, for the reduction of hydrogen production cost, highly dispersed ionomers were introduced to develop the optimized catalyst layers for OER and HER. The effect of dispersing solvents for ionomers on the performance and durability of catalyst layers was mainly investigated. Developed ionomer dispersions showed higher performance and durability in PEM water electrolysis, which result was made by the electrochemical characterization such as I-V polarization, voltage increasing rate during durability test, and so on as well as the microscopic characterization such as SEM and TEM were carried out to evaluate the effect of ionomer dispersions on the performance and durability of HER electrode in PEM water electrolysis.

Acknowledgments

This research was supported in part by the Hydrogen Energy Innovation Technology Development Program of the National Research Foundation (NRF) funded by the Ministry of Science, ICT ＆ Future Planning (NRF-2019M3E6A1063677) and by 2022 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.
Preparation and Characterisation of Microporous Layers Derived from Graphene Foam
Authors: Lee Florence Cecilia , Kusdhany Irfan , Ismail Mohammed , Ingham Derek , Hughes Kevin , Lyth Stephen , Ma Lin , Pourkashanian Mohamed
Published: November 2022

Proton exchange membrane fuel cells (PEMFC) are a viable means to meet global energy demand, reduce dependence on fossil fuels, and mitigate carbon dioxide emissions. Despite recent progress in their development, water saturation remains a challenge to current PEMFC design and efficiency. The addition of a microporous layer improves fuel cell performance largely from the reduction of water accumulation and the enhancement of mass transfer capacity at high current densities. However, optimisation of the microporous layer is necessary to improve its capability to manage liquid water and facilitate mass transfer. In this study, the viability of microporous layers produced from synthesised graphene foams was assessed.

Graphene foam was synthesised from the pyrolysis of sodium ethoxide, the resulting carbon was then subject to pyrolysis in different atmospheres in order to enhance the conductivity. The graphene foams underwent characterisation by electron microscopy and x-ray fluorescence which showed high carbon purity open foams with micron scale pores and graphene-thin walls. Microporous layers were then produced from these graphene foams, commercial graphene and from carbon black; they were then characterised ex-situ and through polarisation curves.

Ex-situ characterisation of the microporous layers was used to determine the micro-structure and physical properties, as well as its ability to repel liquid water and to conduct electron and mass transfer. Electron microscopy and mercury intrusion porosimetry enabled the analysis of morphology and microstructure, and the transport properties of the layer were determined through permeability, electrical conductivity and contact angle measurements. Polarisation curves were performed at low and high relative humidities in order to understand the capability of these microporous layers in a range of operating conditions.

Figure 1
Patterned Nafion Membranes for Improved Transport in PGM-Free PEMFC Cathodes
Authors: Arman Tanvir Alam , Uddin Aman , Ding Shuo , He Yanghua , Cetinbas Cankur , Peng Jui kun , Wang Xiaohua , Ahluwalia Rajesh , Xu Hui , Wu Gang , Komini Babu Siddharth , Litster Shawn , Pasaogullari Ugur , Spendelow Jacob S.
Published: November 2022

Substantial cost reduction is needed to commercialize polymer electrolyte fuel cells. As PGM catalysts are projected to account for ~42% cost of a fuel cell stack (1), replacement of PGMs with PGM-free catalysts is an attractive route to cost reduction. Over the past decade, extensive research efforts have led to significant improvements in kinetic activity (2), but conventional PGM-free catalyst continues to have lower volumetric activity than PGM catalysts. The lower volumetric activity requires use of a thicker cathode catalyst layer (CL), resulting in significant proton and oxygen transport losses (3). Therefore, along with kinetic improvements in oxygen reduction reaction, improved transport of H+ and O2 is needed to achieve performance comparable to PGM catalyst. In this study, we adopt a micro-patterning technique to incorporate non-tortuous ionomer channels in the cathode to increase the ionic conductivity of the thick catalyst layer. As shown in Figure 1, cathode ionomer channels enable rapid transportation of H+ throughout the catalyst layer, compared to thin and tortuous ionomer films in the conventional electrode. Polarization curves obtained in H2/air show significantly higher performance for the CL with ionomer channels compared to the conventional cathode. Electrochemical impedance spectroscopy data in H2/N2 also demonstrate a significant decrease in H+ resistance in the catalyst layer. The ionomer channels lead to a reduction in the H+ transport resistance, reducing ohmic overpotential in the catalyst layer. Further improvement in performance in the mass transport region is achieved through implementing optimized design of the dedicated ionomer channel.

Acknowledgment

This research was supported by the US Department of Energy, the Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office and the LANL LDRD program.

References

D. Papageorgopoulos, DOE Hydrogen and Fuel Cells Program FY2019 Annual Merit Review Proceedings, https://www.hydrogen.energy.gov/pdfs/review19/plenary_fuel_cell_papageorgopoulos_2019.pdf (2019).

H. Zhang, S. Hwang, M. Wang, Z. Feng, S. Karakalos, L. Luo, Z. Qiao, X. Xie, C. Wang, D. Su, Y. Shao and G. Wu, (2017).

S. Komini Babu, H. T. Chung, P. Zelenay and S. Litster, ACS Appl Mater Interfaces, 8, 32764-32777 (2016).

Figure 1
Effects of Catalyst Composition, Loading, and Spray Parameters on the Performance of Unitized Regenerative Fuel Cell Membrane Electrode Assemblies
Authors: Godinez Salomon Jose Fernando , Urena Michael E. , Rhodes Christopher P.
Published: November 2022

Proton exchange membrane unitized regenerative fuel cells (PEM-URFCs) combine the ability to both produce power (in fuel cell mode) and generate fuel and oxidant (in electrolysis mode) from the same cell. Compared with discrete fuel cell and electrolyzer systems, URFCs provide the potential for lower mass, volume, and cost. The composition and structure of the bifunctional oxygen catalyst layer (CL), which facilitates the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the same electrode, significantly affects performance and stability, particularly given the wide potential differences and different mass transport phenomena involved under operation in fuel cell or electrolysis mode. We previously showed bimetallic nanoframes provide bifunctional oxygen electrocatalysts with significantly higher activity compared with monometallic structures, evaluated using a rotating disk electrode configuration.1 Here, we investigated the effects of the oxygen CL composition, loading, and spray parameters on the performance of URFC membrane electrode assemblies (MEAs). Pt black and IrO2 catalysts were combined at different ratios and deposited at different mass loadings. Catalyst layers were sprayed directly onto membranes using an ultrasonic spray system. Within ultrasonically sprayed catalyst layers, higher spray rates resulted in improved fuel cell performance. Higher catalyst loadings improved both fuel cell and electrolyzer performance, but reached a region of diminishing returns at higher loadings. The ratio of the ORR catalyst (Pt) to the OER catalyst (IrO2) modulated the performance in both fuel cell and electrolyzer modes. Different catalyst ratios influence the catalyst utilization at higher loadings. The comparison of URFC performance at same Pt or IrO2 loadings indicates that in addition to the active catalyst itself, the non-catalytically active component influences MEA performance. This result is in line with our previous evaluation of synergistic effects of Pt and IrO2 within rotating disk electrode measurements1 and supports that in addition to the significant effects of catalyst material structure on performance, the electrode structure plays a critical role in fuel cell and electrolyzer performance in URFC MEAs. Repeated switching of URFC MEAs between fuel cell and electrolysis modes indicates that reasonable performance is maintained over the initial cycles within our single cell test configuration.

References

Godínez-Salomón, F.; Albiter, L.; Mendoza-Cruz, R.; Rhodes, C.P. Bimetallic Two-dimensional Nanoframes: High Activity Acidic Bifunctional Oxygen Reduction and Evolution Electrocatalysts. ACS Appl. Energy Mater.
2020,
3, 2404-2421.
http://dx.doi.org/10.1021/acsaem.9b02051
(Digital Presentation) Solving the Mystery of Ohmic Resistance in Zero-Gap Alkaline Water Electrolyzers Using Electrochemical Impedance Spectroscopy and Polarization Curves
Authors: Lira Garcia Barros Rodrigo , de Groot Matheus Theodorus , van der Schaaf John
Published: November 2022

Hydrogen can be produced using renewable energy sources through alkaline water electrolysis (AWE). Alkaline water electrolyzers are made of inexpensive materials such as nickel perforated electrodes and the Zirfon porous diaphragm. However, one of the bottlenecks of this technology is the high internal ohmic resistance compared to other technologies, which implies that the technology is traditionally operated at low current densities. To decrease the ohmic resistance advanced AWE electrolyzers use a zero-gap configuration. However, even with such a zero-gap configuration the ohmic resistance remains relatively high.

An analysis of polarization data on zero-gap alkaline electrolyzers with the commonly used Zirfon diaphragm suggests that the ohmic area resistances are significantly higher than what would be expected based on the properties of the diaphragm supplier [1]. In this study we use Electrochemical Impedance Spectroscopy (EIS) to further investigate this phenomenon [2], since EIS enables the separation of ohmic and charge transfer resistances.

EIS in combination with polarization measurements enables us to determine electrodes overpotentials, diaphragm ohmic losses and bubbles resistance and to estimate key parameters such as the reversible cell potential, the Tafel slopes and the exchange current densities of hydrogen and oxygen evolution reactions. Impedance data were fitted with an equivalent electric circuit, which consist of an ohmic resistance connected in series with two components, each including a resistance and a constant phase element (CPE) in parallel. Besides, the polarization measurements were fitted to a given correlation [1] using MATLAB as shown in Figure 1.

It was found that the ohmic resistance determined with EIS (~0.48 Ω.cm²) is lower than the fitted area resistance from the I-V curve (0.68 Ω.cm²), but is still higher than what would be expected based on the diaphragm properties for Zirfon. Obtained values for Tafel slopes and exchange current densities, both by EIS and I-V curves, are comparable to typical values from the literature. The resistance does not increase with current density suggesting that an increase of bubble volume with current density does not play a significant role in the resistance. Therefore, it still remains unclear what the origin is of the increased ohmic resistance.

[1] M.T. de Groot, A.W. Vreman. Ohmic resistance in zero gap alkaline electrolysis with a Zirfon diaphragm. Electrochimica Acta, 2021, 369, 137684. https://doi.org/10.1016/j.electacta.2020.137684

[2] Rodríguez, J.; Palmas, S.; Sánchez-Molina, M.; Amores, E.; Mais, L.; Campana, R. Simple and Precise Approach for Determination of Ohmic Contribution of Diaphragms in Alkaline Water Electrolysis. Membranes, 2019, 9, 129. https://doi.org/10.3390/membranes9100129

Figure 1
Fuel Cell Imaging with a Wolter Optics Neutron Microscope
Authors: Hussey Daniel , Daugherty Michael Cyrus , Kim Youngju , LaManna Jacob Michael , Jacobson David
Published: November 2022

Wolter optics promise to radically transform neutron imaging by improving the time resolution of the method by at least a factor 1,000 while providing spatial resolution of order a few micrometers [1]. These optics will enable neutron tomography of operating fuel cells with a time resolution of about a few minutes, which will provide unique insight into the water transport phenomena in membrane electrode assemblies of fuel cells and electrolyzers.

Neutron imaging has played a critical role in understanding water transport in proton exchange membrane fuel cells and electrolyzers [2]. The primary limitation of the method is the inherent neutron source strength, which is about a billion times weaker than X-ray synchrotron sources. Additionally, neutrons are difficult to focus using refractive lenses so that neutron imaging beamlines heretofore can be described as pinhole cameras. In a pinhole camera, the best achievable spatial resolution (λg) is determined by the diameter of the pinhole (D ~1 cm), the pinhole-to-detector distance (L ~10 m), and the sample-to-detector distance (Z ~1 cm):

λg = Z D / (L – Z) ~ Z D / L

Returning to the source strength, the neutron fluence rate at the sample position scales as (D / L)2. This means that higher spatial resolution for finite sized objects requires sacrificing neutron intensity and incurring long exposure times. Typical measurements require about 20 minutes for a single two-dimension image of the water content in fuel cell for a spatial resolution of about 10 µm. Such time requirements preclude the use of tomography, which is required to understand the water content in real fuel cell components since the MEA cannot be considered to be planar at the few micrometer level.

We will describe Wolter optics, and the optical system that will be first available in 2022. After the NCNR cold source upgrade is anticipated to yield a time resolution gain of about 10,000 compared to a pinhole camera. We will discuss our expected image acquisition and analysis procedures guided by ray tracing simulations.

Figure 1. Proof of concept Wolter optics image of a fuel cell test section.

[1] D. S. Hussey et al., “Design of a neutron microscope based on Wolter mirrors,” Nucl. Instruments Methods Phys. Res. Sect. A Accel. Spectrometers, Detect. Assoc. Equip., vol. 987, no. October 2020, p. 164813, 2021.

[2] T. A. Trabold, J. P. Owejan, J. J. Gagliardo, D. L. Jacobson, D. S. Hussey, and M. Arif, “Use of neutron imaging for proton exchange membrane fuel cell (PEMFC) performance analysis and design,” Handb. fuel cells, vol. 6, no. Table 1, 2010.

Figure 1
Tailoring Flow Field Channel Aspect Ratio for Efficient Mass Transport and Compression in Fuel Cells
Authors: Parmar Harsharaj Birendrasingh , Chadwick Eric Alexander , Shrestha Pranay , Bazylak Aimy
Published: November 2022

The adverse effects of global warming have made it critical to transition our reliance on fossil fuels to more sustainable energy sources. Polymer electrolyte membrane fuel cells (PEMFCs) can facilitate this transition by providing on-demand power with zero local carbon emissions. However, the high cost and poor durability of fuel cells hinder their widespread adoption. Particularly, PEMFC performance is strongly dependent on the flow fields which should be designed to optimize the transport of reactants and byproducts while maintaining uniform compression with subsequent layers. An important flow field design parameter is the channel aspect ratio which directly influences compression and the transport of reactants and products. Although novel flow field configurations have been studied previously, a comprehensive investigation on the effects of channel aspect ratio on cell performance has yet to be performed. In this study, we compared the electrochemical performance across varying flow field channel aspect ratios (channel width by height) from 0.5-2.0 with a fixed active area. The ohmic and mass transport resistances were quantified using electrochemical impedance spectroscopy. Operando X-ray imaging was performed to spatially resolve water saturation under the land and channel regions of the flow fields. We observed that lower channel aspect ratios (or higher number of channels for the given active area) led to lower ohmic resistance but resulted in higher mass transport losses at higher current densities due to significant water saturation under the hydrophilic ribs of the flow field. Notably, from these results we elucidated that there exists an ideal channel to rib width ratio to facilitate efficient mass transport and effective contact between the porous microstructures.
Gold-Reduced Graphene Oxide Composite Coating on Stainless Steel 316L As Bipolar Plate for Proton Exchange Membrane Fuel Cell
Authors: Seo Jinmyeong , Park Jung-Joon , Qing Wang , Yang Fan , Yoon Sanghwa , Yoo Bongyoung
Published: November 2022

Proton exchange membrane fuel cell (PEMFC) are regarded as one of the most promising fuel cell types for a new generation of power source in portable application due to no harmful byproducts emission, rapid startup and low operating temperature. Although PEMFC has a low output with a single cell, it is overcome by the series of unit stack by using bipolar plate (BPP) to improve the total efficiency. BPP, which conveys electrical current, separates reactant gases and connects single stack unit in series, is one of the most important part of PEMFC, along with catalytic electrode and proton exchange membrane. In recent years, stainless steel 316L (SUS316L) has been touted to as a promising candidate material for BPP with the numerous advantages such as low cost, high machinability and ductility. However, it has critical issues such as low corrosion resistance and high electrical resistance. For this reason, a coating process must be carried out on SUS316L with non-corrosive and conducting materials such as Au, Rh, Ag, Ti etc. Because these materials are high cost or rare-earth metals, anti-corrosive coating process inevitably causes the increase of BPP manufacturing cost.

In this study, Au-reduced graphene composite coating is introduced on SUS316L to improve anti-corrosion resistance and electrical conductivity with in cost-effective manner by minimizing the consumption of Au deposit and the using electrochemical fabricated graphene with low cost. Corrosion properties and electrical properties are investigated with the as-coated samples and in simulated operating condition. By addition of graphene coating process, the consumption of Au is dramatically reduced with the outstanding performance compared to with only Au coating.
Assembly and Testing of a Hydrogen Fuel Cell System to Power an Airship
Authors: Molinero Antonio , Oller Juan Carlos , Barcala José Miguel , Duque Luis , Folgado M. Antonia , Chaparro Antonio M
Published: November 2022

An airship, or dirigible balloon, is an aircraft that gains its lift from a gas less dense than air, like helium. For traction, airships have two or more propellers normally attached to a gondola that is suspended under the balloon. At present, they are used for hovering long times without the need for a high speed, like for aerial observation, advertising, or as camera platforms. In our laboratory, the airship is being used as a platform for testing hydrogen fuel cell systems for aerial applications.

The airship used in this communication is a 3 m3 polyurethane's inflatable zeppelin, with radio control, and three electrical propellers (Fig. 1a). A hydrogen fuel cell system has been developed and integrated with the gondola for powering the propellers and electronics. The fuel cell is a 15 W PEMFC stack prototype able to work fully under passive feeding conditions (Fig. 1b). In addition, three supercapacitors have been implemented, that are recharged by the fuel cell, for eventual larger power demands up to 40 W. Hydrogen is stored in two metal hydride canisters with 2g capacity to provide 30 W h energy enough for a few hours autonomy. In addition, for fuel cell parameters monitoring, different sensors have been implemented that provide voltages of the individual cells, current, and temperatures. The sensors are connected to Arduino board, and measurements are continuously monitored by a Labview software with wifi. Boost dc-dc conversion provides 7V voltage power to feed the motors.

The stack prototype allows for different testing configurations, using cells in series and parallel connection to change power characteristics with different voltage and current. Results of the testing are provided in this communication.

Acknowledgement: The work is partially financed by the ELHYPORT project (PID2019−110896RB-I00), Spanish Ministry of Science and Innovation.

Figure 1
The Ionomer Molecular Structure Effect in the PEFC Ink & Applications
Authors: Choi Won young , Choi Hyunguk , Choi Seo Won , Park Young Je , Jung CHI-Young , Lee Nam Jin , Lee Jong min , Yoon Young Gi
Published: November 2022

The interaction between the perfluorosulfonic acid (PFSA) ionomer and platinum group metal (PGM) catalyst in polymer electrolyte fuel cell (PEFC) inks is a critical issue for designing high-performance PEFC electrodes. During the ink fabrication, the complex interparticle interaction of the ink components determines the agglomerate morphology and size distribution. Among the ink components, the ionomer, which has amphiphilic in nature due to its hydrophobic backbone and the hydrophilic ionic group, mostly effective parameter for interparticle interaction. Therefore, understanding the interaction and molecular structure of ionomer is required for a high-performance catalyst layer. The backbone length of the ionomer which controls the spacing between ionic pendant groups is the main parameter of the ionomer character. In this study, the three different ionic spacing ionomers, made in the Solvay industry: Aquivion D72-25BS, Aquivion D83-24BS, and D98-25BS, were used for investigating the adsorption behavior of the catalyst ink and PEFC catalyst layer morphology. During the fabrication of PEFC ink and catalyst layer, all samples have same sulfonic acid molality to avoid the ionic clustering effect in the side chain. Ex-situ measurements were carried out to quantify the interparticle interaction and agglomerate size distribution in the PEFC ink. The dynamic lights scattering (DLS) carry out to determine the aggregation size distribution. The rheological behavior was conducted to understand the interparticle interactions and the agglomeration behavior of the inks by steady-shear and dynamic-oscillatory-shear measurements. It is noted that increasing the ionomer backbone length, which favors interaction via hydrophobic interaction on a carbon support, suppresses the agglomeration of ink components and decreases ink viscosity. The in situ electrochemical tests were carried out to figure out the relationship between ink formulation and catalyst layer morphology. It was found that the long ionomer backbone length helps to suppress the O2 transport resistance and ORR kinetic loss by uniform distribution from ionomer backbone-carbon supports interaction.
Hydrophobic Quaternized Poly(fluorene) Ionomers for Emerging Fuel Cells
Authors: Park Eun Joo , Adhikari Santosh , Leonard Daniel P , Lim Katie , Fujimoto Cy , Morales Oscar , Brennecke Joan F. , Hu Zhendong , Jia Hongfei , Kim Yu Seung
Published: November 2022

Quaternized polymers as ionomeric binders in the electrode enable the operation of alternative fuel cells under high pH conditions or anhydrous conditions to overcome the challenges of the proton exchange membrane fuel cells. Hydrophobicity of the ionomers derived from high fluorine content is beneficial to electrode performance, but due to the synthetic difficulties, not many fluorinated quaternized ionomers have been reported with their influence on electrode behavior in these emerging fuel cells. In this presentation, we report a series of quaternized poly(fluorene)s with controlled hydrophobicity by changing the length of flexible fluoroalkyl chains. The contact angle of the electrodes containing the ionomers ranged from 108.7 to 163.8°, comparable to that of the perfluorosulfonic acid-bonded electrodes. The anion exchange membrane fuel cells employing the ionomer exhibits improved durability (voltage loss 0.41 mV h−1) through better water management. The high-temperature proton-exchange membrane fuel cell using the ionomer showed superior H2/air performance (1.4 A cm-2 at 0.4 V). The study of the fluorinated poly(fluorene) highlights the benefits of hydrophobic ionomers for highly efficient and cost-effective fuel cell systems.
Durability and Performance Study of Chemically Anchored Heteropoly Acid with Perfluorinated Sulfonic Acid-Expanded Polytetrafluoroethylene Composite Membrane for Proton Exchange Membrane Fuel Cells
Authors: Kim Chuloong (Christoph) , Kuo Mei-Chen , Carmosino Dominic , Lindell Matthew , Jiang Ruichun , Ha Phuc , Gittleman Craig S , Yandrasits Michael , Herring Andrew M.
Published: November 2022

Chemical degradation and mechanical degradation are the major challenges for heavy-duty vehicle fuel cell commercialization. Perfluorinated sulfonic acid is the benchmark material that has high proton conductivity and robust mechanical properties. However, chemical degradation can occur through radical formation during the fuel cell operation. Chemical degradation can also have a synergetic effect with mechanical degradation. Recent studies have used cerium and manganese additives to suppress the radical formation or chemical degradation caused by radicals. The limitation of the metal and metal oxide additives was the migration and agglomeration of the additives. Both migration and clustering can lead to changes in membrane morphology, resulting in a loss in proton conductivity. Our group has previously reported that immobilization of heteropoly acid to a fluoroelastomer can be used to both enhance proton conductivity and chemical degradation. The durability test has shown that the chemical durability was significantly enhanced, but the mechanical durability remained the challenge.

In this study, we hypothesized that when a heteropoly acid can be chemically bound to the perfluorinated polymer and cast on a composite membrane with expanded polytetrafluoroethylene (e-PTFE) will enhance the chemical and mechanical durability without migration. Proton conductivity was measured using impedance spectroscopy. The structure-property relationship was studied using multi-scale morphology analysis methods such as scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and small-angle x-ray scattering (SAXS). The chemical degradation will be tested under the highly accelerated standard test (HAST) condition, a more severe fuel cell operation condition than the accelerated standard condition (AST). The mechanical durability of the composite membrane will also be tested on the HAST condition with humidity cycling.
PFSA Membrane Thickness Impact on Chemical Degradation Rates
Authors: Coms Frank D. , McQuarters Ashley B. , Marks Alex , Green Zachary
Published: November 2022

As the large-scale commercialization of proton exchange membrane fuel cells (PEMFC) for numerous applications, including heavy-duty trucks draws nearer, there is increasing interest in optimizing fuel cell membranes for both improved efficiency and durability. One of the major membrane attributes being considered for optimization is thickness. The current range of (perfluorosulfonic acid) PFSA membrane thicknesses employed for commercial applications range from 8 -25 µm. As with most adjustable materials parameters, there are a host of properties (cost, gas permeability, proton conductivity, etc.) that require co-optimization to provide the overall preferred position. For example, thin membranes will minimize proton resistance, facilitating high power densities, but will simultaneously allow increased gas crossover fluxes that can contribute to both reduced fuel efficiency and increased oxidative stress. On the other end of the spectrum, thick membranes will decrease gas crossover fluxes, offering improved fuel efficiency while simultaneously decreasing power density. A major question surrounding the tradeoffs of membrane thickness involves the chemical durability impact. Here, we report our investigations of PFSA membrane chemical durability as a function of thickness. For the studies reported here, a thickness series (8, 12 and 20 µm) of ePTFE reinforced Nafion®-like PFSA standalone membranes (SAMs) were prepared.

A two-pronged approach was taken for this study. The first involves investigation of intrinsic chemical stability of the ionomer as a function of membrane thickness using an ex-situ H2O2 vapor test. The second investigative mode, which targets the oxidative stress generated by crossover gas flux, employs OCV durability tests of full MEAs. In addition to membrane thickness, gas crossover rates are known to be functions of membrane hydration and gas pressures.1,2 Accordingly, a 3(4-1) fractional factorial experimental design was executed to probe the role of membrane thickness as well as the other factors known to affect gas crossover. The fractional factorial design allows all main effects to be determined and further allows estimation of two factor interactions, if present.

References

T. Sakai, H. Tanenaka, E, Torikai, “Gas Diffusion in Dried and Hydrated Nations” J. Electrochem. Soc., 1986, 133, 88-92

R. Jiang, T. Fuller, S. Brawn, C. Gittleman, “Perfluorocyclobutane and poly(vinylidene fluoride) blend membranes for fuel cells” Electrochimica, Acta, 2013, 110, 306-315
(Digital Presentation) Design of Metal/Metal Oxide Nanomaterials for Highly Active, Selective, and Durable Electrocatalysts
Authors: Sung Yung-Eun , Shin Heejong , Kim Jae Jeong
Published: November 2022

Electrocatalysis is a key part of renewable energy conversion in the future energy system. Sustainable energy conversion and chemical production require catalyst structure with high activity, durability, and product selectivity. In general, nanoscale electrocatalysts suffer various degradation phenomena during electrocatalysis, which leads to critical performance loss. Recently, the various hybrid nanostructures (such as ordered structure, metal/carbon encapsulation, or metal/metal oxide) have been highly investigated to achieve promising catalytic performances and enhanced stabilities.

In this presentation, we will cover three different types of nanomaterials as highly active and stable electrocatalysts for oxygen reduction reaction (ORR). First, the alloy nanoparticles with ordered structures exhibit novel catalytic properties from their unique electronic and geometric structures. In particular, Pt alloys with atomically ordered crystal structures have been found to largely improve both electrocatalytic activity and stability for ORR through increased electronic interaction between Pt and other transition metals. Similarly, we recently demonstrated that well-controlled Co-, Mn- and Fe-based ternary or binary oxide nanocatalysts have an exceptionally high ORR activity, in addition to the promising electrocatalytic stability. Therefore, it is very important to synthesize well-ordered alloy nanocrystals to obtain highly durable and active electrocatalysts with respect to their structural and compositional properties. Second, we will show the strategic employment of carbon shells on electrocatalyst surfaces to enhance stability in the electrochemical process. Carbon shells can beneficially shield catalyst surfaces from electrochemical degradation and physical agglomeration. Thus carbon shells can effectively preserve the initial active site structure during electrocatalysis. The carbon shell also provides a confined environment at interfaces, enabling unconventional electrochemical behaviors. Finally, we will suggest an effective strategy to construct metal/oxide interfaces, precisely modulating the metal/oxide interfacial interactions in the nanoscale. By controlling the interface and strain effect on catalytic activity, we can achieve high active and stable metal oxide systems for ORR. We would like to describe the details of the above results, for investigating structure-activity relationships in electrocatalytic processes. Only when we start to comprehend the fundamentals behind electrocatalysis on the structure and interface of metal/metal oxide nanocrystals, they can be further advanced to be sustainable in long-term device operation.
(Digital Presentation) Molybdenum-Promoted Intermetallic PtCo ORR Catalyst
Authors: Pan Yung-Tin , Lin Liang-Chen , Kuo Chun-Han , Hsu Yu-Hsuan , Chen Han-Yi , Hsu Liang-Ching , Chen Jeng-Lung
Published: November 2022

Molybdenum (Mo)-promoted intermetallic platinum-cobalt (Pt-Co) oxygen reduction reaction (ORR) catalyst with significantly enhance ORR activity was obtained through impregnation and thermal treatments using MoCl5 as a precursor. With an optimized coverage of the Mo promoters, X-ray absorption spectroscopy reveals the cluster-like Mo-Ox species effectively lowered the white line intensity of Pt in its near edge structure (Pt L-edge XANES), suggesting the further weakening of its affinity towards oxygen. The Mo-promoted intermetallic Pt-Co catalyst thus exhibited a high ORR mass activity of 0.89 A/mgPt compared to 0.22 A/gmPt for pure Pt and 0.62 A/mgPt for its parent Pt-Co respectively under RDE testing conditions. The Mo-promoted catalyst showed compelling durability losing only 29 % of its initial 0.95 V mass activity which is even higher than the non-promoted fresh PtCo catalyst (0.32 A/mgPt vs 0.24 A/mgPt). When tested under membrane electrode assembly (MEA) conditions, the high ORR activity further enabled the operation of the fuel cell under low cathode relative humidities (RH) with minimal penalties in ionic transport resistance at low current regions. Density functional theory calculations reveal the beneficial role of molybdenum oxide cluster species in lowering the d-band energy surface Pt atoms, particularly at Pt segregated regions with no Pt-Co phase in proximity to induce the strain or ligand effects.
Improvements of Mechanical Properties and Electrical Resistance of PEMFC Catalyst Layer through Thermal Reconfiguration
Authors: Kim Ji Hun , Pyo Jae-Bum , Kim Taek-Soo , Kim Kiyoul
Published: November 2022

Mechanical integrity of a polymer electrolyte membrane fuel cell (PEMFC) catalyst layer is critical to the fuel cell's performance and long-term durability due to its direct correlation with the increment of contact resistance and the disconnection of charge transporting paths. However, mechanical failures of the catalyst layer during the operation have been inevitable because of the catalyst layer’s fragile nature. In this work, dramatic enhancement of the catalyst layer's robustness is demonstrated beyond the conventional knowledge of the catalyst layer's brittleness. Through thermal reconfiguration of the ionomer binding, the mechanical properties such as tensile strength and the elongation of the catalyst layer are improved more than 10 times compared with the previously reported intrinsic properties. Thermal reconfiguration above the ionomer transition temperature induces melt flow of the ionomer, this structural reconfiguration enhances the continuity of the load-carrying ionomer in the nanostructure, contributing to relieving load concentration. We also reveal nanostructural origin of the charge conducting paths reconstructed by thermal reconfiguration of the electrode catalyst layer. The thermomechanical behavior of the ionomer by thermal reconfiguration can maximize the continuity of ionic and electronic phases, and the nano-networking itself is highly enhanced as the reconfiguration temperature increases. Above the second transition temperature, initially disconnected ionomer-bound carbon agglomerates are connected due to thermal behavior. The catalyst layer demonstrates electronic singularity as the ionomer penetrates into the interstitial space between the carbon particles and creates electron path insulation. Ionic and electronic resistances are enhanced by approximately 40 % compared to the pristine electrode due to the higher nano-networking of the conductors. In conclusion, long-term durability and cell performance improvement can be expected without cracking and delamination under the hygro-thermal buckling loads through thermal reconfiguration of the PEMFC catalyst layer.

Acknowledgements

This work was supported by the BK21 FOUR Program of the National Research Foundation Korea (NRF) grant funded by the Ministry of Education (MOE), the Technology Development Program to Solve Climate Changes through the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2020M1A2A2080859), the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2022R1A2C3009087), the Wearable Platform Materials Technology Center (WMC) funded by the National Research Foundation of Korea (NRF) Grant by the Korean Government (MSIT) (No. 2022R1A5A6000846).
Stability and Degradation of Pt/C Catalysts Explored with IL-TEM
Authors: Smykała Szymon , Pawlyta Mirosława , Liszka Barbara
Published: November 2022

Industrial application of fuel cells, while, hopefully, inevitable, is still hindered by various aspects, one of them being the issue with oxygen reduction reaction (ORR) catalysts. Current state of the art platinum catalysts, while extraordinarily active, still have a long way to go when it comes to stability. In this work we have decided to tackle this problem by employing FW200 carbon black as a support for platinum nanoparticles. The carbon support was treated in 3000 °C to obtain highly ordered, graphitic structure. We’ve discovered that our catalyst, while initially exhibiting lower electrochemical surface area (ECSA) than it’s commercial, Vulcan-based counterpart, degraded with substantially slower rate than the industrial catalyst. We’ve came to that conclusion after subjecting the catalysts to accelerated degradation tests (ADT) on the rotating ring disk electrode in various potential ranges and performing ECSA and activity measurements during and after said tests. Additionally, to explore degradation mechanisms of the catalysts we’ve used identical localization transmission electron microscopy (ILTEM). This technique allows us to track the behaviour of each platinum nanoparticle, before and after electrochemical measurements, by performing ADT on TEM grids covered with catalyst. ILTEM experiments allowed us to prove, that the crystalline structure of graphitized FW200 hinders nanoparticles’ movement across the carbon support, leading to increased resistance to agglomeration. We used inductively coupled plasma optical emission spectroscopy to investigate platinum dissolution’s part in reducing catalyst activity by measuring the amount of platinum left in electrolyte after ADT. Lastly, we’ve investigated the influence of heat treatment in 3000 °C on the structure and electronic properties of the FW200 carbon black using Raman spectroscopy and X-ray photoelectron spectroscopy.

Thorough electrochemical and structural study of platinum catalyst deposited on graphitized FW200 carbon black allowed us to confirm, that our material is highly competitive, in the terms of stability, to commercially available Vulcan-based catalysts. We also think that ILTEM, while exceptionally powerful, is still quite an underutilized technique and we would like to present how joint efforts of microscopists and electrochemists can push the boundaries of knowledge in ORR electrochemistry.
(Invited) Catalyst Challenges for Ion-Pair High Temperature Proton Exchange Membrane Fuel Cells
Authors: Lim Katie Heeyum , Maurya Sandip , Hu Zhendong , Jia Hongfei , Matanovic Ivana , Zulevi Barr , De Castro Emory Sayre , Fujimoto Cy , Kim Yu Seung
Published: November 2022

High temperature proton exchange membrane fuel cells (HT-PEMFCs) have several merits over low temperature PEMFCs, including simplified fuel cell systems and high CO tolerance. Recently developed ion-pair HT-PEMFCs1 has a significantly lower concentration of phosphoric acids in the membrane-electrode assembly (MEA) that allows ion-conducting binders (ionomers) in the electrodes. Here, we first explain the difference in MEA configurations and fuel cell performance between conventional polybenzimidazole-based and ion-pair HT-PEMFCs2. Next, we discuss catalyst challenges for ion-pair HT-PEMFCs by comparing half-cell and single-cell results.

We focus on three critical areas in that electrocatalysts face challenges: i) phosphate anion poisoning on oxygen reduction reaction catalysts, ii) phenyl adsorption on hydrogen oxidation reaction catalysts and iii) phosphoric acid flooding. Research progress mitigating those adverse effects is demonstrated using various commercial Pt-based catalysts and homemade ionomers. Lastly, we provide general directions for designing high-performing catalysts of ion-pair HT-PEMFCs.

References

Lee, K. S.; Spendelow, J. S.; Choe, Y. K. Fujimoto, C.; Kim, Y. S. An Operationally Flexible Fuel Cell Based on Quaternary Ammonium-Biphosphate Ion Pairs, Nature Energy, 1, 16120 (2016).

Lim, K. H.; Lee, A. S.; Atanasov, V.; Kerres, J.; Park, E. J.; Adhikari, S.; Maurya, S.; Manriquez, L. D.; Jung, J.; Fujimoto, C.; Matanovic, I.; Jankovic, J.; Hu, Z.; Jia, H.; Kim, Y. S. Protonated phosphonic acid electrodes for high power heavy-duty vehicle fuel cells, Nature Energy, 7, 248 (2022).
High Performance AEM Water Electrolysis with PGM-Free Electrocatalysts
Authors: Ul Hassan Noor , Shakouri Abolfazl , Adabi Firouzjaie Horie , Duanghathaipornsuk Surachet , Zulevi Barr , Kohl Paul , Mustain William Earl
Published: November 2022

Water electrolysis technologies for hydrogen production are getting much attention due to drastic cost reduction in renewable energy sources, like solar, wind, tidal etc. Traditional alkaline water electrolysis has limitations of low current density operation, slow system response and low hydrogen discharge pressure. Proton exchange membrane (PEM) water electrolysis offers compact design, high current density operation, fast system response and pressurized discharge hydrogen. However, PEM electrolyzers require the use of Platinum Group Metal (PGM) based electrocatalysts, expensive perfluorinated membranes and specialized component materials due to its acidic environment. These are all hurdles to its widespread commercial adoption. A relatively new technology, the anion exchange membrane (AEM) electrolyzer can potentially combine benefits from PEM and traditional alkaline electrolyzers, offering high current density operation, pressurized discharge gas and low cost – by utilizing PGM-free electrocatalysts and inexpensive component materials due to the less corrosive alkaline operating environment.

However, modern AEM electrolyzers have continued to use high loadings of PGM catalysts in both the cathode and anode. Given the magnitude and recent volatility in the market price of many PGM-group metal catalysts (e.g. Ru, Ir, etc.), it is now even more important for AEM electrolyzers to be realized with significantly lower PGM content – and eventually approaching the complete elimination of PGMs.

In this study, we evaluate the performance of several low-PGM and PGM-free electrocatalysts for the oxygen evolution (OER) and hydrogen evolution (HER) reactions for high performance and durability. Here, PGM-free Lanthanum Strontium Cobalt (LSC), Nickel Ferrite (NiFeOx) and low PGM Lead Ruthenate (PbRuOx) were used at the anode for the OER. For the HER cathode, PGM-free Nickel Molybdenum (NiMo) and low-PGM PtNi electrocatalysts were evaluated for their in-situ activity and durability. It will be shown that LSC and NiFeOx show comparable performance to IrOx, with a typical steady-state operating voltage at 60oC and 1.0 A/cm2 (with 0.3 M KOH fed to the anode only) below 1.80 V. Cells with PGM-free anode catalysts were operated stably for over 100 hours. At the cathode, NiMo showed relatively higher overpotentials compared to Pt black, PtNi or Pt/C for the HER. Because of this, various strategies were adopted to reduce the PGM loading while achieving high performance and durable AEM electrolyzer operation. The achieved experimental results provide important insights for the development of AEM based water electrolyzer systems and represent an active step towards its commercial viability.
Mechanisms of Si Stabilization for Future Anode Design
Authors: Cora Saida , Sa Niya
Published: November 2022

Silicon owing to its abundance, low working potential and high theoretical specific capacity has been regarded as one of the promising anode materials for the next generation lithium-ion batteries (LIBs). The bottleneck of Si anode practical application is its large volume variation and formation of reactive silicide species at the anode/electrolyte interface during lithiation which result in continuous SEI formation and consumption of active electrolyte components. The new electrolyte design strategies have shown to stabilize the Si electrode via an in situ electrochemical formation of a metastable ternary Li-Mg-Si phase. In this study, the effect of electrolyte modification on the dynamic formation of solid electrolyte interphase (SEI) on Si anode is investigate in the pre-lithiation versus post-lithiation stages of electrochemical cycling. In addition, combined EQCM-EIS are used to investigate the charge transfer mechanism and the resistivity of the surface film at various stages of cycling. The understanding of the stabilization effect of Mg salt on Si surface chemistry may have a great impact on the development of Si-based anodes for lithium-ion batteries.