bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiscale Modeling of the Membrane Electrode Assembly in Polymer Electrolyte Fuel Cells: Interaction of Pore Size and Wettability of Porous Layers
Authors: Garcia-Salaberri Pablo A. , Sánchez-Ramos Arturo
Published: February 2024

Design of the membrane electrode assembly (MEA) plays a crucial role in polymer electrolyte membrane fuel cells (PEMFCs). However, predictive modeling of mass, charge and heat transport considering primary microstructural information rather than previously measured effective transport properties is challenged by the multiscale pore structure found in an MEA, which spans around 4-5 orders of magnitude (from tens of nanometers in the catalyst layer to tens of micrometers in the gas diffusion layer). It is not clear how to incorporate microstructural information to guide design, while preserving moderate computational cost (see log-scale pore size distribution in an MEA in Figure a). In this work, a 3D two-phase, non-isothermal model is presented, which combines continuum and pore network (PN) formulations in a single CFD framework. Transport at fine pore scales of the catalyst layer and the microporous layer (below 1 um) is modeled by means of a continuum bundle-of-capillary-tubes (BCT) submodel, and transport at coarse pore scales of the gas diffusion layer and manufacturing defects above 1 um (cracks, gaps, etc.) by means of a continuum-based PN submodel. The BCT submodel accounts for microscopic (<20 nm), mesoscopic (20-300 nm) and macroscopic (300 nm-1 um) pore scales considering a subdivision of pore size distributions in the integral volume-averaged formulation. The interplay between pore size distribution and wettability of the various porous layers is analyzed, with a focus on the role of microporous layer wettability and defects, depending on operating relative humidity and temperature (see water distribution in Figure b from an invasion-percolation simulation). Best design practices of porous assemblies are extracted for maximum performance from a large computational campaign, including stochastic effects from different sample realizations. Analysis of degradation phenomena will be the focus of subsequent work to determine optimal microstructures arising from a trade-off between performance and durability.

Figure 1
Simulations of Wolter Optics Tomography of a Fuel Cell
Authors: Hussey Daniel Seth , Daugherty Michael Cyrus , Kim Youngju , Jacobson David , LaManna Jacob Michael
Published: February 2024

Wolter optics present the opportunity to realize a practical neutron lens, which would convert a neutron imaging instrument from a pinhole camera to a microscope. This conversion would result in significant increases in neutron flux (up to 10,000 gain over the pinhole geometry) while maintaining high spatial resolution (about 3 μm). The Wolter optic system is currently being fabricated, and the first mirrors are expected to arrive in SEP 2023. As such, we focus this presentation on image simulation efforts. A ray tracing code has been developed that is able to simulate full three-dimensional imaging of extended objects placed in the Wolter optics neutron microscope. To simulate a fuel cell, we employ tomography measurements based on X-ray tomography and CAD-model derived volumes. The reason the Wolter optics system realizes such a large gain in flux is by focusing much of the flux from an extended neutron guide onto a small spot. Thus, conventional radiography of an extended object will not be possible, as the beam is similar to a cone beam which emanates from a small spot. We derive a tomography algorithm for this spot and will show its effectiveness on reconstructing simulated images. We also report on expected performance of the fabricated optical system in the current instrument configuration.

Figure 1
In-Situ Spectroscopic Investigation of 3-D Gas Diffusion Electrodes for Fuel Cell Reactions in Half-Cell Setups
Authors: Jalan Rameshwori , Gomes Bruna Ferreira , Roth Christina
Published: February 2024

Significant work has already been done in understanding proton exchange membrane fuel cells (PEMFC) over the past decades. In-situ visualization of the fuel-cell reactions has developed considerably and has also helped in understanding the challenges which still exist in various steps of electrochemical processing. Gas diffusion electrode half-cells have been widely promoted for fundamental catalysis research and when coupled with techniques like X-ray absorption spectroscopy (XAS) can be used for in-situ/operando studies of the reaction mechanisms in fuel cell reactions. This is particularly important to address the challenges in low temperature PEMFCs (eg. degradation of catalyst during durability tests) as well as high temperature PEMFCs (eg. poisoning of the Pt catalyst and low oxygen solubility in phosphoric acid).

In this presentation, an effort will be made to illuminate the catalytic characteristics during oxygen reduction reaction using in-situ XAS. The co-adsorption of H3PO3 and CO on platinum catalysts will be investigated using the Δµ XANES technique by following the signatures of different species adsorbed on the catalyst surface, and the Efix technique which follows the variation of signal intensity at a fixed energy near to the white line to follow the changes in Pt oxidation. During CO removal through cyclic voltammetry in the presence of 800 µM H3PO3 (as shown in the figure provided) it is possible to see a clear change in signal intensity around the potential of 250 mVAg/AgCl, which was associated with the oxidation of H3PO3 to H3PO4, since CO oxidation takes place at higher potentials (above 600 mVAg/AgCl). It is also interesting to note that when oxidizing H3PO3 to H3PO4, the platinum surface significantly reduced. With these experiments, it can be concluded that the Efix technique has a great potential to better understand what happens to Pt during the oxidation of H3PO3, as well as to identify more clearly the oxidation potential of this species, which is not easy to do based on the electrochemical data alone. Considering that this species is one of the main species responsible for the poisoning of the Pt catalyst during the operation of fuel cells, it is extremely important to understand the life cycle of this compound so that the operating conditions can be adapted to maximize the performance of the catalyst and develop new catalysts more resistant to poisoning by phosphorous species for HT-PEMFCs.

Acknowledgements:

Prof. Matthias Arenz from University of Bern, Martin Prokopand Tomàs Bystrom from University of Chemistry and Technology Prague, Michael Haumann, Freie Universität Berlin are gratefully thanked for their collaboration. German Research Foundation DFG Project ID RO 2454/19-1, the Bavarian Gender Equality Grant 2019-2021 (for Women in Academia), Petra III DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, P65 beamline (I-20211432) and KMC-3 beamline BESSY (Berlin,Germany).

Figure 1
MRI Study of the Influence of the Catalytic Layer on the Interfacial Water Transfer in PEMFC Membrane-Electrode Assemblies
Authors: Mrad Christine , Perrin Jean-Christophe , El Kaddouri Assma , Guendouz Laouès , Mozet Kévin , Dillet Jérôme , Lottin Olivier
Published: February 2024

A better understanding of the limitations induced by decreasing platinum content in PEMFC membrane-electrode assemblies, both in terms of operation and aging of the electrodes and ionomer membrane is still needed. More specifically, more information and understanding of water transport across the membrane / electrode interface is required. Few experimental techniques can be used to measure the water interfacial resistance in these sandwiches as the method must be able to measure both the water flux through the assembly and the water content at the membrane interface. Among them, magnetic resonance imaging (MRI) can be effectively exploited by using surface coils to enhance the NMR signal and improve the quality of the measurement [1,2]. In the present study, MRI was used to distinguish the water diffusion resistance within thick Nafion-type PFSA membranes from the water transfer interfacial resistance. Measurement of the water profiles across the membrane allowed for accurate evaluation of the evolution of the diffusion coefficient as a function of water content. The determination of the water content at the interface and of the water flux through the membrane allowed the determination of the interface resistance for different hygrometry conditions imposed on both sides. The experiments were then repeated on membrane / electrode and electrode / membrane / electrode samples to evaluate the impact of the electrode layer. Our results show a strong evolution of the interfacial resistance as a function of the air humidity while the influence of the electrode does not seem to be preponderant.

Figure

(left): NMR experimental cell containing a Nafion N1110 sample fed by two streams of humid air with controlled flow rate and relative humidity (RH).

(right): examples of water content () profiles measured by MRI (6 µm spatial resolution) in different RH conditions.

References

[1] Ouriadov, A. et al. J. Magn. Reson. 169(1), 174–186 (2004)

[2] Klein, M. et al. ECS Transactions, 58(1), 283-289 (2013)

Figure 1
Progress in the Measurements of Coupled Transport Mechanisms in the Electrolyte of a PEM Based Thermogalvanic Cell
Authors: Willke Maike , Rahm Nils-Eric , Diedrich Tim , Kabelac Stephan
Published: February 2024

A promising measure to increase the efficiency of energy conversion is the use of low temperature waste heat being readily available in a vast amount. Thermogalvanic cells (TGC) offer the possibility of electrical energy harvesting from such thermal energy. An externally applied heat source leads to a temperature gradient across the electrolyte inducing a gradient in the chemical potential and a difference in the electrical potential between the electrodes. Due to the aim of approaching a homogeneous equilibrium different coupled molecular transport mechanisms are taking place in the electrolyte impacting the performance of the TGC. In contrast to the common approach of using classical transport correlations such as Fourier’s, Ohm’s or Fick’s law to describe these coupled processes this work applies the theory of non-equilibrium thermodynamics (NET). The method considers all interactions of the driving forces and resulting fluxes occurring in the electrolyte and clearly separates the transport phenomena into their origin. The knowledge of these relations, which can be described by characteristic phenomenological coefficients, gives a better understanding of the TGCs internal processes and the opportunity to determine the entropy production aligned with local heat sources inside its electrolyte. In this work a TGC based on a polymer electrolyte membrane with two gaseous hydrogen electrodes of different temperatures was investigated experimentally. Due to the need of water in the electrolyte to ensure ionic transport the TGC was fed with a humidified hydrogen gas. The experimental setup gives the opportunity of precisely adjusting the temperature and composition of the species at both electrodes thus control the gradients in temperature, concentration i.e. chemical potential and electric potential between the electrodes. By suppressing all but one driving force across the electrolyte and measuring the open circuit voltage (OCV) different coupling coefficients as well as the occurring fluxes in the electrolyte were determined for a wide variety of working conditions. By implementing the measured phenomenological coefficients in an earlier published model of the TGC considered in this work a significantly lower deviation of the modeled and measured OCV values compared to the approach of using classical transport coefficients can be determined. This indicates the importance of applying the NET when considering transport phenomena while different gradients being present. We also show that by an aligned combination of the gradients in temperature and chemical potential of the water their impacts on the electrical potential can sum up leading to a higher OCV or even cause a pole reversal due to contrary effects on the electrical potential difference.

Figure 1
Impedance Study of the Effect of Cell Compression on PEMFC Under Various Oxygen Supply Conditions
Authors: Tanaka Akihisa , Nagato Keisuke , Weber Andre , Tomizawa Morio , Nakao Masayuki
Published: February 2024

Cell compression impacts the performance of polymer electrolyte membrane fuel cells (PEMFCs). A previous study has reported a trade-off between mass transport and contact resistances from cell compression [1]. Our study focuses on how the compression pressure affects polarization resistance under various oxygen partial pressure conditions. Without hot pressing the gas diffusion layers, a membrane electrode assembly with an electrode area of 1 cm2 was set in a housing in which the compression pressure could be adjusted [2]. Impedance spectra were measured at 0.7 A/cm2 under various oxygen partial pressure conditions. Figure 1 shows that polarization resistance decreases with increasing compression pressure under low compression pressure conditions, and conversely increases under high compression pressure conditions. The change in polarization resistance is more pronounced under low oxygen partial pressure conditions. In this contribution, the effect of cell compression on the different polarization processes will be discussed, considering the impact of compression pressure on catalyst layer thickness and porosity.

References

[1] N. K. Shrivastava et al., Int. J. Energy Res., 44, 370–385 (2020).

[2] M. Heinzmann et al., J. Power Sources, 402, 24–33 (2018).

Figure 1
(Invited) Leveraging Imaging Techniques to Accelerate the Advancement of Polymer Electrolyte Membrane Water Electrolyzers
Authors: Bazylak Aimy
Published: February 2024

Polymer electrolyte membrane water electrolyzers (PEMWEs) are critically needed to meaningfully incorporate clean renewable energy into our energy, transportation, and manufacturing sectors, for without this energy conversion mechanism, the intermittency of renewable energy will always pose a prohibitive cost barrier to practical use. However, in addition to overcoming the intermittency issue of renewable energy, energy storage also has the power to transform current energy infrastructure, particularly when plagued by older systems that lack modularity and flexibility. For example, electricity grids are often constrained to move electricity in and out of a jurisdiction with careful predictions based on past use and future needs. This comes at a cost when electricity must be sold at a loss to prevent a catastrophic surplus of electricity in the grid. While the potential for PEMWEs is tremendous, we must reduce their capital and operating costs in order to reach widespread adoption. In recent years, important work in the field has contributed to advancing PEMWEs in a variety of areas from new materials to flow field design; however, experimental validation, particularly spatially resolved, is necessary to take a fully informed approach to tailoring these materials and architectures.

In this talk, I will discuss how we use X-ray and neutron imaging, both ex situ and operando, to provide high spatial and temporal resolution experimental performance and materials characterization for PEMWEs to inform our design process for new materials fabrication, new architectures, and operating parameters. We obtained nano-scale, 3D imaging of PEMWE catalyst layers to inform the stochastic simulations used to uncover the influence of pore size and ionomer distributions on electrical and ionic conductivities. We also used operando X-ray imaging to elucidate the influence of catalyst layer and porous transport layer interfacial conditions on liquid and gas transport behaviour. By applying neutron imaging, we elucidated the impact of temperature on the distribution heterogeneity of liquid water reactant at the catalyst layer. I will also discuss how we are using soft X-rays to perform synchrotron-based scanning transmission X-ray microscopy with absorption spectroscopy to uncover heterogeneity across performance and material characteristics for the PEMWE. Through these highly resolved techniques (in terms of time and space), we aim to advance our predictive models for designing next generation materials, interfaces, and flow configurations for high performance water electrolyzers.
Mitigating the Degradation of Electrodes in Alkaline Water Electrolysis during Shutdown Mode by Interrupting Reverse Current
Authors: KIM Bonghyun , KIM Wan Sik , Sim Junseok , Jung Young HAN , Tamboli Asiya Mohaseen , Kim Changhee
Published: February 2024

Alkaline water electrolysis (AWE) is a promising technology for large-scale hydrogen production using renewable energy sources (RES). However, AWE integrated with RES experiences shutdown mode due to their intermittency, resulting in reverse current through open flow path of high ionic conductivity. This induces irreversible phase changes, which lead to electrode degradation and inevitably reduce the performance of the AWE. Therefore, it is important to examine the degradation mechanism and identify effective methods to reduce reverse current in AWE. In this work, we developed AWE system which impedes hydroxide ion transfer using deionized (DI) water circulation when it undergoes a shutdown mode. Cutting off the flow of ionic charges prevents the electrodes from forming irreversible phase change, making long-term operation possible while securing durability. We examined how reduced ionic conductivity mitigates the side effects of reverse current using phase characterization and electrochemical performance tests. Based on these results, we established an optimal way to impede hydroxide ion transfer in shutdown condition of an AWE system integrated with RES. Our findings will overcome fatal shortcomings and operate more efficiently in AWE industry.
Method for Systematic Validation of a Physically Based PEMFC Model By Spatially Resolved Impedance Measurements
Authors: Goosmann Tobias , Oppek Philipp , Weber Andre
Published: February 2024

Loss mechanisms in PEM Fuel Cells related to charge transfer reactions or diffusive gas transport result in a strongly nonlinear performance, which is furthermore affected by operating conditions as temperature, relative humidity of the gases and stoichiometries. These dependencies have to be considered and validated in fuel cell models to ensure accuracy. Thus, the interpretation of the simulated results becomes more reliable.

Direct comparison of simulated and measured current/voltage-relation only allows to evaluate deviations in resulting cell voltages but exclude internal state variables of the model such as overvoltages due to different loss mechanisms. In consequence, simulated and measured values of voltage or current can concur by unnoticed compensation of different errors in magnitude and sign. Additionally, limited numbers of measurements and comparisons increase the probability and impact of this effect.

Aggravating, every single process within the cell depends on the comprehensive combination of all operating conditions and runs simultaneously with all other ones. A direct comparison of individual simulated and measured polarization curves therefore is not a suitable and sufficient validation.

We address this challenge by applying measurements of electrochemical impedance spectroscopy (EIS) during systematically varied operating conditions spatially resolved along the gas flow direction [1]. The loss processes within the cell can be separated by distribution of relaxation times (DRT) and quantified by a physico-chemical meaningful transmission line model. The resulting amount and distribution of resistances caused by loss processes is compared with the corresponding simulated values of a multiphysical model for observation and monitoring during operation [2]. These insights support the investigation of deviations between simulated and measured polarization curves and therefore the validation the model.

In this contribution, the resulting physical interpretation is discussed. Consequences and conclusions for the further development of the cell model are demonstrated.

[1]: P. Oppek et al., „ Spatially Resolved Deconvolution of Loss Processes in PEM Fuel Cells”, 241st ECS Meeting, Vancouver

[2] T. Goosmann et al. „Impedance-Based, Multi-physical DC-Performance-Model for a PEMFC Stack”, 241st ECS Meeting, Vancouver
Efficient High Temperature PEMFC Metallic Stack
Authors: Neofytidis Charalampos , Paloukis Fotios , Athanasopoulos Nikolaos , Neophytides Stylianos G. , Daletou Maria
Published: February 2024

High temperature (HT) polymer electrolyte membrane fuel cells (PEMFCs) are highly beneficial for high power applications [1-3]. They can be used both in stationary, as well as portable power devices [1,4,5] combining the advantages of the PEM type cells (flexibility in dynamic operation, compactness) and high temperature operation (elimination of fuel humidification and carbon monoxide clean up).

This work focuses on the development, construction and testing of an efficient all-metallic HT-PEMFC stack with a power output of 1 kWe [6]. The selection of the proper polymer electrolytes allowed the operation of the stack within the range of 160-190oC. The Membrane-Electrode-Assemblies (MEA) and all components of the stack were designed and prepared in-house. The fuel cell stack characteristics and performance are affected by many parameters such as the materials, components’ design and proper assembly of the stack, as well as the operating conditions.

The stack accomplished 50% electrical efficiency with power output of 1070 W and a power density of about 0.18 W/cm2 at 180°C under pure H2 feed. The same performance was reached with reformate hydrogen feeds. The 1 kW electrical and 1 kW thermal power HT-PEMFC stack presented herein consists of thirty MEAs, metallic bipolar plates and an innovative cost-efficient internal pumpless two-phase equilibrium water-steam cooling. The effective design and construction of the latter secures temperature gradientless and isothermal operation of the stack and the production of high temperature superheated steam, which is an effective carrier of high-quality thermal energy with several commercial and industrial applications.

Acknowledgments

Funding from Region of Western Greece and European Regional Development Fund (RIS3) through DemoCHP DЕР7-0019758 and the Operational Program “Competitiveness, Entrepreneurship & Innovation” (EPAnEK), NSRF 2014-2020 through Solar2HyP Τ2ΕΔΚ-01877.

References

[1] K. Hooshyari et al., Energies 14 (2021) 5440.

[2] A. Chandan et al., Journal of Power Sources 231 (2013) 264–78.

[3] J. Zhang et al., Journal of Power Sources 16 (2006) 872–91.

[4] Y. Liu et al., Journal of Power Sources 311 (2016) 91–102.

[5] Z. Pu et al., Applied Energy 283 (2021) 116376.

[6] C. Neofytidis et al., Energy Conversion and Management 283 (2023) 116944.
Nonuniform Compensation of the Current Density Distribution in the Polymer Electrolyte Fuel Cell Using Local Heating
Authors: Zhou Shangwei , Rasha Lara , Xu Linlin , Du Wenjia , Shearing Paul R , Brett Dan J L , Jervis Rhodri
Published: February 2024

It is well known that reasonable current density distribution can improve fuel cells' output performance and prolong their service life. Which can be achieved by elaborately designed structures and compression, and the reaction occurs evenly in the entire activation area. However, duo the coupling relationships between electrical, thermal and water, the effect of operation conditions (such as the local heating) on the current density mapping is still blank. This paper studies the effect of local heating on polymer electrolyte fuel cell performance and analyses the causes of the output voltage differences through the mapping of the current density distribution. Compared with the inlet and central heating, the heating at the outlet area exhibits the best performance. This is due to the concentration of reactants along the flow field decreases continuously, and the accumulation of liquid water leads to the low current density distribution at the outlet. Here, we show that local heating can compensate for the lowest current density and achieve the more homogeneous current distribution; on the contrary, inlet heating will increase the unevenness of the current density distribution. This study provides practical guidance for the optimal design of the thermal management system.The design of the cooling channel should be locally optimised for more uniform distribution of current density, in addition to the overall temperature balance,
Relevance of GDL Properties Regarding GDL Quality Assurance
Authors: Cremers Carsten
Published: February 2024

Gas diffusion layers are an important part of all types of polymer electrolyte membrane fuel cells (LT-PEMFC, HT-PEMFC or AEMFC). Albeit the conversion reaction is not taking place in the GDL the contributions of the GDL to the function of the cell are essential. So, the GDL needs to homogenise the distribution of reacting gases over the electrode area compensating inhomogeneities created by the channel fin structure of the flow-field of the bipolar plate and at the same time cause a focussing of product streams towards the channels. The GDL needs to conduct electric current between the catalyst layer and the bipolar plate at high current density and transport released thermal energy. The GDL also needs to distribute mechanical pressure of the stack compression.

In order to accomplish all those tasks, the GDL needs to feature the right properties with high homogeneity through-out its area and with high reproducibility batch to batch. Unfortunately, a rather high number of properties can be assigned to a GDL. So, the review paper by Yuan et al. on properties for different LT-PEMFC components1 lists about 15 different properties for GDL which influence their function. As many of these properties are difficult to measure measuring all of them is not a viable approach to the quality assurance of GDL as part of their industrial production.

Within the project QM-GDL Fraunhofer ICT together with the other partners of the project is analysing the relevance of the different properties, comparing the expected impact of deviation from the designed values and the effort, and determining the actual values. The goal is to determine the most relevant parameters which will allow to assure proper functioning of the GDL if their values are controlled keeping the effort for measurements at a reasonable value.

In the presentation the approach for the selection of relevant parameters will be explained at a number of examples. Also, a tentative list of parameters will be presented and discussed.

The presented work is part of the project QM-GDL which receives financial support by the German Federal Ministry of Digital Infrastructures and Traffic under Grant Agreement 03B11016E. The content of the presentation is in the sole responsibility of the author.

X.-Z. Yuan, C. Nayoze-Coynel, N. Shaigan, D. Fisher, N. Zhao, N. Zamel, P. Gazdzicki, M. Ulsh, K. A. Friedrich, F. Girard and U. Groos, Journal of Power Sources,
491 (2021).
Next Generation Fluorine-Free Proton Exchange Membranes for Electrochemical Energy Applications
Authors: Andrenacci Sara , Sandru Eugenia , Fortin Patrick
Published: February 2024

Most commercially available proton exchange membrane (PEM)-based fuel cell and electrolyser systems currently employ perfluorinated sulfonic acid (PFSA)-based PEMs, e.g., Nafion. The use of these fluorinated polymers presents serious health and environmental concerns as their production, degradation, and disposal results in the release of hazardous perfluorinted compounds that have been shown to accumulate in the environment and are toxic to living organisms.[1] Developing non-toxic, safe-by-design hydrocarbon PEMs is therefore crucial to ensure that renewable technologies that rely on proton exchange membranes remain an environmentally friendly solution. Additional shortcomings of PFSA-based PEMs include their expensive synthetic cost, inherently high hydrogen crossover, and limited operating temperature range due to poor thermo-mechanical properties above 90 °C. Hydrocarbon (HC)-based membranes offer advantages over their perfluorinated counterparts in these specific areas, however, the main drawback of HC-PEMs is that they require a much greater density of sulfonic acid groups to achieve similar proton conductivities as PFSA-based polymers.[2] This leads to greater water uptake and excessive swelling which ultimately leads to reduced mechanical stability of HC membranes.

More recently there has been an increasing number of reports exploring the use of block copolymer strategies to limit the water uptake and swelling properties of hydrocarbon PEMs while maintaining good ionic conductivity.[3] As the ion, liquid, and gas transport properties of the membrane are largely attributed to the hydrophilic blocks (i.e., with sulfonic acid groups) and the mechanical, chemical, and thermal stability of the resulting membrane is determined by the hydrophobic blocks (i.e., no sulfonic acid groups), it is postulated that the resulting membrane properties can be tuned by varying the fraction of hydrophilic/hydrophobic blocks.

The overall goal of this project is to synthesise hydrocarbon block copolymer PEMs with reduced gas crossover and enhanced the mechanical properties while maintaining sufficiently high ionic conductivity, ultimately leading to higher performance and greater durability inelectrochemical energy conversion and storage systems, e.g., fuel cells and electrolysers. In this project we have compared the ex-situ properties of novel hydrocarbon block copolymers with PFSA-based Nafion membranes, e.g., water uptake and swelling, conductivity measurements, oxidative stability via Fenton's test, etc., as well as in-situ performance tests in single cell fuel cell and electroylzers.

[1]Feng, M.; Wang, Z. et al.
Sci. Rep.
2015, 5, 9859.

[2]Holdcroft, S. Chem.
Mater. 2014, 26, 381.

[3]Guiver, M. et al.
Chem.
Rev.
2017, 117, 4759.
Species Transport in Hydrophilic Nafion-Coated Cu Catalysts for CO2 Electroreduction
Authors: Adesina Peace O. , Elliott James , Lapkin Alexei A
Published: February 2024

Ionomer coated catalysts have increasingly been utilized in the electrocatalytic reaction of CO2 to multi-carbon products on Cu-based GDEs1,2. Their proton conductivity coupled with the Donnan exclusion due to the charged immobilized ions have served as a means of tailoring the microenvironment of the catalyst to desired products. Whilst there are experimental efforts geared towards the tuning of the local environment to desired products, there is a lack of supporting computational models that elucidate ionic species profile within the Nafion coated catalyst in the presence of fixed negative sulfonate ion charges from Nafion and the negative charges from the electrocatalysts.

On the other hand, hydrated Nafion ionomer in the presence of a supporting electrolyte forms a biphasic polymer matrix which allows the transport of CO2 in both the hydrophilic and hydrophobic regions of Nafion ionomer3. Recent literature has highlighted the transport of CO2 in hydrophobic domains but in not in hydrophilic domains4. In this work, we look a closer look at CO2 transport in hydrophilic domains. We combine mass transport generalized modified Poisson-Nernst-Planck (GMPNP) equations and molecular dynamics to elucidate the transport of reactant/product species in the local environment of Nafion coating on planar Cu catalysts.

We find that the thickness of the Nafion coating, the presence of immobilized sulfonic charges, ionic concentration of electrolyte impacts the availability of CO2, pH and the concentration of cations which are important parameters for CO2 reduction reaction. We also provide a relationship between the pKa of Nafion and the local dielectric constant of the reaction’s microenvironment using molecular modelling and the corresponding impact of Nafion’s ability to effectively minimize carbonate reactions. Our results underscore the need to manage the catalyst-ionomer microenvironments for CO2 reduction on copper electrodes. This model in conjunction with further experimental endeavours can serve as a benchmark for other intricate porous catalyst models that are significant for optimizing catalyst performance for large scale CO2 reduction operations.

Bibliography

Bui, J. C. et al. Engineering Catalyst–Electrolyte Microenvironments to Optimize the Activity and Selectivity for the Electrochemical Reduction of CO2 on Cu and Ag. Acc. Chem. Res.
17, acs.accounts.1c00650 (2022).

Kim, C. et al. Properties of the ionomer under CO 2 R-related environments Tailored catalyst microenvironments for CO 2 electroreduction to multicarbon products on copper using bilayer ionomer coatings. doi:10.1038/s41560-021-00920-8 (2022).

Ren, X., Myles, T. D., Grew, K. N. & Chiu, W. K. S. Carbon Dioxide Transport in Nafion 1100 EW Membrane and in a Direct Methanol Fuel Cell. J. Electrochem. Soc.
162, F1221–F1230 (2015).

García de Arquer, F. P. et al. CO2 electrolysis to multicarbon products at activities greater than 1 A cm−2. Science (80-. ).
367, 661–666 (2020).

Figure 1
Ionomer-Dependent Oxygen Evolution Reaction in a Half-Cell and a Liquid Electrolyzer
Authors: Mora Joy Marie , Li Guangfu , Chuang Po-Ya Abel
Published: February 2024

Electrocatalytic oxygen evolution reaction (OER) is an important area of research due to its significance in water electrolysis, which contributes to the clean-energy storage and conversion techniques. OER exhibits irreversible and sluggish kinetics, which necessitates a high overpotential to achieve the desired reaction rate. In an alkaline medium, non-precious metals (such as Ni, Fe, Co) or metal-free materials (such as 3d-transition metal oxides and heteroatom-doped carbons) can replace expensive iridium and ruthenium oxides, which is otherwise required in an acidic medium to facilitate the reaction. However, developing new catalysts for alkaline OER is limited by the scaling relations among adsorption energetics of key intermediates (i.e., OOH*, OH*, and O*).

The electrochemical reaction kinetics depends critically on the nature of the interface between catalyst and the electrolyte where an electrical double layer (EDL) forms during OER. The current understanding of the EDL structure involves the interfacial interactions between adsorbates and catalyst layer (CL) which can be modified to improve the reaction efficiency. Ionomers are essential components of the CL and are vital in uniformly dispersing catalyst particles in ink solution. The ionomers also act as binder for the catalyst particles in the CL, helping to improve the electrode’s durability and stability over time. In addition, despite the fact that ionomers affect the properties of EDL, the impact of ionomer on the reaction pathway is often overlooked in electrocatalytic research.

In this study, we investigate the role of ionomer in the catalyst layer by comparing different polymer dispersions, including PTFE, Nafion, and commercial As-4. The results indicate that the Nafion-contained CL performs better than other polymer CLs in TF-RDE/RRDE, as it facilitates direct O*-O* coupling. In contrast, anionic ionomer demonstrates superior long-term stability in alkaline liquid electrolyzers, despite oxidization degradation.
Nanocellulose as a Sustainable Polymer Electrolyte
Authors: Lyth Stephen Matthew , Bayer Thomas , Nishihara Masamichi , Sasaki Kazunari
Published: February 2024

Polymer electrolyte membranes in fuel cells and electrolyzers will play a key role in the hydrogen economy. These membranes are generally made of sulfonated fluoropolymers, which have excellent proton conductivity, impressive redox stability, and good gas barrier properties. However, the complex synthetic processes mean that they remain expensive. Their synthesis also involves ecologically damaging perfluorosulfonic acids (PFSAs), otherwise known as “forever chemicals” due to their persistence in the environment. More sustainable and lower cost hydrocarbon electrolytes should therefore be investigated.

Cellulose is the most abundant biopolymer in nature, and is derived from plant matter. It is used at vast scale and low cost to make paper and cardboard. Cellulose can be chemically or mechanically treated to break up the fibers to form “nanocellulose”. Nanocellulose is a low-cost nanomaterial which can be formed into thin membranes which are much stronger than conventional cellulosic paper.

We propose nanocellulose as an alternative electrolyte to replace sulfonated fluoropolymers in fuel cells. We confirmed that unmodified nanocellulose can conduct protons due to acidic hydroxyl groups. We also showed that nanocellulose membranes present a much better barrier to hydrogen compared to Nafion, and can successfully be used as an electrolyte in fuel cells. However, the current-voltage performance of unmodified nanocellulose was insufficient due to a high membrane resistance.

We went on to improve the proton conductivity by introducing sulfonic acid groups and reduced the membrane resistance by using spray deposition to create thinner membranes, resulting in significantly improved fuel cell power density of 160 mW/cm2. We also implemented crosslinking with sulfosuccinic acid to simultaneously improve the ionic conductivity, increase strength, and reduce swelling in water. This work shows that nanocellulose is a promising new class of polymer electrolyte which could significantly reduce the cost and improve sustainability of fuel cell and electrolyser systems.

1. Cellulose Nanocrystals Crosslinked with Sulfonic Acid as Sustainable Proton Exchange Membranes for Electrochemical Energy Applications, O. Selyanchyn, T. Bayer, D. Klotz, R. Selyanchyn, K. Sasaki, S. M. Lyth, Membranes 12 (7), 658 (2022)

2. Spray Deposition of Sulfonated Cellulose Nanofibers as Proton Conducting Membranes for Fuel Cells, T. Bayer, B. Cunning, R. Selyanchyn, B. Smid, S. Fujikawa, K. Sasaki, S. M. Lyth, Cellulose, 28, 1355–1367 (2021)

3. Proton Conductivity in Cellulosic Materials: A Review, O. Selyanchyn, R. Selyanchyn, S. M. Lyth, Frontiers in Energy Research: Fuel Cells, 8, 596164 (2020)

4. High Temperature Proton Conductivity in Nanocellulose: Paper Fuel Cells, T. Bayer, R. Selyanchyn, S. Fujikawa, K. Sasaki, and S. M. Lyth, Chemistry of Materials, 28 (13), 4805–4814 (2016)
Hydrogen Production with Seawater-Resilient Bipolar-Membrane Electrolyzers
Authors: Marin Daniela , Perryman Joseph T. , Stevens Michaela Burke , Nielander Adam C. , Boettcher Shannon W. , Jaramillo Thomas F.
Published: February 2024

Commercial proton exchange membrane water electrolyzers (PEMWEs) are highly efficient when operating in ultra-pure de-ionized water. However, introduction of additional ions leads to a reduction in device durability and efficiency. Chloride (Cl-) ions, typically found in high concentrations in seawater, lead to device performance issues driven in part by the chlorine evolution reaction at the anode. At the acidic anode-cation exchange layer interface, corrosive chlorine species (OCl-, HOCl, Cl-) are readily generated due to the facile kinetics of the 2-electron oxidation reaction relative to the desired 4-electron water oxidation reaction. Bipolar membrane water electrolyzers (BPMWEs), however, contain a locally basic anode-anion exchange layer interface, leading to improved thermodynamic favorability for O2 production rather than corrosive chlorine species production. Furthermore, the bipolar membrane can readily block anions and cations from accessing the desired reaction spaces. In this work, we evaluated ion transport, chloride oxidation, and durability of BPMWEs and PEMWEs operating in salt water. BPMWEs exhibit a low Faradaic efficiency of 0.005% for the oxidation of Cl− to corrosive chlorine species at the anode, compared to PEMWEs that can reach a Faradaic efficiency of up to 10% under similar conditions. In addition, BPMWEs demonstrate a device lifetime that is 140 times longer than that of PEMWEs operating in direct seawater electrolysis conditions. Failure modes for each membrane type have been investigated under both ultra-pure and impure water electrolysis conditions and are discussed in this work.
Suppression of Chemical Degradation By Gas Barrier Polymer Electrolyte Membranes
Authors: Nishihara Masamichi , Gautama Zulfi , I Yang , Hutapea Yasir , Sasaki Kazunari
Published: February 2024

[Introduction]

Polymer electrolyte fuel cell (PEFC) is one of the promising technologies for decarbonization. Especially, PEFC is suitable to power heavy-duty vehicles (HDV) because of its high efficiency and high fuel capacity. However, there are some serious technical challenges for PEFC application for HDV such as the durability. When we focus on the chemical degradation of polymer electrolyte membranes (PEMs), it happens due to attack by radical species. One of the radical formation mechanisms is the reaction at the anode side by the penetrated oxygen from cathode. Therefore, a promising mitigation strategy against chemical degradation is the suppression of oxygen permeability through the PEM.

To verify this concept, we developed high gas barrier PEM. As a model gas barrier PEM, we made a sandwich type PEM with high oxygen barrier property. The sandwich PEM was prepared by depositing a thin interlayer consisting blended poly(vinyl alcohol) (PVA) as a gas barrier material and poly(vinyl sulfonic acid) (PVS) as a proton conductor in between two layers of Nafion 211 membranes. We evaluate chemical durability using the sandwich gas barrier PEM and discuss about the mechanism.

[Experimental]

To fabricate thin sandwich PEMs (15-20 µm), ethanol diluted Nafion dispersion solution (20 mg/ml) and PVA/PVS solution (10 mg/ml) were sprayed on a polytetrafluoroethylene (PTFE) sheet by a spray gun (Tamiya HG wide airbrush). The thickness of each layer was controlled by controlling the deposited weight. Then, membrane characterization procedures such as surface roughness, proton conductivity, and dimensional stability were performed. To evaluate fuel cell performance, the PEMs were mounted to a JARI cell with 1 cm2 active area. Chemically accelerated stress test was performed by open circuit voltage (OCV) holding test following NEDO protocol.

[Results and Discussion]

Several areal densities of PVA/PVS interlayer were successfully incorporated into Nafion membrane to make sandwich PEM. The sandwich PEM shows considerable fuel cell performance, and thin sandwich PEMs show higher performance than the 50 µm sandwich PEM, although it is lower than the thin sprayed Nafion. For example, the peak power density of 15 µm sandwich PEM was 0.44 W cm-2 compared to 0.30 W cm-2 and 0.50 W cm-2 for 50 µm sandwich PEM and 15 µm Nafion, respectively. Furthermore, the incorporation of interlayer to thin PEM can suppress the hydrogen crossover current density from 7.8 mA cm-2 to 5.5 mA cm-2 indicating superior gas barrier property. From the higher gas barrier property, it is predicted thin sandwich PEMs will have higher chemical durability than Nafion with similar thickness.
Improving the Durability and Performance of Anion Exchange Membranes for Water Electrolyzers
Authors: Ceron Maira Raquel , Clemens Auston L. , Yassa Magi Mettry , Karnes John Joseph , Oakdale James Spencer
Published: February 2024

The two major drawbacks of most renewable sources are intermittency and availability. Renewables will naturally need to be efficiently integrated with electrochemical methodologies for storage (batteries), conversion (fuel cells) and application (electrolysis, CO2 reduction reactions). Alkaline anion exchange membranes (AAEM) have attracted considerable interest to navigate some of the economic hurdles native to polymer electrolyte membrane-based technologies. Despite many advances over the past decade, AAEM long-term stability towards hydroxide mediated degradation remains a significant challenge. Here we integrate anion exchange membrane synthesis, accelerated stress testing and characterization (structural, chemical, electrochemical) to understand and mitigate the effect of degradation of AAEM under electrochemical conditions on the performance of these materials.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Funding was provided by Lawrence Livermore National Laboratory Directed Research and Development (LDRD) Grant 21-ERD-013. IM # LLNL-ABS-846373
(Invited) Strategies to Improve the Stability of Fe/N/C Catalysts in PEM Fuel Cells
Authors: Zhang Gaixia , Yang Xiaohua , Dodelet Jean-Pol , Sun Shuhui
Published: February 2024

Proton-exchange membrane (PEM) fuel cells hold promising applications in transportation and stationary, however, their widespread commercialization is greatly hindered by the high cost. Platinum (Pt) represents one of the largest cost components of a fuel cell, therefore, my research interests have been focusing on strategies that will increase the activity and utilization of platinum group metal (PGM) catalysts, and improve the performance and stability, as well as prolong the lifetime of the PGM-free catalysts. In this talk, I will first briefly present our work on developing low-PGM catalysts (various unique nanostructured Pt nanowires, nanotubes, and single atoms) to significantly increase the activity and stability of the Pt-based catalysts for ORR in fuel cells. Then, I will mainly focus on our work on PGM-free catalysts. Based on the major breakthroughs on Fe/N/C catalyst achieved by the Dodelet team at INRS (with the MEA activity and performance approaching that of Pt catalyst) [1,2], in collaboration with Ballard Power Systems and Toyota, we have made important progress on improving the stability of PGM-free catalyst [3-17]. Specifically in the following aspects: (i) identifying the active sites, (ii) understanding the fuel cell degradation mechanisms experimentally and theoretically, (iii) developing approaches to improving the stability of the Fe/N/C catalyst, such as pore size control, and fluorination, and (iv) catalyst layer and electrode optimization, such as catalyst hydrophobicity adjustment, Fe/N/C and ultra-low loading Pt/C hybrid catalyst.

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