bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlling the Activity and Stability of Pt-Based Electrocatalysts By Means of the Lanthanide Contraction
Authors: Escudero-Escribano María , Malacrida Paolo , Vej-Hansen Ulrik Grønbjerg , Tripkovic Vladimir , Velázquez-Palenzuela Amado Andrés , Schiøtz Jakob , Rossmeisl Jan , Stephens Ifan E. L. , Chorkendorff Ib
Published: February 2020

In order to reduce the Pt loading at the cathode of proton exchange membrane fuel cells (PEMFCs) more active and stable catalysts are needed to drive the oxygen reduction reaction. Most research has focussed on achieving this by alloying Pt with Fe, Co, Ni or Cu [1,2]. However, these compounds typically degrade under PEMFC conditions, due to dealloying. Alloys of Pt and lanthanides may be inherently less prone to dealloying under reactions conditions, due to their negative enthalpy of formation [2-4].

Herein we present a systematic study on the trends in activity of seven novel Pt-lanthanide electrodes (Pt5La, Pt5Ce, Pt5Sm, Pt5Gd, Pt5Tb, Pt5Dy and Pt5Tm). The materials are highly active, presenting a 3 to 6-fold activity enhancement over Pt [3-5], amongst the most active polycrystalline Pt-based catalyst ever reported. Moreover, our recent study showed that Pt
x
Gd is highly active in the nanoparticulate form [6]. On the bulk alloys, a Pt overlayer with a thickness of few Pt layers is formed onto the bulk alloys by acid leaching (Fig. 1A) [3-5]. The ORR activity versus the lattice parameter obtained by X-ray diffraction measurements follows a volcano relationship (Fig. 1B). Furthermore, we explain the trends in stability, and present the lattice parameter as a new descriptor that controls both the activity and stability of these materials. Using the lanthanide contraction we demonstrate that the electrocatalytic performance can be engineered by tuning the Pt-Pt distance. 

References

[1] H. A. Gasteiger, S.S. Kocha, B. Sompalli, F.T. Wagner, Appl.
Catal. B
2005, 56, 9.

[2] I.E.L. Stephens, A.S. Bondarenko, U. Grønbjerg, J. Rossmeisl, I. Chorkendorff, Energy Environ.
Sci. 2012, 5, 6744.

[3] M. Escudero-Escribano, A. Verdaguer-Casadevall, P. Malacrida, U. Grønbjerg, B.P. Knudsen, A.K. Jepsen, J. Rossmeisl, I.E.L. Stephens, I. Chorkendorff,  J. Am. Chem. Soc. 2012, 130, 16476.

[4] P. Malacrida, M. Escudero-Escribano, A. Verdaguer-Casadevall, I.E.L. Stephens, I. Chorkendorff, J. Mater. Chem. A
2014, 2, 4234.

[5] M. Escudero-Escribano, et al., to be submitted, 2015.

[6] A. Velázquez-Palenzuela, F. Masini, A.F. Pedersen, M. Escudero-Escribano, D. Deiana, P. Malacrida, T.W. Hansen, D. Friebel, A. Nilsson, I.E.L. Stephens, I. Chorkendorff, J. Catal., in press.,
2015, DOI: 10.1016/j.jcat.2014.12.012

Fig 1. (A) Schematic three-dimensional views of the Pt5M (M = lanthanide) structure during sputter-cleaning and after electrochemistry. (B) Experimental ‘activity-lattice parameter’ volcano plot: ORR kinetic current density measured at 0.9 V vs. RHE as a function of the lattice parameter and the Pt-Pt distance for polycrystalline Pt5M electrocatalysts after initial ORR activity (dark grey squares) and after 10 000 cycles between 0.6 and 1.0 V vs. RHE (grey circles).

Figure 1
MEA with Thin Pore-Filling Anion Exchange Membrane and Water Transport Analysis in SAFC
Authors: Oshiba Yuhei , Hiura Junya , Suzuki Yuto , Yamaguchi Takeo
Published: February 2020

The solid-state alkaline fuel cells (SAFCs) with anion exchange membranes (AEMs) have attracted considerable attention because of applying non-noble metal catalysts in alkaline condition. However, unlike the proton-exchange membrane fuel cells (PEFCs), SAFC is under development and shows low cell performance. One of the reason for the low performance in SAFC is due to flooding occurred by generated water at the anode1). If a thin AEM is used, the generated water at the anode will be able to move easily to the cathode, and as a result, the cell performance will be improved.

In our study, we developed the membrane electrode assembly (MEA) with the thin AEM and analyzed the water transport inside the MEA. Catalyst layers (mixture of the commercial Pt/C catalyst, poly(vinylbenzyl chloride), and Nafion) were transferred via decal method onto the both sides of pore filling membranes synthesized by vinyl benzyl trimethylammonium chloride with different thickness having 25 μm and 5 μm. Then the I-V test was performed at 60 ºC with the humidified H2/O2 supplied. To evaluate the permeance of each AEM, outlet dew point of each electrode was also measured using the water transport analysis system2). As shown in Fig. 1, the I-V performance was greatly improved by the usage of thinner AEM. The permeance of the MEA with 5 μm thickness membrane increased by 2.4 times compared with that with 25 μm thickness. Under the water permeation analysis condition, anode RHs were also calculated from the water mass balance equation of both MEA and the whole cell to estimate the flooding region of each MEA. When the anode RH reached over 100 %, the MEA with 5 μm thickness membrane showed higher current density compared with the MEA using 25 μm thickness membrane. The flooding at the anode can be suppressed by using thinner AEM, leading to increment of I-V performance.

Reference

1) H. Zhang, H. Ohashi, T. Tamaki, T. Yamaguchi, J Phys Chem C, 116, 7650-7657(2012).

2) Y. Oshiba, H. Irizawa, H. Ohashi, T. Yamaguchi, In-Situ Measurement and Analysis of Water Movement in PEFCs, 226th ECS meeting, Cancun (2014).

Figure 1
Membrane Permeability and Water Management in Alkaline Membrane Fuel Cells
Authors: Gottesfeld Shimshon , Page Miles , Paska Yair
Published: February 2020

We address in this paper fundamentals of water management in a hydroxide exchange membrane fuel cell ( HEMFC ), operated in hydrogen/air mode.  In such cell, the water product can be removed to large degree  with the air flow. This would make it unnecessary to remove a significant part of the product water through the anode exhaust and, thereby, prevent underutilization of hydrogen fuel.   However, such water management approach requires to use inlet air RH significantly lower than 1 and, consequently, risks insufficient water content in the cell cathode, resulting in poor cathode performance.

We describe in this talk possible solutions for combining “benign” removal of part of the product water from the HEMFC anode exhaust, while removing the other part of the product water with the air stream. A key facilitator in achieving such optimized water management scheme is the HEMFC membrane. The higher the water permeability of the HEMFC membrane, the easier is the implementation of this optimized scheme and, what counts here is the permeability under cell operation conditions.

When the HEMFC is under current and the air inlet stream under-saturated, the water content may vary strongly along the thickness of the membrane which is  in contact with liquid water on the anode side and water vapor of RH<1 on the cathode side. It is the latter interface which remains a significant challenge regarding  its full description , not to mention proper remediation. In the last two years,  several reports have shown that, for PEMs, a “skin” of inferior transport characteristics develops at the ionomer/gas interface when the RH of the gas is significantly lower than 1.  In the case of the HEMFC, such membrane skin formed next to the cathode could be a critical barrier to water transport into the cathode, with significant deleterious effect on cell performance.

Measurements of the relevant membrane characteristics and the water management options in the HEMFC will be described in this talk.
Accurate Ex-situ Measurements of PEM Fuel Cells Catalyst Layer Dry Diffusivity
Authors: Salari Sina , McCague Claire , Tam Mickey , Saha Madhu S , Stumper Jüergen , Bahrami Majid
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFC) efficiently convert the reaction energy of hydrogen and oxygen to electricity, water and heat. The oxygen reduction reaction occurs on a composite nanostructured catalyst layers (CL) formed from Pt nanoparticles supported on a network of carbon particle agglomerates. Oxygen reaches the reaction site through diffusion. Understanding the diffusion properties of CL is vital to proper design of CL. Measuring the diffusivity of thin porous layers is challenging, as is selecting a suitable substrate and appropriate CL coating procedures.  There are very few CL gas diffusivity experimental studies in the current literature. In this work, CL is coated on 70 μm thick hydrophobic porous polymer substrates with Mayer bar. Diffusivity of CL and the substrate is measured using dry diffusivity test bed and after decoupling diffusivity values are reported for different CL thicknesses.
An Open Cathode Fuel Cell for Atmospheric Flight
Authors: Gould Benjamin D. , Hazard Matthew W. , Rodgers Joseph A. , Stroman Richard O'Neil
Published: February 2020

An open cathode proton exchange membrane fuel cell (PEMFC) could be an ideal power source for unmanned air vehicles because the motion of the aircraft through the atmosphere can be leveraged to provide oxygen to the PEMFC and extract waste heat, eliminating many traditional balance of plant components such as air and coolant pumps, bipolar plates, gaskets, humidifier, and radiator. One challenge presented by this fuel cell arrangement is that the ambient air cannot be conditioned before entering the PEMFC, potentially limiting its operating envelope.  This research examines the performance of an open cathode fuel cell in an environmentally controlled wind tunnel that reproduces the atmospheric flight environment. The cell was constructed by laminating a flexible circuit current collector with a membrane electrode assembly (MEA).  The effects of ambient temperature, ambient relative humidity, air speed and altitude on polarization behavior are discussed in detail.  A simple 1-D fuel cell model shows that the dominant factor influencing the polarization behavior is the temperature of the cell, which is determined by the ability of the cell to reject heat.
New Neutron Imaging Detectors for PEMFC through-Plane Water Content Measurement
Authors: Hussey Daniel S , LaManna Jacob M , Baltic Elias , Jacobson David L
Published: February 2020

The current state-of-the-art in neutron imaging spatial resolution of 10 µm to 20 µm prevents applying the technique to study the through-plane water content of commercially competitive membranes and catalyst layers.  There have been many studies focused on the water distribution in the gas diffusion layer, and some recent work has looked at thick membranes and thick catalysts in order to compare the measured water content with that predicted by models. 

The spatial resolution limit stems from the range of the charged particles that result from the neutron capture reaction which produces a large blur of light.  We have explored several techniques to either reduce this blur, by using higher density scintillators, employing structured illumination, and magnifying the scintillation light, all with the goal of measuring the through-plane water content in commercially competitive materials with a spatial resolution of ~1 µm.  As an example, shown in Figure 1 is a comparison of the measured water content in a fuel cell operated at the same current and voltage conditions when the scintillation light is magnified by a factor of 4.  The top image is the standard setup where the scintillation light is imaged with a 1:1 macro lens, the bottom image is when the scintillation light is imaged with a magnification 4, infinity corrected microscope configuration.

Figure 1
Operando Sub-Second Tomographic Imaging of Water in PEFC Gas Diffusion Layers
Authors: Eller Jens , Marone Federica , Büchi Felix N
Published: February 2020

X-ray tomographic microscopy (XTM) of liquid water in polymer electrolyte fuel cells (PEFC) has proven a valuable tool in order to improve understanding of water transport in the gas diffusion layer (GDL) [1-5]. So far, in-operando X-ray tomographic microscopy was restricted to constant operation conditions since the minimal XTM scan time of a few seconds [4] was not sufficient to capture the dynamics of the water distribution under transient operation.

The presentation reports about the developments to reduce the scan time of in-operando XTM below a second at the TOMCAT beamline of the Swiss Light Source. First of all, this offers the possibility to study the evolution of the liquid water distribution in the GDL during transient PEFC operation conditions. Second, the shorter scan times reduce the X-ray dose to the cell and increase the number of XTM scans before radiation induced degradation biases the cell electrochemistry and consequently the water distribution [6].

The consequences of the reduced exposure time and lower number of angular steps on image quality are discussed and the temporal and spatial development of the water distribution in the channel and the GDL following a current density variation from 0.1 A/cm2 to 1.0 A/cm2 (see Figure 1) will be presented. Special focus will be put on channel vs. land variations, percolation paths of the liquid water and their stability over time.

References

[1] A. Schneider, et al., J. Power Sources, vol. 195 (2010), pp. 6349-6355.

[2] P. Krüger, et al., J. Power Sources, vol. 196 (2011), pp. 5250-5255.

[3] J. Eller, et al., J. Electrochem. Soc., vol. 158 (2011), pp. B963-B970

[4] J. Eller, et al., ECS Trans., vol. 41 (2011), pp. 387-394.

[5] T. Rosén, et al., J. Electrochem. Soc., vol. 159 (2012), pp. F536-F544.

[6] J. Eller, et al., J. Power Sources, vol. 245 (2014), pp. 796-800.

Figure 1: Left: XTM through-plane slice of a single channel cell about 60s after current jump from 0.1 to 1 A/cm2. Cathode flow field is on top and identified liquid water is highlighted in blue. Right: 3D rendering of the water in the cathode. The flow field is removed for visualization of the water accumulation under the ribs.

Figure 1
Ionomer Self-Assembly in Dilute Solution: A Molecular Dynamics Study
Authors: Ghelichi Mahdi , Malek Kourosh , Eikerling Michael
Published: February 2020

Self-assembly of ionomer chains in dilute solution is studied by classical molecular dynamics. Based on a bead-spring ionomer model, the simulation approach captures formation of cylindrical, bundle-like [1] aggregates with a hydrophobic core region, a surface layer of charged anionic headgroups and a halo of counterions (protons) in the surrounding aqueous phase. Ionomer aggregation enforces the stretching and stiffening of ionomer chains, which is caused mainly by the repulsion of anionic headgroups. The strengths of hydrophobic and electrostatic interactions are varied to explore their effect on the aggregation process. Strong hydrophobicity of the ionomer main chain results in greater aggregate sizes. Figure 1a shows the result of the changes in the aggregate size, , over the range of explored hydrophobicity. Strong electrostatic interaction of ionic headgroups decreases the aggregate size, results are shown in figure 1b. Simulations also show the spontaneous formation of networks of ionomer bundles. Results of simulations will be discussed in the context of experimental studies on the formation of rodlike structures in ionomer solutions [2-3] that form the mechanically stable skeleton of polymer electrolyte membranes such as Nafion [4]. Moreover, implications of simulation results for water sorption phenomena [5], proton conductivity [6], membrane degradation [7] and membrane failure will be discussed.

Figure caption: Figure 1. Changes of the average aggregate size, , as a function of variation in strengths of hydrophobic interactions (a) and electrostatic interactions (b).  Strength of hydrophobic interactions are controlled through variation of strength of excluded volume interaction of hydrophobic monomeric beads while the electrostatic strength is varied through changes in the Bjerrum length. 

References:

P.-É. Alix Melchy, M. H. Eikerling, Phys. Rev. E, 89, 032603, (2014).

B. Loppinet, G. Gebel, C. E. Williams, J. Phys. Chem. B, 101, 1884-1892, (1997)

S. Jiang, K. - Q. Xia, G. Xu, Macromolecules, 34, 7783-7788, (2001).

L. Rubatat, A. L. Rollet, G. Gebel, O. Diat, Macromolecules, 35, 4050-4055, (2002).

M. Eikerling, P. Berg, Soft Matter, 7, 5976–5990, (2011).

K. - D. Kreuer, Chem. Mater., 8, 610–641, (1996).

M. Ghelichi, P.-É. Alix Melchy, M. H. Eikerling, J. Phys. Chem. B, 118, 11375−11386, (2014)

Figure 1
Development of Free-Metal Electrocatalyst from Inexpensive Sources of Carbon: A Novel Electrode Material for Cathode Reaction in PEM Fuel Cells
Authors: Alonso-Lemus Ivonne Liliana , Lardizabal Daniel , de la Torre Saenz Luis , Sanchez-Castro Maria Esther , Rodríguez-Varela F.J.
Published: February 2020

The development of alternative energy sources is of great interest in the scientific community in last decades. Fuel cells are a clean and sustainable alternative for power generation. However, the development of the polymer exchange membrane fuel cells (PEMFC) has been limited due that this systems use platinum as catalyst. Platinum is expensive and scarce, which limited the production of the PEMFC at industrial scale. Moreover, oxygen reduction reaction (ORR) is the reaction in the cathode of the PEMFC. This reaction has the slower kinetic, so limiting the kinetics of the entire cell.

Recently, free noble metal electrocatalysts have been obtained, which are capable of carrying out the ORR with comparable performance to Pt. These novel electrocatalysts are doped nanostructured carbon (ej. nitrogen doped carbon nanotubes N-NTC and nitrogen doped reduced graphene, N-rG). Nowadays, the synthesis of these nanostructured materials has several technological challenges, because it production is still expensive and has a significant environmental impact. In this work, we have obtained novel metal-free electrocatalysts from two different inexpensive carbon source: i) an organic waste and ii) mineral coal from Sabinas region in Coahuila Mexico. These electrocatalysts have a significantly lower cost than conventional platinum based electrocatalysts and the recently synthetized nanostructure free-metal catalyst.

The organic waste were pyrolyzed in a nitrogen atmosphere, and then an activation process with chemical agents was carried out. Moreover, in order to increase their surface area and modify the C-N chemical bond, a thermochemical process was carried out for mineral coal.

 The features and electrochemical performance of both electrocatalyst were compared. The electrocatalysts obtained have surface areas until of 2000 m2/g. The morphology and structural features were observed by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Raman Spectroscopy. The electrocatalytic activity for these novel electrocatalysts was evaluated for the oxygen reduction reaction (ORR) by rotary disk electrode technique. The results show that these electrocatalysts are an inexpensive and promising alternative for use as cathodes in PEMFC.
Application of Modified-ACLS Electrodes on Low-platinum PEFCs
Authors: Mei Wu , Fukazawa Taishi , Yang Tianyi , Yoshinaga Norihiro , Kanai Yuta
Published: February 2020

The commercialization of PEFCs is necessary for enabling a sustainable hydrogen-based economy. To reduce platinum (Pt) loading in PEFCs, we have proposed a novel catalyst structure, Alternating Catalyst Layer Structure (ACLS), via depositing different materials alternately on conventional substrate such as carbon papers [1, 2]. The ACLS can be characterized as a unique cabbage-like structure, where Pt “leaves” are partly separated by pore layers (gap layers). Its other features are: support-free and ionomer-free structure, high porosity and continuous Pt surfaces mainly consisting of contracted (111) crystalline planes. In this report, modification of the ACLS in these years and its potential as a powerful candidate for PEFC electrodes will be presented, including the enhancement of ORR activity and load cycle durability. The single cell performance of modified-ACLS electrodes (M electrodes) and its application on PEFC anode will be also introduced.

1)     W. Mei, J. Tamura, M. Yamazaki, T. Nakano, Japan Patent P4861445, US Patent 8128986

2)     W. Mei, T. Fukazawa, Y. Nakano, Y. Akasaka, K. Naito,ECS Trans. 50(2) (2013) 1377

Figure 1
Pt "Monolayer" Electrocatalysts Revisited: Structure, Lattice Geometry Effects, and Ethanol Oxidation Activity of Pt on Au
Authors: Loukrakpam Rameshwori , Brankovic Stanko R , Strasser Peter
Published: February 2020

Effective utilization of the high energy density of ethanol as a fuel for polymer electrolyte fuel cells is contingent upon complete oxidation of ethanol to carbon dioxide. Major problems associated with the development of electrocatalysts for ethanol oxidation are the high content of Pt and partial oxidation of ethanol to acetaldehyde and acetic acid instead of complete oxidation to carbon dioxide via the 12 electron process. Monolayers of Pt on Au have been proposed and reported1 to be beneficial for EtOH oxidation and possibly for C-C bond splitting. We address this issue with atomic scale microscopy and spectroscopy.

In this report, Pt atomic layers supported on both well-defined, extended Au(111) and Au NPs  were studied as electrocatalysts for ethanol oxidation reaction (EOR)2. The catalyst were prepared using galvanic displacement methods using Pt(II) and Pt(IV) precursors. Electrochemical testing of these electrocatalysts showed that Au@Pt(II) had substantially higher activity towards EOR than Au@Pt(IV). The atomic scale structure of the resulting Pt layers on Au will be studied using HAADF-STEM-EDX elemental mapping as well as depth resolved XPS. Evidence is provided that the so-called Pt “monolayer” catalysts actually consist of 2-4 atom layers of Pt, often aggregated in small clusters. The effect of Pt cluster sizes on the Au surface and the tensile strain on Pt due to the underlying Au and their effect on EOR will be discussed. Using in-situ FTIR we also studied the catalytic EtOH activity of the catalysts and their ability to perform C-C bond splitting.

1.            Li, M.; Liu, P.; Adzic, R. R., Platinum Monolayer Electrocatalysts for Anodic Oxidation of Alcohols. J. Phys. Chem. Lett. 2012, 3, 3480-3485.

2.            Loukrakpam, R.; Yuan, Q. Y.; Petkov, V.; Gan, L.; Rudi, S.; Yang, R. Z.; Huang, Y. H.; Brankovic, S. R.; Strasser, P., Efficient C-C bond splitting on Pt monolayer and sub-monolayer catalysts during ethanol electro-oxidation: Pt layer strain and morphology effects. Phys. Chem. Chem. Phys. 2014, 16, 18866-18876.
Microgravity Effect on Ammonia Oxidation at Platinum Nanoparticles Modified Mesoporous Carbon Supports
Authors: Poventud Carlos , Acevedo Raul , Morales Camila , Betancourt Luis E , Diaz-Cartagena Diana C , Rodriguez Manuel A , Larios Eduardo , Jose-Yacaman Miguel , Nicolau Eduardo , Flynn Michael , Cabrera Carlos R
Published: February 2020

Microgravity effect on the electrochemical oxidation of ammonia at platinum nanoparticles modified mesoporous carbon (MPC) substrates, with three different pore diameters, e.g. 64, 100, and 137 Å, have been studied in a parabolic flight between 24,000 and 32,000 ft. Microgravity effects on the chronoamperometric ammonia oxidation current density was a function of the mesoporous carbon support used. This support may be described as graphitic multilayer hollow globules, even though the carbon globules do not present a specific shape as seen in the HRTEM images.  Platinum nanoparticles were successfully chemically deposited, with a high dispersion, throughout the support’s topography.  An onboard accelerometer was the trigger in order to start each chronoamperomtric ammonia oxidation experiments when the microgravity condition of less than 0.02g (i.e. gravitational force) was achieved. Pt/MPC64 sustained the current density between terrestrial and microgravity conditions by a slight margin over Pt/MPC100. However, Pt/MPC137 resulted with the smallest current density decrease under microgravity conditions versus ground based experiments.  Pt/MPC137 has the largest pore diameter and shows a better capacity to sustain the oxidation current, which involves N2 formation.  This effect can be ascribed to an easier diffusional process obtained by the larger pore diameter, which improves the access for the mobility of the ammonia molecules towards the electroactive sites and the corresponding detachment of the gaseous N2molecules (bubbles) from the MPC cavities. Pt/MPC137 catalyst resulted with the smallest current density decrease under microgravity conditions versus ground based experiments. This MPC support has the largest average pore diameter (137 Å) and shows a better capacity to sustain the oxidation current. This effect can be ascribed to an easier diffusional process facilitated by the larger pore diameter, which improves the access for the mobility of the ammonia molecules towards the electroactive sites and the corresponding detachment of the gaseous N2 molecules (bubbles) away from them. In conclusion, it was demonstrated that under microgravity environment a porous infrastructure for a catalyst support has an impact on the mass transfer process of electroactive species, and a current density decreasing factor of ca. 50 - 67% must be taken into account. The lowest being the MCP average pore diameter 137 Å. In order to improve the current densities for ammonia oxidation, (100) faceted Pt nanoparticles need to be achieved.
Study of Polyphenylene Oxide Membranes Containing Long and Short Alkyl Side Chains
Authors: Amel Alina , Ein Eli Yair
Published: February 2020

Investigation on the subject of structure and chemical stability was carried out on two anion exchange membranes that have a great potential for being candidates in alkaline fuel cells. Both of the membranes contain poly(2,6-dimethylphenylene oxide) (PPO) backbone, one has benzyltrimethyl ammonium cation (BTMA) while the other has long (10 carbons) alkyl side chain pendant to the nitrogen-centered cation (C10) as can be seen in Scheme.  Membrane with the long alkyl side chain contributes to better hydrophilic–hydrophobic separation which significantly influence on the ionic channels of the membranes.Membrane morphology and in particular hydrophilic-hydrophobic separation was investigated using tapping-mode AFM. Both of the membranes exhibit phase-separated morphology and connectivity among the hydrophilic domains. AFM measurements show that long alkyl side chain contributed to better phase separation in the C10 membrane, where the hydrophilic domain size was ∼8 nm compared to ∼5 nm in BTMA. In addition, chemical stabilities of the membranes were evaluated under accelerated-aging conditions. Degradation process was determined by measuring FTIR, Elemental analysis and EDS during the aging. It was found that long side chain contributes to its chemical stability under basic and high temperature conditions.

Figure 1
Experimental Study of Thermal Conductivity of Catalyst Layer of Polymer Electrolyte Membrane (PEM) Fuel Cells
Authors: Ahadi Mohammad , Tam Mickey , Saha Madhu S , Stumper Jüergen , Bahrami Majid
Published: February 2020

Efficient operation of a typical automotive PEM fuel cell occurs at a certain range of temperature from 60˚C to 80˚C. At temperatures below 60˚C, the kinetics of the electrochemical reaction slows down, and the electrodes are more prone to being flooded by the liquid water due to the higher possibility of saturation of the produced water at lower temperatures. At temperatures above 80˚C, the membrane dries out, and consequently, ohmic losses attributed to proton transport through the membrane increase. In addition to these performance consequences, PEM fuel cells will face durability issues if they operate outside the mentioned temperature range; breaking down of membrane at high temperatures due to its glass transition at temperatures around 80˚C as well as damage to various components of the fuel cell due to ice expansion during freezing are some of the mentioned durability issues. Therefore, as is clear, water management, thermal control, and degradation minimization are highly and intricately correlated to each other, among which thermal control can be considered as the core controlling factor which directly affects the others. Performing an effective thermal management is hinged on having detailed knowledge about the temperature distribution inside various layers, and the key to finding such information is to have the thermal conductivity of various layers. The thermal conductivity of PEM fuel cell gas diffusion layers (GDL) is well understood, and some experimental data on thermal conductivity of other components have been provided in literature. However, the thermal conductivity of the catalyst layer, where most of the heat generation modes occur, is still unknown. Accordingly, this work is concerned with measurement of this property through two different approaches: the guarded heat flux method and the transient plane source method. In the guarded heat flux method which works based on steady-state measurement of temperature distribution inside the sample, the catalyst samples are placed in between two fluxmeters which introduce a constant heat flow rate through the samples, whereas in the transient plane source method which works based on a transient measurement of temperature inside the sample, two halves of catalyst sandwich the transient plane source sensor.
Resistance Measurements for Multilayer Supported Membranes
Authors: Peppin Daniel M. , Yandrasits Mike , Fochs Austin S
Published: February 2020

In cell, through plane resistance is an important quantity for proper characterization of multilayer supported composite membranes. Through plane resistance of a supported composite membrane is impacted by the addition of a non-conductive supporting material, effectively decreasing the density of acid sites in the composite layer. Additionally, there could be other impacts on through plane resistance due to phenomena such as changes in water transport resulting in localized lambda variation as well as possible tortuosity effects due to the support. 

 It is possible to characterize, separately, the through plane resistance of the neat ionomer skin layers as well as the ionomer filled support composite layer by measuring the through plane resistance for a series of supported membranes varying only in ionomer skin thickness. The conductivity of the composite layer can then be compared to the conductivity of the neat ionomer, allowing for the determination of a "conductivity restriction" factor. This conductivity restriction factor can then be compared to the volume fraction of nonconductive support material in the composite layer to determine whether the impact on conductivity is due solely to acid site dilution or if there are additional losses. This analysis can be used to compare various support materials for their impact on through plane resistance. The results of this work will help guide the choice of support materials to optimize mechanical properties while minimizing the impact on through plane resistance.
Current Density Distribution in the Lateral Direction of Conventional and Interdigitated Flow Field
Authors: Shrivastava Udit N , Tajiri Kazuya
Published: February 2020

In proton exchange membrane fuel cells, diffusion is a primary mechanism to transport gaseous species (oxygen and water vapor) between the flow channel and the catalyst layer in conventional flow field, whereas in an interdigitated flow field convection and diffusion both play vital role. Similarly, in a conventional flow field capillary effect is dominant in removal of liquid water, while in an interdigitated flow field both capillarity and the pressure difference between inlet and outlet channels contribute to the liquid water removal. Many computational studies available in literature have proven that this fundamental difference in transport mechanisms results in the differences in the overall cell performance and in the current density distribution in the land-channel direction between PEMFCs with interdigitated flow field and conventional flow field such as [1-2]. However, to best of our knowledge there is no study present in literature to experimentally show the current distribution in land-channel direction.

Our objective is to measure current density distribution in the land-channel direction and compare current density distribution profile for interdigitated and conventional flow field. A segmented cell is developed to measure current density distribution in the land-channel direction at sub-millimeter resolution of 350 μm. This technique is then applied to study current density distribution in land-channel direction of PEM fuel cell with interdigitated flow field and conventional flow field (see Figure 1a and b).

Figure 1. Current density distribution in the land-channel direction at 0.2 V, 60 oC and 90% RH a) conventional b) interdigitated flow field

A. Kazim, H.T. Liu, P. Forges. Journal of Applied Electrochemistry, 29, 1409 (1999).

L. Chen, H. B. Luan, Y.L. He, W. Q. Tao. International Journal of Thermal Sciences, 51 132 (2012).

Figure 1
Activity and Durability of a Membrane Electrode Assembly Fabricated with Supportless Pt Hollow Spheres for Polymer Electrolyte Fuel Cells
Authors: Cho Seonghun , Lim Eun Ja , Yang Tae-Hyun , Yim Sung-Dae
Published: February 2020

Extensive studies on the supportless Pt or Pt alloy catalysts with controlled morphology have led to significant enhancement in catalytic activity as well as in durability for polymer electrolyte fuel cells (PEFCs). However, the supportless Pt still shows lower performance than the state of the art Pt/C when the catalysts were fabricated to a membrane electrode assembly (MEA) due to not efficient catalyst layer architecture of the supportless Pt catalysts. In order to achieve high MEA performance, the catalyst should be designed in terms of catalyst layer architecture as well as oxygen reduction reaction (ORR) activity. Here we report supportless Pt hollow sphere (PtHS) catalyst that is composed of assembled Pt nanoparticle shell and hollowed center for 3-dimensional cathode catalyst layer architecture. The PtHS is expected to be efficient for high MEA performance mainly due the following aspects: (i) PtHS with submicron size will form large mean pore size and high pore volume in the catalyst layers, which will be beneficial in preventing water flooding and in improving water management for facile oxygen transport; (ii) hollow structure of PtHS will be used as liquid water reservoir at high currents and consequently enhance oxygen transport; (iii) thin-layered PtHS shell composed of assembled Pt nanoparticles would lead to large Pt surface area and high Pt utilization; (iv) assembled supportless Pt nanoparticles will increase the catalyst durability by preventing the aggregation and sintering of Pt nanoparticles. These potential merits of PtHS in terms of activity and durability will be demonstrated in a half-cell as well as in a single cell with the PtHS-based MEAs. The activity and stability of PtHS-based MEAs will be compared with the commercial Pt/C-based MEAs in a single fuel cell.
Water Management in an Alkaline-Exchange-Membrane Fuel Cell
Authors: Shiau Huai-Suen , Zenyuk Iryna V , Weber Adam Z
Published: February 2020

Among the existing fuel cell types, alkaline exchange membrane fuel cells (AEMFC) have intriguing features as compared to proton exchange membrane fuel cells. For example, their advantage is the high current density and mainly the possibility of using non-noble catalysts due to faster ORR kinetics in the alkaline media than in the acidic media. However, CO2, reacting with hydroxide ions to form carbonate ions, has a harmful effect on the air-breathing AEMFC by reducing the number of hydroxide available for the hydrogen oxidation reaction at the anode. Thus, AEMFC typically operates on pure oxygen, which dramatically increases its cost. Herein, we developed a first electrochemical model that can predict the response of AEMFC according to variations of operating parameters, such as the CO2 concentration in the oxidant flow and the relative humidity of inlet gases. The result in Figure 1 shows that current density significantly decays with higher CO2 concentration mainly due to hydroxide depletion by carbonate formation at the cathode. Other possible reactions are also accounted for in the model, such as the reverse water-gas shift reaction (RWGS) and the participation of carbonate ions in the hydrogen oxidation reaction. Water management and mass transport characteristics of an AEMFC assembly are discussed in detailed. With experimental verification, our model can be used to demonstrate different strategies for reducing harmful effects of CO2 poisoning, significantly increasing the possibility of AEMFC commercialization.

Figure 1
Studies of MEA Durability in Proton Exchange Membrane Water Electrolysis
Authors: Xu Hui , Rasimick Brian , More Karren L. , Alia Shaun M , Pivovar Bryan S
Published: February 2020

Hydrogen production from proton exchange membrane (PEM) water electrolysis is attractive due to its simple and clean nature. Membrane and electrode assemblies (MEAs) of PEM electrolyzers typically use iridium (Ir) as an anode catalyst and Pt as a cathode catalyst. The durability of MEAs plays an essential role for the electrolyzers’ lifetime and cost. However, unlike the well-established MEA durability protocols of PEM fuel cells, there have been a lack of effective procedures for PEM electrolyzer MEA durability evaluation.    

The objective of this work is to establish a series of test protocols that can help to rapidly evaluate PEM electrolyzer MEA durability. Three testing approaches have been used in this work, which include high-voltage hold (>1.8 V), voltage cycling (1.4 to 1.8 V or 2.0 V), and constant low-current operations. The electrochemical surface area (ECSA) and polarization curves of the MEAs will be obtained after each test.

Two categories of anode catalysts have been evaluated using the above durability test protocols: one is the commercial Ir black and the other is Ir supported on tungsten-doped titanium oxide (Ir/WxTi1-xO2) developed at Giner. The supported Ir/WxTi1-xO2 catalyst proves to possess 8-10 x higher mass activity than the Ir black. The MEAs made of these two anode catalysts have been evaluated at a variety of loading, low (0.1 mg/cm2), medium (0.4 mg/cm2) and high (1.0 mg/cm2).  Figure 1 shows the durability of these two catalysts after voltage cycling from 1.4 V to 1.8 V: (a) 2 mg/cm2 Ir from Ir black; (b) 0.4 mg/cm2 Ir from Ir/WxTi1-xO2.  It can be seen that at medium to high Ir loadings, these two catalysts demonstrates minimal performance decay after voltage cycling.  

The morphology and structure of MEAs after durability tests will be characterized to correlate to their performance and to elucidate their degradation mechanisms.    

Acknowledgement: The financial support is from the Department of Energy under the Contract Grant DE-SC0007471.

Figure 1
In-Situ Analysis of Gas Crossover in PEM Water Electrolysis - the Effect of Membrane Variation
Authors: Lüke Wiebke , Carmo Marcelo , Schalenbach Maximilian , Stolten Detlef
Published: February 2020

Polymer electrolyte membrane (PEM) water electrolysis is well identified today as a sustainable solution for the production of hydrogen, and of paramount importance when coupled to renewable but intermittent power sources such as wind and solar.

PEM water electrolysis is based on a solid polymer electrolyte concept first realized by Grubb in 1960s, where a thin solid sulfonated polystyrene membrane is used as an electrolyte. The polymer electrolyte membrane is responsible for providing high proton conductivity, compact system design, and low gas crossover. However, depending on the power load range, operating temperature, pressure range, membrane thickness, and a number of other parameters diffusion processes of the product gases through the membrane occur. The diffusion of hydrogen into the oxygen compartment for example reduces the efficiency of the electrolyzer, and allows the extensive mixing of gases that must be avoided in order to preserve efficiency and safety. This is particularly severe at a low power load – important when coupling to intermittent power sources – where the oxygen production rate decreases, thus drastically increasing the hydrogen concentration to unwanted and dangerous levels (lower explosion limit > 4 mol-% H2).

Nevertheless, PEM water electrolysis can operate at high current densities, capable of achieving values above 4 Acm-2, provided by very low ohmic losses. Though, very high current densities (over 6 Acm-2) can only be achieved if thin membranes (20 – 50 µm) are used which lead to lower cell resistances. In this case unfortunately, the crossover of gases across the membrane is drastically enlarged, if compared to the use of thicker membranes (100 – 200 µm).

In any case, PEM electrolysis is recognized for practically covering a wide power density range. However, the practical power operation range of PEM water electrolysis has not been consistently evaluated yet, especially when considering the variation of perfluorosulfonic acid (PFSA) membrane, thickness, and operation pressure.

In this study, the in-situ crossover aspect of a series of PFSA Nafion membranes at different operation conditions will be evaluated and compared to a simulation study of the gas permeation pathways. The main message is to clearly define the power load and pressure range for the PEM water electrolysis technology when using different membrane alternatives, providing a road map in order to aid scientists with regards to the R&D of PFSA membranes for PEM water electrolysis.
New Polymer Structures for Anion Exchange Membranes
Authors: Zhu Liang , Pan Jing , Hickner Michael
Published: February 2020

New membranes for alkaline fuel cells and other ion transport applications continue to generate a lot of interest in the electrochemical community.  Over the last 10 years there has been great progress in determining the key attributes of anion exchange membranes that lead to high fuel cell performance and moderate lifetime devices.  A current limitation of the field is the lack of readily available membranes and ionomer solutions.  Scalable, inexpensive materials are needed to promote more studies of electrode fabrication, device operation, and optimization, particularly in the area of longevity.

Our group has demonstrated a number of new polymer structures based on commercially-available polymers and inexpensive modification reagents.  We have focused on poly(phenylene oxide) as a backbone platform and employed ammonium cations that have relatively good stability in light of their low cost and reasonable performance.  In previous work, we employed alkyl chains to cause phase separation in random copolymers.  This phase separation increased the conductivity and decreased the water uptake of the materials.  We have since continued to investigate crosslinking and interpenetrating networks as further methods to optimize the properties of anion exchange membranes.  Many of these polymers have shown reasonable performance in anion exchange membrane devices, but more work is required to extend the lifetimes of the cells beyond 1000 hours.

This talk will highlight our recent work on new polymer structures and demonstrate how stability and conductivity can be increased by iterating on quaternary ammonium poly(phenylene oxide)-based materials.
Understanding Liquid-Water Management in PEFCs Using X-Ray Computed Tomography and Modeling
Authors: Zenyuk Iryna V , Weber Adam Z
Published: February 2020

Optimal liquid-water management is essential for commercializing polymer-electrolyte fuel cells (PEFCs), especially those with next-generation material sets. At low operating temperatures there is a need to remove liquid water from the cathode electrode where it can impede reactant transport. Optimization of water transport and removal requires a careful design consideration for the porous carbon components, specifically the gas-diffusion layers (GDLs). These heterogeneous materials serve a multifunctional purpose of conducting electrons and heat in the solid phase, providing structural support to the membrane and electrodes, and delivering reactants to the electrode and removing product water. Two-phase transport inside the GDLs, especially during operation, is complex and requires detailed knowledge of a given GDLs’ morphology and transport properties. In this talk, we will elucidate the GDL’s morphological properties using synchrotron-based X-ray micro computed tomography (XCT) and study in-situ water-distributions for different materials. Conditions studied include varying liquid pressure, gas-channel flow-rate, and land-channel compression. The XCT studies are complemented with two-dimensional modeling studies to gain an understanding of liquid-water transport under in-operando conditions.

Acknowledgement

This work was funded by Assistant Secretary for Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02-05CH11231, program manager Donna Ho. This work made use of facilities at the Advanced Light Source (ALS), supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy.
Electrospun Ni nanofibres as Pt supports for PEMFC electrodes
Authors: Ercolano Giorgio , Cavaliere Sara , Jones Deborah Jacqueline , Rozière Jacques
Published: February 2020

A thriving market for emerging and established mobile devices, operating on electrical energy is pushing the research and the market demands towards continuous sustainable and clean sources of energy. In particular key operators of the automotive industry are seeking a leading market position introducing hybrid and electric vehicles.  Proton exchange membrane fuel cells (PEMFC) provide clean and long lasting electrical energy while being portable and operated at relatively low temperatures and would be the obvious power source for those applications. However a reduction of the fabrication costs and an improved durability are pivotal to a successful market introduction of this technology. A more effective utilisation of the highly priced Pt catalyst and the use of more durable materials for the catalyst supports are the core of the development of novel, market ready PEMFC.

A paradigm shift from Pt nanoparticles supported on carbon to thin layers of platinum deposited on metals, metal oxides or carbon could be achieved adopting electrochemical Pt deposition techniques like the galvanostatic displacement of Ni and Cu ions with Pt 1 , self-terminated Pt electrodeposition 2 or electrochemical atomic layer deposition 1. This novel morphologies could push the boundary of Pt exploitation further and vastly increase the stability of the electrodes, therefore the sought after reduction of fabrication costs and increased stability are within the reach of current researches.

Electrospinning is a proven technique and is reliable and scalable for the production of nanowires made of several metals 3, metal oxides 4 or carbon 5. The capability to finely control the diameter and composition of the nanowires makes this technique appealing in the search of novel catalyst support materials and morphologies. Our research group is actively testing different Pt deposition techniques on electrospun carbon, metal oxide nanowires, pristine and doped, as well as metallic nanowires.

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