bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface Characterization and Platinum-like Electrocatalytic Activity of Nano-Scale Platinum Deposited on Transition Metal Carbide Nanotubes via Atomic Layer Deposition
Authors: Saha Shibely R. , Witters Zachary Everett , Leonard Brian M. , Li Dongmei 
Published: February 2020

Due to the similar electronic and geometric structures between transition metal carbides (TMC) and Platinum (Pt), Pt supported on TMC surfaces (a.k.a., Pt/TMC) has been the focus of significant research interest. This presentation focuses on a new class of electrocatalyst fabrication in which high purity β-molybdenum carbide (referred to as Mo2C hereafter) was synthesized into hollow nanotubes and subsequently modified with nanoscale platinum particles (1-5 nm) deposited via rotary Atomic Layer Deposition (ALD) (referred to as Pt/Mo2C). X-Ray diffraction (XRD) measurements of Mo2C and Pt/Mo2C showed no molybdenum peaks and a very small amount of unreacted multi-wall carbon nanotubes (MWCNT) in the Mo2C samples, indicating that Pt was primarily supported on Mo2C nanotubes. Strong interaction between Pt nanoparticles and the Mo2C nanotube support was observed in lattice spacing changes from high resolution transmission electron microscopy (HRTEM) images, in addition to Pt binding energies from x-ray photoelectron spectroscopy (XPS) results of Pt/Mo2C. Atomic adsorption spectroscopy (AAS) measurements of Pt mass in Pt/Mo2C samples showed an average of 2.4% Pt loading in Pt/Mo2C nanoparticles. The electochemically active surface area (ECSA) of the 2.4% Pt/Mo2C was found to be 70% higher than commercial 20% Pt/C, indicating an increased number of electrochemically active sites, possibly resulting from the interaction between ALD-deposited Pt nanoparticles and Mo2C nanotube support.
Cyclic voltammograms of the 2.4% Pt/Mo2C catalyst showed higher hydrogen oxidation reaction (HOR) activity than commercial 20% Pt/C, while bare Mo2C did not demonstrate any significant HOR activity. For the hydrogen evolution reaction (HER), the 2.4% Pt/Mo2C showed similar activity to the 20% Pt/C, while bare Mo2C nanotube showing noticeable, but not significant HER activity. Another focus of this talk is to present the 2.4% Pt/Mo2C catalyst performance in a PEMFC anode (HOR), which outperformed the commercial 20% Pt/C with up to a 403% increase in peak power density and 448% increase in current density. Consequently, the reported Pt/Mo2C validates a new fabrication approach for practical nanoscale electrocatalysts where the supported catalyst is deposited via atomic layer deposition onto high purity transition metal carbide nanotubes. Ongoing work in our group focuses upon long-term stability, the corrosion mechanism, and ORR activity of the Pt/Mo2C catalyst. Furthermore, we are conducting systematic investigations on how the number of ALD cycles affects the size and distribution of Pt on Mo2C nanotube and subsequent HER, ORR activity and PEMFC performance of resultant catalysts.
Materials and Cell Designs for Bipolar Fuel Cells
Authors: Ahlfield John M. , Deshpande N. A. , Liu Lisha , Huang Wenjiao , Chu Deryn , Kohl Paul A 
Published: February 2020

Bipolar membranes fuel cells utilizing both anion and cation conductive materials have several advantages compared to their purely acidic or alkaline counterparts due to improved water management and electrode kinetics. Material transport properties play an important role in determining viability of membrane and ionomer materials. Additionally, the material at the cation/anion junction is critical to device performance, as it must conduct ions to the interface in addition to mechanically binding the membranes. A series of devices using different interfacial materials has been fabricated for use in direct methanol and hydrogen fuel cells. These fuel cells were characterized by performance metrics and electrochemical impedance spectroscopy to determine specific areas for improvement in the bipolar devices. Operation under varying humidity was studied in order to understand water management necessary for bipolar fuel cells. This work will drive the future optimization of bipolar devices.
Financial support from US Office of the Deputy Assistant Secretary of the Army for Defense Exports and Cooperation (DASA-DE&C) is gratefully acknowledged.
Platinum Dissolution from Carbon Supported Nanoparticles
Authors: Wang Zhongqi , Tada Eiji , Nishikata Atsushi 
Published: February 2020

Platinum (Pt) dissolution concerns the instability of Pt-based cathode catalysts for polymer electrolyte fuel cells (PEFCs). Studies on unsupported Pt, polycrystalline plates or electroplated films, suggest that Pt dissolution relates to Pt oxide formation and reduction. Pt dissolution from the carbon supported nanoparticles, however, is rarely discussed. In this study, we investigated Pt dissolution using commercial carbon supported nanoparticles (Pt/C). We prepared Nafion-free inks by mixing Pt/C samples with H2O and isopropyl alcohol (IPA). We evaluated the amount of Pt dissolution over potential cycling tests using inductively-coupled plasma-mass spectrometry (ICP-MS). We also scrutinized the Pt dissolution behaviors from the Pt/C in a single cycle using a channel flow double electrode (CFDE)1.
The Pt/C samples we used were produced by Tanaka Kikinzoku Kogyo (TKK); the Pt particle size distributions before test were characterized by TEM. For each Pt/C sample, we mixed about 10 ~ 15 mg Pt/C with 3.8 ml H2O and 1.2 ml IPA, and sonicated the mixture in an ice bath for 60 mins. We loaded an appropriate amount of ink on a glassy carbon (GC) substrate. The Pt/C electrode was then dried under an ambient atmosphere for 120 mins. The Pt/C electrode was cycled 30 or more times between 0.05 and 1.4 V (vs. SHE) in 0.5 M H2SO4 to remove organic adsorbents and to obtain a reproducible electrochemical surface area (ECSA). The ECSA was used for normalization of Pt dissolution.
First, we conducted 300 cycles of potentials cycling in 0.5 M H2SO4 in a stationary cell. The geometric surface area of the GC was ca. 0.25 cm2 and we loaded about 2 µl ink on it. Two upper potential limits (E
U) of 1.0 and 1.4 V were used with a same lower potential limit (EL

) of 0.4 V. The testing solutions were analyzed by ICP-MS.
Second, we tested Pt dissolution from the Pt/Cs using a CFDE in argon-deaerated 0.5 M H2SO4. The CFDE consisted of a GC working electrode (WE) and a gold (Au) collector electrode (CE). The geometric surface area of the GC was ca. 0.05 cm2 and we loaded about 0.6 µl ink on it. The CV of a 46wt% Pt/C obtained in the CFDE at 25oC shows that the Pt/C is relatively stable without Nafion. Pt dissolution from the Pt/C-WE was monitored by the CE. The CE collected 30% of dissolved Ptn+. We set the CE at 1.4 V for detecting Pt2+, and at 0.7 V for Pt4+. We also set the CE at 0.3 V for collection of both Pt species.
The ICP-MS data evaluate the overall amount of Pt dissolution and CFDE data provide details of the dissolution behaviors against potential. Using both data, we discuss the mechanism of Pt dissolutions from the Pt/Cs with respect to temperature, E
U, and Pt particle size.

Reference

1. Z. Wang, E. Tada, and A. Nishikata, J. Electrochem. Soc., 161 (4), F380 (2014).

Figure 1
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, <k>, 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, <k>, 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