bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Texturization of MoS2 Surface to Enhance Catalytic Property of Hydrogen Evolution Reaction
Authors: Kiriya Daisuke , Lobaccaro Peter , Nyein Hnin Yin Yin , Javey Ali 
Published: February 2020

Molybdenum disulfide (MoS2) has been gathered attention as a non-precious metal catalyst for hydrogen evolution reaction (HER); however, pristine MoS2 (bulk mineral) is known to be a poor catalyst. The fundamental challenge to improving the catalytic performance of MoS2 is to increase the density of active reaction sites on the surface of MoS2. Usually, the crystalline plane (0001) is inert to the HER whereas the edges of MoS2 are active. In this presentation, we will show how our thermal texturization method improves the HER performance of MoS2 using a simple annealing procedure in forming gas (hydrogen and nitrogen mixture). The annealed bulk MoS2 shows a roughened surface including a higher density of edge sites. As a result, the catalytic performance of the annealed MoS2 shows more 100 mV reduction of overpotential to obtain 10 mA/cm2 of HER current density. We show that this treatment is generally applicable to many morphologies, including bulk, microflake, and nanoflakes of MoS2 to use as an efficient HER catalyst. The simplicity of this procedure suggests this method would be scalable, and furthermore could be applicable for other chalcogenide-based 2D materials.
(Invited) Microfluidic Synthesis of Functional Nanomaterials
Authors: Sun Jiashu 
Published: February 2020

The controlled synthesis of functional nanoparticles with tunable structures and properties has been extensively investigated for cancer treatment and diagnosis. Among a variety of methods for fabrication of nanoparticles, microfluidics-based synthesis enables enhanced mixing and precise fluidic modulation inside microchannels, thus allowing for the flow-mediated production of nanoparticles in a controllable manner.
We present a hollow-structured rigid nanoparticle fabricated by a multi-stage microfluidic chip in one step, to effectively entrap various hydrophilic reagents inside, without complicated synthesis, extensive use of emulsifiers and stabilizers, and laborious purification procedures. The nanoparticle contains a hollow water core, a rigid poly (lactic-co-glycolic acid) (PLGA) shell, and an outermost lipid layer. The entrapment efficiency of hydrophilic reagents such as calcein, rhodamine B and siRNA inside hollow water core is ~ 90 %. In comparison with the combination of free Dox and siRNA, the hollow-structured rigid nanoparticle that co-encapsulates siRNA and doxorubicin (Dox) reveals a significantly enhanced anti-tumor effect for a multi-drug resistant tumor model. Lipid-covered PLGA NPs or liposomes of the same size and surface properties, but different rigidity by controlling the interfacial water layer, can be realized using a two-stage microfluidic chip. It enables us to explore how rigidity of NPs regulates the cellular uptake and elucidate the intrinsic mechanism. Given the only significant difference between those two types of NPs is the rigidity, the experiments suggest that rigidity could dramatically alter the cellular uptake efficiency, with rigid NPs being easier to get through members than soft ones. The mechanisms revealed here suggest that tuning of rigidity of NPs is one appealing way in improving therapeutic efficiency.
A Microfluidic Electrochemical Cell with Integrated Palladium Hydride Reference Electrode
Authors: Fanavoll Espen Vinge , Harrington David A. , Sunde Svein , Seland Frode 
Published: February 2020

Microfluidic devices have potential to be a great addition to the aqueous electrochemistry toolbox, for instance as an analog to the rotating ring-disk electrode, with an enhanced control of mass transport due to laminar flow. The photolithography process makes fabrication of various cell designs relatively fast, and it is possible to make electrodes of many different materials, including electrocatalyst particles. While the restricted volume of a microchannel provides excellent mass transport control, it introduces a very high solution resistance. This will create a significant shift in solution potential in the channel even at moderate currents, and makes the measurement of electrode potentials in the microchannel a challenge. In order to accurately measure potentials of electrodes in a microfluidic cell it is essential to characterize and minimize the effects of this potential distribution. Using a traditional reference electrode, and placing it in an outlet chamber essentially maximizes the uncompensated solution resistance, due to the necessity of having the counter electrode downstream of the working electrode.
To solve the problems with the potential distribution, we fabricated a microfluidic electrochemical cell with an integrated palladium hydride reference electrode in a side channel upstream of the working electrode. A schematic of a cell is shown in Figure 1a. The cell design is relatively simple, and does not require salt bridges or ion conducting membranes in the cell to provide electrical contact to the reference electrode. This configuration results in low uncompensated resistance for single electrode experiments, and minimizes it for multiple electrode experiments. The placement of the reference electrode in a stagnant side channel eliminates influence of the species in the main channel on the reference electrode potential. Using PdH as the reference electrode makes the use of a wide range of acid and buffered electrolytes possible, and the presence of unfavorable ions such as chlorine can be eliminated. The reference electrode was charged in situ from a thin-film palladium electrode, and was able to hold a stable potential for up to eight hours of experiments.
The relationship between the potential shift at one electrode, the cell geometry, and current through electrodes located upstream was probed using the half-wave potential of Ru(bpy)3
3+ oxidation and oxygen evolution as model reactions. Figure 1b shows how the potential for oxidation of Ru(bpy)3
3+ shifts at the SE at different anodic currents through the WE. This is the best case scenario for a cell with 100 µm wide electrodes and a 100 µm gap between the electrodes. If we allow for potential shifts up to 5 mV at the SE, the maximum current at the WE becomes 4 µA, using a 0.1 M Na2SO4 supporting electrolyte.

Figure 1
Dual Gate Black Phosphorous Field Effect Transistors on Glass for NOR Logic and OLED Switching
Authors: Kim Jin Sung , Lim June Yeong , Yu Sanghyuck , Ahn Jongtae , Im Seongil 
Published: February 2020

As promising Two-dimensional (2D) materials, transition metal dichalcogenide (TMD) nanosheets recently attracted much attention in respects of its relatively high mobility and distinct energy band gap of 1.2~1.8 eV. Black phosphorus nanosheet emerged after appearance of TMD, but with some similarity to graphene, since it contains one element, phosphorus (P), quite high mobilities which are depending on its thickness and bandgap.
So, We have fabricated transistor with 12 nm-thin black phosphorus channel on glass substrate, where our black phosphorus field effect transistors (FETs) have a patterned-bottom gate structure with 30 nm-thick atomic layer deposited Al2O3 dielectrics on top and bottom of black phosphorus channel. Top gate dielectric has simultaneously been used as device encapsulation layer, slightly controlling the threshold voltage of FETs when FETs mainly operate under bottom gate bias. Bottom, top, and dual gate-controlling mobilities were respectively estimated, to be 270, 90, and 210 cm2/V s. As a result, our dual gate BP FETs demonstrate organic light emitting diode (OLED) switching for green and blue OLEDs, also demonstrating NOR logic functions by separately using top- and bottom-input.

Figure 1
New Insights into Mechanistic Aspects of Oxygen and Hydrogen Peroxide Reduction in Aqueous Electrolytes
Authors: Georgescu Nicholas Stefan , Feng Zhange , Xu Jing , Scherson Daniel 
Published: February 2020

Certain aspects of the interpretation of rotating ring-disk electrode, RRDE, data for the oxygen reduction reaction, ORR, in aqueous electrolytes under forced convection have been examined. This presentation will highlight three specific topics:

• The correct interpretation of the fraction of the oxygen consumption that generates H2O2(aq), as extracted from the ratio of ring current to disk current denoted as XH2O2

, A plot of this ratio vs ω-1/2, where ω is the rotation rate of the disk, should be linear and, with a slope proportional to k3
/XH2O2
where k3

is the rate constant for the reduction of solution-phase hydrogen peroxide1.

• Changes in the electrocatalytic activity of Pt for the oxygen and hydrogen peroxide reduction reactions (ORR, and HPRR, respectively) in an aqueous acidic electrolyte induced by the adsorption of bromide, as a model impurity, have been investigated using chronoamperometric techniques. Significant drops in the diffusion-limited currents for O2 reduction, as well as an increase in the measured H2O2(aq) at the ring were induced by the presence of 10 M KBr, and could only be observed for Br- > 0.25 regardless of Estep. This behavior was found to be consistent with a simple blockage of surface active sites by adsorbed bromide, as predicted by the attenuation model proposed by Levart.

• An analysis of O2
- generation at the disk and subsequent oxidation at the ring (see Figure 1) of a RRDE, which undergoes a subsequent second-order dismutation2.

Acknowledgements: This research was supported by a grant from NSF: CHE-1412060

References

1. N. S. Georgescu, A. J. J. Jebaraj and D. Scherson, ECS Electrochemistry Letters, 4, F39 (2015).
2. Z. Feng, N. S. Georgescu and D. A. Scherson, Analytical Chemistry, 88, 1088 (2016).

Figure 1
Oxygen Reduction Reaction Mechanism of Connected Platinum-Iron Nanoparticle Catalysts Probed By EC-XPS
Authors: Matsumoto Masashi , Yogi Chihiro , Arao Masazumi , Kuroki Hidenori , Tamaki Takanori , Yamaguchi Takeo , Imai Hideto 
Published: February 2020

The widespread use of polymer-electrolyte fuel cells (PEFCs) requires more active, stable, and low cost electrocatalysts than platinum. Bimetallic electrocatalysts such as platinum-iron (PtFe) have been attracting a great deal of attention as an oxygen reduction reaction (ORR) catalyst since they have demonstrated both higher oxygen reduction activity and improved stability with much smaller amounts of platinum. Connected PtFe-nanoparticle catalyst with a beaded network by connected PtFe nanoparticles and a superlattice structure (a chemically-ordered face-centered tetragonal (fct) structure) exhibit specific ORR activity that is higher than those of the commercial Pt catalyst supported on carbon black (Pt/C) and even fct-PtFe nanoparticles (without any beaded networks) supported on carbon black. [1] Thus, the unique structures of connected PtFe-nanoparticle catalysts, such as connected beaded network and hollow structure, enhance an ORR activity.
Electrochemical x-ray photoelectron spectroscopy (EC-XPS) applied for the reaction mechanism analyses of PEFC catalysts. Electrochemical reactions occur at catalyst electrode surface, and then, the electrode is transferred to an UHV chamber immediately. Finally the electrode surface involving reaction intermediates is analyzed by using XPS without exposing to the air. Since structure of electrochemical-double layers is maintained during the measurement process, we can identify the intermediate species, and evaluate adsorption strength, etc., namely, we can analyze reaction mechanism. In this study, we performed electrochemical x-ray photoelectron spectroscopy (EC-XPS) measurements in order to understand the factors that influence the high ORR activity of the connected PtFe-nanoparticle catalyst. The EC-XPS results for connected PtFe-nanoparticle catalysts under ORR conditions showed the adsorption of oxygen species on the catalyst surfaces, indicating that ORR intermediates were detected. We could observe ORR processes of connected PtFe-nanoparticle catalysts. In this presentation, we will also show the EC-XPS measuring data for other platinum catalysts and discuss the factors that influence the high ORR activity of the connected PtFe-nanoparticle catalyst in detail.
[1] T. Tamaki, H. Kuroki, S. Ogura, T. Fuchigami, Y. Kitamoto, and T. Yamaguchi, “Connected nanoparticle catalysts possessing a porous, hollow capsule structure as carbon-free electrocatalysts for oxygen reduction in polymer electrolyte fuel cells”, Energy Environ. Sci., 2015, 8, 3545-3549.
Identifying Performance-Limiting Mechanisms in Alkaline-Exchange-Membrane Fuel Cells Using Modeling: Strategy for Internally-Humidified Fuel Cells
Authors: Shiau Huai-Suen , 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 (PEMFC). Their major advantage is the possibility of using non-noble catalysts due to faster oxygen-reduction reaction (ORR) kinetics in alkaline than in acidic media. However, water management is a more serious concern in AEMFCs because OH- conductivity is more highly dependent on water content and the ORR consumes water. Compared to PEMFCs, the lower performance of AEMFCs is mostly caused by extremely nonuniform distribution of water in the ionomer phase between the anode and cathode as well as the increased overpotential for the hydrogen oxidation reaction. In this presentation, we will discuss the performance-limiting mechanisms specific to different operating conditions (e.g. varying inlet relative humidity (RH)) based on a cell-level mathematical model. For example, anode flooding can be a critical issue at 100% RH, whereas at lower RH high ionic transport resistance in the cathode dominates due to dehydrated ionomer phase at high current, where the impact of water-consuming ORR kinetic polarization is also critical. Low AEMFC performance at high current is not simply due to mass transport issues with vapor/membrane water, but a consequence of poor water distribution leading to sluggish OH- conduction and ORR kinetics. A sensitivity analysis of design parameters including the humidifying condition and membrane property is performed to identify the most significant factors controlling performance. Overall, water management and ionic/mass transport characteristics of an AEMFC assembly are discussed in detailed. The developed model will be used to examine and elucidate performance bottlenecks and enable strategies to overcome them, significantly increasing the possibility of AEMFC commercialization.

Acknowledgements

This work was funded by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, of the U. S. Department of Energy under contract number DE-AC02-05CH11231, program manager David Peterson.
Benchmarking MEA Performance and Durability for PEM Water Electrolysis
Authors: Rasimick Brian , Zhao Shuai , More Karren , Pivovar Bryan S , Xu Hui 
Published: February 2020

Proton exchange membrane (PEM) water electrolysis has become increasingly attractive due to the penetration of renewable energy (e.g, solar and wind). Hydrogen production from PEM water electrolysis is advantageous over other technologies 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.
Performance and durability of the MEAs play an essential role for the cost and viable commercialization of PEM water electrolysis. However, unlike the well-established MEA benchmarks of PEM fuel cells, the performance and durability of PEM electrolyzer MEAs have not been thoroughly studied. The objective of this work is to establish benchmark MEA performance and durability for PEM water electrolysis. For this purpose, a series of oxygen evolution reaction (OER) catalysts, which includes commercial Ir black and various Ir nanostructures, has been evaluated under test protocols established at Giner Inc. These approaches include high-voltage hold (>1.8 V), accelerated stress test (e.g., voltage cycling from 1.4 to 2.0 V), and constant low-current operations. The polarization curves of the MEAs will be obtained after each test. The morphology and structure of MEAs after durability tests will be characterized to correlate to their performance and durability.
The established performance and durability may provide metrics and guidance to the community of PEM water electrolysis.

Acknowledgement: The financial support is from the Department of Energy under the Contract Grant DE-SC0007471.
(Invited) Core-Shell Hydride Nanoarchitectures for Reversible Hydrogen Storage
Authors: Aguey-Zinsou Francois 
Published: February 2020

The properties of nanomaterials are known to be size depend. Such size depend effects could offer powerful means to finally control both the thermodynamic and kinetic properties of hydride materials at the molecular level [1] and thus enable the practical design of hydrogen storage materials from these effects. However, investigations through such an approach require new strategies to both synthesise and stabilise nanoparticles of highly reactive hydride materials and the understanding to control the key parameters that will allow reversibility with high storage capacity. The use of porous host structures offers such a route, however the storage capacity usually remains limited by the intrinsic difficulty of entirely fill the porosity.
Herein, the potential of a new core-shell confinement approach and recent progress we have made through this nanosizing method will be discussed [2]. Since, complex hydrides still undergo phase transitions including melting at the nanoscale, this core-shell approach has proven to be an very effective strategy to stabilise and simultaneously catalyse the reversible storage of hydrogen with hydrides including borohydrides and alanates (Figure 1). It also provides us with new means to stabilise against oxidation highly reactive nanoparticles of elements such as lithium.

References

[1] K.-F. Aguey-Zinsou and J.-R. Ares-Fernandez, Energy Environ. Sci., 3 (2010) 526.
[2] M. Christian and K.F. Aguey-Zinsou, ACS Nano, 6, 9, (2012) 7739.

Figure 1. (a) Approach for the synthesis of core-shell borohydrides and (b) TEM and associated elemental mapping of NBH4@Ni, and (c) corresponding hydrogen cycling.

Figure 1
Anion Conducting Multiblock Copolymers with Partial Fluorination and Long Side Chains
Authors: Liu Lisha , Ahlfield John M. , Chu Deryn , Kohl Paul A 
Published: February 2020

Anion Exchange Membrane (AEM) fuel cells are a possible route to overcoming fundamental issues with acid-based fuel cells. The issues include the high cost of platinum catalysts, complex water management, and sluggish electrochemical reactions. However, the performance of AEM fuel cells is not as good as that of Proton Exchange Membrane (PEM) fuel cells partially because of the limitations of current anion exchange membranes, such as low ionic conductivity, poor stability at high pH, and high water uptake.
A series of partially fluorinated multiblock copoly(arylene ether)s with long head-group tether were synthesized for use in AEM fuel cells and electrolyzers. The multiblock copolymers were synthesized via polycondensation of hydroxyl-terminated oligomers and fluoro-terminated oligomers. The resulting multiblock structure has one hydrophilic block and one hydrophobic block. It was designed so that nanophase-separation occurs and efficient conductive channels are formed with low water uptake. Multiblock copolymers with different block lengths and ion exchange capacity (IEC) were synthesized to maximize ion conductivity and explore the relationship between chemical structures and membrane properties. Table 1 shows the membrane properties. A non-linear relationship was found between the number of head-groups on a hydrophilic block and the conductivity. Doubling the number of head-groups more than doubled the hydroxide conductivity. Hydroxide conductivity as high as 119 mS/cm at 80°C have been observed with a specific size block size: X5.4Y7, where X is the hydrophobic block and Y is the hydrophilic block. The hydrophobicity of the backbone has allowed synthesis of polymers with minimal water uptake. The ratio of conductivity-to-water uptake shows that less water is absorbed compared to conventional materials. The number of waters per ion within the polymer is as low as 4. This is reflected in the measurement of the amount of free-water and bound-water. No conductivity loss was observed after soaking the membrane in 1M NaOH solution at 60°C for over 700 hours.
Financial support from US Office of the Deputy Assistant Secretary of the Army for Defense Exports and Cooperation (DASA-DE&C) is gratefully acknowledged.

Figure 1
(Invited) Pt Based Fuel Cell Catalysis
Authors: Herein Daniel 
Published: February 2020

Pt based fuel cell catalysts are well known since many decades. The main principles of tuning activities and stabilities of especially Pt based Carbon Black fuel cell catalysts seems to be well understood. Therefore only little interest has been shown in new research and developments activities in Pt fuel cell catalysts based on commercial Carbon Blacks. Form pure scientific research view there seems to be only little or nothing new requiring a deeper understanding of the main catalytic principles and properties regarding pure Pt based Carbon Black fuel cell catalysts.
On the other hand Pt based Carbon Black fuel cell catalysts are the most important commercial fuel cell catalysts. The starting and growing mass production of these type of fuel cell catalysts for all different applications requires a well-controlled synthesis process and quality check procedure including activity testing in MEA´s. Controlling the synthesis process on industrial scale on one hand requires a deep understanding of all properties of the final Pt based carbon Black catalyst. On the other hand the property control of the catalyst material is done by controlling all process steps including the understanding of correlations in-between different process parameters.
From industrial view the challenge of producing such simple and for decades well known Pt based Carbon Black catalysts starts with the reproducibility of the catalytic important properties from batch to batch and in all different batch sizes. In addition to this challenge of manufacturing reproducible amounts of fuel cell catalysts the question arises how to measure the main catalytic important properties, such as the mass activity, air performance and ECSA, in a reproducible way using dependably equipment and test procedures.
In this talk all aspects regarding the question of reproducible synthesis processes on different manufacturing scales as well as determining the catalytic properties in a reproducible way will be discussed using the example of such a simple catalyst type such as the Pt based on Carbon Black fuel cell catalyst.