bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Nanoscale Morphology Control in Halide Perovskite/Polymer Composites for Printed LEDs and Beyond
Authors: Yu Zhibin
Published: February 2020

Recently, astounding optoelectronic properties have been discovered in halide perovskites (perovskites). Such materials have a general ABX3 chemical formula, in which A is a cesium (Cs+) or an aliphatic ammonium (RNH3
+) cation, B is a divalent Pb2+ or Sn2+ cation and X is an anion such as Cl-, Br- or I-. Their crystal structures resemble the one commonly found in BaTiO3. The halide perovskites can be processed like polymeric semiconductor materials using solution based processes; and may be coated into large area thin films on arbitrary substrates; they may also be crystallized into three-dimensional periodic structures and behavior like conventional inorganic semiconductors including the superior charge transportation properties.

In this talk, our recent work of developing perovskite/polymer composites towards the realization of fully printable LEDs will be presented. The perovskite/polymer composites possesses all the remarkable optoelectronic characteristics of pure perovskites. For instance, we have demonstrated their use for blue, green and red LEDs.  In addition the device efficiencies exceeded those of pure perovskite LEDs. The perovskite/polymer composites have shown advantages in improving the processability and quality of the perovskite thin films; and enhancing the structural stability of the perovskites especially at high humid fabrication and service environments. By embedding the perovskite crystals inside a polymer matrix, the perovskites can be less toxic and more environmentally benign compared to pure perovskite. At the end of the talk, other potential applications of perovskite/polymer composites will be briefly discussed.
(Invited) Thermally-Enhanced Photo-Electrochemical Water Splitting
Authors: Chueh William C
Published: February 2020

Transition-metal-oxide semiconductors are promising photoanodes for solar water splitting due to their excellent chemical stability and appropriate bandgaps. However, in absorbers such as BiVO4, TiO2, α-Fe2O3, and WO3, charge carriers localize as small polarons or become trapped, leading to low minority carrier mobilities. This limits the minority carrier collection efficiency in the quasi-neutral region of the light absorber, and lowers the overall photoactivity. In this work, we demonstrate that modestly elevating the temperature activates minority carrier hopping in monoclinic BiVO4, significantly enhancing the saturation photocurrent without a substantial anodic shift of the onset potential, and is an attractive alternative to employing complex passivation layers and nanostructured templates towards achieving the theoretical photocurrent density. Specifically, using a Mo:BiVO4/SnO2/Si tandem photoanode/photovoltaic, increasing the absolute temperature by 11% from 10 to 42 °C elevates the saturation photocurrent from 1.8 to 4.0 mA cm−2. This strong temperature enhancement, 3.8% K−1, is 5 times greater than that in α-Fe2O3. Concurrently, the onset potential shifts slightly from 0.02 V to 0.08 V versus the reversible hydrogen electrode (or equivalently, from −1.22 V to −1.13 V versus the equilibrium potential of oxygen evolution). Our observation contrasts with the prevailing understanding that the energy conversion efficiency generally decreases with temperature as a result of reduced photovoltage. Thermally-activating minority carrier transport represents a general pathway towards enhancing the photoactivity of light absorbers where hopping conduction limits the minority carrier collection in the quasi-neutral region.
(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.
Towards Understanding the Ion Transport in Polyelectrolyte-Modified Nanopores with Bipolar Charges
Authors: Lin Chih-Yuan , Yeh Li-Hsien , Hsu J.P.
Published: February 2020

Fundamental understanding of ion transport is crucial for designing nanofluidic/nanopore devices. In particular, nanopores modified with synthetic or biological polyelectrolyte (PE) brushes have emerged as a potential tool for rectifying ionic current and characterizing individual biomolecules. Due to its asymmetric charge density distribution, bipolar nanopore exhibits strong ionic current rectification (ICR) behavior, which is observed as a diode-like current-voltage characteristic. In this work, the ion transport is theoretically investigated by using a continuum-based model, including Poisson−Nernst−Planck (PNP) equations and Stokes and Brinkman equations. In this study, we examine the influences of the bulk salt concentration and the charge density on ICR behavior. The simulated results suggest that the degree of ICR decreases with increasing bulk salt concentration. Besides, the ionic enrichment/depletion is more significant when the charge density becomes larger, resulting in a larger degree of ICR. However, if the positive and negative charge densities are asymmetrically distributed on the either side of the nanopore, the degree of ICR displays a local maximum. The results obtained also imply that the ICR behavior in a PE-modified nanopore with bipolar charges can be regulated by its surface modification.
(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
Dynamic Characteristics of Air-Water Interface in a Patterned Microchannel
Authors: Zhang Jingxian , Jie Yucheng , Yao Zhaohui
Published: February 2020

Dynamic characteristics of air-water interface are investigated in a microchannel, fabricated from silicon wafers using photolithography. The sidewalls of the microchannel were designed having reentrant microstructures, which can capture air between their gaps due to the surface tension, and form a hydrophobic state. With these structures on the sidewall, the micro cavities on the microchannel sidewall are occupied by air when the channel is filled with water, which forms the air-water interface. However, the interface between the micro gaps is unstable and will deform as time goes on. Digital microscope system was used to observe and record the deformation process of the air-water interface. Meniscus interface was observed as soon as the water fills the microchannel. Driven by the pressure difference (the static pressure of the water and the pressure of the air in the cavities) and surface tension, the interface deformed from a meniscus to a bulge within 3 minutes. After this process, the air in a cavity finally formed an air bubble, merged with the neighbor air bubble, and formed an air bridge connected two corresponding micro cavities on the two opposite sidewalls. Pushed by the flow, the air bridge transported downstream, interacted with the downstream air bulges, and finally escaped from the outlet. In our observation, the process first occurs at the outlet, and then repeats periodically and sequentially from the downstream to the upstream. This process will lasts until the air pressure in the cavities is not large enough to form a bulge, and the water fill into the cavities, which finally destroyed the air-water interface. Investigation on these processes may help us understand the instability of the air layer on superhydrophobic surfaces, the deformation of an air-water interface in a microchannel, and the dynamic characteristics of air bubbles in a microchannel.
Numerical Simulation of Thermal Diffusion and Convection in Electrokinetic Microchannel Flow
Authors: Zhang Kai , Lv XiaoFei
Published: February 2020

Abstract: In a confined microfluidic straight channel with
one heater and two detectors
micro-fabricated on suspended silicon bridges, the numerical study of
thermal diffusion and convection in electro-osmosis flow
was carried out. Heat pulses created by the heater are transported downstream by the flow, and by performing a cross correlation between the detected and the injected signals,
the linear relation between flowrate and thermal pulse's time-of-flight can be achieved, then it can provide a very accurate a linear measurement of the flowrate over long range without independence of the thermal characteristics of the fluid. These conclusions may be helpful to integration of accurate flowmeter in some portable electrokinetic micro-total-analysis systems.

Key words: Electroosmosis; Thermal-pulse; Time-of-flight; Micro-flowmeter
Single and Few Layered WS2 Nanoflowers: Synthesis, Characterization and Their Piezoresponce
Authors: Wu Jyh Ming , Srinivaas Masimukku
Published: February 2020

Two Dimensional (2D) transition metal dichalcogenides (TMDS) plays an emerging key potential applications in optoelectronics, electronic devices, sensors, batteries, supercapacitors, biomedicine and electrocatalytic and photocatalysis owing its wide range of chemical, electrical and mechanical properties. Until now, a wide range of synthesis approaches have been developed for the preparation of single or few-layered TMD hybrid nanostructures, which can be synthesized directly from both physical and chemical vapor depositions. Here we demonstrate the single and few layered tungsten disulfide (WS2) as synthesized by solvothermal method. The morphologies of WS2 were recorded by field emission scanning electron microscopy (SEM), the size of the Nanoflowers ranges from 400-600nm. The XRD pattern shows a crystalline hexagonal structure. All the diffraction peaks could be indexed to the p63/mmc space group, JCPDS no. 08-0237. To further revel the layered charactertistics, HRTEM and XPS spectra was collected. The piezoresponse force microscopy (PFM) image reveals that the WS2 nanoflowers exhibits a significantly piezoelectric potential up to 12mV. The WS2 exhibited significantly piezoresponse, which may result from the single and fewlayers due to its noncentrosymmetric structure. The unique piezoelectric property of the crystalline WS2 nanoflowers is opening up the new field applications such as low-power consumption of logic-circuit switchers, and ultrasensitive biological sensors, and piezoelectric nanogenerators.
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
Yolk-Shell Nanocrystals for Efficient Photoelectrochemical Water Splitting
Authors: Lai Ting-Hsuan
Published: February 2020

Here we demonstrate the practical use of yolk-shell nanocrystals for efficient photoelectrochemical water splitting. The samples were prepared by using Au-Cu2O core-shell nanocrystals as the growth template. By performing selenization treatment on Au-Cu2O accompanied with the Kirkendall effect, abundant voids were generated inside the structure, resulting in the formation of Au-Cu2Se yolk-shell nanocrystals. Steady-state photoluminescence spectra show that charge separation efficiency was particularly prevalent in yolk-shell nanocrystals. Time-resolved photoluminescence data further reveal that yolk-shell nanocrystals displayed significantly larger interfacial charge transfer rate constant than the core-shell counterpart. The samples were further employed as photocathode for photoelectrochemical water splitting to illustrate their applicability. Four different samples including Au-Cu2Se, Au-Cu2O, pure Cu2Se and pure Cu2O were compared to illustrate the applicability of yolk-shell nanocrystals. The yolk-shell nanocrystals were found to exhibit substantially higher photocurrent generation than the other three counterpart samples. Both the moveable Au particle core and the void-space structural feature have contributed to the resultant superior photoelectrochemical performance of Au-Cu2Se. The influence of void size and shell thickness on the water splitting efficiency of yolk-shell nanocrystals is also studied. The results show that large void space and thicker shell thickness may lead to higher photoelectrochemical efficiency.
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.
Metal Mesh Gas Diffusion Layers for PEM Fuel Cells
Authors: Fahy Kieran F. , Lapinski Jacek , Kucernak Anthony R. J.
Published: February 2020

As fuel cells gain increased volumetric power density, there is a need for thinner GDLs that give increased thermal and electrical conductivity, and mechanical stiffness. This has been demonstrated by the introduction of advanced GDL/bipolar plate designs that have been implemented in commercial fuel cells such as that seen in the Toyota Mirai (1).

The use of metal GDLs has been previously examined in ethanol and methanol fuel cells (2,3) but have been largely ignored in PEMFCs due to the corrosive conditions present in PEMFCs which considerably reduce the lifetime of cells with non-passive metals present. Spun carbon fibre GDLs, such as Toray and Avcarb, have previously been the main choice for PEMFC GDLs due to the passivity and gas and water transport properties of these materials. With increased power density in fuel cells however these materials can incur losses due to a lack of thermal and electrical conductivity as well as being relatively thick and brittle.

In this study we have examined a number of metal meshes used in place of carbon paper GDLs in fuel cells. Meshes with different aperture sizes were examined with regard to fuel cell performance as well as flooding of the electrodes and performance under high mass transport conditions. The aperture sizes of these meshes played a significant role in performance in the cell, both in terms of electrical conductivity and water management.

Surface passivation of the meshes by nitriding and using carbon and other passive coatings was also examined in order to increase their durability in the cell. The surface energy properties of these coatings was also examined ex situ via droplet shape analysis in order to achieve the best properties for use in a fuel cell. Adjustment of the hydrophilicity and hydrophobicity of these coatings was also used to improve water management.

The performance of some of these meshes and foams was seen to exceed some of the commercially available carbon papers even without significant optimisation. These materials could soon replace carbon fibre GDLs in PEMFCs leading to much higher volumetric power densities and improved performance.

References

T. Yoshida, K. Kojima, Electrochemical Society Interface, 24 (2015), pp. 45–49.

S. Arisetty, A. K. Prasad, S. G. Advani, Journal of Power Sources, 165, 1, (2007).

W. Yuan, Y. Tang, X. Yang, Z. Wan, Applied Energy, 94 (2012).

Figure 1 (a) Water droplet on metal mesh surface before surface treatment, and (b) after surface treatment. (c) PEM fuel cell performance of a metal mesh GDl compared with two common commercial carbon papers (Toray HGP-H-080 and SGL 24 BC).

Figure 1
Anion Exchange Membrane Separators Based on Polystyrene-Block-Poly(ethylene-ran-butylene)-Block-Polystyrene Triblock Copolymers
Authors: Wang Zhongyang , Parrondo Javier , Ramani Vijay K
Published: February 2020

There is a growing interest in using anion exchange membranes (AEMs) as separators in alkaline membrane fuel cells (AMFCs) and in other energy conversion and storage systems such as redox flow batteries (RFBs), alkaline water electrolyzers (AWEs) and reverse electrodialysis (RED) cells. The most commonly used cation in AEMs is the benzyl trimethylammonium cation. It is easy to synthesize due to the basicity of the trimethylamine, results in relatively large ion exchange capacities (IECs), and the resulting AEMs have good ionic conductivities. AEMs based on the benzyl trimethylammonium cation are good candidates for separators in redox flow batteries. However, it had been shown that the quaternary-ammonium-based AEMs are sensitive towards Hofmann elimination and direct nucleophilic elimination reactions under alkaline conditions, which impedes their use in AMFCs and AWEs. To solve the alkaline stability problem encountered by quaternary ammonium cations, researchers have investigated cations without alpha hydrogens to avoid degradation through ylide formation. Gu and Yan (1) first synthesized a polysulfone based ionomer containing the benzyl tris-(2,4,6-trimethoxyphenyl) phosphonium (TTMP+) cation and they found it had an outstanding stability under alkaline conditions. In our lab, we attempted to attach TTMP to polyphenylene oxide (PPO) and other polymer backbones to make alkaline stable AEMs, but the resultant AEMs were extremely brittle. Therefore, we have devoted attention to studying more robust backbones.

Polystyrene-block-poly-(ethylene-ran-butylene)-block-polystyrene (SEBS) is a chemically stable and elastomeric triblock copolymer, which deforms elastically to accommodate bulky cations (TTMP+) without becoming too brittle. There have been several attempts to make SEBS-based AEM by chloromethylation, however, the degree of functionalization (DF) obtained were relatively low due to gelation during the reaction (2, 3). In our work, we have optimized the chloromethylation conditions by selecting the appropriate solvent, temperature and reaction time. The resulting polymers have DFs up to 0.3 (mol of chloromethyl groups per polymer repeat unit). We have been able to synthesize highly robust SEBS-based AEMs containing benzyl trimethyl ammonium (TMA+) and benzyl tris- (2,4,6-trimethoxyphenyl) phosphonium (TTMP+) cations. 1H-NMR spectroscopy, ion exchange capacity and tensile tests were employed to characterize the AEMs. We will report the results obtained.

References

1. S. Gu, R. Cai, T. Luo, Z. Chen, M. Sun, Y. Liu, G. He and Y. Yan, Angewandte Chemie International Edition, 48, 6499 (2009).

2. R. Vinodh, A. Ilakkiya, S. Elamathi and D. Sangeetha, Materials Science and Engineering: B, 167, 43 (2010).

3. L. Sun, J. Guo, J. Zhou, Q. Xu, D. Chu and R. Chen, Journal of Power Sources, 202, 70 (2012).
Effect of Chemical Structure on Properties of Multiblock Copolymers for Alkaline Membrane Fuel Cell
Authors: Shin Dongwon , Lee Sojeong , Kim Eunyoung , Bae Byungchan
Published: February 2020

Alkaline membrane fuel cells (AMFCs), which use anion exchange membrane (AEM) as a solid electrolyte, continue to receive increased attention because of their advantages of fast oxygen reduction reaction in alkaline media, efficient water management, and the ability to use non-precious metal catalysts (e.g., nickel, cobalt, silver, iron, and etc.). Hydrocarbon-based aromatic polymers have been widely used as AEMs due to their good thermal and mechanical stabilities and easiness of synthesis and functionalization. However, poor chemical stabilities under strong alkaline environment and low ionic conductivity of AEMs should be improved for commercialization of AMFCs. Hydrophilic and hydrophobic phase separation is helpful for improvement in chemical stability and ionic conductivity. Well-developed hydrophilic domains form effective ion transport pathways resulting in enhanced ionic conductivity, while hydrophobic domains maintain mechanical and chemical stabilities because most nucleophilic sources, which can attack polymer backbone and cationic groups, are in hydrophilic domains. It is well known that block copolymers are the most promising chemical architecture for developing hydrophilic and hydrophobic phase separation.

Based on these backgrounds, we synthesized poly(arylene ether sulfone) based block copolymers to investigate the effect of chemical structure on AEM properties. These block copolymers were functionalized with cations after selective chloromethylation of hydrophilic blocks. The degree of chloromethylation was controlled to optimize ion exchange capacity values of block copolymers. The molecular weight of each oligomer was controlled by changing the feed ratio of monomers and confirmed by nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). All block copolymers showed well-developed morphology and outstanding AMFC performances. More detailed results will be discussed.
Investigation of a Correlation Between Structures of Mesoporous Carbon an Gas Adsorption Characteristics
Authors: Katagami Masataka , Akiba Etsuo , Hayashi Akari
Published: February 2020

Introduction

PEFCs are paid much more attention since the commercialization of FCVs and are deeply related to carbon materials, which are components of PEFCs themselves and also related systems. In our group, we have been studying mesoporous carbon (MC), which has meso-channel structures with about 10 nm diameter, as a catalyst support and have successfully improved durability of PEFCs, so far. In order to further improve performance and durability of PEFCs and related systems, it is important to understand the fundamentals of adsorption properties of fuels involving hydrogen gas, oxygen gas, and water vapor. In this research, a correlation between structures of mesoporous carbon and gas adsorption characteristics is investigated.

Experimental

General MC was synthesized by mixing Pluronic® F127, resorcinol, formaldehyde, and trimethyl orthacetate and heated under nitrogen atmosphere. Other MC materials1 were also made by slightly different conditions as shown in Table 1. Then, gas adsorption properties of each sample were evaluated after the ball milling and heat treating at 900 oC.

Results & discussion

Hydrogen adsorption dependence on the pore size of MC is discussed here. If MC#1 and MC#2 in Table 1are compared, MC#2 has larger pores based on the pore distribution obtained from nitrogen adsorption measurements. The values of BET specific surface area of the MC#1 and the MC#2 results in not very much different, 615 m2/g and 650 m2/g, respectively. The maximum hydrogen absorption content (wt%) at 7 MPa has resulted in 0.6 % for MC#1 and 0.35 % for MC#2. Considering Chahine rule2 for carbon materials, revealing that linear relationship between the hydrogen absorption content and the specific surface area, our results are against that rule. Therefore, hydrogen adsorption properties can be explained by other than the specific surface area in our materials. The possible mechanism of hydrogen adsorption is further discussed through the analyses of several MC materials.

(1) Y. Sonoda, A. Hayashi, Y. Minamida, E. Akiba, Chemistry Letters, 44, 503-505 (2015).

(2) R. Chahine, T.K. Bose, 11th WHEC, 1996; Pergamon Press: Oxford, U.K., 1259 (1996).

Figure 1
Oxygen Reduction Reaction at Carbon-Based Particles Prepared by Microwave-Assisted Catalytic Decomposition Measured in Acetonitrile
Authors: Kodera Fumihiro , Yoshida Narumi , Ishikawa Hiroya , Saito Ryo , Nakagawa Shogo , Miyakoshi Akihiko , Umeda Minoru
Published: February 2020

New carbon-based particles prepared using methane by microwave-assisted catalytic decomposition has been developed. The prepared carbon-based particles contained a nanographene-covered nickel, carbon nanotube, and others. In non-aqueous solvent, an oxygen reduction reaction (ORR) at the prepared carbon-based particles treated with acidic solution in advance was evaluated by using a porous microelectrode and milimeter-size diskelectrode based on electrochemical methods. The ORR was compared to commercially available glassy carbon, carbon fiber, Au, and Pt electrodes. As a result, the onset potentials for ORR at the prepared carbon-based particle were slightly better than other electrodes.
A General Approach to Preferential Formation of Active Fe-Nx Sites in Fe-N/C Electrocatalysts for High-Performance Polymer Electrolyte Fuel Cells
Authors: Sa Young Jin , Woo Jinwoo , Kim Min Gyu , Kim Tae-Young , Joo Sang Hoon
Published: February 2020

Non-precious-metal catalysts (NPMCs) for oxygen reduction reaction (ORR) have been of tremendous interests in energy conversion and storage devices. Among several classes of NPMCs, iron and nitrogen supported on carbon (Fe-N/C) have shown the most promising ORR activity. It has been widely suggested that an active site structure for Fe-N/C catalysts contains Fe-Nx coordination. However, the preparation of Fe-N/C catalysts mostly involves a high-temperature pyrolysis step, which generates not only Fe-Nx sites, but also a significant portion of less active large iron-based particles. This poses a great challenge to rational design of Fe-N/C catalysts with abundant Fe-Nx species. We developed “silica-protective-layer-assisted” synthetic approach that can preferentially generate the catalytically active Fe-Nx sites in Fe-N/C catalysts while suppressing the formation of large Fe-based particles. The catalyst preparation consisted of an adsorption of Fe porphyrinic precursor on carbon nanotubes (CNTs), silica layer overcoating, high-temperature pyrolysis, and silica layer etching, which yielded CNTs coated with thin layer of porphyrinic carbon (CNT/PC) catalysts. In situ X-ray absorption spectroscopy during the preparation of CNT/PC catalyst revealed that the interaction between the silica layer and Fe-N4 in a porphyrin precursor appears to protect the Fe-N4 site and to prevent the formation of large Fe-based particles. The CNT/PC catalyst showed very high ORR activity and remarkable stability in alkaline media. Importantly, an alkaline anion exchange membrane fuel cell (AEMFC) with a CNT/PC-based cathode exhibited record high current and power densities among NPMC-based AEMFCs. In addition, a CNT/PC-based cathode exhibited a high volumetric current density of 320 A cm-3 in acidic proton exchange membrane fuel cell, comparable with 2020 DOE target (300 A cm-3). We further demonstrated the generality of this synthetic strategy to other carbon supports including reduced graphene oxides and carbon blacks.