bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Effects of Composition and Doping on the Optoelectronic Properties of Lead Halide Perovskite Nanocrystals
Authors: Robel Istvan , Makarov Nikolay S. , Liu Wenyong , Guo Shaojun , Pietryga Jeffrey M. , Klimov Victor I. 
Published: February 2020

Colloidally synthesized lead halide perovskite nanocrystals have been recently demonstrated as active materials with great promise for a range of applications, from high-efficiency photovoltaics to color-converting phosphors and light-emitting diodes. Tailoring their optical and electronic properties through various synthetic routes in order to meet application-specific design parameters requires a good understanding of structure-property relationships. Here, by using a variety of steady-state and time-resolved spectroscopies, we explore carrier-carrier and carrier-dopant interactions in cesium lead halide nanocrystals as their halide component (Cl, Br, I, and their mixture) and doping level (Mn2+) is continuously tuned through a wide parameter space. We quantify such fundamental optical properties as exciton radiative lifetimes, absorption cross-sections, and derive the degeneracies of the band-edge electron and hole states. We also characterize the rates of intraband cooling and nonradiative Auger recombination and evaluate the strength of exciton–exciton coupling.1 Through impurity doping with Mn2+ ions, we also introduce new optical functionalities such as dual-color emission and establish the mechanism of carrier-dopant coupling in these materials.2

References:
1. N. S. Makarov, S. Guo, O. Isaienko, W. Liu, I. Robel, and V. I. Klimov, Spectral and Dynamical Properties of Single Excitons, Biexcitons, and Trions in Cesium–Lead-Halide Perovskite Quantum Dots, Nano Lett.
16, 2349-2362 (2016)
2. W. Liu, Q. Lin, H. Li, K. Wu, I. Robel, J. M. Pietryga, and V. I. Klimov, Mn2+-Doped Lead Halide Perovskite Nanocrystals with Dual-Color Emission Controlled by Halide Content, J. Am. Chem. Soc.
138, 14954-14961 (2016)
Excitonic Properties of 3D Hybrid Organic-Perovskites
Authors: Lauret Jean-Sébastien , Diab Hiba , Allard Gaëlle , Garrot Damien , Lédée Ferdinand , Deleporte Emmanuelle 
Published: February 2020

A renewed interest in hybrid organic perovskites (HOPs) has emerged since 2012 following the increase of HOP solar cell efficiency. Despite the impressive performances of the devices, there is still lot of room for improvement. In particular, the development of applications will benefit of a better understanding of the photophysics of HOPs.
In this talk, we will discuss about the excitonic properties of CH3NH3PbI3 (MAPI) single crystals at low temperature, and compare them to those of thin polycrystalline films. The main feature is the appearance of a sharp emission line (FWHM ~ 5 meV) at high energy that is attributed to the free exciton signature, and which is completely absent in thin-films. The observation of the free excitonic emission in the low temperature phase allow to monitor the huge thermal broadening due to electron-LO-phonon coupling [1].
References:
[1] Hiba Diab, Gaëlle Trippé-Allard, Ferdinand Lédée, Khaoula Jemli, Christèle Vilar, Guillaume Bouchez, Vincent L.R. Jacques, Antonio Tejeda, Jacky Even, Jean-Sébastien Lauret, Emmanuelle Deleporte, and Damien Garrot, The Journal of Physical Chemistry Letters 7, pp 5093–5100 (2016)
(Invited) Synthesis of Fine Controlled Sub-Nano Pt Particle As an Advanced Catalyst
Authors: Yamamoto Kimihisa 
Published: February 2020

We show that tinchlorides, SnCl2 and FeCl3 complexes to the imines groups of a spherical polyphenyl- azomethine dendrimer in a stepwise fashion according to an electron gradient, with complexation in a more peripheral generation proceeding only after complexation in generations closer to the core has been completed. The metal-assembly in a discrete molecule can be converted to a size-regulated metal cluster with a size smaller than 1 nm as a molecular reactor. Due to the well-defined number of metal clusters in the subnanometer size region, its property is much different from that of bulk or general metal nanoparticles.
Dendrimers are highly branched organic macromolecules with successive layers or “generations” of branch units surrounding a central core. Organic inorganic hybrid versions have also been produced, by trapping metal ions or metal clusters within the voids of the dendrimers. Their unusual, tree-like topology endows these nanometre-sized macromolecules with a gradient in branch density from the interior to the exterior, which can be exploited to direct the transfer of charge and energy from the dendrimer periphery to its core.
Here we show that tin ions, Sn2+, complex to the imines groups of a spherical polyphenylazo- methine dendrimer in a stepwise fashion according to an electron gradient, with complexation in a more peripheral generation proceeding only after complexation in generations closer to the core has been completed. By attaching an electron-withdrawing group to the dendrimer core, we are able to change the complexation pattern, so that the core imines are complexed last. By further extending this strategy, it should be possible to control the number and location of metal ions incorporated into dendrimer structures, which might and uses as high performance electronic devices, tailored catalysts, or fine-controlled clusters for advanced materials.
Transesterification As a Pretreatment to Bind an Anticorrosive Coating on an Aluminium Alloy
Authors: Paez Maritza Angelica , Muñoz Lisa , Gulppi Miguel , Tamayo Laura , Rabagliati Franco , Encinas Maria , Zhou Xiaorong , Thompson George 
Published: February 2020

The conditions necessary to improve the adhesion of polymeric coatings to surfaces of aluminum alloys, AA2024-O (AA), were studied. The process considered a pre-conditioning of the metal surface by a transesterification reaction process with methyl methacrylate as an ester, by the generation of a terminal double bond on the surface of the alloy.
The potentiodynamic measurements show that coated specimens that were preceded by a transesterification process (AA-TE-PMMA), reveal a significantly lower corrosion current than those coated without transesterification pretreatment and a greater region of passivity.
From the analyzes obtained by XPS spectroscopy and also from the morphologies and thicknesses of the coatings obtained by SEM observations of the ultramicrotomed sections of the coated specimens, it is possible to infer the formation of a bond between the monomer group carrying the double bond and the metal surface. Furthermore, it is evident that the presence and lability of the double bond in the monomer, which functionalizes the surface, allows improving the adhesion of the polymer film, subsequently generated by radical polymerization. The protective capacity of the coating is even evident after 30 days of immersion in an aqueous solution of chloride.
(Invited) Electrical Atomic Force Microscopy for 2D Transition Metal Dichalcogenide Materials
Authors: Celano Umberto , Virkki Olli , Mascaro Marco , Mehta Ankit Nalin , Bender Hugo , Chiappe Daniele , Asselberghs Inge , Paredis Kristof , Hoflijki Ilse , Franquet Alexis , Huyghebaert Cedric , Radu Iuliana , Vandervorst Wilfried 
Published: February 2020

As Si-based electronic devices are approaching their projected scaling limits, layered two-dimensional (2D) materials such as transition metal dichalcogenides (TMDs) are extensively studied as potential new channel materials and fundamental building blocks of emerging sensors and devices.[1-2] In this context, MoS2, WS2 and WSe2 to name a few, are now available for deposition trough different top down approaches. However, their outstanding properties are often degraded during the fabrication processes required for the device integration. For example, the selective growth of 2D TMDs their patterning and the electronics properties fine tuning still remain elusive. Here we report on electrical atomic force microcopy (AFM) and beam analysis techniques which are used to develop a framework of analysis for 2D materials. The latter is applied to understand the local properties of MoS2 comparing pristine material and structures which are selectively grown and patterned.[3] Different growth techniques are investigated. After modelling the tip-sample contact system, we assess the impact of the plasma-induced damages combining the electrical AFMs and Auger emission spectroscopy. We study the local electrical properties of grain boundaries and their transport respectively in pristine and patterned structures for FET devices by conductive atomic force microscopy (C-AFM).
[1] G. Fiori, F. Bonaccorso, G. Iannaccone, T. Palacios, D. Neumaier, A. Seabaugh, S. K. Banerjee, and L. Colombo, “Electronics based on two-dimensional materials,” Nat. Nanotechnol., vol. 9, no. 10, pp. 768–779, 2014.
[2] Desai, S. B., Madhvapathy, S. R., Sachid, A. B., Llinas, J. P., Wang, Q., Ahn, G. H., Javey, A. (2016). MoS 2 transistors with 1-nanometer gate lengths, 354(6308), 2–6.
[3] Chiappe, D., Asselberghs, I., Sutar, S., Iacovo, S., Afanas’Ev, V., Stesmans, A., … Thean, A. (2016). Controlled Sulfurization Process for the Synthesis of Large Area MoS2 Films and MoS2/WS2 Heterostructures. Advanced Materials Interfaces, 3(4), 1–10.
Improvement of Performance By Using Catalytically Etched Carbon Paper As Electrode for Vanadium Redox Flow Batteries
Authors: Abbas Saleem , Hwang Jinyeon , Mehboob Sheeraz , Shin Hyun-Jin , Ha Heung Yong 
Published: February 2020

The environmental aspects of fossil fuels and depletion of their reservoirs are main reasons for the growing use of renewable energy sources and environmentally sustainable storage technologies in recent years. Solar, wind, biomass and tidal are among climate-friendly energy sources. But the integration of these sources into large scale grid application is limited by their intermittent nature. Electrical energy storage (EES) technology solves this issue by storing energy on large scales. Redox flow batteries (RFBs) due to unique advantages of design flexibility, long cycle life, decoupled scaling of power and energy, are amongst suitable candidates of EES. All Vanadium Redox Flow Battery (VRFB) introduced in 1980s by Maria Skyllas-Kzacos et al has advantage over conventional RFBs as it employs four different oxidation states of vanadium; V4+/V5+ to cathode side and V2+/V3+ to anode side hence minimizes crossover effect through membrane. A typical VRFB contains two electrolyte reservoirs connected to cell sandwiching an ion exchange membrane between electrodes. V4+ is oxidized to V5+ on cathode while V3+ is reduced to V2+ on anode during charging and these charged species are reversed back during discharging.
Carbon paper or felt due to its large reactive surface area, chemical stability in highly acidic solution has been widely used as electrode in VRFB, however poor electrochemical activity, low kinetics toward oxidation and reduction of vanadium ions, and less wettability arising from its hydrophobic nature limit its wide-spread application. Several modification techniques have been used to improve the catalytic activity of carbon electrode toward vanadium redox couples mainly including thermal, chemical and electrochemical treatments. Most of the modification techniques result increased activity of carbon electrode attributed to its enhanced available surface area and surface functional groups. In this work carbon paper is etched by using cobalt oxide (Co3O4) as catalyst and is used as electrode for vanadium redox flow battery cell. The etched carbon paper is found better than pristine one in terms of charging overpotential, IR drop, charge/discharge capacities and energy efficiency at all working current densities. Etched carbon paper showed almost 31.0 Ah/L discharge capacity at initial working current density of 50 mA/cm2 compare to 16.0 Ah/L of pristine one, While 16 Ah/L at 150 mA/cm2 where pristine and thermally treated (TT) carbon paper have no performance. Similar effect was noticed in terms of energy efficiency, the etched carbon paper showed 70% energy efficiency at 150 mA/cm2 which is dramatically higher than pristine and thermally treated carbon paper electrodes. The improved performance is attributed to increased surface area, wettability and presence of microscopic pores on the surface of etched carbon paper.
Novel Power Allocation Method to Distribute the Working Current of Parallel-Connected Lithium-Ion Battery Packs
Authors: Zhang Jian-Bang , Tang Hsiang-Wen , Chen Kuo-Ching 
Published: February 2020

Owing to the growing environmental awareness, finding alternative energy sources of petroleum has become an important issue. Out of the total petroleum consumption, vehicle transportation accounts for up to half of it. Therefore, electric vehicles have swept the globe, and lithium-ion battery is among the best electric energy-storage candidates because of its high working voltage, high energy density, and long cycle life without memory effect.
For high power equipment, a battery pack which is composed of large number of batteries in series and parallel is necessary. However, after cyclic charging and discharging loops, the uniformity in the parallel-connected battery pack is destroyed; consequently, electrical current appears in the pack between any two batteries with potential difference. Therefore, it can be easily expected that analysis of paralleled batteries becomes more and more complicated while the number of batteries increases. For example, in a set of 100 parallel-connected batteries, 4950 directional branch currents are needed to be manipulated to satisfy Kirchhoff Circuit Laws. Obviously, heavy computational load makes the analysis of mass batteries based on the electrochemical model impossible. In this study, we propose a novel solution in combination with the ESP (enhanced single particle) model as proposed in Ref. [1] to enable an electrochemical analysis even with a huge amount of batteries in the pack.
The main idea of the novel solution originates from the “power allocation”, which means that when an electron leaving a certain battery owns a larger kinetic energy, the current dedicated by this battery accounts for a higher proportion of the total output current. Since the kinetic energy of an electron amounts to the electrical potential difference, the current distribution of a certain battery k in a parallel-connected battery pack with a total of n batteries can be assumed to be Eq.(1), where is the summation of equilibrium currents between the battery k and all the other batteries, and it can be obtained from the view of electrical work as Eq. (2), where is a weighting factor which is related to the convergence. Accordingly, the working current of the battery k at the next time interval () can be calculated from the current and voltage information at the time t, i.e., Eq. (3).
From the simulated discharge-charge curve shown in Fig. 1, it can be seen that by employing this method, the working voltage of the parallel-connected battery pack with 100S120P reaches the same in a dozens of time steps. The corresponding discharge and charge current distributions within each parallel string are presented in Fig. 2 and 3, respectively. This method finds an approximate solution instead of the exact solution from KCL, however, the deviation of the result is only within 10-3~10-5 volt, which is a tolerable error range.

REFERENCES

[1] N. Baba, H. Yoshida, M. Nagaoka, C. Okuda, and S. Kawauchi, J. Power Sources, 252, 214 (2014).

Figure 1
(Energy Technology Division Graduate Student Award Address) Advanced Water Management in Fuel Cells Using Engineered Gas Diffusion Layers with Patterned Wettability: From Concept to Fuel Cell Application
Authors: Forner-Cuenca Antoni , Manzi-Orezzoli Victoria , Biesdorf Johannes , Gubler Lorenz , Schmidt Thomas J. , Boillat Pierre 
Published: February 2020

The water management in PEFCs is a rather complex issue. On one hand side, some water is needed in order to hydrate a proton conductive membrane and ionomer in the catalyst layers. Therefore, humidified gases are fed into the cell. On the other hand, excessive amounts of water in the porous layers lead to blockage of available pores for gas transport and consequently increased mass transfer limitations, especially at high current densities when large amounts of water are produced. The gas diffusion layers (GDLs) are highly porous carbon fiber materials which are sandwiched between electrodes and flow fields and provide several functionalities: conduction of electricity and heat, mechanical integrity of the membrane, distribution of reactant gases and removal of the liquid water produced. These functions imply a triple set of contradictory requirements: high diffusivity of the gas phase, high permeability of the water phase, and high thermal and electrical conductivity of the solid phase.
The creation of artificial pathways for water removal within the porous material would permit the development of advanced water management strategies; however none of the existing approaches proposed a method to produce such materials in a way compatible with mass productions. To tackle this issue, we invented a method to produce GDLs with patterned wettability based on radiation grafting [1]. The method permits creating hydrophilic patterns throughout the complete material thickness while the remaining areas remain hydrophobic [2]. The first part of the talk will focus on the synthetic method details [3] and particularly on the effect that electron beam energy has on the achievable resolution of the hydrophilic patterns [4].
In the second part, the capillary pressure characteristic of the modified materials will be shown and the influence of various material parameters (substrate type, pattern width, coating load, etc.) will be discussed. The water distribution was imaged at various capillary pressures using neutron radiography (NR) and X-ray tomographic microscopy [5]. Finally, electrochemical characterization of operando cells combined with NR will demonstrate the potential of these materials to improve power density at various conditions [6].
[1] P. Boillat et al., 2014
European Patent 15165515.6.
[2] A. Forner-Cuenca et al., Adv. Mater.
2015, 27, 6317-6322.
[3] A. Forner-Cuenca et al., J. Electrochem. Soc. 2016, 163 (8), F788-F801.
[4] A. Forner-Cuenca et al., Radiat.
Phys. Chem., Submitted.
[5] A. Forner-Cuenca et al., J. Electrochem. Soc. 2016, 163(9), F1038-F1048.
[6] A. Forner-Cuenca et al., J. Electrochem.
Soc. 2016, 163 (13), F1389-F1398.
Oxygen-Reduction Active Carbon Supports for Pt Cathode Catalysts in Polymer Electrolyte Fuel Cells
Authors: Wu Gang 
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFCs) have been widely considered one of environmentally friendly and highly efficient electric power sources for a wide variety of power applications ranging from portable and stationary power supplies to transportation. However, some of the most critical barriers to their commercialization are the intrinsic high cost and insufficient long-term performance durability. Among others, the spherical carbon black particle support used for Pt catalyst in MEAs have a number of intrinsic structural disadvantage. It is partially responsible for current insufficient performance and durability of MEAs. They include (1) inefficient O2 transport due to significant tortuosity in carbon black-based cathode, (2) non-uniform distribution of ionomer due to significant microporosity of carbon blacks, (3) catastrophic corrosion during start-up/shut-down events due to low corrosion resistance, (4) low electrical conductivity, and (5) weak binding sites with Pt nanoparticles.
University at Buffalo, SUNY has developed a new type of high-surface areas (up to 850 m2/g) and large size nitrogen-diped graphene tubes (NGT) in a highly controlled manner and at high yields. The diameters of these graphene tubes can be tuned from 50 to 500 nm, which is much larger than conventiona carbon nanotubes (20 nm). It should be noted that the graphene tube is low cost using inexpensive dicyandiamide as precursors ($1-2/kg) and the synthesis method is easily scaled up. Apart from the obvious advantage of high electronic conductivity and enhanced corrosion resistance, the large tube size provided better Pt nanoparticle dispersion and more facil mass transfer including O2 and H2O. Importantly, the NGT exhibited oxygen reduction reaction (ORR) activity in acidic media comparable with state of the art PGM-free catalsyts. Thus, the novel ORR active nitrogen-doped graphene tubes are able to not only offer remarkable support effects by geometrically and electronically modifying the deposited Pt nanoparticles, but also provide a large amount of complementary nonprecious ORR active sites, thereby significantly improving the overall activity and durability of the Pt catalysts. Thus, relative to conventional carbon blacks, the highly graphitized and active N-GT is an ideal support for low-PGM catalysts for high-performance MEAs with enhanced mass transport and durability along with ideal interfaces with ionomer.
Pd-Monolayer Catalysts for CO2 Electrochemical Reduction
Authors: Liang Zhixiu , Vukmirovic Miomir B , Adzic Radoslav R 
Published: February 2020

The ever increasing consumption of fossil-fuels for transportation causes climate change by emitting large amounts of CO2, a green-house gas, and a growing concern about future availability of fossil-fuels as energy sources due to their limited reserves. The concept of ‘CO2 neutral fuels’ based energy cycle can reduce our dependence on fossil-fuels and eliminate the detrimental effects of fossil-fuel consumption on environment. The principle of ‘CO2 neutral fuels’ based energy cycle is that the energy from renewable energy sources would be used to synthesize carbon based fuels from captured CO2 and such fuels are then used to power vehicles.
One of the products of CO2 electrochemical reduction is formic acid, which is used as fine chemical and a fuel in direct formic acid fuel cell. Therefore, efficient production of formic acid attracts a lot of attention in recent years [1]. It was reported that palladium and palladium based catalysts are very promising towards such process for lowered overpotential and improved selectivity as well as durability [2, 3]. Here we report high performance Pd monolayer catalysts for CO2 electrochemical reduction to formic acid. Pd monolayer catalysts were chosen in order to manipulate its activity toward formic acid production by their electronic interaction with the supporting core material. Cores with high electron affinity metal, the CO-Pd bond can be weaken thus to enhance the reaction kinetics.
Pd monolayer catalysts were prepared via Cu-UPD followed by Pd galvanic replacement [4]. Au@Pd/C and Pt@Pd/C showed improved activity and CO poisoning resistance compared to Pd/C catalyst via final product NMR analysis and CO-stripping experiment respectively. More detailed discussion on the origin of such improvement will be given on the presentation. Our work demonstrates the great potential of Pd-monolayer catalyst for CO2 electrochemical reduction reaction.
Acknowledgements
This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.
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Figure 1