bluuebunny/crossref_metadata_2025 huggingface dataset:
Derivatization of chlorin e6 with maleimide enhances its photodynamic efficacy in HepG2 cells
Authors: Guo Xiuhan , Wang Shisheng , Zhang Fan , Li Guangzhe , Li Yueqing , Zhao Weijie
Published: May 2020

Three derivatives of chlorin e6 (1–3) were synthesized by introduction of maleimide, cysteine and glutathione at C-13 carboxyl of the chlorin scaffold. The evaluation of their PDT effects showed that compound 1, the derivative with a maleimide group, exhibited more potent photocytotoxicity against HepG2 cells (IC[Formula: see text] 3.2 [Formula: see text]M) than 2 (IC[Formula: see text] 6.7 [Formula: see text]M) and 3 (IC[Formula: see text] 10.2 [Formula: see text]M), although the cellular uptake of 1 was slightly lower than that of 2 and 3. The high PDT effect of 1 was found to be in agreement with the high level of intracellular singlet oxygen. Further investigation of the mechanism revealed that 1 can significantly lower the GSH level in HepG2 cells due to the addiction reaction of maleimide and GSH, thus resulting in the reduction of ROS scavenging and the enhancement of cellular oxidative stress. This approach to improve PDT effects of photosensitizers by means of interfering with the cellular redox system and enhancing cellular oxidative stress offers a new strategy for development of photosensitizers in cancer therapy.
Postbuckling Analysis of a Nonlocal Nanorod Under Self-Weight
Authors: Juntarasaid Chinnawut , Pulngern Tawich , Chucheepsakul Somchai
Published: May 2020

This paper presents the postbuckled configurations of simply supported and clamped-pinned nanorods under self-weight based on elastica theory. Numerical solution is considered in this work since closed-form solution of postbuckling analysis under self-weight cannot be obtained. The set of nonlinear differential equations of a nanorod including the effect of nonlocal elasticity are investigated. The constraint equation at boundary condition technique is introduced for the solution of postbuckling analysis. In order to solve the set of nonlinear differential equations, the shooting method is utilized, where the set of these equations along with boundary conditions are integrated by the fourth-order Runge-Kutta algorithm. Numerical results are obtained and the highlighting influences of the nonlocal elasticity on postbuckling behavior of nanorods are discussed. The obtained results indicate that the rotation angle and the postbuckled configurations of nanorods are varied by changing the nonlocal elasticity parameter. The effect of nonlocal elasticity shows the softening behavior in comparison with the Euler beam. The present formulation together with constraint boundary condition technique is an effective solution for postbuckling analysis of a nanorod under self-weight including the effect of nonlocal elasticity.
Non-communtative Iwasawa main conjecture
Authors: Witte Malte
Published: May 2020

We formulate and prove an analogue of the non-commutative Iwasawa Main Conjecture for [Formula: see text]-adic representations of the Galois group of a function field of characteristic [Formula: see text]. We also prove a functional equation for the resulting non-commutative [Formula: see text]-functions. As corollaries, we obtain non-commutative generalizations of the main conjecture for Picard-[Formula: see text]-motives of Greither and Popescu and a main conjecture for abelian varieties over function fields in precise analogy to the [Formula: see text] main conjecture of Coates, Fukaya, Kato, Sujatha and Venjakob.
Tunable high-Q SAW resonator loaded on a changing capacitance
Authors: Karapetyan G. Ya. , Kaydashev V. E. , Kutepov M. E. , Minasyan T. A. , Kalinin V. A. , Kislitsyn V. O. , Kaidashev E. M.
Published: May 2020

A tunable high-Q surface acoustic wave (SAW) resonator in the form of several parallel-connected interdigital transducers loaded on a varying capacitance on lithium niobate substrates was developed and studied. The working frequency range was 90–2450[Formula: see text]MHz. A method of calculating such resonators, considering losses in the metal film as well as losses due to the propagation of SAWs and transformations into bulk waves is proposed. Such a design allows one to obtain a quality factor over 5000 in the frequency range 2400–2483[Formula: see text]MHz. The resonant frequency shifts by 600[Formula: see text]kHz when the capacitance changes by [Formula: see text]% of the value of 21[Formula: see text]pF (or 32[Formula: see text]ppm/pF) and has an almost linear character.
Functional Ecology of Forest Disease
Authors: Oliva Jonàs , Redondo Miguel Ángel , Stenlid Jan
Published: May 2020

Global change is pressing forest pathologists to solve increasingly complex problems. We argue that understanding interactive effects between forest pathogens and global warming, globalization, and land-use changes may benefit from a functional ecology mindset. Traits can be more informative about ecological functions than species inventories and may deliver a more mechanistic description of forest disease. Myriad microbes with pathogenic potential interact with forest ecosystems at different organizational levels. Elucidation of functional traits may enable the microbial complexity to be reduced into manageable categories with predictive power. In this review, we propose guidelines that allow the research community to develop a functional forest pathology approach. We suggest new angles by which functional questions can be used to resolve burning issues on tree disease. Building up functional databases for pathogenicity is key to implementing these approaches.
Employer Decision Making
Authors: Rivera Lauren A.
Published: May 2020

The decisions employers make are of critical importance to sociological understandings of labor market stratification. While contemporary research documents employment outcomes with ever-growing precision, far less work examines how employers actually make decisions. In this article, I review research on the process of employer decision making, focusing on how employers evaluate, compare, and select workers in personnel decisions. I begin by summarizing the most prevalent theories of employer decision making in sociology, grouping them into competency-based, status-based, and social closure–based approaches. A common thread underlying much of this work is the assumption that employers are utility maximizers who base decisions on systematic, even if flawed, cognitive calculations of worker skill and workforce productivity. I then turn to recent research from sociology and beyond that challenges this notion and highlights the importance of understanding how employers themselves—their emotions, identities, and environments—affect decisions. I conclude by suggesting directions for future research.
(Nanocarbons Division Robert C. Haddon Research Award Address) Chemical Functionalization of Synthetic Carbon Allotropes
Authors: Hirsch Andreas
Published: May 2020

Chemical functionalization of new C-allotropes is of fundamental interest and opens the door to unprecedented materials applications. In principle, the physical and chemical properties of fullerenes, carbon nanotubes (CNTs) and graphene are related to each other, although their levels of development vary considerably. In order to efficiently explore the reactivity of the less developed CNTs and especially that of graphene it is our goal to provide a unifying approach for the chemistry of all three new carbon allotropes. The fullerenes present the first family of synthetic carbon allotropes. Since their availability in macroscopic quantities numerous investigations with respect to their physical characterization and chemical functionalization have been carried out. CNTs - the second new family of C-allotropes - exhibit at least the same potential for unprecedented applications. Their chemistry, however, is much less developed. Although many protocols for covalent and non-covalent CNT functionalization have been published there are still many fundamental problems to be solved. This includes inter alia the highly selective functionalization of metallic- or semiconducting SWNTs, the high throughput isolation of SWNTs with single helicity, the development of general concepts allowing for tunable doping of individualized tubes with single helicity or least defined transport characteristics (metallic – semiconductive). Finally, the youngest representative in the list of new C-allotropes is graphene and its chemical functionalization opens exciting opportunities towards the development of precisely structured high performance materials. We will talk on the systematic investigation of the chemical properties of graphene both in homogenous solution and deposited on solid substrates. We have revealed fundamental reactivity principles, such as role of defects, charging and substrate. Moreover, we have disclosed for the first time basic fundamental topicity concepts. This allows us to tailor highly integrated graphene based 2D-materials. An example is the introduction of reversible covalent 2D-structuring providing the basis for chemical data storage.
(Invited) Covalent Functionalization of Surface-Supported Graphene and Transition Metal Dichalcogenides: Chemistry and Nanostructuring
Authors: De Feyter Steven
Published: May 2020

The research on graphene prompted emergence of related layered materials such as black phosphorous, silicene, germanene and transition metal dichalcogenides (TMDs) such as MoS2. These materials offer virtually endless opportunities for fundamental research as well as cutting edge applications.

Most of these layered materials however exist as single layers only when supported by another solid surface or when stabilized by physisorbed or chemisorbed organic molecules.

In this contribution, I will discuss covalent modification, sometimes in a nanostructured fashion, of graphene, graphite and MoS2 using diazonium and other chemistries. Special focus is on sub-nanometer characterization of modified materials using scanning tunneling and atomic force microscopy (STM and AFM). The use of covalently modified surfaces for applications will also be discussed.
Plasma Thinning of Large Black Phosphorus Flakes
Authors: Lefebvre Valerie , Schué Leonard , Clément Christophe , Martel Richard
Published: May 2020

The growing interest over the 2D materials has led to the discovery of exfoliated black phosphorus (bP), a semiconductor with a thickness-dependent bandgap. The direct bandgap energy varies from 0.3 eV for bulk materials to 1.9 eV for the monolayer of black phosphorus. The fabrication of thin layers is, however, difficult because the layers photo-oxidize in air into phosphoric acid with kinetic that gets faster for thinner layers1. Inspired by a new method to produce thin layers of black phosphorus using oxygen plasma, we work to optimise the process for making large few-layers bP flakes2. Using ICP-RIE oxygen plasma, exfoliated flakes of black phosphorus were etched in a controlled way and Raman spectroscopy was used to evaluate the quality of the flakes after plasma treatments. The results show no sign of high-degradation of the bP crystal structure after the plasma treatment. Here we show that the method can be adapted to produce high quality thin flakes of black phosphorus towards incorporation into electronic and optoelectronic applications.

1 Favron, A., Gaufrès, E., Fossard, F. et al. Photooxidation and quantum confinement effects in exfoliated black phosphorus. Nature Mater 14, 826–832 (2015)

2 Pei, J., Gai, X., Yang, J. et al. Producing air-stable monolayers of phosphorene and their defect engineering. Nat Commun 7, 10450 (2016)
Electric Field Quenching of Graphene Oxide Photoluminescence
Authors: Lee Bong Han , Naumov Anton V , Ryan Conor Augustine , Paz Thomas , Grote Fabian
Published: May 2020

With the advent of graphene, there has been an interest in utilizing this material and its derivative, graphene oxide (GO) for novel applications in biotechnology, electronics, photonics, materials and environmental science. Although GO exhibits lower conductivity and structural stability, it possesses an energy band gap that enables fluorescence emission in the visible/near infrared leading to a plethora of optoelectronic applications. In order to enable fine-tuning of its optical properties in the device geometry, new physical techniques are required that unlike existing chemical approaches yielding substantial alteration of GO structure, enable electronically-controlled and, ideally, reversible changes in GO optoelectronic properties. In this work, we for the first time investigate the methods to controllably alter the optical response of GO with the electric field and provide theoretical modelling of the electric field-induced changes. Field-dependent GO emission is studied in bulk GO/PVP films with up to 6% reversible decrease under 1.6 V/µm electric fields. On an individual flake level a more substantial 50% quenching is achieved for select GO flakes in polymeric matrix between interdigitated microelectrodes subject to two orders of magnitude higher fields. This effect is modelled on a single exciton level by utilizing WKB approximation for electron escape form the exciton potential well. In an aqueous suspension at low fields GO flakes exhibit electrophoretic migration indicating a degree of charge separation and a possibility of manipulating GO materials on a single-flake level to assemble electric field-controlled microelectronics. As a result of this work, we suggest the potential of varying the optical and electronic properties of GO via the electric field for the advancement and control over its optoelectronic device applications.
(Invited) Hexagonal Boron Nitride Ionogel Electrolytes for Solid-State Batteries
Authors: Hersam Mark C.
Published: May 2020

Ionogel electrolytes based on ionic liquids (ILs) and a gelling solid matrix are an attractive alternative to conventional liquid electrolytes for energy storage applications. In particular, ILs offer several advantages as an electrolyte including nonflammability, nonvolatility, high electrochemical stability, and high ionic conductivity. Moreover, combining ILs with a gelling solid matrix leads to a solid-state electrolyte that is sufficiently mechanically robust to replace both the liquid electrolyte and separator in a single component, thus allowing easier packaging, streamlined manufacturing, and minimal risk of leakage. For ionogel electrolytes, hexagonal boron nitride (hBN) is an especially desirable solid matrix due to its excellent chemical and thermal stability in addition to its mechanical robustness [1]. This talk will address recent efforts to realize high-performance hBN/IL ionogel electrolytes using hBN that has been solution-exfoliated into two-dimensional nanosheets using ethyl cellulose (EC) stabilizing polymers [2]. In addition to the intrinsic advantages of hBN, EC-exfoliated hBN nanosheets significantly enhance both ionic conductivity (> 1 mS/cm) and mechanical strength (storage modulus > 1 MPa) compared to conventional hBN microparticles, providing additional competitive advantages for energy storage applications [3]. The high thermal stability of hBN/IL ionogel electrolytes also enables safe, high-rate operation (up to 10C charge/discharge rate) at high temperatures up to 175 °C, which represents the highest operating temperature to date for solid-state lithium-ion batteries.

[1] K.-S. Chen, et al., ACS Energy Letters, 2, 2026 (2017).

[2] A. C. M. de Moraes, et al., Advanced Functional Materials, 29, 1902245 (2019).

[3] W. J. Hyun, et al., ACS Nano, 13, 9664 (2019).
(Invited) Growth of Van Der Waals Materials: New Insights from Real-Time Studies
Authors: Fortin-Deschênes Matthieu , Moutanabbir Oussama
Published: May 2020

The existence of thousands of new 2D materials has been predicted and several of them have been fabricated, mostly by exfoliation from bulk crystals. In addition to their attractive properties, the availability of these 2D materials also creates a wealth of opportunity to engineer complex van der Waals (vdW) heterostructures, thus laying the groundwork to tailor manipulate the basic properties and device performances. However, despite its numerous advantages, this class of materials is yet to be integrated in real technological applications due to several challenges such as the lack of scalable fabrication processes. With this perspective, quasi-epitaxial growth methods have recently been explored to synthesize 2D materials and vdW heterostructures. Herein, by using group V 2D materials as a model system, this presentation will address the current understanding of vdW growth and the key mechanisms governing the nucleation, growth and stability on weakly interacting surfaces. New insights on the interplay between kinetics and thermodynamic driving forces will be described and discussed based on in situ low-energy electron microscopy and diffraction (LEEM/LEED) studies. The combination of LEEM and LEED with ex situ characterization methods allowed us to elucidate the growth mechanisms of stable and metastable 2D-Sb allotropes and 2D-AsSb alloys on conventional semiconductor substrates and graphene. These results lay the groundwork for the development of scalable vdW epitaxial growth methods for emerging 2D materials and vdW heterostructures.

Acknowledgment:

The authors acknowledge contributions from Robert Jacobberge, Hannes Zschiesche, Andrea Locatelli, Tevfik O. Menteş, Olga Waller, Charles-Antoine Deslauriers, Francesca Genuzio, Gianluigi Botton, Michael S. Arnold.
(Invited) Nanoscale Optics of 2D Materials for Multi-Dimensional Sensing
Authors: Rotkin Slava V. , Ignatova Tetyana
Published: May 2020

Starting with thorough nanoscale characterization of 2D materials (2DM) with a scattering-type scanning near-field optical microscope (sSNOM), further sensing applications of the surface modified 2DMs are discussed. sSNOM imaging and spectroscopy reveals subwavelength features and correlate optical properties of 2DMs to the surface structure. When supplemented by other scanning probe techniques (KPFM/EFM), correlation of the sSNOM maps of the same surface area in MIR and visible range allows an additional information to be extracted. Surface polariton waves are discussed in relation to the surface optical impedance of the structures. Far-field measurements are finally matched to the near-field data.

SVR acknowledges help of Ms. X. Li (PSU) and samples provided by NSF 2DCC MIP (Dr. J. Redwing and Dr. J. Robinson). Research of TI was partially supported by the UNCG Faculty First Award. sSNOM facility is partially funded by Penn State Quantum Characterization Infrastructure initiative.
(Invited) Ultrafast Photocurrents from Interlayer Excitons in Twisted and Stacked 2D Materials
Authors: Graham Matt W
Published: May 2020

Using time-space resolved ultrafast microscopy on individual 2D crystal grains, we show how long-range interlayer electronic coupling can be selectively enhanced either by applying an E-field or by twisting the layer stacking orientation. Considering first twisted bilayer graphene (tBLG), we discovered how stacking-angle tunable absorption resonances form a strongly-bound exciton state as a consequence of the symmetrized rehybridization of constrained interlayer 2p orbitals. Using two-photon photoluminescence and intraband-transient absorption microscopies, we have recently imaged the photoemission and exciton dynamics from single-grains of tBLG. After resonant excitation, our results suggest the formation of strongly-bound (up to 690 meV), quasi-stable interlayer exciton states. Unlike stacked graphene, semiconducting 2D transition metal dichalcogenides (TMDCs) have diffuse interlayer d-orbital overlap. To enhance interlayer electronic coupling in TMDCs, we apply an interlayer directed E-field, inducing electron-hole dissociation. Time-resolved photocurrents show that stacked WSe2 devices can have both IQE >50% and fast (<50 ps) picosecond electron escape times. Remarkably our photocurrent response function produces the same E-field-dependent electronic escape and dissociation rates for both the optical and PC addressed ultrafast measurements. To confirm the fast electronic escape rates, we show the ratio of the electronic rates accurately matches our overall TMDC device IQE in the limit of zero Auger recombination. Collectively, we show how optical and photocurrent-based ultrafast microscopies provide an accurate timeline of photocurrent generating dynanamics in both TMDCs and tBLG van der Waals materials.
Towards High-Mobility 2D Semiconductors
Authors: Liu Yuanyue
Published: May 2020

One of the major challenges that limits the development of 2D semiconductors is the low carrier mobility. Here using advanced first-principles calculations methods, we will show the intrinsic mobility for a variety of 2D semiconductors, including transition metal dichalcogenides and monoelemental materials, and their mobility-limiting factors [1,2]. Moreover, we will show that strain can significantly change the carrier mobility of certain materials, and the underlying physical origin [3].

[1] L. Cheng, Y. Liu, JACS, 2018 DOI: 10.1021/jacs.8b07871

[2] L. Cheng, C. Zhang, Y. Liu, JACS 2019 DOI: 10.1021/jacs.9b05923

[3] L. Cheng, C. Zhang, Y. Liu, in preparation
(Invited) Processing of 2D Materials Using Ion Implantation
Authors: Pereira Lino M C
Published: May 2020

Functionalization of 2D materials generally requires the modification of their physicochemical properties. Several approaches have been explored: the use of different substrates, creation of intrinsic defects (e.g. vacancies), adsorption and intercalation (of atoms, clusters or molecules), substitutional doping, among others. For incorporation of substitutional or intercalated elements, despite the numerous approaches that have been investigated, a major challenge remains: the limited control over the concentration and form of incorporation. An alternative approach is to incorporate the foreign species by ultra-low energy (ULE) ion implantation, precisely tuning the number of implanted ions and their kinetic energy. Here, I review our recent work on ULE ion implantation of 2D materials, with emphasis on substitutional doping and intercalation of graphene. Our approach is based on a wide range of characterization techniques (structural and electronic), including scanning tunneling microscopy and spectroscopy (STM/STS), synchrotron-based X-ray photoelectron spectroscopy (XPS), angle-resolved photoemission spectroscopy (ARPES), X-ray magnetic circular dichroism (XMCD), transport measurements, among others. These experimental studies are complemented by density functional theory (DFT) and molecular dynamics (MD) simulations.
Improving Rechargeable Battery Dynamics
Authors: Schumm Brooke
Published: May 2020

A series of experiments was undertaken to study the effects of additive changes on the plating of zinc metal from zinc chloride solutions. From these simple examples it was hoped to offer explanations for several different effects seen in battery performance.

The avenue chosen was to observe the effect of adding a leveling agent and then a pH adjustment with a particular chemical based on previous experience to see if an outstanding result would be observed. Accidentally it was more important to find that the specific characteristics of the current supply were more important than the additives. Nonetheless the best result was achieved with a combination of these factors.

It was hoped at the same time to better understand the effects of diffusion on the chemical process and its response to changes in the diffusion, especially locally. It is necessary to recognize that knowing the chemical reactions on paper does not accurately predict what happens in an active rechargeable cell. The effects of diffusion limit the concentration of chemicals and often the actual reactions in both the separator structure and in the electrolyte and in the surface regions contacted by the electrolyte. This is true for both the discharging and charging cell environment. Photos and current analysis will be shown.

From these or similar experiments it may be possible to predict the parallel performance in lithium or lithium ion cells and how to extend cycle life. Discussion will be invited.
Spatial Variation of Corrosion Behavior in Pb-Ca-Sn Battery Grids
Authors: Buquiz Jan Lowell , Mena Manolo
Published: May 2020

Comparison of the corrosion behavior between two different locations in an as-cast Pb-Ca-Sn battery grid was conducted. Optical microscopy was used to characterize the microstructures of the two grid locations. Electrochemical impedance spectroscopy diagrams, and an equivalent circuit analysis were used to evaluate the electrochemical response at varying H2SO4 concentrations and working temperatures. Photomicrographs show that Location A has coarser grain and cellular sizes than Location B. The EIS results show that the corrosion resistance of both grid locations decreases as the H2SO4 concentration and working temperature are increased. The experimental results also show that Location A has a higher corrosion resistance than Location B.
The Photoactive Cation-Substituted Spinel Cobaltite XCo2O4 (X = Fe, Co, Ni, and Mn) Using As Air Cathodes in Zinc-Air Batteries
Authors: Tomon Chanikarn , Sarawuthanukul Sangchai , Duangdangchote Salatan , Sawangphruk Montree
Published: May 2020

The development of catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are attracted enormous interest for improving the performance of Zn-air batteries (ZABs). However, the use of cation-substituted spinel cobaltite XCo2O4 (X = Fe, Co, Ni, and Mn) as photo-electrocatalysts for OER/ORR in ZABs has not yet been reported. The XCo2O4 materials were synthesized by using an electrospinning method followed by a calcination process at 700oC. Among these XCo2O4 catalysts, the NiCo2O4 exhibits the superior performance for both OER (η = 300 mV at 10 mA/cm2) and ORR (η = 460 mV at E1
/
2). It mainly attributes to the narrowest band gap energy at 1.50 eV which corresponds to the ratios of X2
+/X3
+ and Co2
+/Co3
+ that investigates by the UV-vis spectroscopy, Mott-Schottky plots, and XPS analysis. Under the exposure of light, the NiCo2O4 provides the lower in overpotential of OER and ORR around 10% - 30% due to the occurring of electron(e-) – hole (NiCo2O4
+) separation from absorbing the photon energy. Both of e- and NiCo2O4
+ can accelerate the ORR and OER, which is confirmed by in
-
situ XAS under the light and dark conditions. Finally, the as-fabricated artificial ZAB cell by using NiCo2O4 as a photo-electrocatalyst presents the superb ZAB performance.

Figure 1
Binder Selection Towards Improved Stability of Rechargeable Aqueous Zinc-Ion Batteries with Manganese Oxide Cathodes
Authors: Muramatsu Tatsuki , Kao-Ian Wathanyu , Kheawhom Soorathep , Yonezawa Tetsu , Cheacharoen Rongrong
Published: May 2020

Rechargeable aqueous zinc-ion batteries are promising alternatives due to its abundance of active materials, safety, and lower cost. However, development of a suitable cathode that is earth abundance, such as manganese oxide, which can also produce high performance battery needs to be further carried out. Binders play a key role in achieving desirable properties, such as mechanical, electrical, electrochemical etc. of a battery. Specifically, selecting the right binder will promote stability throughout operation and enable tuning the thickness of a cathode to load more active materials to increase the capacity. This work explores three different binders, Carboxymethyl cellulose(CMC), Cellulose acetate (CA), and Polyvinylidene fluoride (PVDF), in aqueous electrolyte with ZnSO4 salt to investigate the effect of hydrophilicity level on performance and stability of the battery. The result shows that a cathode with PVDF as a binder yields the highest specific capacity regardless of charge/discharge rate. While, CA cathode works well at low rate and their performance started to drop at higher rates. CMC based cathode yields the lowest capacity from low to medium rate and starts to excel at higher rates. The relationship between different degree of electrolyte wettability on cyclability of the batteries will also be discussed. Further investigation using the Galvanostatic Intermittent Titration Technique (GITT) shows that there are two regions of ionic diffusion in all samples. During high state-of-charge (SOC) all three cathodes behave the same, while at lower SOC, CA based electrode seems to be limited by ionic diffusion. This explains why CA cathode performance dropped a lot at a higher rate. Our binder selection criteria for zinc-ion batteries can be further adapted in wider rechargeable zinc-based batteries for a variety of applications.

Figure 1
Controlling Reactive Battery Interfaces Using Electron-Accepting Surface Layers
Authors: Hankins Kie , Prabhakaran Venkateshkumar , Roy Swadipta , Johnson Grant , Shutthanandan Vaithiyalingam , Thevuthasan Suntharampillai , Balbuena Perla B. , Murugesan Vijayakumar , Mueller Karl T
Published: May 2020

Understanding the reactivity of electrolyte and solvent molecules as well as electroactive species at operating battery interfaces enables the rational design of improved battery technologies. This molecular-level understanding, however, is often challenging to obtain due to the heterogeneity of electrode surfaces and the complexity of chemical transformation occurring under applied electric fields. For example, battery electrode surfaces contain various distributions of metal-oxides, -hydroxides, -carbonates, and -halides. Subsequently, redox and electron transfer properties vary widely over these heterogeneous surfaces. In this work, we provide a comprehensive outlook and delineate the reactivity of selected polysulfide electroactive ions on well-defined reactive lithium surfaces and propose an approach to modulate the surface reactivity by using electron-accepting surface layers. We used ion soft landing to deposit mass-selected lithium polysulfide ions (LiS4
- and Li5S12
-) on oxidized and fluorinated lithium surfaces. Ion soft-landing is a versatile mass spectrometry-based deposition technique that allows ionic molecules to be selectively deposited onto electrode surfaces without counter-ions and solvent molecules. The reactivity of the deposited polysulfide ions was studied using a combination of experimental and theoretical approaches. Specifically, i
n-situ X-ray photoelectron and Raman spectroscopy revealed the presence of both reduced (Li2S) and oxidized (LixSOy) polysulfide species on electron-accepting lithium oxide surfaces. Ab-initio molecular dynamics calculations corroborated the formation of species observed in the experimental study. Bader charge analysis of the systems showed multi-electron transfer reactions for sulfur atoms, starting from neutral species and reacting to oxidation states ranging from +3 to -2. Calculations also indicate that a relatively thick (> 1 nm) surface oxide layer is required to promote reactivity, and that thinner layers can inhibit reaction. Our study provides fundamental insights into the complex redox chemistry and decomposition mechanism that occurs at heterogeneous lithium electrodes and will lead to rational design of efficient and stable battery interfaces.
Polyoxometalate/Metal-Organic-Framework Hybrid Materials As Electrodes for Electrochemical Capacitors
Authors: Toh Lock-Kiat , Chen Han-Yi
Published: May 2020

Tremendous effort has been focused on developing electrochemical capacitors with various applications such as portable electronics, heavy hybrid vehicles, load leveling, and uninterruptible power supplies.Electrochemical capacitors have the advantage of providing high power density which enable faster charge/discharge rates than batteries, as well as long cycle life.

Polyoxometalates (POMs) are transition metal oxide clusters, and they possess fast and reversible multi-electron redox reactions.Several POMs have been studied in supercapacitors, such as H3[PMo12O40], H3[PW12O40],H4[SiMo12O40], H4[SiW12O40]. However, most of POMs can be dissolved in aqueous electrolyte. Therefore, some of them were combined with carbon materials or conducting polymers.

In this study, we synthesized a vanadium-based POM combined with a metal-organic-framework (MOF) as electrode material in electrochemical capacitors. The electrochemical properties of this V-POM/MOF electrodes are studied by electrochemical measurements such as galvanostatic charge/discharge and cyclic voltammetry. Furthermore, a hybrid energy storage device which combines V-POM/MOF as negative electrode and activated carbon as positive electrode was assembled to demonstrate the potential for electrochemical capacitor applications.
Direct Numerical Simulation of Electric Double Layer Formation
Authors: Qu Danqi , Yu Hui-Chia
Published: May 2020

We will present an innovative method to simulate the formation of electric double layers on complex electrode geometries. Electric double layers are omnipresent and affect the ionic diffusion in many natural systems. It plays the most crucial role in the energy storage of supercapacitors and electric-field desalination. Upon imposing an electrostatic potential, the cations and anions near the electrode surface separate to form a localized polarization counterbalancing the potential. The charge-separated region usually spans 20 to 50 nanometers, whereas other significant length scales, e.g., particle size or inter-particle space in electrodes, are in tens to hundreds of microns. A direct numerical simulation in the continuum scale requires to resolve the ionic concentration and potential gradients across 3~4 orders of magnitude in spatial scales and is incredibly challenging. Therefore, continuum-scale numerical studies are limited to one-dimensional or simple symmetric geometries, or in nanoscales where double-layer thickness and particle size are comparable. In this work, we use the smoothed boundary method that defines complex microstructures with a phase-field-order-parameter-like continuous function to reformulate the Nernst-Planck-Poisson equations and solve the equations on adaptively refined meshes. Thus, the method allows for accurately simulating the charge separation and potential distribution in arbitrarily complex geometries with resolutions spanning from nanometers in the double layer to micron/millimeters in the particle/electrode scales. Simulations of the dynamics during double layer formation and the resultant capacitance on complex electrode microstructures will be presented. The coupling of charge separation and fluid mechanics in simulating the electric-field desalination process through porous electrodes will also be discussed.
Effect of Cations in Imidazolium-Based Ionic Liquids on 18650 Supercapacitors of Activated Carbon and Graphene Aerogel
Authors: Wuamprakhon Phatsawit , Donthongkwa Ruttiyakorn , Sawangphruk Montree
Published: May 2020

The energy storage device with high energy and power densities with good cyclability is required. Supercapacitors (SCs) are the energy storage devices having high specific power (500-10,000 W/kg), fast charging-discharging process, and long cycle stability (>500,000 cycles); however, their specific energy is rather low (typically 5–10 Wh/kg) as compared to those (>100 Wh/kg) for Li-ion batteries. In principle, the energy density or specific energy is proportional to the square of working potential window. In this work, different ionic liquids (ILs) with wide working potential windows are used as the electrolyte of supercapacitors using activated carbon and graphene aerogel. ILs of imidazolium-based structures with different sizes of alkyl chain are synthesized to investigate their effects on the performance and charge storage mechanism of supercapacitors. Also, we fabricated the 18650 cylindrical cells of symmetrical supercapacitors.
Laser-Based Micro-Manufacturing of Thin-Film and Miniaturized Supercapacitors
Authors: Sundriyal Poonam , Bhattacharya Shantanu
Published: May 2020

The miniaturized and thin-film energy storage devices are urgently needed for the on-chip electronic devices.[1] The selection of a suitable manufacturing method for the development of miniaturized devices is a critical step.[2-4] Here, we report laser-based direct and one step printing as a suitable method for the efficient development of such devices. The graphene and graphene- MnO2 composites were successfully developed using chemical methods, and the planar micro-supercapacitors with different shapes and sizes were developed over flexible and stretchable substrates using laser printing based pattern development and material sintering. The polymer-based ionic electrolytes were used, and the devices have stable performance upto 2.8 V. The developed devices exhibit excellent electrochemical performance with excellent capacitance, good energy density, and excellent power density. These devices also demonstrated high mechanical flexibility and long cyclic lifetime. This study suggests that the laser printing method has a huge potential for the development of miniaturized electronic device s for portable electronic applications.

References:

1. Djuric, S.M., et al., Miniature graphene-based supercapacitors fabricated by laser ablation. Microelectronic Engineering, 2017. 182: p. 1-7.

2. Kyeremateng, N.A., T. Brousse, and D. Pech, Microsupercapacitors as miniaturized energy-storage components for on-chip electronics. Nature nanotechnology, 2017. 12(1): p. 7.

3. Sundriyal, P., et al., Recent Advancement in the Fabrication of Energy Storage Devices for Miniaturized Electronics, in Nano-Energetic Materials. 2019, Springer. p. 215-240.

4. Sundriyal, P. and S. Bhattacharya, Inkjet-Printed Electrodes on A4 Paper Substrates for Low-Cost, Disposable, and Flexible Asymmetric Supercapacitors. ACS Applied Materials & Interfaces, 2017. 9(44): p. 38507-38521.
Flexible Solid-State Supercapacitor Using 2D White Graphene
Authors: Malekkhouyan Adel , Kaur Jasneet , Zarrin Hadis
Published: May 2020

Future inventions and technologies like miniaturize electronics with various functionalities, wearable devices, and bio-implantable sensors have demand for reliable and efficient flexible energy storage devices that can stand mechanical deformation. The flexibility of energy storage devices depends upon configuration, and assembly design to integrate all components into a single flexible unit. In this work, we exhibit a flexible all solid-state supercapacitor which consists of two flexible electrodes, fabricated by modified activated carbon with 2D nanostructure of hexagonal boron nitride (h-BN) ionomers. The electrodes are separated by a nano-engineered electrolyte membrane developed in our previous work. The surface-functionalized h-BN (FhBN) ionomers and nanocomposite electrolyte membranes showed superionic conduction with through- and in-plane ion conductivity of 0.1 S.cm−1 and 0.41 S.cm−1, respectively, which are 14 and 7 times higher than the commercial Nafion ionomer and membrane. The performance of the flexible supercapacitor was validated by cyclic voltammetry, constant current charge/discharge tests, and electrochemical impedance spectroscopy (EIS). These tests are performed in symmetric assembly of supercapacitor and displayed outstanding areal-specific capacitance which was ~2 times higher than that of a supercapacitor made of commercial Nafion electrolyte. Furthermore, we observed that the FhBN-based flexible supercapacitor can conserve its capacitance during the bending test under the mechanical stress, demonstrating its outstanding mechanical flexibility while maintaining its electrochemical performance. With the exceptional mechanical and electrical robustness, the FhBN-based flexible supercapacitors promises an exciting candidate for high-performance flexible energy storage devices in wearable electronics.
The Effect of Deposition Cycles on Intrinsic and Electrochemical Properties Ofmetallic Cobalt Sulfide By Simple Chemical Route
Authors: Ighodalo Kester Osasle
Published: May 2020

Cobalt Sulfide Thin Film Was Synthesized on Glass and Steel Substrates Via Chemical Route. Thestructure, Surface Morphology, and Optical Characterization of the Deposited Thin Films Indicated a Strong Relationship between the Number of Deposition Cycles and Intrinsic Properties. the Scanning Electron Microscope(SEM) Showed a Uniform Morphology with Randomly Oriented Nano-Grains of Cobalt Sulfide Film at Varying Deposition Cycles. the XRD Spectra Revealed That the Films Became Amorphous As the Number of Deposition Cycles Increased. the Crystalline Films Had a Hexagonal Structure of Average Crystallite Size of 27.55 Nm. the Optical Transmission Spectra of the Films Gave a Direct Band Gap Energy Which Varied between 1.90 Ev and 2.20 Ev with an Average Value of the Optical Conductivity Was 1.77 1017 S ̶ 1. the Electrochemical Energy Storage Behavior of the Electrodes Was Evaluated Using Cyclic Voltammetery (CV), Galvanostatic Charge-Discharge (GCD) Technique and Electrochemical Impedance Spectroscopy (EIS) in a Neutral Electrolyte of 0.1M Solution of Na2SO4 Performed on Films Deposited on a Steel Substrate. a Specific Capacity of 298.4 Mah/g at a Scan Rate of 20 Mv/s Was Obtained at 30 Deposition Cycles. the SILAR Deposited Cos Thin Film Electrodes Is a Promising Material for Both Energy Storage and Optoelectronics Application Based on the Electrochemical Properties Obtained. the Material Showed about 80% Charge Capacity Retention after 1000 Cycles.
(Invited) Control of Diffusion Behavior of Metal Ions Close to Electrode By Using of Local Structure of Ionic Liquid Electrolyte
Authors: Imanishi Akihito
Published: May 2020

Ionic liquids (ILs) have attracted keen attention due to its applicability to various kinds of electrochemical devices. However, we still lack enough knowledge on the interface structure and spatial distribution of chemical species during the electrochemical processes. In our previous study, we succeeded in the observation of the spatial distribution of XPS spectra close to the electrode under the applied potential using scanning electrochemical photoelectron spectroscopy (Scanning EC-PES) we originally developed. Interestingly, the shape of the diffusion layer (The spatial distribution of the concentration of the metal ions) was largely different from the concave function usually supposed in the case of aqueous solution. By a numerical simulation, we revealed that the characteristic shape of the diffusion layer of IL electrolyte was formed due to the fact that the metal ions diffused by the fast hopping-like mechanism, in which the apparent diffusion coefficient increased with increasing of the concentration of 'holes' (vacancies formed between IL molecules) acting as hopping sites. Based on these results, we proposed the new diffusion model in which hopping diffusion and conventional diffusion (which follows Stokes-Einstein equation) coexist. The most prominent feature of our diffusion model is that the local structure of ionic liquid (hole density, arrangement of the holes and/or IL molecules) strongly affect the diffusion behavior of metal ions.

On the other hand, it can be anticipated that the local structure of ILs can be systematically controlled by the IL species (e.g. the alkyl chain length of imidazole cation, shape and size of anion), additive ions and/or temperature of solution. By using of these techniques for controlling the local structure of ILs, we can strictly control the diffusion behavior of metal ions close to the electrode. In other words, we will be able to propose the new strategy for controlling the diffusion behavior of solutes in ionic liquid solutions close to the electrode. In this study, we investigated the factors for controlling the diffusion behavior of metal ion in IL electrolyte based on our proposing diffusion model, and revealed that the behavior of metal ions can be controlled by some factors mentioned above.
(Invited) High-Yield Singlet Fission of Tetracene Derivatives Utilizing Organic-Inorganic Hybrid Systems for Light Energy Conversion
Authors: Hasobe Taku
Published: May 2020

Singlet fission (SF) is highly expected to improve the solar energy conversion properties by generating two excitons from one photon absorption. Among various organic compounds, acene derivatives such as tetracene and pentacene are promising for occurrence of efficient SF. Pentacene derivatives sufficiently meet the energy-level matching condition between a singlet and two triplet states: [E(S1) ≥ 2E(T1)]. Although tetracene is well-kwown as a good candidate for SF, the number of high-yield and long-lived triplet excited states through SF is extremely limited because of the relative acceleration of the reverse triplet-triplet annihilation (TTA) considering the above-mentioned energy matching condition. Consequently, the precise control of orientation and distance between two neighboring Tc units is definitely required for long-lived individual triplets through SF but not correlated triplet pair. Because the longer lifetime of the individual triplet states is useful for efficient light energy conversion.

Therefore, we first demonstrate the quantitative sequential process from intramolecular SF to intermolecular two-electron transfers using 2,2′-biphenyl-bridged tetracene dimer (Tet-BP-Tet). The obtained high-yield and long-lived triplet excited states of Tet-BP-Tet by intramolecular SF (quantum yield of individual triplet states: ΦT = 175 ± 5% and lifetime of individual triplet states: τT = 0.29 ms) resulted in the quantitative intermolecular two-electron transfer process with chloranil in benzonitrile (electron transfer yield: ΦET = 173 ± 5%).1 Then, we also propose a novel supramolecular strategy utilizing the mixed self-assembled monolayers (SAMs) with two different chain lengths. Specifically, mixed tetracene-SAMs on gold nanoclusters, which are prepared by a tetracene-modified hetero-disulfide with two different chain lengths, attain high-yield SF (Φ
SF: ~90%) and individual triplet yields (Φ
Τ: ~160%).2

References

Nakamura, S.; Sakai, H.; Nagashima, H.; Kobori, Y.; Tkachenko, N. V.; Hasobe, T. ACS Energy Lett.
2019, 4, 26-31.

Saegusa, T.; Sakai, H.; Nagashima, H.; Kobori, Y.; Tkachenko, N. V.; Hasobe, T. J. Am. Chem. Soc.
2019, 141, 14720-14727.
(Invited) Exploitation of Innovative Materials and Process of Perovskite Solar Cells Toward Commercialization
Authors: Jung Hyun Suk
Published: May 2020

All solid-state solar cells based on organometal trihalide perovskite absorbers have already achieved distinguished power conversion efficiency (PCE) to over 25% and further improvements are expected up to 27%. Now, the research on perovskite solar cells has been moving toward commercialization. To facilitate commercialization of these great solar cells, some technical issues such as long-term stability, large scale fabrication process, and Pb-related hazardous materials need to be solved. Also, flexible perovskite solar cell using plastic substrate can be used in niche applications such as portable electrical chargers, electronic textiles, and large-scale industrial roofing.

This talk is dealing with our recent efforts to facilitate commercialization of perovskite solar cells. For examples, we introduce a recycling technology of perovskite solar cells, which covers the regeneration process of Pb contained perovskite layer as well as recycling process of Au electrodes and transparent conducting oxide glass. Also, recent interesting results regarding ultra-flexible perovskite cells will be discussed in terms of stress analysis. Finally, simple fabrication technologies for realizing large scale perovskite module is going to be introduced.