bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Chemical Functionalization and Transformation of 2D Layered Chalcogenide Materials
Authors: Wang Qing Hua 
Published: May 2020

Layered chalcogenide materials are a diverse class of crystalline materials that consist of covalently bound building blocks held together by van der Waals forces. Among these materials are the transition metal dichalcogenides (TMDCs) which can be exfoliated into two-dimensional (2D) nanosheets, and the pnictogen chalcogenides (PCs) which can be exfoliated into one-dimensional (1D) nanoribbons and 2D nanosheets. Controlling the electronic and optical properties of these materials, as well as forming interfaces with other materials structures, is important for a wide range of potential applications, and can be achieved using a set of strategies for chemical modification that has been pursued in our laboratory. This talk will highlight our recent work on covalent chemical functionalization, structural and geometric conversion, and self-assembly of organic van der Waals heterostructures.
In the first strategy, semiconducting MoS2 is covalently functionalized using aryl diazonium salts that form out-of-plane bonds on the basal plane. Detailed imaging studies of the reaction under a range of parameters combined with density functional theory (DFT) calculations show that the functionalization initiates at point defects but then propagates in a chain-like morphology across the MoS2 surface. The reaction is also shown to be well-described by Freundlich and Temkin isotherm models, and to have pseudo-second-order kinetics. The diazonium salts can also be modified to enable tethering of proteins to the MoS2 surface. The same reaction scheme is also extended across the TMDC and PC layered chalcogenides including MoSe2, WS2, WSe2, Bi2S3, and Sb2S3. In the second strategy, MoO3 and WO3 nanoscrolls are formed by transformation from 2D MoS2 and WS2 nanosheets, respectively, via atmospheric plasma treatment. The combination of different radicals in the plasma simultaneously oxidize the layered disulfides and initiate delamination from the substrate, so that the strain of the altered crystal structure is relieved by rolling into nanoscroll geometries. In the final strategy, we form a self-assembled monolayer of fullerene molecules on WSe2, and use atomic resolution scanning tunneling microscopy to show that the molecules exhibit a 2x2 rotational superstructure due to the interplay of molecule-molecule, molecule-substrate, van der Waals, and Coulomb interactions. The system forms a charge redistribution network with long-range ordering.
(Invited) Optimizing 2D Material-Based Electrodes for Electrochemical Energy and Conversion Devices
Authors: Worsley Marcus A. 
Published: May 2020

Electrochemical energy storage (EES) and conversion devices (e.g. batteries, supercapacitors, and reactors) are emerging as primary methods for global efforts to shift energy dependence from limited fossil fuels towards sustainable and renewable resources. These electric-based devices, while showing great potential for meeting some key metrics set by conventional technologies still face significant limitations. For example, an EES device tends to exhibit large energy density (e.g. lithium-ion battery) or power density (e.g. supercapacitor), but not both. This inability of a single device to simultaneously achieve both metrics represents a major obstacle to widespread adoption of EES devices. Improvements in materials, such as the integration of 2D materials (e.g. graphene, dichalcogenides, MXene, etc.) into electrochemical devices has yielded some exciting results towards tackling this issue, but significant improvements are still needed. Our approach to simultaneously achieving high energy and power density is to focus on one of the fundamental processes that occur in these systems: mass (or charge) transport. The efficient transport of ions within EES devices is critical to realizing both large power and energy densities. The pore structure of the electrode is a key factor in determining this transport phenomena, but in many cases, engineering the pore structure in a highly deterministic fashion is not pursued or even possible for many electrode materials. In this work, we explore a number of additive manufacturing methods (e.g. direct ink write, projection microstereolithography, etc.) to engineer the pore structure of device electrodes. We also determine effective electrode geometries using both simple theory and topology optimization techniques. The topology optimization couples the solution of the forward electrochemical problem over the full electrode domain with gradient-based optimization. The output of our code is a three-dimensional CAD representation which optimizes over specific performance metrics and which can be used to print functional electrodes. This work provides a systematic path toward automatic design and fabrication of engineered electrodes with precise control over the fluid and species distribution.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
(Keynote) The Rise of MXenes
Authors: Gogotsi Yury 
Published: May 2020

Numerous compounds, ranging from clays to boron nitride (BN) and transition metal dichalcogenides, have been produced as 2D sheets. Although many of these materials remain subjects of purely academic interest, others have jumped into the limelight due to their attractive properties, which have led to practical applications. Among the latter are carbides and nitrides of transition metals known as MXenes (pronounced “maxenes”), a fast-growing family of 2D materials. The family of 2D transition metal carbides and nitrides (MXenes) has been expanding rapidly since the discovery of Ti3C2 at Drexel University in 2011 [1]. More than 30 different MXenes have been reported, and the structure and properties of numerous other MXenes have been predicted using density functional theory (DFT) calculations [2,3]. Moreover, the availability of solid solutions on M and X sites, control of surface terminations, and the discovery of ordered double-M MXenes (e.g., Mo2TiC2), i-MAX phases and their MXenes offer the potential for producing dozens of new distinct structures.
This presentation will describe the state of the art in the field. The manufacturing of MXenes, their delamination into single-layer 2D flakes and assembly into films, fibers and 3D structures will be briefly covered. Synthesis-structure-properties relations of MXenes will be addressed on the example of Ti3C2. The use of MXenes in ceramic- metal- and polymer-matrix composites, smart fibers and textiles will also be discussed. The versatile chemistry of the MXene family renders their properties tunable for a large variety of applications [3-5]. Oxygen or hydroxyl-terminated MXenes, such as Ti3C2O2, have been shown to have redox capable transition metals layers on the surface and offer a combination of high electronic conductivity with hydrophilicity, as well as fast ionic transport [4]. This, among many other advantageous properties, makes the material family promising candidates for energy storage and related electrochemical applications [4], but applications in plasmonics, electrocatalysis, biosensors, water purification/ desalination and other fields are equally exciting.
References
1. M. Naguib, M. Kurtoglu, V. Presser, J. Lu, J.-J. Niu, M. Heon, L. Hultman, Y. Gogotsi, M. W. Barsoum, Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2, Advanced Materials, 23 (37), 4248-4253 (2011)
2. M. Naguib, O. Mashtalir, J. Carle, V. Presser, J. Lu, L. Hultman, Y. Gogotsi, M.W. Barsoum, Two-Dimensional Transition Metal Carbides, ACS
Nano
6 (2) 1322–1331 (2012)
3. B. Anasori, Y. Gogotsi (Ed.) 2D Metal Carbides and Nitrides (MXenes): Structure, Properties and Applications (Springer), 2019
4. B. Anasori, M. Lukatskaya, Y. Gogotsi, 2D Metal Carbides and Nitrides (MXenes) for Energy Storage, Nature Reviews Materials, 2, 16098 (2017)
K. Hantanasirisakul, Y. Gogotsi, Electronic and Optical Properties of 2D Transition Metal Carbides and Nitrides (MXenes), Advanced Materials, 30 (5
Capacitive Charging Mechanisms at the Molybdenum Disulfide/Ionic Liquid Interface
Authors: Pope Michael A , Lashkari Sima 
Published: May 2020

Molybdenum disulfide (MoS2) is a 2D material of the transition metal dichalcogenide family which has recently gained significant attention for use in supercapacitors. MoS2 can exist as several polymorphs such as the 2H and 1T which are semiconducting and semi-metallic, respectively. The 2H phase, found in nature, is the most stable form of MoS2. The 1T phase is metastable and can be obtained by chemical methods such as via lithium intercalation. It shows a much higher conductivity (100 S/m). Furthermore, restacked single layers of 1T-MoS2 can be intercalated by smaller ions such as Na+, Li+, H+ and K+, in aqueous electrolyte, allowing the electrolyte to access their interlayer spacing and therefore providing impressively high volumetric capacitance of between 400 – 700 F/cm3. Hence, molybdenum disulfide is a promising material for supercapacitor application.
While these high values are achieved in aqueous electrolyte, few studies have examined their capacitive behavior in room temperature ionic liquid (IL) electrolytes which exhibit much higher electrochemical stability windows > 3-4 V. The potential of coupling high capacitance materials with high voltage operation has the potential to lead to high energy densities due to a supercapacitor’s square dependence of the energy density on cell voltage. However, it is currently unknown whether these electrolytes can intercalate between restacked 1T-MoS2. Furthermore, the intrinsic capacitance of the 1T-MoS2/IL electrolyte remains largely unexplored along with the impact that defects and oxidation may have. To investigate the charging behavior in IL electrolytes, we examined the electrochemical behaviour of monolayer MoS2 deposited on highly oriented pyrolytic graphite (HOPG), using cyclic voltammetry and electrochemical impedance spectroscopy. The monolayer MoS2 is deposited using a Langmuir Blodgett (LB) deposition method. Multilayers are deposited by sequential layer-by-layer deposition. The negligible roughness and surface coverage of the monolayers are confirmed and estimated by atomic force and scanning electron microscopies. Highly purified 1-ethyl, 3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI) is used as the electrolyte and the monolayers are electrochemically probed in custom-made O-ring sealed electrochemical cell. Using these analyses, we probe the frequency and potential-dependence of the intrinsic capacitance of the MoS2/IL interface and provide design criteria for building improved IL-based supercapacitors.
Disorder-Features in Exfoliated Graphene from Variable Intercalation Times and Intercalant-Mix
Authors: Momodu Damilola , Sharif Farbod , Karan Kunal , Roberts Edward P.L. 
Published: May 2020

Efficient exfoliation of relatively good-quality graphene with high-yield from graphite is critical for its extensive application in different emerging technologies. The cost-implication when undertaken via electrochemical exfoliation makes upscaling even more likely. In addition, the ability to constructively tune the final graphene properties (in terms of the defect metrics in the graphitic lattice) to fit a specific required application could be achieved by controlling operational parameters adopted during the intercalation and exfoliation steps.
In a recent study, we demonstrated a one-step electrochemical exfoliation process carried out in an inorganic electrolyte containing ammonium phosphate [1]. Phosphate groups on the resulting graphene led to a thermally stable material. The present study evaluates the incorporation of phosphate functionalization during the intercalation step of a two-step electrochemical exfoliation process.
Here-in, a systematic evaluation of the nature of defects is elucidated with respect to varying intercalation times and intercalant mix using an acid-blend containing sulphuric acid (H2SO4) and phosphoric acid (H3PO4). The type and location (edge or grain boundary-type), and relative concentration (%) of available defects is discussed with respect to increasing the intercalation times slightly beyond the point it attains a threshold intercalation voltage. Thermal stability of the graphene has also been explored based on the quantity of phosphoric acid content in the intercalant-mix. The exfoliated graphene sheets were characterized using Scanning Electron Microscopy, X-ray Diffraction, Thermal Gravimetric Analysis, X-ray Photoelectron and Raman Spectroscopy in detail to quantify defects and phosphorus contents in the doped-graphene framework. A thermally stable graphene was obtained with a constant “boundary-layer type” defect signature retained for increasing phosphoric acid in the mix. A shorter time to achieve the threshold intercalation voltage was observed with increasing H3PO4-acid content.
This study provides a facile and energy efficient recipe for synthesizing graphene nanostructures with signature defects relevant for use in energy storage and water treatment applications.
Insight into the Superior Photoactive Electrochemical Performances of NiCo2S4 for Efficient Bifunctional Catalyst Towards Oer/ORR in Rechargeable Zn-Air Batteries
Authors: Sarawutanukul Sangchai , Tomon Chanikarn , Phattharasupakun Nutthaphon , Sawangphruk Montree 
Published: May 2020

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are considered to be a fundamental basis of many energy conversion and storage technologies. Many studies have been devoted to developing high active ORR and OER bifunctional electrocatalysts to improve the efficiency of Zinc-air batteries (ZABs)[1]. However, the possibility of using free solar energy in ORR/OER electrocatalysts to enhance the efficiency of ZABs has not yet been recognized. Herein, we report a photoactive bifunctional catalyst of spinel-type NiCo2S4 (NCS) urchin-like structure with rich mesopores and direct band gap energies of ca. 1.4 and 2.4 eV which is good agreement with computational calculation. The NCS catalyst exhibits high catalytic activities for both OER (ɳ=338 mV at 10 mA cm-2) and ORR (ɳ=475 mV at E1/2), comparable to that of the state-of-the-art counterparts (e.g., Pt/C for ORR, RuO2 for OER). Under light illumination, the p-type photoactive NCS catalyst can absorb visible light, generating photogenerated holes and photoelectrons via the photoelectric effect for direct conversion of photoenergy into electric energy with increasing kinetic charge transfer process and provides ca. 10% and 18.5% lower OER and ORR overpotential than those under the dark condition. In addition, the as-fabricated zinc-air battery with the photoactive NCS as cathode exhibits the decrease in voltage gap from 0.82 to 0.60 V with an increase in round-trip efficiency from 59.2% to 68.8% after exposed to visible light. The zinc-air battery with a reversible redox reaction for simultaneous conversion of chemical and photoenergy into electric energy could open a new pathway for the utilization of a single energy conversion and storage device.

Figure 1. The schematic of photocatalytic Zn-Air-Batteries with NiCo2S4 cathode.

Keywords: Zn-air batteries, photoactive catalyst, Nickel cobalt sulfide.
References
1. Liu, W., et al., Defect-Enriched Nitrogen Doped–Graphene Quantum Dots Engineered NiCo2S4 Nanoarray as High-Efficiency Bifunctional Catalyst for Flexible Zn-Air Battery. Small, 2019. 15(44): p. 1903610.

Figure 1
Micro-Scale Study of Redox Flow Battery Using Pore Network Modelling
Authors: Shokriafra Mohammadjavad , J. Niasar Vahid 
Published: May 2020

Producing energy from intermittent renewable energy sources has been extensively developed over the past decades. One of the goals at the grid scale is to provide sustainable energy output to the end-users. To this end, efforts must be done to store huge amount of energy in robust batteries to provide stable and flexible electricity to the costumers during peak hours. Redox flow batteries have been attracted attention to be one of the best candidates amongst electrochemical technologies. Many researchers have focused on these batteries to find the best electrolyte pairs, optimise the electrode structure and efficiently manufacture membrane which prohibits cross-flow while transfer charges.
Despite efforts has been made in RFB area, these batteries are not economical in large scales. The main problem is losses related to charge and mass transport in electrodes. Focusing on the modelling the electrode design, seems to be a reasonable solution mostly because of time consuming nature of experiments and difficulties arising in experimental procedures. As an example, electrode is only a few hundred microns thick and measuring concentration, electric field or pressure inside that is impossible. Many researchers have developed several control-oriented and continuum macroscopic models. However, those models have investigated macroscopic features, but are deficient in considering microscopic characteristics of electrodes like pore structure.
Alternatively, pore-scale studies pave the way to investigate several processes in the electrodes. The complex porous electrode transformed to a network of connected pores and throats, and transport processes are directly applied for that network. This method can take into account electrolyte flow, electrochemical reactions, charge transport and ion transport, those are simultaneously occurring in RFB. Several paper works show the result of using pore network modelling in RFB, but these works neglect complex concepts like interaction between channels and pores. Additionally, they are not able to manage large scale simulations and consume considerable time that is not costly effective. In this work, electrode pore network is reconstructed from X-ray computed tomography image of carbon cloth. This work focuses on hydrogen bromine RFBs that hydrogen gas is oxidised in the anode and the produced protons goes to the cathode to reduce bromine in the cathode as the following equation.
Stokes flow equation for electrolyte, convection, diffusion and reaction equations for bromine and electro-migration equation for electron are considered as governing equations in the pore network. All resulted equations are solved with C++ code and the results are going to be validated with experimental results.

Figure 1
Computational Modelling Studies of Structural Transition in Li1+XMn2O4 (0≤x≤1) Nanoparticles
Authors: Hlungwani Donald , Ledwaba Raesibe Sylvia , Ngoepe Phuti E 
Published: May 2020

Lithium-ion batteries, comprising nanoparticulate Ni-Mn-Co (NMC) cathodes that have been used to power electric vehicles, can be improved by blending NMC with LiMn2O4 (LMO). However, LMO undergoes a cubic to tetragonal phase change during charge cycling, which cracks and pulverises the material resulting in capacity fading [1]. Structural characterisation during the phase transition is the first step in mitigating capacity fading and can be challenging experimentally and computationally. The simulated amorphisation and recrystallisation method, based on empirical interatomic potentials were utilised to generate Li-Mn-O composite nanoparticles, with approximately 3000 atoms, and are amnenable to linear scaling DFT methods. The techniques was previously successfully used to study nanostructures of MnO2 [2], with composite structures. A wealth of microstructural features such as heterostructures, point defects and grain boundaries were observed. The discharge process of the nanoparticle was simulated by lithiating the Li-Mn-O composite nanoparticle. The nanoparticle was characterized by radial distribution functions and simulated X-ray diffraction patterns (XRDs). Furthermore, the structural changes with lithiation were visualised and details of various defects, including grain boundaries could be observed from microstructures. The presence of layered and spinel components were also noted and validated by XRDs. Linear scaling density functional theory methods were used to determine voltage profiles of simulated structures.
References
1. Okumura T., Yamaguchi Y., Shikano M. and Kobayashi H., J. Mater. Chem. A, 2, 8017, (2014).
2. Sayle, T.X.T, Kgatwane K., Ngoepe P.E. and Sayle D.C., J. Mater. Chem. A
4, 6456 (2016).
Enhanced Corrosion Performance By Micro Arc Oxidation Coating with the Addition of 2-Aminobenzimidazole Loaded Halloysite Nanotubes on AZ31 Alloy
Authors: Wu Wen-Xin , Lee Howard , Lin Hsin-Chih 
Published: May 2020

The application of Magnesium alloys has drawn great attention in recent years. As the lightest structure metal on earth, the usage of Mg is attractive to the automotive, aerospace and electronics industries owing to its high weight-to strength ratio. Unfortunately, the poor corrosion resistance impedes the development of Mg alloys. To date, several methods have been proposed to improve the anti-corrosion ability, such as conventional anodizing, sol-gel coating, and micro arc oxidation (MAO). MAO is an innovative technique for generating surface oxide coatings on valve metals and alloys, which exhibits strong adhesion to the substrate, high thickness, hardness, corrosion and wear resistance, and provides an environmentally-friendly alternative to acid-based anodizing treatment.
Despite all these advantages, the intrinsic structural imperfection of MAO coatings, including a loose structure featured by micro-pores and micro-cracks, facilitate quicker penetration of the corrosive ions into the base magnesium, and thus, increase the rate of corrosion. To overcome the problem of porous MAO film, composite coatings with self-healing ability that are capable to repair themselves when damage occurs have been utilized. In this study, the concept of self-healing is carried out by incorporating corrosion inhibitors, 2-aminobenzimidazole (2-ABI), loaded nanocontainers, halloysite nanotubes (HNT), to silicate-based electrolyte to obtain MAO coatings on AZ31 alloy in single step. The coatings are evaluated by SEM, EDX, and XRD. Corrosion performance is studied with EIS, PDP and salt spray test. The effects of various electrical parameters, including current density, frequency and working time, on the coating are also investigated. Experimental results indicate that the corrosion resistance of MAO films with the addition of 2-ABI loaded HNT is significantly improved, and thus confirms the feasibility of 2-ABI as corrosion inhibitor to Mg alloys.