bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mxenes: A New Family of Two-Dimensional Materials and Its Application As Electrodes for Li and Na-Ion Batteries
Authors: Naguib Michael , Gogotsi Yury , Barsoum Michel W. 
Published: February 2020

Two-dimensional, 2D, materials, such as graphene, possess a unique morphology that endows them with interesting and novel properties. Currently, the number of non-oxide materials that have been exfoliated is limited to two fairly small groups, viz. hexagonal, van der Waals bonded structures (e.g. graphene and BN) and layered transition metal chalcogenides.
The MAX phases are a well established family of machinable layered ternary carbides and/or nitrides, with a composition of M
n

+1AX
n
, where M is an early transition metal, A is one of A group elements, X is C and/or N; with n = 1, 2, or 3. Selective etching of the A layers from the MAX phases results in exfoliating of the latter producing 2D layers of transition metals carbides and/or nitrides. We labeled the resulting 2D M
n

+1X
n
layers "MXenes" to emphasize the loss of the A group element from the MAX phases and the suffix "ene" to emphasize their 2D nature and their similarity to graphene.
The etching process is typically carried out using aqueous hydrofluoric acid at room temperature. Nine different MXenes have been reported to date, viz., Ti2C, Nb2C, V2C, (Ti0.5,Nb0.5)2C, Ti3C2, (V0.5,Cr0.5)3C2, Ti3CN, Ta4C3, and Nb4C3. The as-synthesized MXenes are terminated with a mixture of OH, O, and/or F groups.
When select MXenes were tested as electrode materials for Li-ion batteries (LIBs), each phase showed unique electrochemical characteristics. In principle, some could be used as cathodes while others as anodes for LIBs. All the tested MXenes showed excellent capability to handle quite high cycling rates (as high as 36 C) as electrode materials for LIBs, which suggest they can be used in Li-ion capacitors as well. The lithiation and delithiation mechanisms were found to be due to redox intercalation/deintercalation reactions.
As synthesized MXenes can be pressed, at room temperature, into freestanding discs, > 300 µm thick. Some of these discs can be used as electrodes for LIBs with high areal capacities exceeding 5 mAh/cm2. In addition to LIBs, some MXene also showed good capacity as electrode material for other ion batteries such as Na-ion batteries.
Herein the progress in the synthesis of MXenes, in addition to their performance as electrode materials in LIBs and Na-ion batteries will be discussed, with special emphasis on the lithiation and delithiation mechanisms for Ti3C2.
Carrier Doping of Few-Layer MoS2 with Ionic Polymers and MoS2 Quantum Dots with Atmospheric Water
Authors: Briggs Donovan , Nguyen Phong , Fager Cody , Sreenivasan Sreeprasad , Berry Vikas 
Published: February 2020

Thin layered MoS2 has emerged as a remarkable 2D semiconductor material with great potential due to its direct band gap (thickness dependent), photoluminescence, and high on/off FET rectification. Additionally, molecular gating has proven to be an effective technique to dope nanomaterials for specific electronic applications. Here, we show two avenues for molecular gating: (A) Carrier doping and electrical properties of few layer MoS2 were controllably modulated by interfacing it with the polyanionic polymer, polystyrene sulfonate (PSS) and the polycationic polymer, polyallylamine hydrochloride (PAH); and (B) MoS2 quantum dots interfaced with a microfiber of PAH were reversibly doped with water molecules by altering the local humidity. PSS interfacing with few layer MoS2 resulted in a blue shift of the Raman E1
2g and A1g Raman peaks in MoS2 corresponding to hole doping, as expected for negative potential gating. PAH adsorption on PSS doped MoS2 led to a recovery of the A1g peak, while the E1
2g peak red shifted slightly attributed to over compensation by PAH and electron doping. Similar results were attained with PAH interfacing on MoS2 few layer sheets resulting in electron doping. Electrical characterization confirmed the carrier doping observed by Raman. MoS2 quantum dots interfaced with a microfiber of PAH were reversibly doped with water molecules by changing the local humidity. The p-doping of water absorbed by the polymer microfiber reduced the electron density in n-type MoS2 quantum dots. The change in the carrier concentration (5.24 x 1011 cm-2) was confirmed by electrical measurements and Raman spectra were analyzed to understand the lattice bonding of MoS2 during the self-assembly process onto PAH microfibers. Both of these avenues demonstrate chemical modification or interfacing providing a path for tuning the electronic properties of MoS2 for use in future electronic devices.
Synthesis of Metal Nanoparticle Graphene Nanocomposites Using Atmospheric Pressure Microplasma Assisted Electrochemistry
Authors: Huang Huin Ning , Chiang Wei Hung 
Published: February 2020

Graphene represents a new type of carbon materials and have attracted lot of attention is due to its exceptional physical and chemical properties. Recently experimental and theoretical studies have been shown that the composites of metal nanopaticles (NPs)/graphene can process superior electrocatalytic property, making them promising candidates for fuel cell electrodes. However, conventional approach to synthesis metal NPs/graphene composites usually involve time-consuming and laborious wet-chemistry-based methods. Here we present a facile synthesis metal NPs/graphene composites using a novel atmospheric-pressure microplasma-assisted electrochemistry. Microplasmas are defined as gaseous discharges formed in electrode geometries where at least one dimension is less than 1mm. Additionally, microplasmas can be operated with an aqueous solution as an electrode. Energetic species formed in the microplasma are capable of initiating electrochemical reactions and nucleating particles in solution without the need for a chemical reducing agent. In our experiments result, we found metal NPs can be synthesis in a minute time scale using atmospheric-pressure-microplasma-assisted electrochemistry, and we further extend this technology to synthesis metal NPs/graphene composites. As-produced samples were characterized by SEM, XRD, Raman and UV-Vis spectrocopy.

Figure 1
(Invited) Microwave Chemistry Enabled Controlled Fabrication of Graphene with Tailored Structures for Designed Applications
Authors: He Huixin 
Published: February 2020

Due to its excellent electronic, optical, thermal and mechanical properties, and its large surface area and low mass, graphene holds great potential for a wide range of applications. It seems that the research in graphene has now proceeded from the initial phase of developing myriad strategies for the synthesis of graphene sheets to the use of graphene in various research fields. Mass production of reduced graphene oxide and graphene nanoplatets has recently been achieved. However, it is still challengingto controllably produce solution processable highly conductive graphene sheets in large quantity, at low cost, via eco-friendly and energy saving process, with optimal sheet size, layer thickness, defective (vacancies and holes) and molecular structures (oxygen containing groups and non-defective graphene domains). All these structural parameters determine their electronic, thermal and mechanical properties of graphene, which are the key warrants for their practical application in various devices. As examples, fundamental studies and high-frequency electronics require pristine graphene. However, “bulk” applications such as flexible macroelectronics, and mechanically and electronically reinforced composites, require large quantities of solution-processible highly conductive large graphene sheets manufactured at low cost. On the other hand, holey graphene, referred to graphene with nanoholes in their basal plane, demonstrates much better performance in their application as metal free catalysts and in energy storage. Finally, there is a surge of interests in nanosized graphene sheets for solar cells and various biological applications due to their unique size effects, edge effects, and even quantum confinement effects. Most importantly, most of the commercial available solution processible graphene sheets were fabricated via a long multiple- step process (several hours to 5 days).
By exploiting the unique thermal and kinetic effects induced by microwave heating and the right selection of graphite oxidation chemistry, we developed series of quick and scalable strategies to produce a family of “clean” graphene sheets (without surfactants and without metal ions and/or toxic residues) with controlled porous structures, and controlled sizes from a few nanometers to tens of micrometers. By choosing a series of cheap biomass molecules, also with the help of microwave heating, bottom-up fabrication approaches are developed to produce heteroatom (N, B and/or P) doped graphene sheets and graphene quantum dots with bright emission. The applications of these graphene sheets and graphene quantum dots in Lithium battery, metal free-catalysts, and multifunctional drug delivery will be discussed.
Controllable Modification of Optical Properties of Graphene Oxide
Authors: Naumov Anton V , Galande Charudatta , Ajayan Pulickel M , Weisman R. Bruce 
Published: February 2020

Controllable generation of band gaps in graphene is one of the important current tasks in modern nanoelectronics. To investigate whether this can be achieved by controllable functionalization, we have studied the changes in optical properties of graphene oxide in water suspension upon ozone-induced oxidation of reduced graphene oxide (RGO). The reduced graphene oxide, whose properties strongly resemble graphene, was produced by oxidizing graphite using the Hummers method followed by a hydrazine reduction. Exposure of the resulting RGO to ozone for the periods of 5 to 35 minutes caused a dramatic bleaching of the sample’s visible and ultraviolet absorption and the concurrent appearance of strong visible fluorescence in previously nonemissive samples. These observed spectral changes suggest a functionalization-induced band gap opening. The ozone treatment also caused solubilization of RGO in water. Such fluorescence emission from graphene oxide was found to be highly pH-dependent. Sharp and structured excitation and emission features resembling the spectra of molecular fluorophores were present near 500 nm in basic conditions. In acidic conditions fluorescence spectra reversibly broadened and shifted to 680 nm, while the excitation spectra remained similar in shape and position, suggesting the excited state protonation of the emitting species in acidic media. Oxygen-containing addends resulting from the ozonation treatment were detected by XPS and ATR FTIR spectroscopy and computational modeling was used to relate their presence to optical transitions in localized graphene oxide fluorophores. Further research on controlled ozonation-induced functionalization of graphene will be directed towards producing graphene-based optoelectronic devices with tailored and controllable optical properties.
Bottom-up Synthesis of Sub-10 Nm Semiconducting Graphene Nanoribbons with Smooth Armchair Edges on Ge(001)
Authors: Arnold Michael S. , Jacobberger Robert , Kiraly Brian , Fortin-Deschenes Matthieu , Lévesque Pierre , McElhinny Kyle , Delgado Richard , Singha Roy Susmit , Mannix Andrew , Lagally Max G , Evans Paul , Martel Richard , Hersam Mark C. , Guisinger Nathan 
Published: February 2020

The rational synthesis of graphene nanoribbons that are semiconducting with sub-10 nm width, controlled crystallographic orientation, and well-defined edges on non-metallic substrates has been a significant challenge. The growth of nanoribbons on metal substrates precludes their direct use in semiconducting electronics due to the conducting substrate, and the direct synthesis of nanoribbons in solution is complicated by challenges of their post-synthetic assembly.
In this talk, we demonstrate the scalable synthesis of graphene nanoribbons from the bottom-up via chemical vapor deposition (CVD) on Ge(001). Low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) show that the ribbons are self-orienting ±2.9° from the Ge[110] directions and are self-defining. The nanoribbons have predominately smooth armchair edges that give rise to electron interference patterns that are indicative of the high quality of the edges. By tuning the precursor flux, growth time, and growth temperature, the ribbon anisotropy and growth kinetics can be tailored to yield ribbons with controlled width < 10 nm and aspect ratio > 60. Compared to previous reports of the growth of low aspect ratio crystals of graphene on Ge, we find that in order to realize high aspect ratio nanoribbons, it is critical to operate in a regime in which the growth rate is especially slow, on the order of 5 nm/h for growth in the width direction. Scanning tunneling spectroscopy shows that the ribbons have electronic structures that are consistent with semiconductors with bandgaps that are > 500 meV and that vary inversely with width.
This work is important because unlike continuous two-dimensional graphene, which is semimetallic, one-dimensional graphene nanoribbons can be semiconducting, allowing for the substantial modulation of their conductance and enabling their application in semiconductor logic, optoelectronics, photonics, and sensors. Moreover, the direct synthesis of ultranarrow and smooth graphene nanoribbons on Ge demonstrated here provides a scalable, high throughput pathway for integrating semiconducting graphene directly on conventional large-area semiconductor wafer platforms that are compatible with planar processing.
Electrochemical Behaviors of Pt-Decorated 3D Network Architectures Based on Graphene Oxide and Melamine for Fuel Cells
Authors: Kim Seok , Song Chang Yoon , Jung Yongju 
Published: February 2020

Platinum (Pt)-based materials are known to be the most active catalysts for methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs). However, the low conductivity, poor stability, high cost and slow electron-transfer kinetics are the weakness of metal oxides as support materials for large-scale commercial applications[1].
Thus, recent investigators have develop various pt based nanoparticles with desired nanostructure by chemical and physical methods such as Pt-supported on nanostructured carbonaceous materials such as Pt-carbon nanotube (pt/CNT), Pt-carbon black(Pt/CB), and Pt-graphene nanosheets (Pt/GN)[2-4].
Recently, among kinds of nanostructured carbonaceous materials, Graphene or Graphene oxide (GO) have been widely explored. Graphene, a 2-D carbon material consisting of hexagonal sp2-hybridized monolayer, is layered materials with strong in-plane bonding and weak out-of-plane interactions. Graphene has given rise to intense interest with advaced materials due to its excellent physical and electronic properties. In particular, in order to make the wide dipersion of Pt nanoparticles, three-dimensional (3D) architectures built from Graphene oxide (GO) have attracted intense interest due to its high surface and high volume[5].
In this work, the novel hydrid support nanocomposite composed of Graphitic carbon nitride (g-C3N4) and Graphene was synthesized via an aqueous solution process of melamine and GO. In order to use the catalysts on the anode for DMFCs, Pt nanoparticles were deposited on the surface of the resultant 3D Pt/g-C3N4@RGO.
The Electrocatalytic activity of the resultant 3D Pt/g-C3N4@RGO was examined by cyclic voltammogram (CV). The potential range of CV was measured from -0.25 V to 1.0 V in 0.5M H2SO4 at a scan rate of 50 mV/s. The catalytic activities of 3D Pt/g-C3N4@RGO, Pt/reduced graphene oxide (RGO), and Pt/carbon black (CB) were compared. The 3D Pt/g-C3N4@RGO shows the higher current density than Pt/RGO, and Pt/C. From the results, the 3D-graphene having Carbon nitride (CN) stucture are more favorable for immorbilization of Pt noanoparticles than the pristine graphene.

Acknowledgments

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning, Korea (Grant No.: NRF-2011-0009007).

References

[1] Y. Tan, C. Xu, G. Chen, N. Zheng, Q. Xie, Energy & Environmental Science 5 (2012) 6923.
[2] A. Halder, S. Sharma, M. S. Hegde, and N. Ravishankar, J. Phys. Chem. C 113 (2009) 1466.
[3] S.Kim, S.J.Park , Electrochim. Acta 52 (2007) 3013.
[4] J.Y. Park, S. Kim, J. Electrochem. Soc., 161(4) (2014) F518.
[5] L. Jiang, Z. Fan, Nanoscale 6 (2014) 1922.
A New Method for Fabrication of Solid State Batteries
Authors: Isaacson Mark , Hu Matthew , Sword Mike , VanMuijen Brook , Spotnitz Robert , Talin A. Alec , Upadhaya Deepak 
Published: February 2020

Commercially available solid-state lithium and lithium-ion batteries with inorganic electrolytes are typically low capacity, low energy density and high cost devices. This paper discusses a new manufacturing technology with the potential to enable the development of high capacity solid-state batteries with very high energy density at very low cost.
The process is called Battery-on-Wire (BoW) and is shown in Fig. 1. It consists of a single, cylindrical vapor phase reactor with multiple reactor zones. A metal wire, which acts as the cathode current collector, is continuously fed into the top of the reactor and cathode, electrolyte, anode and anode current collector layers are sequentially deposited on the wire. The result is a complete solid-state cell in the form of a thin flexible wire.
A wide variety of anode, electrolyte and cathode materials can be deposited by judicious selection of reactants. Electrode and electrolyte morphology and chemical composition can be modified by controlling the reactor temperature and the partial pressures of the reactants. The various reactor sections are isolated to prevent cross contamination and the deposition rates are usually several orders of magnitude higher than those in the processes typically used to fabricate solid-state batteries with inorganic electrolytes.
Fig. 2 shows SEM images of anode, cathode and electrolyte deposits. The anode and cathode coatings exhibit some porosity and surface roughness with surface features on the order of 1-2 μm. The electrolyte coating is smooth and non-porous.
Fig. 3 shows initial cycle life data for a Si-based anode. There is some capacity fade in the early cycles but the discharge capacity is almost constant after cycle 5 and the coulombic efficiency is near 100% after cycle 10. The specific capacity of the anode material is estimated to be between 2500 and 3000 mAh/g. Additional data for anode, cathode and electrolyte materials and complete cells will be shown in the presentation.

Figure 1
A Glucose Fuel Cell with Graphene-Coated Carbon Fiber Cloth
Authors: Hoshi Kazuki , Muramatu Kazuo , Sumi Hisato , Nishioka Yasushiro 
Published: February 2020

Enzymatic glucose biofuel cells that generate power in human body fluids have been strongly demanded to supply electric power to microelectric systems such as heart pacemakers. This is because they work under mild conditions of room temperature, neutral pH and atmospheric pressure, which make them amenable to the human body. Porous carbon electrodes have been commonly used in glucose biofuel cells [1]. However, it was not very easy to avoid release of enzymes form these porous carbon electrode during operation of the biofuel cells. In addition, these porous carbon films were not flexible, and they were easily fractured. On the other hand, a carbon fiber woven fabric (CF) has been reported to have high flexibility and conductivity. Moreover, there were some trials to deposit graphene on each carbon fibers in CF, and it is called as graphene-coated carbon fiber cloth(GC) [2]. Thus, it is considered to be possible to increase the effective surface areas to absorb more enzymes on GC surface.
In this study, a glucose fuel cell was fabricated using GC as flexible electrodes in glucose biofuel cells. The SEM image of the GC used in this study is shown in Fig. 1. Many nanostructures were observed on carbon fibers. We used this GC as the anode and cathode of the fabricated micro biofuell cells, and the area of the anode and cathode electrodes were 3 × 10 mm2, respectively. The anode was modified with glucose oxidase (GOD) and ferrocene. The cathode was modified with bilirubin oxidase (BOD). Figure 2 shows comparison of the relationship of the power density and voltage of biofuell cells using GC or CF. The power was measured by immersing the biofuel cells in phosphate buffer solution with 100 mM glucose at room temperature. The maximum power for the CF biofuel cell was 16.3 μW / cm2 at 0.07 V, and the maximum power for GC biofuel cell was 30.7 μW / cm2 at 0.096 V. These results indicated the advantages of using GC on flexible glucose biofuel cells.
[1] M. Togo, A. Takamura, T. Asai, H. Kaji, M. Nishizawa, Electrochim. Acta 52(2007) pp.4669–4674.
[2] http://incu-alliance.co.jp/
Modeling Diffusivity in Catalyst Layer of a PEMFC Based on a Unit Cell Approach
Authors: Salari Sina , McCague Claire , Tam Mickey , Stumper Jüergen , Bahrami Majid 
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFC) convert the reaction energy of hydrogen and air to electricity without harmful emissions. PEMFC rely on a membrane-electrode assembly (MEA) constructed from multiple layers of micro/nano porous materials and associated interfaces. The MEA includes a polymer electrolyte membrane (PEM) that conducts protons, a composite nano-structured catalyst layer (CL), and a fibrous gas diffusion layer (GDL) that distributes reactant gases and collects current. The production cost and limited durability of the platinum catalyst layer is a significant challenge for the commercialization of hydrogen fuel cells. The greater the activity of the Pt nanoparticles, the lower the required Pt loading on the carbon support, and the lower the production costs for the catalyst layer. Hydrogen and oxygen reactants diffuse to the catalyst Pt particles. Existing models for the diffusivity of CL are either not accurate or computationally demanding, making them difficult to use for CL optimization. In this study, the CL is represented by unit cells based on porosimetry and analysis of SEM images of CL structure. The mass diffusion problem is analytically solved for the unit cell to calculate effective diffusivity of CL. Unlike other simple models which use porosity as the only input to calculate diffusivity the proposed model considers the pore size distribution as well as structure of CL, which improves the accuracy. The model presented in this study shows results within acceptable accuracy respect to published experimental data.
A Planar Zebra Battery Based on Low Cost Intermediate-Temperature Na-FeCl2 Redox Chemistry
Authors: Li Guosheng , Lu Xiaochuan , Kim Jin Yong , Viswanathan Vilayanur , Meinhardt Kerry , Sprenkle Vincent 
Published: February 2020

A novel intermediate-temperature (IT) planar ZEBRA battery using a molten sodium anode and Fe cathode has been demonstrated in this work. Because of unique sulfur-based additives in the cathode, this Na-FeCl2 battery was able to be assembled in the discharged state and then activated at intermediate-temperature (<200°C). Initial testing of the battery shows excellent cycling capability with superior energy density (discharge) of 135 Wh/kg (60% depth of discharge) and high energy efficiency exceeding 92% at an intermediate operating temperature of 190°C. The long term cell cycle tests of IT planar Na-FeCl2 battery show a minimal capacity fade and well-defined charge-discharge profiles. Our results demonstrate that the IT planar Na-FeCl2 battery technology developed could be a promising alternative to the traditional Na-NiCl2 chemistry by substantially lowering the material cost, thus helping to deploy ZEBRA battery technologies in stationary energy-storage and micro-grid applications.