bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Progress Towards a Novel Technology for Non-Contact Strain Measurements Based on SWCNT Fluorescence Spectroscopy
Authors: Bachilo Sergei M. , Sun Peng , Zhao Jackie , Nagarajaiah Satish , Weisman R. Bruce
Published: February 2020

One of the most distinctive properties of semiconducting single-walled carbon nanotubes (SWCNT) is their emission of structure-specific fluorescence (band gap photoluminescence) in the short-wave infrared (SWIR) spectral region. The fluorescence peak from each (n,m) structural species shifts in wavelength as the nanotube’s band gap is altered by axial strain. These shifts are known from theory and experiment to depend on the nanotube’s chiral angle and on its mod (n-m,3) value, and they are linear with strain for realistic axial deformations. We have previously shown that this effect may lead to a new strain measurement technology (called S4, for strain-sensing smart skin) in which individualized SWCNTs embedded in a polymeric film serve as strain sensors and readout is achieved by non-contact optical methods.1 Recent research progress aimed at enabling such an implementation will be described. Focus areas include processing and dispersing SWCNTs for effective use in S4; comparing suitability of different polymer formulations as S4 hosts; applying and stabilizing the S4 films; understanding factors that influence interfacial adhesion between SWCNTs and host molecules; miniaturizing the optical hardware to allow excitation and capture of SWCNT fluorescence spectra with hand-held devices; refinement of data analysis methods for deducing strains from spectral data; tests of sensitivity and reproducibility for S4 measurements with plastic, aluminum, and steel substrates; and construction of two-dimensional strain maps from sets of single-point measurements.

1 P. A. Withey, V. S. M. Vemuru, S. M. Bachilo, S. Nagarajaiah, and R. B. Weisman, Nano Lett. 12, 3497 (2012).
(Invited) Photoluminescence Carrier Dynamics and Photon Statistics of Covalent Dopant-Induced Trap States in Single Wall Carbon Nanotubes
Authors: Doorn Stephen K. , Ma Xuedan , Hartmann Nicolai F. , Yalcin Sibel E. , Htoon Han
Published: February 2020

Recent advances in low level covalent functionalization of carbon nanotubes are receiving significant attention due to new emitting states being introduced by chemically stable oxygen1,2 and aryl diazonium dopants3 that increase photoluminescence quantum yields.  Recent low-temperature studies have further elucidated the associated chemical and electronic structure.4  We report here photoluminescence studies of dynamic behaviors of the dopant sites.  Relevant to their potential uses in imaging and as novel photon sources, we demonstrate blinking behaviors and discuss a range of response as a function of dopant species.  We also report across a range of dopants photoluminescence decay dynamics obtained at the ensemble and single tube levels.  We find that localization of excitons at dopant sites dramatically increases photoluminescence lifetimes, indicating the importance of exciton trapping as a route to limiting non-radiative decay pathways arising from exciton mobility.  Relevant to interest in these new emitting states as single photon emitters for quantum information processing, we also demonstrate an approach to stabilizing emission output while also introducing solitary dopant sites.  Finally, lifetime and photon correlation studies enabled by superconducting nanowire single-photon detectors will be presented.  Evolution of behaviors as a function of temperature will be discussed in the context of realizing room-temperature photon antibunching.

1.  S. Ghosh, et al., Science, 330, 1656 (2010).

2.  Y. Piao, et al., Nature Chem., 5, 840 (2013).

3.  Y. Miyauchi, et al., Nature Photon., 7, 715 (2013).

4.  X. Ma, et al., ACS Nano, 8, 10782 (2014).
(Invited) Low Temperature Photoluminescence of Individual SWNTs Emitting at Telecommunication Wavelengths
Authors: Ardizzone Vincenzo , Chassagneux Yannick , Vialla Fabien , Delport Géraud , Robert-Philip Isabelle , Voisin Christophe , Lauret Jean-Sébastien
Published: February 2020

In the quest for a nanoscale light emitter, carbon nanotubes have exceptional assets: they have a diameter dependent band-gap compatible with telecom wavelengths, they can possibly be operated at room temperature due to huge exciton binding energies and they emit anti-bunched photons, as required for quantum telecommunications. Here, we will present a complete set of low temperature photoluminescence (PL) experiments on single SWNTs emitting at the telecommunication wavelengths showing statistically relevant narrow line widths. These nanotubes are produced with a high temperature synthesis method (laser ablation – L-SWNTs), which is known to lead to a higher crystalline quality. The narrowing of the lines will be discussed in terms of a reduction of the exciton-phonon coupling in L-SWNTs. An exciton localization up to 6 times larger than in CVD-grown SWNTs is reported suggesting that the crystalline quality play a major role in the optical properties of nanotubes at low temperature. This study shows that several degrees of exciton localization are achievable in SWNTs. Therefore, identification of high crystalline quality nanotubes is a key step towards the control of exciton localization, going continuously from 0D to 1D confinement.
Anchoring Semiconductor and Metal Nanoparticle on Graphene Oxide for Simultaneous Sensing and Degradation of Contaminants
Authors: Kamat Prashant V , Alam Rabeka
Published: February 2020

Manipulation of photoinduced charge transfer processes on a graphene based catalyst mat has allowed us to tailor the properties for photocatalytic and sensing applications. We have deposited luminescent CdSe quantum dots and SERS active silver nanoparticles to introduce photocatalytic and sensing properties. The role of the GO sheet is to establish electronic communication between semiconductor and metal NPs and promote adsorption of molecules near the silver nanoparticle surface. The GO-assisted communication between semiconductor and metal NPs in particular has enabled us to enhance the detection limit for low level nitroaromatic compounds in water. For example, CdSe emission is quenched upon adsorption of nitrobenzene. Following excitation with visible light the reduction of nitro group to amine proceeds at the CdSe surface and restores the emission.  Thus the multifunctional hybrid assemblies designed in this study enable us to achieve greater detection sensitivity as well as capability to degrade the organic contaminants from water.
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.
Degradation and Electronic Confinement in Exfoliated Black Phosphorus
Authors: Martel Richard , Gaufrès Etienne , Favron Alexandre , Fossard Frederic , Phaneuf Anne-Laurence , Lévesque Pierre , Loiseau Annick , Leonelli Richard , Francoeur Sebastien
Published: February 2020

Thin layers of black phosphorus have recently raised interest for their two-dimensional (2D) semiconducting properties, such as tunable bandgap with layer thickness and high carrier mobilities. This lamellar crystal of P atoms can be exfoliated down to monolayer 2D-phosphane (also called phosphorene) using procedures similar to that for monolayer graphene. The devices are however challenging to fabricate due to fast degradation of the thin layers upon exposure to light in air. We investigated this degradation process using in-situ Raman and transmission electron spectroscopies and reported on a thickness dependent reactivity of the layers. Moreover, the degradation process was identified to be due to an ubiquitous photo-induced oxidation of the layers by adsorbed oxygen in water. Optimum experimental conditions to prepare n-layer 2D-phosphane in their pristine states were applied to determine the Raman signatures of degradation. Here, we report on the kinetics of the photo-oxidation and provide sigantures in the Raman spectra that could be used to assess the crystal quality.
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.
Selection, Characterization, and Application of High Affinity Microcystin-Targeting Aptamers in a Graphene-Based Biosensing Platform
Authors: Eissa Shimaa , Ng Andy , Siaj Mohamed , Zourob Mohammed
Published: February 2020

The development of successful biosensing platforms is highly dependent upon the biorecognition properties of the recognition receptor and the sensitivity of the transducer of the binding signal. The integration of the high affinity and specificity of DNA aptamers, and the unique properties of the carbon nanomaterial graphene, offers an excellent avenue for sensitive and selective biosensing architectures. In this work, novel microcystin-targeting DNA aptamers were successfully selected using systematic evolution of ligand by exponential enrichement (SELEX). Then, highly sensitive and selective aptasensor which utilizes an unlabeled aptamer noncovalently assembled on a graphene electrode for microcystin-LR detection was developed. Assembly of the DNA aptamer on the graphene-modified electrodes caused a marked drop in the square wave voltammetric reduction signal of the [Fe(CN)6]4−/3− redox couple. The presence of microcystin-LR, on the other hand, caused a dose-responsive increase in peak current, allowing the quantification of microcystin-LR through the measurement of peak current change. Under optimal conditions, the detection limit of the developed aptasensor was 1.9 pM in buffer, a concentration much lower than those offered by previously reported biosensors for microcystin-LR. The developed aptasensor also exhibited excellent selectivity for microcystin-LR with no detectable cross-reactivity to okadaic acid, microcystin-LA and -YR. Moreover, the proposed aptasensor has been applied for the analysis of spiked tap water and fish samples showing good recovery percentages. We also demonstrated in this work that the mechanism of the detection was based on the conformation change in part of the aptamer without complete release from the graphene surface. This novel, simple, high performance and low-cost detection platform would facilitate the routine monitoring of microcystin –LR in real samples.
Novel Functionalized Graphene Oxide-Polymer Nanocomposite Anion Exchange Membranes
Authors: Movil-Cabrera Omar , Garlock Michael , Staser John A
Published: February 2020

Anion-exchange membranes (AEMs) have recently gained considerable interest toward applications in fuel cells, electrolyzers and membrane separation processes. The aim of the current work is to fabricate novel functionalized graphene oxide-polymer nanocomposite AEMs with improved hydroxyl conductivity, selectivity and thermo-mechanical stability. For this purpose, graphene oxide sheets (GO) were functionalized with different cations (ammonium, pyridinium, and immidazolium) using a covalent bonding approach. Then, the functionalized graphene oxide sheets (FGO) were incorporated into two commercially available AEMs, Fumapem® FAA-3 and Fumapem® FAAM via solvent-casting method. The effects of some variables such as cation type, functionalization degree and FGO content on the material properties of these new-developed materials were investigated. FTIR, Raman, XPS, TGA, UV-vis, XRD, TEM, SEM and impedance spectroscopy were used to characterize both FGO and the nanocomposite AEMs.
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.
Enhancing the Interfacial Bonding Strength of Carbon/Epoxy Composites Using Silane-Functionalized Graphene Oxides
Authors: Kim Soo Young , Lee Chang Yeong , Bae Ji-Hun , Kim Tae-Yoon , Chang Seung-Hwan
Published: February 2020

Silane-functionalized graphene oxides (sGOs) were fabricated with four different self-assembled monolayers (SAMs) to reinforce an epoxy adhesive, with the aim of improving the bonding strength of carbon/epoxy composites. The oxygen-containing groups on the surface of GO were converted by the SAMs to amine, epoxy, or alkyl groups. The successful reaction between the silane molecules of the SAMs and functional groups of GO was evidenced by the results of different characterization methods such as Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and synchrotron-radiation photoemission spectroscopy. It was found that the average thickness of the sGO flakes was higher than that of GO flakes regardless of the SAM used, which also suggested the presence of silane-functionalized groups on the GO sheets. The bonding strength of a carbon fiber/epoxy composite, tested with a single lap joint bonded with an epoxy adhesive, was increased by 53% after the addition of a sGO that contained amine groups. These results show that sGOs, especially those containing amine functional groups, can strengthen the interfacial bonding between the carbon fibers and epoxy adhesive. Therefore, it is thought that sGOs could be used in adhesive bonding applications to increase the bonding strength.

AcknowledgementsThis research was supported by the Mid-Career Research Program (2014-1051098) through the National Research Foundation of Korea (NRF), which is funded by the Ministry of Education, Science, and Technology.
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
Activity and Stability of Perovskite Oxides at Neutral pH for Oxygen Evolution Catalysis
Authors: Han Binghong , Risch Marcel , Lee Yueh-Lin , Ling Chen , Jia Hongfei , Shao-Horn Yang
Published: February 2020

Recently, many perovskite oxides have been well studied as the electrocatalysts for the oxygen evolution reaction (OER) in alkaline electrolytes. However, the OER electrocatalysis of perovskite catalysts at near-neutral pH is still less investigated, which is critical in many electrochemical techniques for the storage and application of sustainable energy, such as photo-electrochemical devices and metal-air batteries. In this work, we systematically studied the activity and stability of a series of highly active and common perovskite catalysts for OER at pH 7. For activity, we found that many previous design principles for oxide catalysts to achieve high OER activity at pH 13, such as having an eg filling close to unity or having an O p-band close to Fermi level, are still appropriate activity descriptors at pH 7. For stability, which was a greater challenge at pH 7 than at pH 13, we identified two different modes of catalyst degradation. Perovskites with O p-band close to Fermi level showed leaching of A-site atoms and surface amorphization at any condition in pH 7 electrolyte, while those with O p-band far from Fermi level were stable under low OER current/potential but unstable at high current/potential accompanied with the leaching of B-site atoms. These two degradation modes can be explained and supported by the respective formation energies of the modified surfaces from DFT calculation. These new findings provided new insights into the degradation mechanism of oxides OER catalysts, as well as new design principles for developing high-stability and high-activity perovskite OER catalysts for neutral-pH or low-pH applications.
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.
Oxidation Controlled Anode Materials for Li Ion Battery
Authors: Jeong Je Jun
Published: February 2020

Silicon is considered one of the best candidates as an anode material for the next generation of Lithium ion batteries due to its enormous capacity of 3579 mAh/g (Li15Si4) compared to that of graphite (372 mAh/g). However, Lithium ion insertion and extraction results in a volumetric expansion of 300 ~ 400%, which can lead to fracture that cause the capacity fading and poor cycle efficiency of the silicon anode during electrochemical cycling.

In this study, we introduce a Si-based alloy covered with oxide layer on the surface of particles. Inactive oxide layer component plays a structural buffering role to minimize the mechanical stress induced by huge volume change of active silicon. Si-Fe powders from ferrosilicon and Fe2O3 were synthesized by a high-energy mechanical milling process. The electrochemical properties were measured using coin cell with LCO as the counter electrode. From the electrochemical cell test, we observed the smaller degradation of the initial capacity and better efficiency compared to that of Si-Fe, and the capacity retention rate is also improved compared to that of Si-Fe alloy. A high-resolution transmission electron microscope and X-ray diffraction were used for detailed phase analysis of Si-Fe-O compounds.

Figure 1
Nucleation and Growth Controlled Polyol Synthesis of Size-Focused Nanocrystalline LiFePO4 Cathode for High Performance Li-Ion Batteries
Authors: Baboo Joseph Paul , Gim Jihyeon , Song Jinju , Kim Sungjin , Alfaruqi Muhammad Hilmy , Jo Jeonggeun , Lee Jun , Kim Jaekook
Published: February 2020

Mono-dispersed and densely packed, LiFePO4 cathodes with high rate performance versus lithium were synthesized using a two-step polyol process. The particle-size distribution and packing density of LiFePO4 nanoparticles were fine-tuned via separation of the nucleation and particle growth processes in the polyol medium by varying reaction time and temperature. Precisely, the LiFePO4 samples were synthesized by heating the reaction mixtures at 200 °C for various reaction times (0, 1, 3 and 6 h) to facilitate nucleation and thereafter the solution temperature was raised and maintained at 320 °C to facilitate the crystal growth process. XRD studies confirmed the formation of olivine phase in all the samples. The FE-SEM, FE-TEM and particle-size distribution studies illustrate that the particle-size of olivine nanocrystals may be tuned to approximately 200 nm by controlling the aging time at 200 °C or in other words separating the nucleation and crystal growth process. The olivine cathodes synthesized by maintaining 3-6 h aging time demonstrate improved discharge capacities and cycle performances in comparison to those of the remaining samples. In particular, the 6 h olivine cathode registered average discharge capacities of 130, 87 and 64 mAh/g at 5 C, 10 C and 15.7 C current rates respectively.
Interrogation of Alkaline AA Batteries Using in Operando Electrochemical ­Acoustic Time-of­-Flight Analysis and in Operando energy Dispersive X-Ray Diffraction
Authors: Bhadra Shoham , Steingart Daniel A , Hertzberg Benjamin Joseph , Hsieh Andrew , Gjeltema Peter J
Published: February 2020

Recently, in operando Electrochemical ­Acoustic Time-of­-Flight (EAToF) analysis has been shown to provide information about the state of charge (SoC) and state of health (SoH) of a number of battery geometries and chemistries using ultrasonic interrogation of the density and modulus shifts that occur during charge and discharge. The technique has thus far offered a general understanding of these batteries, but has not been used for in depth analysis of individual battery chemistries.

In this work, we performed EAToF measurements on commercially available alkaline Zn/MnO2 AA batteries of a number of different brands under discharge and charge conditions. The data from this method were compared to in situ energy-dispersive x-ray diffraction (EDXRD) data from comparable alkaline AA batteries. Changes in the waveforms in the ultrasonic time-of-flight measurements were shown to correlate with phase transitions in the MnO2 cathode and densification and dehydration of the Zn anode, as shown by peak evolution in the EDXRD data. The mechanisms by which the phase and morphology transitions can change the transmission and reflection of an ultrasonic pulse and the utility of EAToF analysis in determining material differences between different brands of alkaline cells are discussed.
Towards High Performance Non-Aqueous Flow Cells
Authors: Milshtein Jarrod David , Darling Robert M. , Brushett Fikile R.
Published: February 2020

Non-aqueous redox flow batteries (NRFB) have opened a new pathway towards achieving economically viable grid-level energy storage1. As such, a number of studies have reported on the electrochemical behavior of newly developed active species, salt, and solvent combinations (i.e. Brushett et al.2, Escalante-Garcia et al.3, etc.). Most of these redox chemistries, however, have been demonstrated only in beaker cells or un-optimized flow cells; system-level studies toward grid-scale applications have yet been realized.  In order to meet aggressive grid storage cost targets, NRFB’s must meet the following power requirements: 3.5 V, 130 mA cm-2, 91% voltaic efficiency4. Hence, designing high performance non-aqueous flow cells tailored for different chemistries becomes a daunting task given the breadth of available chemistries and lack of materials properties (i.e. viscosity) knowledge required for cell design.

To ease the design process, this study demonstrates a chemistry-agnostic design cycle for non-aqueous redox flow batteries. Specifically, this design cycle will specify flow field geometries and porous electrode materials properties, which optimize the power output and voltaic efficiency of an unspecified NRFB chemistry. First, transport through interdigitated flow fields is modeled (Figure 1) to predict polarization as a function of various dimensionless groups. This modeling study develops guidelines for geometry and flow conditions as a function of materials properties in order to optimize electrochemical performance. Second, a single-electrolyte study5 (Figure 1) is employed to verify the impact of cell design on the cell performance for model active compounds (i.e., TEMPO6). The single-electrolyte configuration also allows us to study cell performance at fixed states of charge by collecting polarization and impedance data at varying flow rates. Ultimately, this experimental technique will verify trends discovered through the transport modeling. This modeling-experimental approach creates a tool for predicting optimized cell architectures given a set of input materials and chemical properties.

Acknowledgments

            We gratefully acknowledge the financial support of the Joint Center for Energy Storage Research and the National Science Foundation Graduate Research Fellowship Program.

References

1. R. M. Darling, K. G. Gallagher, J. A. Kowalski, S. Ha, and F. R. Brushett, Energy Environ. Sci., 7, 3459–3477 (2014).

2. F. R. Brushett, J. T. Vaughey, and A. N. Jansen, Adv. Energy Mater., 2, 1390–1396 (2012).

3. I. L. Escalante-García, J. S. Wainright, L. T. Thompson, and R. F. Savinell, J. Electrochem. Soc., 162, A363–A372 (2015).

4. R. M. Darling, K. G. Gallagher, W. Xie, L. Su, and F. R. Brushett, Transport Property requirements for flow battery separators, submitted.

5. R. M. Darling and M. L. Perry, J. Electrochem. Soc., 161, A1381–A1387 (2014).

6. X. Wei et al., Adv. Mater., 26, 7649–7653 (2014).

Figure 1
Graphite-Based Non Precious Metal Catalyst for Oxygen Reduction Reaction
Authors: Dumont Joseph H , Martinez Ulises , Mohite Aditya , Purdy Geraldine M , Atanassov Plamen , Zelenay Piotr , Gupta Gautam
Published: February 2020

The high cost of Pt-based catalysts for the anode and cathode has greatly limited the distribution and the commercialization of polymer electrolyte fuel cells (PEFCs). Non-precious metal catalysts (NPMCs) have shown high activity and low hydrogen peroxide yields [1, 2], and are a possible alternative to Pt-based catalysts for oxygen reduction reaction (ORR) in the PEFC cathode. In this work, we explore the development of graphite-based catalysts for fuel cell applications. The desired mechanical and chemical stability of graphite could improve durability of NPMC systems. However, implementation of graphite as a catalyst precursor presents new challenges as it is chemically inert. Given the fact that NPMCs are composed of carbon, nitrogen, and transition metals, a systematic approach will be presented to incorporate transition metal and nitrogen precursors into graphite structures. Graphite as a starting material will be treated with high temperature and pressure to intercalate transition metals and/or nitrogen compounds. The formation of active sites will be induced by the increase of defects in the material by harsh acid treatments and by microwaved synthesis. Structural, chemical, and morphological information will be presented via X-ray (XRD and XPS) techniques along with electron microscopy (SEM, TEM). The electrochemical activity for the ORR using RRDE for these graphite-based catalysts will be presented in both alkaline and acidic media. Our preliminary results indicate an improvement of the catalytic activity upon addition of defects, metal and nitrogen compounds.

References:

[1] Wu, G., More, K. L., Johnston, C. M., Zelenay, P., Science, 332, 443-447 (2011).

[2] Bashyam, R., Zelenay, P., Nature, 443, 63-66 (2006).