bluuebunny/crossref_metadata_2025 huggingface dataset:
Unraveling the “Switching” Mechanism of Liquid Crystals for Laser Mitigation to Advance Aviation Safety
Authors: Santefort David , Smyth Sean Alexander , Hofmann James , Crowder Chuck D , Keleher Jason J.
Published: February 2020

Laser light illuminations threatened the commercial and private aviation industry for the last decade, with attacks having doubled over the past five years. Furthermore, the intensity of the incoming laser light can distract, or even flash blind, pilots during critical phases of flight. To decrease the intensity of incoming laser light, the liquid crystal (LC) N-(4-Methoxybenzylidene)-4-butylaniline was deposited between two pieces of conductive Indium Tin Oxide coated glass. Data have shown that the test cell is capable of decreasing up to 80% of incoming laser light by transitioning from its transparent, liquid phase to its opaque, pseudo-crystalline phase, with the cell being able to return to its transparent phase in less than three seconds. This research proposes that the test cell uses a mechanism which reduces the intensity of laser light by increasing the spread of the light, making the cell look opaque. To further investigate this mechanism, the cells were analyzed using polarization microscopy, which allowed for the pseudo-crystalline regions of the liquid crystals to be observed. The constant formation and motion of these regions result in dynamic light scattering within the cell due to the LC’s orientation-dependent index of refraction. This mechanism will be used to further increase the mitigation of laser light and the responsiveness of the LCs to an applied voltage.
MXene-Based Flexible Supercapacitors for AC Line-Filtering with Ultrafast Frequency Response
Authors: Jung Mingyu , Gund Girish Sambhaji , Rana Harpalsinh H. , Kota Manikantan , Park Jeonghee , Gogotsi Yury , Park Ho Seok
Published: February 2020

Slow charging-discharging rate of flexible electrochemical capacitors (FECs) is a critical challenge of current self-powered portable electronics. Mostly, FSCs function as a power source at direct current, but quit functioning of pulse energy harvesting and current ripple filtering, like conventional capacitors. Thus, portable electronics calls for high frequency response FECs. Motivated from this requirement, we demonstrate ultrafast frequency response of FECs integrating conducting polymer/MXene hybrid electrodes and polymer gel electrolyte. The composite ratio and thickness of material matrix dramatically influences the frequency response behavior of FECs. The FECs with optimized electrode material features accomplished excellent volumetric capacitive and frequency response with bending functionality. Additionally, the real-life capability of fabricated FECs for AC line filtering was demonstrated through LED as DC indicator with bent ECs. Therefore, the high volumetric capacitance and robust frequency response of fabricated FECs offers the most requisites of self-powered portable electronics.
Optical Studies of Reactively Sputtered CuGaO2 Thin Films
Authors: Saikumar Ashwin Kumar , Sundaram Kalpathy B
Published: February 2020

Transparent conducting oxide semiconductors have been researched extensively in the past. Majority of that research has been focused primarily on the n-type transparent semiconductors. Studies on p-type transparent semiconductors have been comparatively lesser. In order to advance in the field of transparent p-n junction and other active devices, more and more researches are being done on p-type transparent semiconductors. CuGaO2 is one of the p-type transparent semiconductor that has the future prospects of being used extensively in the transparent electronics field.

For this work, CuGaO2 (50:50 of Cu2O: Ga2O3) thin films was RF sputter deposited onto both glass and quartz slides. Optical transmission studies was performed on these thin films to extract the band gap. Subsequently, optical transmission studies were performed on CuGaO2 thin films which were systematically post-sputtering annealed. The band gap extraction results of these annealed CuGaO2 thin films are reported.
Electrochemical Characteristics of the Na-Ion Hybrid Capacitors Assembled with Fibrous Composite Separator Containing Core-Shell Structured SiO2 Nanoparticles
Authors: Ko Hyesoo , Park Myungsoo , Kim Dong-Won
Published: February 2020

Sodium is currently being investigated as efficient energy storage due to its abundance in nature. Na-ion hybrid capacitors (NHCs) exhibit the characteristics of high power density as well as high specific energy. The need for development on the NHCs arises as they incorporate the advantages of capacitors and rechargeable batteries as well as cost-effectiveness. As one of the main components in NHCs, an electrolyte plays an essential role in several aspects such as safety, electrochemical characteristics and cycling performance. Conventional liquid electrolytes provide high ionic conductivity and good electrochemical properties, however, they raise safety concerns. A gel polymer electrolyte (GPE) is a promising alternative for liquid electrolyte, as it possesses great safety features and mechanical properties, but suffers from low ionic conductivity due to poor ion transport. In this study, to develop a gel polymer electrolyte with high ionic conductivity and enhanced safety, PVdF-HFP copolymer was electrospun with core-shell structured SiO2(Na+) particles. Core-shell structured SiO2(Na+) nanoparticles were synthesized and utilized as fillers to increase ionic conductivity by releasing Na+ ions into gel polymer electrolyte. Incorporation of core-shell structured nanoparticle fillers can also improve mechanical properties as well as thermal stability. Composition of the composite separators was optimized in consideration of ionic conductivity and mechanical property. Finally, the electrochemical performance of the Na-ion hybrid capacitors employing optimized gel polymer electrolyte was evaluated.

References

S. H. Ju, Y.-S. Lee, Y.-K. Sun, and D.-W. Kim, J. Mater. Chem. A, 1 (2013) 395-401.

S.-R. Park, Y.-C. Jung, W.-K. Shin, K. H. Ahn, C. H. Lee, and D.-W. Kim, J. Membr. Sci., 527 (2017) 129-136.
Probing Oxide-Nitride Selectivity As a Function of CeO2 Valence State Relevant to STI CMP
Authors: Sherry Brian M , Wortman-Otto Katherine M , Mikos Allie M , Keleher Jason J. , Dickmann Dan S , Her Bob , Urban Nathaniel D
Published: February 2020

Electrical isolation within a desired circuit requires shallow trench isolation (STI) to separate active regions with tetraethyl orthosilicate (TEOS) filled trenches. STI chemical mechanical planarization (CMP) is used to facilitate bulk oxide removal by selectively targeting TEOS overburden with colloidal suspensions (slurries) containing ceria (CeO2) nanoparticles. A critical factor in maintaining high removal rates is the presence of CeO2 surface oxygen vacancies (Ovac); commonly associated with unoxidized Ce3+ particles which when filled, change the oxidation state to a less reactive Ce4+ form. The goal of this work is to utilize modified slurries at various Ce3+/Ce4+ ratios and determine the influence of oxidation state on oxide/nitride removal rates. Characterization of the CeO2 particles was determined through UV/Visible and fluorescence spectroscopy along with a novel UV/Visible spectroscopic flow cell technique. The modified slurries were then used to polish both TEOS and Si3N4 wafers to probe selectivity with respect to various mechanical parameters. Preliminary results show that greater concentrations of Ce3+ valence states, in slurries containing a novel reducing agent, result in higher oxide removal rates than the unmodified slurry. Future work will focus on characterization of the post polish effluent to determine the influence of polishing on certain particle properties, such as oxidation state, zeta potential, and size.
Cellulose-Based Nanoporous Materials That Incorporate the Antimicrobial Metal-Organic Framework HKUST-1
Authors: Rickhoff Thomas A. , Kissel Daniel S. , Keleher Jason J.
Published: February 2020

The growing demand for cost-effective clean water solutions has resulted in increased interests in advanced adsorbent materials capable of remediating a wide variety of pollutants. The work presented here focuses on the development of two spherical cellulosic nanoporous materials utilizing different copper-based particles. The copper-based Metal-Organic Framework, MOF-199 (HKUST-1), was incorporated into a cellulose acetate slurry and polymerized into nanoporous beads. The MOF-cellulose beads exhibit an increased number of binding sites that allow for adsorption driven primarily through intraparticle diffusion. Additionally, the MOF-199 framework within the beads acts as a template for post-synthetic modification, which yields a novel nanoporous material containing reduced copper particles capable of enhanced dye remediation. Incorporation of the MOF and reduced copper have been validated by microscopic imaging of the surface and characterized using infrared spectroscopy and thermogravimetric analysis. The presence of copper in both materials allows for a “self-cleaning material” capable of inhibiting the growth of the Gram-negative bacterium Escherichia coli. Further post-synthetic modifications to both the polymer and MOF-199 framework allow for the potential to create advanced adsorbent materials capable of remediating a broader range of pollutants including organic compounds and toxic metal ions.
Durability Test of Anode-Supported Solid Oxide Fuel Cell Under Diverse Load Conditions
Authors: Kim Youdong , Saqib Muhammad , Park Jun-Young
Published: February 2020

Solid oxide fuel cells (SOFCs) provide an appealing electrochemical devices to convert chemical energy into electrical power with high efficiency and negligible carbon emissions. For utilizing in a wide spectrum of applications, SOFCs need to prove the operational stability over 40,000 h with less than 10% of power decay [1]. The performance deteriorations of SOFCs are induced by complex factors such as redox cycle [2], carbon deposition [3], S poisoning [4], and Cr poisoning. Therefore, understanding of fundamental degradation mechanisms under various operating conditions are important to improve the lifetime of SOFCs.

For past few decades, the durability study of SOFCs has carried out under prolonged periods of time in mainly ‘laboratory conditions’, i.e. constant current operations, well controlled fuel composition, and low level of impurities [5,6]. However, the real operating conditions normally include harsh conditions such as temperature fluctuations, current fluctuations, and fuel and air stop. Especially, the different load conditions can result in accelerating the degradation of cell components because of the local potential and temperature changing.

In this research, systematic durability investigations of anode-supported SOFCs are performed under a wide range of operating conditions including load cycle and load trip. In order to understand degradation mechanisms of the cell, various electrochemical investigations are performed such as the current-voltage polarization and electrochemical impedance spectroscopy. The morphology and microstructure of anode-supported cell are examined using field emission scanning electron microscoy and electron probe X-ray microanalyzer.

References

Y.-S. Chou, J.W. Stevenson, J.-P. Choi, J. Power Sources 250 (2014) 166–173.

T. Klemensø, C. Chung, P.H. Larsen, M.Mogensen, J. Electrochem. Soc. 152 (2005) A2186–A2192.

Mai, M. Becker, W. Assenmacher, F. Tietz, D. Hathiramani, E. Ivers-Tiffee, D. Stöver, W. Mader, Solid State Ionics 177 (2006) 1965–196

H. Yokokawa, T. Horita, K. Yamaji, H. Kishimoto, T. Yamamoto, M. Yoshikawa, Y. Mugikura, K. Tomida, Fuel Cells 13 (2013) 526–535.

Hagen, J.V.T. Høgh, R. Barfod, J. Power Sources 300 (2015) 223–228.

H. Yokokawa, ECS Trans. 35 (2011) 207–216.

T.-H. Lee, K.-Y. Park, J.-T. Kim, Y. Seo, K.B. Kim, S.-J. Song, B. Park, J.-Y. Park, J. Power Sources 276 (2015) 120–132.
A General Room Temperature Synthesis of Self-Assembled Urchin-like Nanostructured Vanadates for Lithium-Ion Batteries
Authors: Hu Yang , Chen Jing , Pan Anqiang , Liang Shuquan , Cao Guozhong
Published: February 2020

Vanadium based materials are widely investigated as high-performance cathode materials for Lithium-ion batteries due to their high specific capacities, good reversibility and abundant resources in the earth's crust. Unlike commonly reported solvothermal synthesis of nanostructured materials at high temperature, herein, a novel general room temperature approach is presented for the synthesis of different vanadium based precursors with nanorods self-assembled urchin-like hierarchial structure, which can be readily transformed into several vanadates, including Na0.33V2O5, Ag0.33V2O5, Ag1.2V2O5 and LiV3O8, when calcined in air. The as-prepared vanadates materials well retained the unique urchin-like hierarchial nanostructure and showed good cycling performance and rate capability as cathode materials for Lithium ion batteries. Specifically, the as-synthesized Na0.33V2O5 cathode materials delivered a high specific capacity of 278 mAh/g when cycled at a current density of 100 mA/g. Compared with commonly used solvothermal synthesis at elevated temperature, this presented approach is more economic and more energy saving, as the nanostructure can be obtained at room temperature. In addition, this approach can be easily generalized to synthesize all kinds of other vanadates such as copper vanadates, cobalt vanadates, and potassium vanadates.
Optical and Magnetic Properties of Ni-Doped Cuse Nanowires
Authors: Wang Chiu-Yen
Published: February 2020

In this study, Ni-doped CuSe nanowires (NWs) is prepared by by using a vacuum hydraulic pressure injection process by using anodic aluminum oxide (AAO) template assisted. The prepared steps are including: the first is nanotubular template fabricated by anodization process. Second, enlarged the tube diameter of the template by a chemical etching process. Third, Ni-doped CuSe bulk is prepared by melting the mixed element powders of Cu, Se and Ni with a sealed quartz tube. After homogenizing the bulk, the operated chamber was vacuumed and heated up to melt the Ni-doped CuSe bulk and press the liquefied Ni-doped CuSe into the AAO template then cool the sample to room temperature. The last, the AAO were removed with chromic acid + phosphoric acidsolution at 60 °C for 40 minute then cleaned with de-ionized water to get the products that stored in alcohol solution for further characterization. As-grown Ni-doped CuSe nanowires were studied by scanning electron microscope (SEM), , X-ray diffractometer (XRD) transmission electron microscope (TEM), Raman spectroscopy cathodoluminescence spectroscopy and superconducting quantum interference device (SQUID). The SEM result shows the nanowire is 100 nm and 10~30 µm in diameter and length, respectively. The TEM and XRD results confirm the product is Ni-doped CuSe nanowire with <5 at% Ni. CL spectra demonstrated that the emission of Ni-doped CuSe nanowires at ~600 nm (2.1 eV) and could be change with varied Ni concentration. The magnetic properties of Ni-doped CuSe nanowires are analyzed with SQUID and shows the Curie temperature of product is above room temperature. The unique optical and magnetic properties of AAO template-assisted grown Ni-doped CuSe nanowires could be potential application of spintronic device.
2D MoSe2 Field Effect Transistor with Small Threshold Voltage for Piezoelectric Touch Sensor Applications
Authors: Jeong Yeonsu , Park Ji Hoon , Ahn Jongtae , Lim June Yeong , Im Seongil
Published: February 2020

Being implemented as an active component in the circuits, two dimensional (2D) transition metal dichalcogenide (TMD) transistors have two kinds of difficulties. First, regardless of carrier type, threshold voltage (Vth) of TMD 2D field effect transistors (FETs) is located far away from 0 V. Second, gate bias induced hysteresis exists in general 2D TMD transistors, causing an unstable operation of FETs. Here, we have fabricated stable n-channel MoSe2 FETs with a relatively small Vth of -5 V and minimized-hysteresis of 0.5 V. And we have checked the stable operation by integrating a smart touch sensor circuit composed of piezoelectric P(VDF-TrFE) polymer, the MoSe2 FET, and organic light emitting diode (OLED). To minimize the Vth and gate voltage hysteresis of 2D FET, we inserted ultrathin (8.46 nm) polystyrene (PS)-brush layer between MoSe2 channel and 50 nm-thin Al2O3 dielectric. Our MoSe₂ FET has showed a maximum drain-current (ID) of ~9 μA at VDS of 1 V along with a high linear mobility of 11.2 cm2/Vs. In the analogue touch sensor circuit gated by piezoelectric film of large scale Al/50 μm-thick P(VDF-TrFE)/ITO/glass, the MoSe₂ FET exhibites high ON/OFF ratio and ON-state ID which quite well demonstrated OLED pixel operation.

Figure 1
Synthesis of γ’-Fe4n, a New Soft Magnetic Material for Inductors and Transformers
Authors: Stevens Tyler E , Pearce Charles Joseph , Atcitty Stan , Monson Todd
Published: February 2020

γ’-Fe4N has many attractive properties, such as high saturation magnetization and electrical resistivity, making it an ideal candidate to replace current magnetic materials in power electronics. Doing so would allow transformers and inductors to operate in tandem with new high frequency semiconductor switches, ultimately enabling smaller devices. However, synthesis of γ’-Fe4N is challenging, especially if bulk material is desired. Furthermore, products often contain multiple phases of iron nitride or undesirable morphology and particle size. Our efforts are focused on the synthesis of nanoscale γ’-Fe4N as these materials have been shown to exhibit high permeability and therefore low loss as frequency is increased. Efforts toward the synthesis of this material, including nitridation of nanoscale iron and electrochemical nitridation of iron wire, will be presented.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
Plasmonic-Enanced Remote Phosphor Layers for White LEDs
Authors: Kwon Oh Hyeon , Jang Jin Woo , Lee Che Yoon , Cho Yong Soo
Published: February 2020

This work introduces a way of improving luminescent properties of a planar phosphor layer printed on a common glass substrate. The planar phosphor approach is a coming technology for a large-scale coverage with one-step printing process in the next generation white LED. The combination of wave-guiding ZnO nanorods with dispersed plasmonic Au nanoparticles induces a significant improvement in luminous efficacy. It is the very first report of applying the plasmonic nanostructure directly to the phosphor layer for high efficiency white LED. A nanostructure consisting of ZnO nanorods with dispersed Au nanoparticles was successfully demonstrated as a critical addition for enhancing significantly the luminescence characteristics of a planar silicate-based phosphor layer printed in micro-scale thickness. The optimal luminous efficacy of ~84.26 lm/W obtained with the controls of the length of nanorods and Au concentration corresponds to a ~18% improvement compared to the value for a flat structure. A longer length of nanorods with a sufficiently low Au concentration of 12.5 ppm was found to be beneficial in achieving the best performance. The results suggest that this plasmonic nanostructure can be extensively adjusted to improve luminescence properties for next generation planar light-emitting diodes.
Probing Electrode-Electrolyte Interfaces Using Nano-Gap Surface-Enhanced Raman Spectroscopy and Imaging
Authors: Yang Guang , Ivanov Ilia N. , Ruther Rose E. , Sacci Robert L , Subjakova Veronika , Hallinan Daniel T. , Nanda Jagjit
Published: February 2020

Performance of portable electronic devices and electric vehicles is currently limited by the energy density, lifetime and safety of lithium rechargeable batteries. Overcoming those limitations requires in-depth understanding of the electrode-electrolyte interfaces. Surface-enhanced Raman spectroscopy (SERS) can provide a critical component to this effort as an in situ technique with ultrahigh surface sensitivity that provides quantitative molecular specificity. SERS relies on local electromagnetic field amplification generated by surface plasmon resonance (SPR) at the surface of metal nanoparticles (NPs) with sub-wavelength dimensions. The most significant Raman enhancements have been observed when the local SPRs of multiple NPs interact. This occurs when the NPs are in close proximity (less than 10 nm), which could be achieved in ordered NP monolayers if they could be assembled reproducibly. Methods to assemble gold NPs into large area (cm2) monolayers will be presented. The interparticle gap can be tuned between 1 and 4 nm by using surface ligands of different sizes. The Au NP monolayers exhibit high SERS sensitivity (enhancement factor greater than 107). This allows for the measurement of electrolyte components across a broad range of concentrations. Components include lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC), ethylene carbonate (EC) and diethyl carbonate (DEC). The investigation of solutions of LiPF6 in EC + DEC binary solvents using SERS allows for the determination of the solvent coordination numbers, which range from 2 to 5. This result is in sharp contrast to the bulk values calculated from infrared spectroscopy, which range from 3 to 7. Numerical simulations show that the electromagnetic field is concentrated in the nanogap, indicating the information of the aprotic electrolyte solution structures is obtained from the immediately adjacent area of the solid substrate. Our findings facilitate a better understanding of the structure of solvated ions in close proximity to the electrode surface.

Acknowledgment

This work is funded by Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy. R.L. Sacci is supported by Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Confocal Raman microscopy experiments were conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.
NiMo-Ceria-Zirconia Catalyst for Inert-Substrate-Supported Tubular Solid Oxide Fuel Cells Running on Model Gasoline
Authors: Zhao Kai , Norton M. Grant , Ha Su
Published: February 2020

A novel NiMo-ceria-zirconia catalyst was developed for an inert-substrate-supported tubular single cell running on isooctane fuel. The catalyst with composition of 11 wt.% Ni, 3 wt.% Mo and 86 wt.% ceria-zirconia showed high activity for reforming of isooctane/air mixture and excellent coking tolerance. This catalyst was applied in the tubular single cell consisted of an inert porous yttira-stabilized zirconia (YSZ) supporter, Ni-Ce0.8Sm0.2O1.9 (Ni-SDC) anode, YSZ/SDC bilayer electrolyte and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode. By packing the catalyst into the tubular channel of the single cell, the mixture of isooctane and air can be efficiently reformed to simple syngas (a mixture of hydrogen and carbon monoxide) at 750 °C. The carbon conversion reached 75% and the hydrogen and carbon monoxide yields were over 50%, which were much higher compared with the cell with no catalyst (carbon conversion: <50%, syngas yields: <35%). As a result, the maximum initial power density of the single cell increased from 240 to 306 mW cm-2 by applying the catalyst. Moreover, the single cell displayed significantly improved stability during the 18 h performance test. The results suggest the feasibility of applying the NiMo-ceria-zirconia catalyst for operating the tubular single cell using isooctane fuel.
Effect of NI-Doping on Electrochemical Performance of Olivine LiFe1-XNixPO4 for Sodium-Ion Batteries
Authors: Huynh Le Thanh Nguyen , Nguyen Nguyen Thi Huong , Nguyen Hoang Van , Man Tran Van , Le Phung My Loan
Published: February 2020

In 21th century, rechargeable batteries are main key of modern technology in many applications from portable devices (smartphone, laptop…) to large-scale (hydride electric vehicle-HEV, smart grid system…). Among the rechargeable batteries, Li-ion battery (LIB) is outstanding member due to the highest gravimetric as well as volumetric capacity; and Sodium-ion batteries (SIBs) can have contribution to alternating LIBs in large-scale application. Li-ion and Na-ion batteries have the same configuration with an insertion/extraction reversible of Li+ ions and Na+ ions into electrode positive and negative during charge-discharge process. This work aimed to investigate the effect of Ni-doping on the electrochemical performance of olivine LiFePO4 in sodium secondary batteries. The Ni-doping olivines LiFe1-xNixPO4 (0 < x ≤ 0.25) were prepared by hydrothermal route which exhibited a high crystallization and good distribution grains in nanometric scale. The delithiated phases Fe1-xNixPO4 were obtained by the electrochemical oxidation at rate C/20. In charge-discharge profile in Na-cell, a specific capacity was found out 125 mAh/g with a capacity retention of 95% after 50 cycles.
(Invited) Inkjet-Printed Terahertz Detector
Authors: Léonard François
Published: February 2020

Terahertz waves have shown promise for a number of applications but challenges in developing sources and detectors in this frequency range have prevented broader adoption of the technology. On the detector side, recent work has focused on developing imaging arrays and in improving their performance, which often requires cooling of devices made by photolithography on rigid substrates. Here we present a different approach that focuses on room-temperature detection using inkjet-printed carbon nanotube (CNT) devices. The inkjet printing approach allows for facile, on-the-fly design and printing of devices, including in array format. The structural flexibility of the devices opens new avenues for imaging in non-planar geometries. In this presentation, I will discuss the challenges in developing and printing CNT inks for this particular application, and their properties in the THz. Results of THz detection of CNT pixel arrays will be presented, as well as the factors that impact performance.
(Invited) Functional Hybrids of Single-Walled Carbon Nanotubes Via π-Preserving Covalent Attachment
Authors: Reich Stephanie
Published: February 2020

Single-walled carbon nanotubes have outstanding electronic and optical properties including ballistic transport and tunable infrared light emission. These properties arise from the delocalized π electrons of the sp
2 carbon structure and confinement effects around the nanotube circumference. There has been a long-standing need to controllably tailor single-walled nanotubes through the covalent attachment of functional groups. We recently introduced a novel way of nanotube functionalization using triazine anchors that preserves the p electrons of single-walled carbon nanotubes.[1] Infrared light emission from the optically active E
11 exciton was observed even at high degree of functionalization (4% of the carbon atoms). In this talk I will discuss functional hybrids that are built using the triazine groups to anchor functional units on single-walled carbon nanotubes. I will show how our platform provides routes toward controlled doping in carbon nanotubes and manipulating nanotube luminescence intensities via molecular switches and gold nanostructures. The presented hybrids have interesting application in ultra-high resolution bioimaging that will be discussed.

[1] Preserving π-conjugation in covalently functionalized carbon nanotubes for optoelectronic applications, A. Setaro, M. Adeli, M. Gläske, D. Przyrembel, T. Bisswanger, G. Gordeev, F. Maschietto, A. Faghani, B. Paulus, M. Weinelt, R. Arenal, R. Haag, and S. Reich, Nat. Comm.
8, 14281 (2017).
(Invited) Delayed Fluorescence from Single-Walled Carbon Nanotubes Induced By Energy Transfer from Singlet Oxygen
Authors: Bachilo Sergei M. , Lin Ching-Wei , Weisman R. Bruce
Published: February 2020

Semiconducting Single-Walled Carbon Nanotubes (SWCNT) have small bandgaps between the ground state and the lowest singlet excited state. Such a low singlet-state bandgap will also result in even a smaller triplet bandgap between the ground state and the lowest triplet state. Due to big variations in singlet bandgaps with the nanotube diameter, it is possible to expect that some small-diameter SWCNT species will possess triplet states above the singlet oxygen level, corresponding to ~1270 nm wavelength, and some larger-diameter SWCNTs will be below. Correspondingly, smaller-diameter SWCNT may generate excited singlet oxygen if their triplet state will be quenched by molecular oxygen, while other may be efficient quenchers of singlet oxygen. Both processes are highly important for different photochemical and photophysical effects.

In the presented work we have discovered and investigated fluorescence of SWCNTs resulting from interaction of their water-based and toluene-based dispersions with singlet oxygen generated by sensitizers. Applying chopper-offset and photon-counting time-resolved techniques has allowed us to obtain luminescence spectra and kinetic dependencies for SWCNT and also for singlet oxygen. Among other observations we have determined a cut-off for energy transfer from singlet oxygen to SWCNT triplet, corresponding to approximate equality between the triplet state energy in SWCNT species (7,6) and the singlet oxygen energy. Nanotubes of smaller diameters have triplet states above the singlet oxygen level, but those of larger diameters – below it, and, correspondingly, can generate or quench singlet oxygen. While a direct triplet state lifetime for SWCNT was not possible to resolve in these experiments because it was shorter that the singlet oxygen lifetime, the data indicate it is on the order of a microsecond and decreases with the SWCNT bandgap. For some SWCNT species, especially (8,6), the delayed luminescence after triplet formation is rather efficient and its intensity could be compared with prompt fluorescence with direct excitation.

Thermal activation is the main mechanism for the conversion to a SWCNT excited singlet state after formation of its triplet state by energy transfer from singlet. This is not a surprising result because of rather small (~ 1000 wavenumbers) singlet-triplet splitting between the lowest excited singlet and triplet states, as determined here. However, triplet-triplet annihilation and some other photophysical and photochemical processes also influenced the intensities and kinetic traces of the delayed fluorescence. No SWCNT phosphorescence (emission from the triplet states) was observed, as consistent with usual properties in other organic molecules.
(Invited) Fundamental Understanding and Optimal Design of Low-Dimensional Carbon Nanomaterials for Supercapacitors
Authors: Hwang Gyeong S
Published: February 2020

Nanostructured carbon materials, such as graphene and nanoporous carbon, have become increasingly prominent for use as electrodes in supercapacitors, owing to their high specific and volumetric surface area and good electrical conductivity. A conventional understanding of supercapacitors relates the high power to fast ion accumulation at the polarized electrode interface, forming the so-called electric double layer, and the low energy to limited electrode surface area (SA). As such, low-dimensional carbon nanostructures have been extensively explored. However, anomalous and nonlinear relationships between observed capacitances and SAs have prompted a need to revise our mechanistic understanding of charge storage. In this talk, we present our recent findings regarding charge storage mechanisms in carbon-based supercapacitors from combined quantum mechanical and classical molecular dynamics simulations. Our first-principles studies suggest that the total interfacial capacitance (CT
) of graphene-based supercapacitors is determined from both electrode (CQ
) and electric double layer (CD
) capacitances which are in series. It has also been demonstrated that the CQ
, and thereby CT
, can be significantly enhanced as a result of changes to the electronic structure through chemical functionalization, doping, and/or structural deformation. Furthermore, our voltammetric molecular dynamics simulations have revealed the complex non-equilibrium processes associated with extreme confinement of ionic liquid electrolytes within subnanometer pores. Based on these results, we will also discuss a mechanistic perspective centered around ion reorganization kinetics, particularly the dependence of ion migration efficiency, and relatedly, the capacitance, on pore morphology.
Three-Dimensional Ordered Nanoporous Nickel Electrode for Oxygen Evolution Reaction: Toward Highly Efficient and Ultra-Stable Water Electrolysis
Authors: Kim Sungsoon , Cho Yoonjun , Park Jong Hyeok
Published: February 2020

Hydrogen generation by water electrolysis has been comprehensively studied for several decades, although it still faces many difficulties in commercialization due to low efficiency. Even though IrO2 and RuO2 have superior activities to oxygen evolution reaction (OER), such novel metal catalysts still need high overpotential compared to hydrogen evolution reaction. To overcome the limitation of OER, former researches have been studied with various materials which are cheaper and perform better than the novel metal-based electrocatalysts. Among them, nickel is considered as the best catalyst candidate due to hydroxide state transformation between Ni(OH)2 and NiOOH during the surface reaction.

Apart from the intrinsic properties, the morphology construction to the nanoscale structure is another useful way to enlarge the surface area, which is directly correlated to the overpotential decrease. Nanostructuring can inhibit continuous growth of bubbles on the surface and detach much easily. The bubble blocking effect on the electrode surface has been deeply studied within mechanical category but this effect has been poorly regarded for enhancement of the OER activity of the electrode. Also, the bimetallic system of nickel/iron chosen in this research enables great improvement for OER.

Herein, we synthesized three-dimensional ordered nanoporous mesh-like (3D-NM) nickel electrode by the photolithography method, which outperforms conventional porous nickel electrode. Successfully synthesized ordered nanoporous mesh-like structure provides highly extensive surface area within thickness of only 5 μm. In addition, we investigated that fast bubble formation/detachment from the pore can reduce the bubble blocking effect, which disturbs supply of electrolyte to the catalyst surface. 3D-NM nickel electrode only generates 12 times smaller extraordinary small bubbles compared to the typical bubbles in basic electrolyte. In line with the size of bubbles, impedance during the OER with 3D-NM nickel electrode smoothly undergoes while the nickel foam shows unstable graph.

Owing to the enlarged surface area and the fast bubble formation/detachment effect, overpotential measured at 10 mA cm-2 was 372 mV and the calculated Tafel slope was 94.4 mV dec-1. Through the unique nanoporous structure of nickel electrode, outstanding stability for 50 hours was achieved. To further improve the OER activity of as-prepared 3D-NM nickel electrode, the decoration of nickel and iron was conducted. The final 3D-NM NiFe electrode showed 261 mV of overpotential at 10 mA cm-2 with 43.8 mV dec-1 of Tafel slope.

Figure 1
Magnetic Property of Metallofullerenes within Metal-Organic Framework
Authors: Wang Taishan
Published: February 2020

Endohedral fullerenes are formed by placing atoms or clusters in empty fullerene cages. Among them, magnetic endohedral metallofullerenes with unpaired electron spin have attracted many interests due to their potential application in quantum information processing (QIP), high-density data storage, and magnetoreception system. Notably, the arrangement of these magnetic endohedral fullerenes in solid state is essential for further applications. The metal-organic frameworks (MOFs) have been intriguing many interests due to their porous structures and excellent crystallinity. Particularly, the ordered nano-sized pores in MOF crystals make them good host for these metallofullerenes. In previous report of fullerene-containing host-guest complex, the fullerene carbon cages are always prone to interact with the planar aromatic motif of the host molecules through strong π-π interactions. In MOF structures, there are many similar planar aromatic contents. For example, MOF-177 has cage-shaped pore with two sets of parallel quasi-planar triphenylbenzene unit, 1.4 nm apart from each other. Therefore, the MOF-177 can well accommodate metallofullerenes and the ordered pores of MOF would lead to special solid state magnetic system.

Herein, we report the preparation and magnetic property of metallofullerenes (Y2@C79N, Sc3C2@C80, and DySc2N@C80) accommodating in MOF-177 crystal through a bottom-up approach. In Y2@C79N@MOF-177 complex, the Y2@C79N molecules tend to reside along the c-axis of MOF-177 crystal lattice under low temperature as disclosed by its axisymmetric electron spin resonance (ESR) characters. The confined effect of MOF’s pores plays a significant role in steering the electron spin on endohedral fullerene, leading to anisotropic paramagnetic solid system. In Sc3C2@C80@MOF-177 complex, it was disclosed that the ESR signals of Sc3C2@C80 can sense the tiny transformation of flexible pores under external stimuli. Furthermore, the changes of MOF-177 pores under different conditions exhibit reversible process as shown by Sc3C2@C80 EPR signals, which demonstrates the breathing of MOF-177 frameworks. In DySc2N@C80@MOF-177 complex, the magnetic properties of DySc2N@C80 can be effectively altered by means of imprisoning the molecule in MOF-177. Typically, its quantum tunnelling of magnetism (QTM) is suppressed through spin-phonon couplings.
(Invited) Graphene Nanoribbons through Directed Molecular Assembly and Reagent-less Stitching
Authors: Rubin Yves , Jordan Robert , Li Yolanda L. , Lin Cheng-Wei , McCurdy Ryan D. , Lin Janice B. , Brosmer Jonathan L. , Marsh Kristofer L. , Khan Saeed I. , Houk K. N. , Kaner Richard B.
Published: February 2020

We have recently developed a reagent-less approach to graphene nanoribbons exploiting the topochemical polymerization of 1,4-diarylbutadiynes to generate polydiacetylenes (PDAs), which are thermally converted to graphene nanoribbons with precise widths. The latest results on this project will be described, including the formation of nitrogen-doped graphene nanoribbons.
(Invited) Stable Azaheterometallofullerene M2@C79N (M = Y, Gd, Tb) in Novel Electronic and Magnetic Applications
Authors: Kirkpatrick Kyle M , Liu Xiaoyang , Li Yanlong , Duchamp James , Tao Chenggang , Popov Alexey A. , Dorn Harry C
Published: February 2020

Endohedral metallofullerenes (EMFs) have attracted significant attention as promising spherical molecules for biomedical and material applications due to their unique properties. Endohedral metallofullerenes (EMFs), possessing a metal cluster encapsulated within the carbon cage, have demonstrated altered electronic and magnetic properties as a result of charge transfer from the metal(s) to the carbon shell, which allows a unique structure – property relationship to emerge. One family of EMFs that exhibit these unique features is the azaheterometallofullerene class containing two metals (M = Y, Gd, Tb) in a cage of 79 carbons and one nitrogen atom (M2@C79N). Our work demonstrates the importance of the azaheterometallofullerenes Gd2@C79N and Tb2@C79N as the basis for new, novel nanomaterials, such as molecular switches and single molecule magnets.
Influence of Al-Zn Anode Alloy Composition on the Electrochemical Performance of Me–Air Batteries with Neutral Aqueous Solutions
Authors: Durmus Yasin Emre , Montiel Guerrero Saul Said , Tempel Hermann , Hausen Florian , Kungl Hans , Eichel Rüdiger-Albert
Published: February 2020

Increased demand on resource efficient battery technologies and development of materials has urged an interest on Me–air batteries, such as Zn–air and Al–air, due to their high theoretical specific energies as well as using low cost, safe and abundant materials. In this regard, while employing pure metals as anode material is one line of development [1,2], modification of the electrode by alloying with other elements is also subject to recent investigations [3]. Up to now, the influence of the alloying on the electrochemical properties of the electrode, i.e. interactions between the microstructure constituents, impact on the potential, corrosion behavior as well as the electrolyte decomposition (water or oxygen reduction), have not been systematically investigated for alloys in the Al/Zi system.

The main objective of this work is to characterize the electrochemical properties of Al-Zn alloys in neutral aqueous solutions. Al-Zn alloys with six different compositions were prepared in a muffle furnace and shaped to anodes. Microstructure of the anodes in the initial state was analyzed with respect to the fractions of its constituents. The electrochemical characterization of the prepared alloy anodes encompass (i) open circuit potential, (ii) potentiodynamic polarization measurements and corresponding determination of corrosion parameters, (iii) galvanostatic discharge/charge experiments under various current densities. The potentiodynamic polarization results are further discussed with Evans diagrams considering on possible scenarios for the galvanic interactions of the different microstructure constituents. A comprehensive analysis of the surface characteristics of the alloys is also carried out after the electrochemical experiments in order to reveal the interactions during discharge. Based on the electrochemical results on potentials, charge/discharge and corrosion behavior, the Al/Zi alloys are evaluated with respect to their suitability for application in batteries.

References:

[1] Sumboja, A., Ge, X., Zheng, G., Goh, F. W. T., Hor, T. S. A., Zong, Y., Liu, Z., Journal of Power Sources 332, 330–336 (2016).

[2] Fan, L., Lu, H., Leng, J., Electrochimica Acta 165, 22–28 (2015).

[3] Pino, M., Herranz, D., Chacon, J., Fatas, E., Ocon, P., Journal of Power Sources 326, 296–302 (2016)
Current Density Improvement for Vanadium Redox Flow Cell Having Interdigitated Flow-Field
Authors: Mushtaq Kashif , Monteiro Ricardo , A. Zaidi Asad , Delgado Nuno , Mendes Adelio
Published: February 2020

Tuning of operational conditions and by using pre-treatment of electrodes can lead to the increase in performance of Vanadium redox flow cell (VRFC) as evident through our published article [1]. This work reports the tuning of operational conditions of a VRFC having impregnated graphite bipolar plate with interdigitated flow-field as compared to conventional flow-field. The schematic is shown in figure 1.

The as-received Fumatech FAP-450 anion exchange membrane (AEMs) were used without any treatment. All membranes were cleaned in 1M H2SO4 solution at 80 oC until all vanadium stains were removed and stored in deionized water before being used again. The electrolyte consisted of a commercially available 4 M sulfuric acid-based vanadium solution (1.6 M V3+/V4+ 50:50 M ratio, GfE Metalle und Materialien GmbH, Germany) and it was used without further treatment or purification. Graphite felt electrode (GFE) of thickness 4.6 mm was used with compression ratio of 25%. GFE were boiled in 1M H2SO4 for 12 hours and then left for another 12 hours inside the same solution. Then, GFE are washed with DI water and dried at 100 oC in oven. Afterwards, GFE are thermally treated at 390 oC for 12 hrs inside the furnace injected by air and then cooled down in the furnace upto room temperature. These arrangements allowed to reach higher current density at lower flowrate than used in published article [1].

Charge discharge cycling was done at 40ml/min using current densities of 120mA/cm2, 150mA/cm2, 170mA/cm2, 190 mA/cm2 and 210 mA/cm2. Results of efficiencies (%), energy density (Wh/L) and capacity (mAh) are shown in attached figure 2,3 and 4 respectively. Electrochemical impedance spectroscopy (EIS) is carried out to measure the contribution of Area Specific Resistance at 40 ml/min which is 1.36 Ωcm2 for interdigitated flow-field. EIS results are further fitted using equivalent circuits to determine the contribution of each component.

As per the previous article [1], in the absence of flowfield, it was observed that increase in flowrate is feasible to increase the energy efficiency. But, current work highlighted the significance of using flowfields as an efficient way is to decrease the pressure drop to avoid continous increase in flowrate. This approach helps to reach higher current densities at much lower requirement of pumping flowrate.

Energy efficiency start decreasing significantly with increment in current density. Only voltaic efficiency is effected whereas columbic efficiency remain around 98% at all current densities. More research efforts are required to optimise the treatment of electrodes and also flowrate distribution to get higher efficiency at higher current density.

Reference:

[1] R. Monteiro, J. Leirós, M. Boaventura, and A. Mendes, "Insights into all-vanadium redox flow battery: A case study on components and operational conditions," Electrochimica Acta, vol. 267, pp. 80-93, 2018.

Figure 1
Novel Polymer Gel Electrolytes for Facile Fabrication of Efficient and Durable Electrochromic and Photoelectrochemical Devices
Authors: Lee Ji-Eun , Kang Bo-Sung , Kim So-Eun , Song Hyeon-Bee , Kim Do-Hyeong , Kang Moon-Sung
Published: February 2020

Polymer gel electrolytes (PGEs) have been widely investigated and utilized in various electrochemical applications such as lithium secondary batteries and dye-sensitized solar cells because they possess moderate ion conductivity and high physical stability. They have also been developed for the application to electrochromic devices (ECDs). Recently, ECDs have been attracting much attention owing to their use as a smart window. A smart window or a smart glass can effectively control the light transmission properties for the purpose of proper lighting or heating etc. The PGEs as one of the key components of the ECDs can dominate the major characteristics of transmittance and colored time etc. Especially, the ion conductivity and volatility of the PGEs should be optimized for the fabrication of efficient and durable ECDs. In addition, efficient injection process of highly viscous PGEs during the fabrication of large area ECDs should also be considered. In this work, therefore, we have developed the PGEs which can be easily loaded as a film and then in-situ polymerized through UV irradiation. The PGEs have also been applied to photoelectrochemical cells (i.e. dye-sensitized solar cells) for the efficient energy harvesting from solar irradiation.

Acknowledgments:

This work was supported by a grant (No.2017000140002/ RE201702218) from the Environmental Industry Advancement Technology Development Project of Korea Environmental Industry & Technology (KEITI) funded by Korea Ministry of Environment (MOE).