bluuebunny/crossref_metadata_2025 huggingface dataset:
High Capacitance Supercapacitors Based on Polypyrrole and Carbon Nitride Composites
Authors: Pereira Ernesto , Gonçalves Roger , Paiva Robert , Lima Thiago , Paixao Marcio
Published: February 2020

In this work, an one step green electrochemical synthesis of a supercapacitor with high performance and stability based on carbon nitride and polypyrrole is described. The new composite was easily obtained through the electrodeposition of polypyrrole on the surface of carbon nitride using an aqueous suspension. This material was fully characterized using both theoretical studies and experimental techniques. The sample showed a capacitance value of 810 F g-1 (at 0.2 A g-1), retaining 92% of its initial value after 6000 charge-discharge cycles. Furthermore, the composite material retains 75% of the capacitance compared to the data measured at 0.2 A g-1 ( 810 F g-1) and 9.0 A g-1 (610 F g-1). Finally, normalizing the capacitance considering only the polypyrrole mass it was found a capacitance value of 3029 F g-1. To explain these results, it was used impedance spectroscopy and DFT calculations. The computational experiments showed the formation of hydrogen bonds between the N-H of the polypyrrole and the π-system of the carbon nitride which stabilized the structures. Besides, a planarization effect could also be observed over the polypyrrole chains. Both results are supported by the experimental data collected from the impedance experiments.
Facile Synthesis of Carbon Supported Porous Metal Oxide Nanofibers for Prospective Supercapacitor Electrodes
Authors: Guo Hui , He Zizhou , LaCoste Jed , Ardoin Sydney , Cook Ryan , Fei Ling
Published: February 2020

Supercapacitors (SCs) have received great attention due to their rapid charging-discharging rate and long life cyclic stability. Transition metal oxides (TMOs) have been widely investigated as electrode materials for their theoretically higher specific capacitance. Here, a facile and effective synthesis route of metal oxide embedded in porous carbon nanofiber support has been developed. First, the corresponding metal salts were dissolved in a homogenous polyacrylonitrile (PAN) and cellulose diacetate (CDA) polymer solution. Fresh fibers were obtained by electrospinning the polymer solution. Then it was annealed at high temperature in N2 atmosphere to obtain the carbonized samples. During the thermal treating process, metal salts are converted to less oxidation states or even only metal, while PAN forms carbon backbone and CDA as the sacrificial polymer is burned to form pores. For samples with only metal formed, the hydrothermal treatment is subsequently performed for further oxidation. When tested for supercapacitors, the 3D connected porous nanofiber structure can provide transport channel for electrolyte during charging-discharging process. In detail, porous TMOs/carbon fibers including cheap and high performance TMOs, such as NiO, Co3O4, MnO2 and ZnO based materials, or even multiple metal TMOs will be systematically investigated. The effects of different annealing temperature on the compositions, porous structure and electrochemical performance will also be investigated. The preliminary results show that TMOs supported by the porous carbon fiber demonstrated greatly improved electrochemical performance, indicating that this facile synthesis method can be a promising alternative to prepare TMOs electrode materials with high performance.
(Invited) Benzothiadiazole-Based Dye Photosensitizers for Water Splitting Using Dye-Encapsulated Carbon Nanotubes
Authors: Takaguchi Yutaka , Miyake Hideaki , Sagawa Ryohei , Miyamoto Daiki , Tajima Tomoyuki
Published: February 2020

A donor-acceptor-donor (D-A-D) dye consisting of ferrocene units (donors) and a benzothiadiazole unit (acceptor) was synthesized to use the photosensitizer for hydrogen evolution reaction (HER) from water within semiconducting single-walled carbon nanotube (s-SWCNT). The dye was easily encapsulated into s-SWCNT by a solution method to form dye-encapsulated s-SWCNTs (dye@SWCNTs). Subsequently, physical modification of dye@SWCNTs by a fullerodendron gave dye@SWCNT/fullerodendron nanohybrids having dye/s-SWCNT/C60 coaxial heterojunction. Interestingly, dye@SWCNT/fullerodendron nanohybrids act as the photosensitizer for HER in the presence of sacrificial donor, electron relay, and co-catalyst due to the mobile carrier generation upon photoexcitation of the dye molecules.
The Feasibility of Energy Extraction from Acidic Wastewater By Capacitive Mixing with a Molecular-Sieving Carbon Cathode
Authors: Shapira Barak , Avraham Eran , Aurbach Doron
Published: February 2020

Capacitive mixing is a newly emerging technique for the production of renewable energy from differences in salinity. The method is based on the controlled mixing of two streams with different salt concentrations which are alternatingly brought into contact with pre-charged porous electrodes, taking advantage of the fact that modification of the electrical double layer of the electrodes results in changes in the solution salinity. In most research, the renewable energy resources are seawater and river water. Here, we demonstrate that energy extraction by capacitive mixing can take place with acidic wastewater and seawater as energy resources. This concept is proved by means of the fabrication of a proton-selective carbon cathode (the negatively polarized electrode), achieved by carbonation of cellulose filter paper, followed by mild activation in concentrated nitric acid. Considerable energy extraction was demonstrated even when the concentration of the saline solution was tenfold that of the acidic solution.

Figure 1
Single-Walled Carbon Nanotube-Clostridium Ljungdahlii hybrid for Carbon Dioxide Fixation to Value-Added Chemicals
Authors: Li Zhaodong , Svedruzic Drazenka , Xiong Wei , Tremolet de Villers Bertrand J. , Blackburn Jeffrey L.
Published: February 2020

Direct electricity-powdered production of value-added carbon organic compoundsfrom CO2 and H2O, a process that mimics natural Wood–Ljungdahl pathway (WLP), is of fundamental and practical interestfor renewable energy applications. The process depends on electrotrophy, the ability of some microorganisms to use electrons derived from an electrode as the sole energy source to reduce carbon dioxide. In this work, an acetogenic microorganism Clostridium ljungdahliiis immobilizedon carbon felt (CF) andhighly enriched semiconducting single-walled carbon nanotube (SWCNT) scaffolds under different conditions (physical soaking and growth under electrochemical bias). As a proof of principle, we demonstrate that this conductive carbon-bacteria system can utilize electrical current to fix CO2 under to multiple chemical targets, such as acetate and ethanol. The porous structure of the hybrid electrode provides the large surface area needed for high bacteria loading and excellent diffusion kinetics, while the s-SWCNTs appear to facilitate unique modes of bacterial adsorption and strong interfacial interactions. As such, the hybrid system enables low overpotential (η < 200 mV) and high Faradaic efficiency (> 90%). With the SWCNT modification and bacteria electrochemical growth, the hybrid electrode exhibited much higher performance on acetate production due to the enhanced bacteria-electrode interface quality for charge transfer. I will also discuss our efforts to understand the biochemicalpathways and possible underlying charge transfer mechanisms of CO2reduction of this SWCNT-Clostridium ljungdahliisystem. These results suggest a potential route for using SWCNTs to facilitate efficient microbial electrochemical biofilm formation and energy storage, furthering the potential applicability in bioelectrochemical systems.
(Invited) Non-Precious Metal Catalysts with Designed Carbon Nanostructures and Controlled Active Sites for Oxygen Reduction Reaction and CO2 Reduction
Authors: Lee Jinwoo
Published: February 2020

To replace scarce and expensive Pt-based oxygen reduction reaction (ORR) catalysts in acidic conditions, non-precious metal catalysts (NPMCs) based on third-row transition metals and N-doped carbon (M/N/C) have been intensively studied to date. Here, we present a novel versatile strategy to control and enhance the activity of the single Fe-N4 site by incorporating electron-withdrawing/donating functionalities on the carbon plane. These incorporated functionalities change the strength of the electronic effect, which is derived from the delocalized pi-band of carbon plane to the d-orbital of the Fe ion in Fe-N4 site; therefore, the adsorption strength of ORR intermediates at the Fe-N4 site was controlled by incorporated functionalities. Electrochemical CO2 reduction reaction (CO2RR) has attracted a lot of interest as a highly potential CO2 utilization system. Due to the high overpotential in CO2RR, the development of an effective catalyst is highly required for CO2 based long-term energy storage system. We present a metal-organic hybrid catalyst (Co-PPy-C), which consists of Co and polypyrrole, as a highly active electrocatalyst for CO2RR. Co-PPy-C exhibited high Faradaic efficiency and metal mass activity for CO production at low overpotential region.
Hybrid Graphene/Metal Oxygen Reduction Reaction Catalyst: An Insight at Sandwiched Single Layer Graphene Interdiffusion Barrier, Preserving Sharp Metallic Interface for Atomically-Thin Core@Shell Architectures
Authors: Abdelhafiz Ali , Vitale Adam , Alamgir Faisal M.
Published: February 2020

The concept of a core–shell metallic structures, with well defined atomically-thin “shell” material delineated from the “core” support with atomic-scale sharpness opens the door to a multitude of surface-driven materials properties that can be precisely controlled. However, in practice, such architectures are difficult to preserve due to the entropic cost of a segregated near-surface architecture, and the core and surface atoms inevitably mix through interdiffusion over time or under processing conditions (e.g. in Proton Exchange Membrane Fuel Cells (PEMFC)).

Herein, We present a systematic study of interdiffusion in a Au@Pt Core@Shell architectures and the role of an interrupting monolayer graphene sandwiched in between. The physical and chemical structure of the near-surface is probed via mean-free-path tuned X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy (HRTEM), and probing the oxygen reduction reaction (ORR) as an electrochemical performance indicator. We find that at operating temperatures above 100 °C, there is a potential for interdiffusion to occur between the shell and support metals, which can diminish the catalyst activity toward ORR. The introduction of a single-layer graphene, at the interface between the core and shell metals, acts as a barrier that prevents unwanted core leaching and/or surface-alloying between the layered metals. STEM imaging shows that fully wetted Pt monolayers can be grown on stand-alone single graphene template, allowing a high level of surface utilization of the catalyst material. We present how the use of graphene as an interdiffusion barrier mitigates the loss of surface catalytic sites, showing much improved retention of Pt monolayer surface at elevated temperatures.
Development of Bimetallic Non-Platinum Group Metal Catalysts Based on Metal Organic Framework Precursors
Authors: LaRochelle Richard Lynne , Jia Qingying , Mukerjee Sanjeev
Published: February 2020

It has been postulated that non-platinum group metal (non-PGM) catalysts for the oxygen reduction reaction (ORR) must meet four criteria: metal, carbon, nitrogen, and pyrolysis. The precise nature of the catalytic active site remains under debate. Many permutations of metal, nitrogen, and carbon are formed during pyrolysis, only a few of which are catalytically active. Results from multiple studies indicates that metals surrounded by four pyridinic nitrogen atoms form at least part of the active site. It stands to reason that the greater the number of metal-nitrogen-carbon (M-Nx-Cy) sites formed, the greater the active site density will be. However, nanoparticle formation is likely to compete at very high densities. Other groups have demonstrated enhanced catalytic activity in bimetallic catalysts for both ORR and hydrogen evolution reaction (HER) using first and second row non-PGM transition metals in M-N4-Cy centers. The present research focuses on the use of metal organic frameworks (MOFs), primarily zinc imidazolate frameworks (ZIFs), as precursors for bimetallic catalysts. ZIFs are of interest because they are highly porous, contain a high density of M-N4-Cy centers, and are simple to prepare. Metal choice in ZIF precursors (Zn or Co) affects the porosity and graphitization of the heat-treated material. Cobalt catalyzes the formation of carbon nanotubes upon pyrolysis. This research is an investigation of the effects of MOF precursor type, heat treatment, and non-PGM metal pairs (Fe, Co, Mn or Mo) on catalytic activity. It is hypothesized that carbon nanotubes and other graphitic structures formed during pyrolysis of Co-containing ZIFs facilitate the cooperation of proximal metal sites in electron transfer. This will be demonstrated by evaluation of bimetallic Co-containing catalysts in HER or ORR by varying the degree of graphitization while holding the weight percent ratio of Co and another metal (e.g. Fe) constant. Comparison of this data with catalysts prepared from precursors with optimal graphitization and varying the ratio of Co to the other metal will elucidate the relative importance of local carbon structure and electron transfer between two different metal centers.

This work was supported by the U.S. Department of Energy under award number DE-EE0008416. The authors declare no competing financial interests.
(Invited) Design and Application of Advanced Materials in Electrochemical Energy Storage Systems
Authors: Chen Zhongwei
Published: February 2020

Green, efficient energy storage and conversion systems are an important means of addressing global environmental and energy crisis. The current battery systems have been difficult to meet the increasing market demand due to their relatively low energy densities, therefore it is urgent to develop new energy storage technologies with high energy density and low cost. To this end, Professor Zhongwei Chen and his research group adhere to a bottom-up “material-electrode-battery-system” strategy to develop a variety of advanced energy storage technologies, including lithium-ion batteries, zinc-air batteries, fuel cells, for a wide range of energy storage applications. Through the rational material design and engineering, various high-performance electrodes with hierarchical micro- and nanostructures have been developed. Moreover, the electrode structures are controlled and optimized toward high recharge efficiency and energy density. Together, these innovate materials and electrode architectures practically allow industrial assembly and production of more efficient, affordable, and safer battery systems for clean and sustainable energy storage.
(Energy Technology Division Graduate Student Award Address sponsored by Bio-Logic) Biomass-Derived Carbon Materials for Next-Generation Electrochemical Energy Storage Systems
Authors: Gao Zan , Li Xiaodong
Published: February 2020

With rising energy concerns, efficient energy conversion and storage devices are urgently required to provide a sustainable, green energy supply. Electrochemical energy storage devices, such as supercapacitors and batteries, have been proven to be the most effective energy conversion and storage technologies for practical application. Currently, carbon materials hold the key for the development of high-performance electrochemical energy storage devices. However, the widely used carbon materials, such as graphite and activated carbon are often derived from non-renewable resources under relatively harsh environments, which hinders the sustainable development of electrochemical energy storage systems. In this context, biomass demonstrates many desired properties to derive renewable carbon materials for both electrochemical energy storage applications, because of its natural abundance and unlimited availability. Here, natural biomass, such as cotton textile, wheat flour, and corncobs, have been explored to produce renewable carbon materials via a low-cost and high throughput manufacturing process for energy storage systems design. Excitingly, the biomass-derived renewable activated carbon scaffolds not only demonstrated hierarchically porous structures but also excellent flexibility, making them ideal backbones for next-generation energy storage design. Specifically, activated cotton textile (ACT) with excellent flexibility and conductivity has been successfully derived from cotton textile for flexible energy storage systems design, such as flexible supercapacitors, flexible lithium-ion batteries, and flexible lithium-sulfur batteries. Besides flexible ACT, carbon nanotubes (CNTs) have also successfully derived from the natural yeast-fermented wheat dough without using any extra-catalysts or additional carbon sources. Yeast-derived carbon nanotubes from the fermented wheat dough not only provide an ideal sulfur host for lithium-sulfur batteries with a record lifespan of 1500 cycles but also expand our current understanding of the synthesis of carbon nanotubes. Biowastes-corncob, have also been explored to derive onion-like carbon materials for energy storage application. These research activities not only brought new insights on the deriving renewable carbon materials from natural abundant biomass resources but also boosted the design and fabrication of next-generation flexible energy-storage devices, which hold great promise for future wearable/flexible electronics.
(Invited) Carbon Nanostructures for Energy Storage
Authors: Harutyunyan Avetik R
Published: February 2020

Nanomaterials are anticipated to be promising storage media owing to their high surface-to-mass ratio. Therefore, wide variety of natural and synthetic carbon nanoallotropes are of central of importance for energy storage applications, particularly in Li-ion batteries. Accordingly, for last two decades number of experimental studies have been reported on the synthesis of carbonaceous electrode materials for battery with Li storage capacity larger than theoretical limit for graphite (LiC6). However, the origin of excess capacity and feasibility of battery performance remain controversial. Therefore, it is not clear whether these new structures could have a higher capacity than graphite. Our experimental and theoretical studies of wide range of various type of carbon allotropes for Li-ion battery electrodes help to clarify the fundamentals of Li storage in carbon nanostructures and shed light on the rational design of nanoarchitectures for energy storage.
(Invited) Directional Flow-Aided Sonochemistry Yields Graphene with Tunable Defects to Provide Fundamental Insight on Sodium Metal Plating Behavior
Authors: Mitlin David
Published: February 2020

This is the first report of a novel directional flow-aided sonochemistry (FAS) exfoliation method to synthesize graphene with nearly ideal structure. The FAS treatment allows for control of graphene structural order and chemical uniformity not possible through prior top-down wet methods. Graphite is exfoliated into single-nm scale thickness graphene that is nearly defect free (at-edge sonication graphene "AES-G") or is highly defective (in-plane sonication graphene "IPS-G"). The AES-G has a Raman G/D band intensity ratio of 14.3 and an XPS derived oxygen content of 1.3 at.%, while the IPS-G has IG/D of 1.6 and oxygen content of 6.2 at.%. Graphene and related carbons are widely employed as templates and protection layers to improve metal plating behavior in sodium and lithium metal battery (SMBs, LMBs) anodes. We then use AES-G and IPS-G to examine the role of structure and chemistry of graphene supports in promoting efficient Na metal cycling. The graphene serves a dual role in stabilizing the Na metal anode, being a nucleation template and serving as a protective layer to keep the metal from severely reacting with the electrolyte. We are the first to demonstrate that graphene defects are actually quite deleterious for efficient Na plating and stripping. AES-G yields state-of-the-art Na performance, with stable cycling at 2 mA/cm2 at 100% Coulombic efficiency (CE), and an areal capacity of 1 mAh/cm2. Meanwhile IPS-G performs on-par with the baseline Cu support in terms of severe charging instability. The explanation is that the defective graphene demonstrates much more copious SEI formation due to its defects and oxygen groups being catalytic. A thicker SEI results in a larger overpotential and worse CE loss during subsequent Na plating/stripping, manifesting in severe mossy metal dendrite growth and periodic electrical shorts. We therefore propose the following design rule for next-generation supports for Na metal: An ideal architecture will not only possess a large surface area for copious preferred heterogenous nucleation, but itself will be non-catalytic for SEI formation.
Bipolar Electrochemically Exfoliated Graphene for Supercapacitor Application
Authors: Khakpour Iman , Rabiei Baboukani Amin , Allagui Anis , Wang Chunlei
Published: February 2020

Developing a simple, cost-efficient, and scalable process for the production of graphene attracted a considerable interest, since, the production of graphene-based devices still suffers from various challenges. At one hand, the graphene products are not optimal for practical applications because they contain a large distribution of size and numbers of layers. At another hand, the common processes for production and integration of graphene not only suffers from being costly, time-consuming, and complicated but also the quality, performance and surface condition of produced material are hard to control.

In this study, we used the bipolar concept to design a single step, eco-friendly, cost-efficient, and simple process to simultaneously fabricate and in-situ deposit high-quality graphene-based layers directly on conductive substrates. Formation of graphene oxide and reduced graphene oxide on the substrates are confirmed by different materials characterization methods. The symmetrical 2 electrode systems were assembled and electrochemical performance of produced electrodes was investigated using electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge tests. The excellent performance of the supercapacitor electrode was confirmed and promising results for AC/DC filter application were obtained. The results will be presented in detail at the conference.

Key words: bipolar electrochemistry, graphene, supercapacitor, energy storage, AC filter
High Performance Supercapacitor Electrode Material from PAN/6FDA-Daba Polymer Blends
Authors: Ferraris John P. , Balkus Kenneth J. , Panangala Samitha Dilhani
Published: February 2020

Immiscible polymer blends yield carbon materials with fine and controlled pore architectures for supercapacitor applications. Aromatic polyimides derived from 4,4’-hexafluoroisopropylidine diphthalic anhydride (6FDA) have attracted attention as high performance polymers due to their high free volume and thermal stability. In this study, 6FDA and DABA (3,5-diamino benzoic acid) were used as monomers to synthesize 6FDA-DABA polymer. The synthesized polymer was blended with polyacrylonitrile to prepare a series of immiscible polymer blend compositions which were electrospun, subsequently carbonized and tested for electrochemical performance. Both polymers afford carbons upon thermal treatment up to 1000 °C under an inert environment. 6FDA-DABA has a carboxylic moiety which acts as an in-situ porogen upon decarboxylation, creating pores in electrospun fibers which are accessible to electrolyte ions. Preliminary studies show promising results upon only carbonization as an electrode material for supercapacitors. Results obtained from further activation by CO2 at 1000 °C were: specific capacitance of 137 F/g, with an energy density 66 Wh/kg, and a power density of 1.7 kW/kg with an excellent capacitance retention of 99% after 1500 cycles.
Xeno Nucleic Acid Nanosensors for Enhanced Stability
Authors: Gillen Alice Judith , Kupis-Rozmyslowicz Justyna , Gigli Carlo , Schuergers Nils , Boghossian Ardemis Anoush
Published: February 2020

The omnipresence of salts in biofluids creates a pervasive challenge in designing sensors suitable for in vivo applications. Fluctuations in ion concentrations have been shown to affect the sensitivity and selectivity of optical sensors based on single-walled carbon nanotubes wrapped with single-stranded DNA (ssDNA-SWCNTs). We herein observe fluorescence wavelength shifting for ssDNA-SWCNT-based optical sensors in the presence of divalent cations at concentrations above 3.5 mM. In contrast, no shifting was observed for concentrations up to 350 mM for sensors bioengineered with increased rigidity using xeno nucleic acids (XNAs). Transient fluorescence measurements reveal distinct optical transitions for ssDNA- and XNA-based wrappings during ion-induced conformation changes, with XNA-based sensors showing increased permanence in conformational and signal stability. This demonstration introduces synthetic biology as a complementary means for enhancing nanotube optoelectronic behaviour, unlocking previously unexplored possibilities for developing nano-bioengineered sensors with augmented capabilities.
(Invited) Novel Three-Dimensional Fuzzy Graphene (3DFG)-Based Platform for Interrogation of Excitable Cells
Authors: Rastogi Sahil Kumar , Scopelliti Matteo , Bliley Jacqueline , Johnson Nicholas , Shiwarski Daniel , Garg Raghav , Feinberg Adam , Chamanzar Maysam , Cohen-Karni Tzahi
Published: February 2020

Investigating and modulating electrical activity of cardiomyocytes and neurons is essential to understanding their physiology, regeneration of excitable cells/tissues, and treatment of various disorders. Recently, microelectrode arrays (MEAs) have gained tremendous popularity since they enable multi-site recordings at sub-msec temporal resolution, provide two-way interaction with cells i.e. recording and stimulation, and have well-established microfabrication methods. However, currently used planar MEAs are not able to record and stimulate at sub-cellular resolution due to significant increase in electrode impedance which reduces the signal-to-noise ratio (SNR) of recorded signal. Currently there is a need to (i) enable high density electrode arrays, (ii) provide high spatial resolution, and (iii) prevent averaging of signals from multiple cells.

To address these needs, we have developed three-dimensional out-of-plane grown fuzzy graphene (3DFG)-based MEA. Out-of-plane growth of single-to-few layers of graphene flakes leverages graphene's outstanding surface-to-volume ratio. The high surface area leads to significant reduction in impedance, thus enabling electrical recordings with high SNR and development of ultra-microelectrode arrays to perform sub-cellular measurements. Furthermore, the high flake density of graphene in 3DFG lead to high photo-absorbance in UV-NIR range. This opens up avenues to enable photo-thermal stimulation of cells with high precision and sub-cellular resolution. Our presented approach would greatly impact our basic understanding of signal transduction in complex cellular assemblies. Furthermore, it would provide a platform for developing and screening of therapeutics, and treatment of various cardiac and neurological diseases.
(Invited) DNA Library Evolution of Carbon Nanotube Molecular Recognition
Authors: Landry Markita P , Jeong Sanghwa
Published: February 2020

Molecular recognition is fundamental to the design of therapeutics, diagnostics, and sensors. Many of these technologies rely on natural molecular recognition elements such as antibodies, which have evolved to be highly selective for their molecular targets. However, despite their exquisite selectivity, antibody-based molecular recognition suffers from limited stability outside narrow ranges of temperature, pH, and salt concentration, and have limited ex-vivo stability. Conversely, synthetic molecular recognition has enabled detection of molecular targets over a broad range of extraphysiological conditions but with varying success in selective and sensitive detection of target analytes. Recent developments in synthetic molecular recognition include synthetic antibodies based on electrostatic pinning of bio-mimetic polymers to the surface of single-walled carbon nanotubes (SWNT), whereby the polymer serves as the molecular recognition element, and the SWNT provides a near-infrared fluorescent signal in response to analyte binding. In this and other embodiments of nanosensor platforms, the principal challenge lies in the process of identifying synthetically-produced selective and sensitive molecular recognition elements. Herein, we describe a polymer evolution-based platform, in which 10^12 unique SWNT-pinned polynucleotide polymers can be screened for their ability to bind a target analyte and provide a selective near-infrared fluorescence signal. Iterative selection of analyte-binding polymers that form a SWNT-surface-adsorbed phase for target recognition are identified through ionic desorption of sub-optimal polymers, and exponential amplification of synthetic polymers that recognize the target analyte. Next-generation sequencing identifies SWNT-polynucleotide conjugates selective and sensitive for the desired analyte. We demonstrate the utility of this platform for the evolution of a SWNT-polymer conjugate for neuromodulator serotonin, which we show to be reversible, to have a detection limit of 100 nM, and to have a dynamic range appropriate for in vivo imaging of serotonergic neuromodulation. Our platform is fundamentally generic in enabling the evolution of molecular nanosensors from synthetic polymer-nanoparticle conjugates for any desired analyte.
(Invited) Near-Infrared Fluorescence Modulation of Refolded DNA Aptamer-Functionalized Single-Walled Carbon Nanotubes for Optical Sensing
Authors: Lee Kwan , Nojoomi Amirali , Jeon Junha , Lee Chang Young , Yum Kyungsuk
Published: February 2020

Selective modulation of near-infrared (NIR) fluorescence of single-walled carbon nanotubes (SWNTs) is important for their applications as NIR optical sensors and devices. Here we present the target molecule-mediated NIR fluorescence modulation of refolded DNA aptamer-functionalized SWNTs, using platelet-derived growth factor (PDGF) and a PDGF-binding aptamer as a model system. The aptamer–SWNT complexes use SWNT as nanoscale NIR optical emitters and DNA aptamers as molecular recognition elements. The binding of target molecules, PDGFs in this study, to PDGF-binding aptamers on the surface of SWNTs induces a conformation change of the aptamers, which modulates the NIR fluorescence of SWNT emitters. This study suggests that PDGF-binding aptamers noncovalently assembled on the SWNT surface can undergo a temperature and divalent ion-induced conformational change into a folded structure through multiple stages, which renders aptamer-functionalized SWNTs optically responsive to target molecules. In addition, our experimental and theoretical results show that the aptamers have a nanotube diameter-dependent affinity for SWNTs. We demonstrate that refolded aptamer-functionalized SWNTs reversibly modulate their NIR fluorescence in response to PDGF at the nanomolar range of 0.1 to 10 nM with apparent dissociation constants of ~0.71 nM (solution-phase complexes) and ~3.1 nM (complexes in hydrogels). This study could open new opportunities to design label-free, reversible NIR optical sensors that can detect various target molecules.
(Invited) Tuning Transport and Emission Properties of Sorted Carbon Nanotube Networks
Authors: Zaumseil Jana
Published: February 2020

With the availability of purely semiconducting and even monochiral dispersions of single-walled carbon nanotubes in large amounts, the tailored engineering of network properties in optoelectronic devices becomes an intriguing possibility. Charge transport and light emission can be tuned by and investigated at variable temperatures, with different network compositions, in different dielectric environments and dopant concentrations, with light-switchable dipoles, via introduction of sp3-defects and by using responsive wrapping polymers. A few of these examples will be presented and discussed in terms of gained insights into the network properties of sorted carbon nanotubes and their practical applications.
Modeling of the Thermal Behaviors of an Ultracapacitor and Comparison with Measurement Data
Authors: Koo Boram , Shin Chee Burm , Lee Ha-Young , Choi Jongrak
Published: February 2020

Ultracapacitors (UCs), known by different names such as supercapacitors, electrochemical double-layer capacitors, double-layer capacitors or electrochemical capacitors, have the potential to meet the high pulse power capability of the energy-storage systems for automotive applications. The primary advantages of UCs are higher power density and longer shelf and cycle life as compared to those of batteries. In the high pulse power operations for automotive applications, a large amount of heat is produced inside a UC cell. Because the lifetime and performance of a UC depend strongly on temperature, it is important to predict accurately the thermal behaviors of a UC for the efficient and reliable systems integration from an application perspective.

In this work, a three-dimensional thermal model is presented to predict the thermal behaviors of the UC. Both of the irreversible and reversible heat generations inside the UC cell are considered. The effective density and specific heat capacity of the various compartments of the cell are estimated based on the mass fractions of the components of each cell compartment. The effective thermal conductivities of the various compartments of the cell are estimated based on the equivalent networks of parallel and series thermal resistances of the cell components. The validation of the three-dimensional thermal model is provided through the comparison of the modeling results with the experimental IR image at various charge/discharge currents.
Transition Metals Ion Behavior of Cathode Materials for Li Ion Battery By Electron Beam Irradiation in Scanning Transmission Electron Microscopy
Authors: Shim Jae-Hyun , Kim Young-Min
Published: February 2020

Investigating the structural properties of Li-ion batteries (LIBs) and, if possible, determining the overall structure is important in understanding the physical and chemical properties. Understanding the structural properties and the electrochemical properties of the arranged atoms of cathode materials is therefore essential for new battery material design and system optimization. Particularly, cathode materials such as LiNixMnyCo1-x-yO2 (NMC), lithium-rich Li(LiyNix-yMnxCo1-2x)O2, lithium-rich / manganese-rich xLi2MnO3 (1-x)LiMO2 are analyzed by the scanning transmission electron microscopy (STEM) techniques to identify structural characteristics, leading to the conversion of the layer structure to the spinel and/or salt structure, leading to increased impedance, voltage reduction and capacity of the LIBs.

The atomic behavior of Li ion in the cathode materials that determines LiBs performance is hardly characterized by transmission electron microscopy (TEM) owing to its weak electron-scattering power. In this sense, annular bright-field (ABF) STEM, in which the contrast has a low scaling rate with the atomic number, has been proven to be a robust technique for simultaneous imaging of light and heavy elements. However, it is very important to understand the damage mechanism of cathode materials by electron-beam irradiation in STEM and to develop this technique. In this study, we investigated the effect of electron-beam irradiation damage on the surface reaction layer and LiNi0.6Co0.2Mn0.2O2 material during STEM data acquisition. This electron-beam irradiation damage process is similar to the lattice reconstruction and chemical evolution caused by the charge-discharge cycle. Furthermore, based on the phase transition phenomenon by the electron-beam irradiation, it is examined whether the electron beam irradiation damage in the lattice structure substituted by Al and Ti affects the phase transition phenomenon.
Stress-Controlled Three-Dimensional Phase Evolution in Lithium Iron Phosphate
Authors: Yang Kaiqi , Tang Ming
Published: February 2020

Many battery compounds undergo first-order phase transformations induced by ion (de)intercalation during battery operation, and their rate capability is often controlled by the kinetics of two-phase boundary movement. LiFePO4, a commercial cathode materials for Li-ion batteries, is a model system for studying the unique aspects of phase transitions in battery intercalation compounds. In a recent in-situ scanning transmission X-ray microscopy (STXM) study [Ohmer et al. Nature Communication 6, 6045 (2015)], Li deintercalation and phase evolution in microsized LiFePO4 single crystal upon delithiation are found to be highly non-uniform. FePO4 phase was observed to form [010]-aligned filaments growing into the LiFePO4 crystal, which is postulated to be dominated by elastic effects. In this work, we performed three-dimensional phase-field simulation to examine in the details phase evolution in LiFePO4 and the effect of misfit strain energy arising from the lattice match between FePO4 and LiFePO4. Our simulation reproduces the filamentary growth morphology of FePO4 phase (Figure 1) as observed in experiment, and confirms the dominating role of misfit stress in causing such behavior. We show that phase evolution in LiFePO4 goes through two steps during delithiation. In the first step, phase separation occurs in LiFePO4 via surface-mode coherent spinodal decomposition and results in the formation of individual FePO4 domains on particle surface. Next, FePO4 grows into the LiFePO4 matrix as wedge shaped domains that coarsen at the same time. The filamentary morphology of FP phase within (001) plane is mainly a result of the anisotropic misfit strain between LiFePO4 and FePO4, which favors the elongation of FP domains along the [010] axis to reduce elastic strain energy. Simulation reveals that Li diffusion anisotropy also significantly influences the phase growth morphology. The existence of three-dimensional Li diffusion in LiFePO4, which results from the presence of antisite defects, is found to be essential for the development of filamentary FePO4. The excellent agreement between the phase-field simulation and in-situ STXM experiment suggests that misfit stress plays an important role in triggering non-uniform Li (de)intercalation especially in large electrode particles, which is detrimental to battery performance and life and deserves close attention.

Figure 1
Structural Characterization of Anodic Porous Alumina Formed By Galvanostatic Anodizing in Etidronic Acid
Authors: Iwai Mana , Kikuchi Tatsuya , Suzuki Ryosuke O. , Natsui Shungo
Published: February 2020

Anodizing aluminum in etidronic acid (1-hydroxyethane-1,1-diphosphonic acid) causes the formation of porous alumina at higher voltage more than 200 V. Highly ordered porous alumina with a large-scale cell can be easily fabricated via two-step constant voltage anodizing in etidronic acid. However, extremely little has been reported on the growth behavior during galvanostatic anodizing in etidronic acid and its structural characterization. In the present investigation, we demonstrate the details of the anodizing behaviors and nanostructures of the porous alumina formed via galvanostatic anodizing in etidronic acid under various operating conditions.

High-purity aluminum plates were electrochemically polished, and then were anodized at a constant current density of 0.005-500 Am-2 in 0.03-3 M etidronic acid solutions (273-333 K). After anodizing, the specimens were immersed in a 0.20 M CrO3/0.51 M H3PO4 solution (353 K) to dissolve the porous alumina, and the aluminum dimple array was exposed to the surface. The surface and cross-section of the anodized specimens were examined by field-emission scanning electron microscopy (FE-SEM). The cell size (interpore distance) of the porous alumina was calculated using image analysis software.

As the electropolished aluminum specimens were anodized galvanostatically under various conditions, the voltage linearly increased, gradually decreased, and then reached plateau value (U
p). However, excess current density led to a burning phenomenon and the formation of non-uniform porous alumina. Figure 1 shows the changes in the plateau voltage, U
p, and the current density, i
a, during anodizing in a 0.3 M etidronic acid solution. The plateau voltage greatly increased with the current density at each temperature, and various porous alumina films were successfully fabricated by anodizing at a wide voltage range measuring 7-218 V. Figure 2 shows the relationship between the cell size, D
c and the anodizing voltage, U
a. The cell size linearly increased with the anodizing voltage at each solution temperature and current density. A linear proportional constant of 2.5 nmV-1 was obtained, which is similar to the self-ordering condition via constant voltage anodizing.

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Alkaline Corrosion-Resistant Anodic Aluminum Oxide Formed By Etidronic Acid Anodizing
Authors: Suzuki Yusuke , Kawahara Kai , Kikuchi Tatsuya , Suzuki Ryosuke O. , Natsui Shungo
Published: February 2020

A newly discovered electrolyte for anodizing aluminum, etidronic acid (CH3C(OH)[PO(OH)2]2), operates at high voltages of more than 200 V, and ordered porous alumina measuring 400-670 nm in cell diameter (interpore distance) can be fabricated via constant voltage anodizing. Because such porous alumina film formed at high voltages possesses a thick barrier layer, etidronic acid anodizing may be useful for corrosion protection of aluminum. Here, we describe the alkaline corrosion-resistant porous alumina formed by high voltage anodizing in an etidronic acid solution, and its hydration behavior in boiling water was investigated.

Highly pure aluminum plates (99.999 wt%) were anodized in 0.3 M sulfuric acid, 0.3 M oxalic acid, 0.3 M citric acid, and 0.3 M etidronic acid solutions (293 K) at a constant current density of 30 Am-2 or a constant voltage of 250 V. The anodized specimens were immersed in a 2.5 M NaOH solution (293 K). The nanostructural changes were examined by electrochemical impedance spectroscopy (EIS). The anodized specimens were immersed in boiling water to seal the pores in the porous alumina film. The surface and cross-section of the specimens were characterized by field-emission scanning electron microscopy (FE-SEM)

The plateau voltages during anodizing aluminum at a constant current density of 30 Am-2 in sulfuric and etidronic acid solutions exhibited approximately 16 V and 197 V, respectively. As the specimen anodized in sulfuric acid was immersed in a 2.5 M sodium hydroxide solution, H2 gas evolution was observed from the surface at the beginning of immersion, and the amount increased with the immersion time. In contrast, the specimen anodized in etidronic acid did not result in hydrogen gas evolution during immersion until 8 min. Here, the capacitance (Cb
) is inversely proportional to the thickness of the barrier layer. Figure 1 shows the changes in the reciprocal Cb
with the immersion time, ti
. Complete dissolution of porous alumina formed in etidronic acid takes 15 times longer than dissolution of the alumina formed by sulfuric acid anodizing due to the formation of a thick barrier layer.

As the porous alumina formed by etidronic acid anodizing is immersed in boiling water, plate-like hydroxides were formed at the bottom of the pores in the initial immersion stage. The thickness of the hydroxide layer increased with the immersion time, and the nanopores are completely sealed by long-term immersion.

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(Invited) Stoner Ferromagnetism in Two-Dimensional Materials
Authors: Houssa Michel , Meng Ruishen , Iordanidou Konstantina , Pourtois Geoffrey , Afanas'ev Valery V. , Stesmans Andre
Published: February 2020

Two dimensional (2D) materials are currently attracting considerable interest due to their promising applications in future nanoelectronic devices. Ferromagnetic 2D materials are also gaining attention, for their possible use in novel spintronic devices [1]. Hole-doping in monolayers of GaX, InX (X=S or Se) and SnO has been recently predicted to induce a paramagnetic to ferromagnetic phase transition in these 2D materials, for typical hole densities in the range of 1013-1014/cm2 [2-6]. Ferromagnetism in these materials arises from an exchange splitting of electronic states at the top of the valence band, where the density of states exhibits a sharp van Hove singularity, resulting in a so-called Stoner (magnetic) instability; this behavior is typical of materials with “Mexican-hat” energy band edges, as predicted in GaX, InX and SnO monolayers.

In this talk, the results from first-principles simulations of the hole-doping induced Stoner ferromagnetism in various 2D materials will be discussed. The possibility to dope these materials with holes, either by intrinsic or extrinsic defects, will be considered. The possible Stoner ferromagnetism in other 2D metal oxides will also be highlighted.

[1] W. Han, APL Mater. 4, 032401 (2016).

[2] T. Cao et al., Phys. Rev. Lett. 114, 236602 (2015).

[3] L. Seixas et al., Phys. Rev. Lett. 116, 206803 (2016).

[4] M. Houssa et al., ECS Trans. 80, 339 (2017).

[5] M. Houssa et al., AIP Adv. 8, 055010 (2018).

[6] K. Iordanidou et al., ACS Appl. Nano Mater. 1, 6656 (2018).
Design Principles of Dielectric Layers for High Density Flash Memories
Authors: Baik Seung Jae
Published: February 2020

High density flash memory is based on layered dielectric including charge trapping layers [1]. Device scaling can be facilitated by decreasing equivalent electrical thickness of the layered dielectric, which also induces degradation of charge retention. Moreover, the thickness combination of each dielectrics need to be optimized to give minimum charge loss at zero applied voltage (power-off condition). The optimal thickness combination can be experimentally found by characterizing bias dependent charge loss, at which combination, thickness scaling limitation for a given layered dielectric can be established. By applying higher dielectric constant materials, the equivalent electrical thickness of the layered dielectric can be reduced; where additional materials engineering is necessary. In this work, we have applied various compositional alloys of HfO2 and AlO2, and their spatial grading. As a result, it is shown that high post-deposition process temperature critically induces charge retention degradation, and the physical reasoning of compositional and spatial grading optimization is obtained for minimum charge losses. In addition, optimal thickness combination for minimum charge loss at zero bias is formulated supported by experimental evidence. Moreover, high energy edge of trap states are extracted from charge loss characteristics, which are compared for various dielectric materials and bias conditions.

Keywords: dielectric; charge trap; flash memory.

Acknowledgements

This work was supported by NRF grant (NRF-2017R1D1A1B03029764) funded by Korean Government.

Reference

S. Choi, S. J. Baik, J.-T. Moon, Technical Digest of International Electron Device Meeting 2008, 2008, 925-928.

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