bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-Performance Supercapacitors of N-Doped Graphene Aerogel and Its Nanocomposites
Authors: Sawangphruk Montree 
Published: February 2020

Nitrogen-doped reduced graphene oxide aerogel (N-rGO aerogel) with high porosity and ionic conductivity were synthesized by a hydrothermal reduction of graphene oxide with hydrazine and following freezing-dry method. N-rGO aerogel was spray-coated on carboxyl-modified carbon fiber paper with a hydrophilic surface and used as the supercapacitor electrode. Not only can the N-rGO aerogel electrode accelerate the diffusion of the electrolyte but also it can store electronic charge via a surface redox reaction due to the N-containing groups. Among the electrolytes studied, the ionic liquid-based supercapacitor of the N-rGO aerogel provides a wide working potential of ca. 4.0 V and rather high specific capacitance of 765 F/g at 1 A/g with a capacity retention of 86% over 3000 charge–discharge cycles. The device prototype fabricated in a single coin cell shape (CR2016) can supply electricity to red LED over 17 min. In addition, high-performance supercapacitors of N-rGO aerogel composites with other materials will be discussed in my presentation.
General Synthetic Method for N-Doped Macroporous Graphene-Encapsulated Mesoporous Metal Oxides and Its Application As New Anode Materials for Sodium-Ion Hybrid Supercapacitors
Authors: Kim Min Su , Lim Eunho , Lee Jinwoo 
Published: February 2020

Employing graphene as an electrode material is advantageous for energy storage devices because it is flexible, highly electrically conductive, chemically stable, and has large theoretical surface area. However, graphene generally suffers from serious agglomeration and re-stacking due to its strong pi-pi stacking and van der Waals interactions between graphene nanosheets during charge-discharge process. To fully use the potential merits of graphene and improve the kinetics of electrode materials in energy storage devices, composites of graphene and metal oxides have been tested as electrode. Metal oxides in the composites, prevent the re-stacking of graphene. Graphene layers in the composites also suppress the volume change and agglomeration of metal oxide and provide a highly conductive matrix for metal oxide. We report a general method to synthesize mesoporous metal oxide@N-doped macroporous graphene composite by heat-treatment of electrostatically co-assembled amine-functionalized mesoporous silica/metal oxide composite and graphene oxide, and subsequent silica removal to produce mesoporous metal oxide and N-doped macroporous graphene simultaneously. Four mesoporous metal oxides (WO3-x, Co3O4, Mn2O3 and Fe3O4) were encapsulated in N-doped macroporous graphene. Used as an anode material for sodium-ion hybrid supercapacitors (Na-HSCs), mesoporous reduced tungsten oxide@N-doped macroporous graphene (m-WO3-x@NM-rGO) gives outstanding rate capability and stable cycle life. Ex situ analyses suggest that the electrochemical reaction mechanism of m-WO3-x@NM-rGO is based on Na+ intercalation/de-intercalation. To the best of our knowledge, this is the first report on Na+ intercalation/de-intercalation properties of WO3-x and its application to Na-HSCs.
Simultaneous Electrochemical Exfoliation and Functionalization of Graphene By Diazonium Compounds
Authors: Aynalem Andinet Ejigu , Dryfe Robert AW , Kinloch Ian A 
Published: February 2020

Covalent functionalisation of graphene is considered as one method for enhancing the processability of graphene for various applications. The majority of the study to-date has focused on the functionalization of pre-made graphene.1-3 In this contribution, we describe single stage simultaneous electrochemical exfoliation and functionalisation of graphene using diazonium compounds. Caesium salt (dissolved in dimethyl sulfoxide) as intercalating ions in combination with diazonium salt (either 4-nitrobenzenediazoniumtetrafluoroborate, 4-bromobenzenediazonium tetrafluoroborate or anthraquinone-1-diazonium chloride) as functionalisation moieties were used. Simultaneous exfoliation and functionalisation is beneficial for a number of reasons. First, the presence of diazonium salt in the exfoliation solution not only plays a role in functionalisation but also facilitate the exfoliation process through the generation of N2 gas which assists the separation of the functionalised graphene layers. Second, this process is selective for edge functionalisation and finally as both functionalisation and exfoliation occurs at the same time, monolayer or few layer graphene can be functionalised in situ before they aggregate. Significantly, functionalisation enhanced the dispersibility of graphene in aqueous solution and its solubility was two orders of magnitude larger than the non-functionalised electrochemically exfoliated graphene. As also shown in Figure 1, the functionalisation introduced surface active redox reactions when used as a supercapacitor electrode. The redox reactions enhanced the charge storage capacity of graphene and the specific capacitance found to be highly dependent on the degree of graphene functionalization.
1. J. R. Lomeda, C. D. Doyle, D. V. Kosynkin, W.-F. Hwang and J. M. Tour, J. Am. Chem. Soc., 2008, 130, 16201-16206.
2. E. Bekyarova, M. E. Itkis, P. Ramesh, C. Berger, M. Sprinkle, W. A. de Heer and R. C. Haddon, J. Am. Chem. Soc., 2009, 131, 1336-+.
3. J. Greenwood, T. H. Phan, Y. Fujita, Z. Li, O. Lvasenko, W. Vanderlinden, H. Van Gorp, W. Frederickx, G. Lu, K. Tahara, Y. Tobe, H. Uji-i, S. F. L. Mertens and S. De Feyter, ACS Nano, 2015, 9, 5520-5535.

Figure 1. Cyclic voltammograms recorded at 100 mV s-1 in 6.0 M KOH (aq) using symmetrical coin cells constructed from electrochemical exfoliated restacked graphene and graphene functionalised insitu with 4-nitrobenzenediazoniumtetrafluoroborate (G-NBD). The voltage was swept between 0.0 V to 1.0 V

Figure 1
A New Form of Electrochemical Kinetics, at the Single Layer Graphene – Electrolyte Interface
Authors: Bandaru Prabhakar R , Narayanan Rajaram , Yamada Hidenori , Lipomi Darren , Marin Brandon 
Published: February 2020

The “all-surface” characteristic of single–layer graphene (SLG) offers a remarkable paradigm for the exploration of novel physical and chemical phenomena. However, in many cases it is unclear as to how a graphene surface manifests clearly different chemical characteristics compared to any other surface. In this work, we report on a characteristic, experimentally demonstrated, that is unique to the two-dimensional nature of SLG in terms of a completely new type of electrokinetics in stark contrast to the accepted Marcus-Hush-Chidsey (MHC) formalism.
We will indicate that the specific consideration of the unusual linear variation of the two-dimensional density of states (DOS) in SLG, would cause a deviation from both Arrhenius activation relation based Butler-Volmer kinetics as well as the MHC kinetics, which assumes a constant DOS. Consequently, we propose a new lower-dimensional DOS based reaction rate constant and experimentally show that aspects related to a non-ideal DOS were explained through electron and hole puddles formed in wrinkled graphene.
Our experiments and related fitting of the data considerably supplements the presently used standard models to analyze the variation of the reaction rate constants and has significant implications wherever nanoscale electrodes are utilized in energy storage and transduction.
Quantum Chemical Predictions for Alkaline Earth (AE)-Doped Graphene: A Density Functional Theory (DFT) Based Investigation for a Novel Class of Carbon-Based Two-Dimensional Nanomaterials Toward Electrochemical, Catalytic and Electronic Applications
Authors: Serraon Ace Christian Feraren , Padama Allan Abraham Bustria , del Rosario Julie Anne Dalmacio , Cervera Rinlee Butch , Ocon Joey Duran 
Published: February 2020

Graphene doping is a known route towards increasing the reactivity of graphene, particularly for the oxygen reduction reaction in fuel cells and metal-air batteries. The most prominent dopants in graphene for ORR are non-metals near to carbon in the periodic table. While alkaline-earth elements, such as beryllium, magnesium, calcium, strontium and barium are relatively abundant in the Earth’s crust, graphenes modified with these elements have not been fully explored.
Graphene systems, which were substitutionally doped with alkaline-earth elements, were investigated through density functional theory (DFT) calculations to elucidate its energetics and electronic properties. A localized ionic bonding between alkaline-earth elements and the graphene substrate was observed, with greater charge transfer as inferred by Bader analysis for Be and Mg. The localized nature of the charge transfer from the dopant to the adjoining carbon atoms in the substrate is a novel property of AE-doped graphene. Semi-metallic properties due to strongly localized states near the Fermi level have been observed for all AE-doped graphenes except for Be. For Be, p-type semiconductor properties were observed consistent with previous studies on Be doped graphene.
This will provide the groundwork for further study towards the use of alkaline-earth metal dopants in an alternative precious-metal free cathode material for metal-air battery and fuel cell applications. The basic and exploratory nature of this scientific study is also expected to open a path towards other emergent applications for the catalysis of other reactions, as well as in electronics and other domains. Observable trends between different alkaline-earth doped graphenes have also been investigated.

Figure 1
(Invited) Strongly-Bound Interlayer Exciton States in Twisted Bilayer Materials
Authors: Graham Matt W 
Published: February 2020

When two sheets of a 2D material such as graphene are stacked at a twisted angle, the 2p orbitals rehybridize, giving angle-tunable absorption resonances. By comparing the ultrafast intra-band and multi-photon transient absorption spectra, our results agree best with a recent theoretical model that predict that overlapping interlayer 2p orbitals interfere to produce symmetrized bound exciton states that are decoupled from lower lying continuum states. We further map out the excited state manifold of exciton fine states using 2-photon photoluminescence microscopy. Our spectral analysis suggests the observed photoluminescence emission is a bright exciton state that is thermally populated by a lower-lying, long lived dark-exciton state. For this dark state, both our ultrafast transient absorption and two-photon photoluminescence studies support a large binding energy of the order of ~0.6 eV. If resonantly excited, we believe twisted bilayer graphene is the first 2D metallic material that can form stable, strongly bound excitons. Our results support that twisted bilayer graphene and similar materials are novel example of 2D hybrid material, where resonantly excited excitons are strongly-bound and quasi-stable from inherently weak coupling to the continuum metallic states. The formation mechanism of this dark state is very general, and holds exciting promise for other twisted stacked 2D materials.
[1] R. W. Havener, Y. Liang, L. Brown, L. Yang, J. Park, Van Hove Singularities and Excitonic Effects in the Optical Conductivity of Twisted Bilayer Graphene, Nano Letters, 14, 3353-3357 (2014).
[2] Y. Liang, R. Soklaski, S. Huang, M. W. Graham, R. Havener, J. Park, L. Yang, Strongly Bound Excitons in Gapless Two-dimensional Structures, Phys Rev. B, 90, 115418-3 (2014).
[3] H. Patel, R. Havener, L. Brown, Y. Liang, L. Yang, J. Park, M.W. Graham, Tunable Optical Excitations in Twisted Bilayer Graphene Form Strongly Bound Excitons, Nano Letters, 15, 5932-7 (2015).

Figure 1
Classification of Graphene Islands Via Confocal Raman Spectra Cluster Analysis
Authors: Blades Michael , Ignatova Tetyana , Ta Huy Q. , Bachmatiuk Alicja , Rummeli Mark Hermann , Lee Young Hee , Rotkin Slava V. 
Published: February 2020

Since it was first isolated in 2004, monolayer graphene has been studied for its unique optical, electrical, and thermal properties. Recently, interest is growing in the rich physics of twisted bilayer graphene, especially with optical tools such as Raman spectroscopy[1]. In this work, we study the micro-Raman spectra of bi- and tri-layer graphene islands, and develop methods to classify features of these spectra.
Graphene islands were grown on monolayer graphene via the CVD method[2], and then transferred to a Si/SiO2 substrate. Micro-Raman hyperspectral maps were taken from bi- and tri- layer islands with a wide variety of shapes and sizes. Using homemade code we fit the spectra from each pixel in the maps and extract the peak parameters for all of the major graphene Raman features. These pixels define a coordinate manifold, with the peak parameters building a hyperdimensional space over these coordinates. Principal Component Analysis was used to find the vectors where the spectra vary most widely, and data clusters were identified along these principal vectors. These clusters were further decomposed using this method iteratively.
When all reasonable clusters are identified, the clusters can be remapped to the individual islands, allowing one to classify distinct regions on the islands with similar spectral features. Correlations between the peak parameters can be extracted from each cluster, and then fitted to determine the relationships between them. These relationships reflect the unique physics of the few-layer graphene system, such as biaxial strain or doping level. By classifying regions with similar behavior, we can determine how this physics is influenced by the geometry of the system.

Acknowledgement: This work was supported by: NSF ECCS-1509786

References:

[1]Ado Jorio, Luiz Gustavo Cançado, Raman spectroscopy of twisted bilayer graphene, Solid State Communications, Volumes 175–176, December 2013, Pages 3-12, ISSN 0038-1098, http://dx.doi.org/10.1016/j.ssc.2013.08.008.

[2]Huy Q. Ta, David J. Perello, Dinh Loc Duong, Gang Hee Han, Sandeep Gorantla, Van Luan Nguyen, Alicja Bachmatiuk, Slava V. Rotkin, Young Hee Lee, and Mark H. Rümmeli, Stranski–Krastanov and Volmer–Weber CVD Growth Regimes To Control the Stacking Order in Bilayer Graphene, Nano Letters 2016 16 (10), 6403-6410, DOI: 10.1021/acs.nanolett.6b02826

Figure 1
(Invited) A First-Principles Study on Photoinduced Hole Injection into Organic Molecule on Metal Halide Perovskite Surface
Authors: Sugimoto Manabu 
Published: February 2020

The perovskite solar cell (PSC) is one of the emerging photovoltaic devices with rapid enhancement of the energy conversion efficiency. For further improvement, versatile efforts have been made to uncover important factors determining to the device performance. In particular, carrier injection across material interfaces in the device is considered to be the most critical electronic process.
In this presentation, we will report our recent computational study on photo-induced hole injection rate at the interface between the metal halide perovskite (PVK) and organic hole transport materials (HTM). In this study, we use the density functional theory (DFT) for geometry optimization and excited state calculations. The rate constant is evaluated by using the Marcus theory in which several electronic excited states assigned to the local excitation in PVK are taken into account as initial state for the carrier injection process. The final state is assumed to be the lowest excited state assigned to a charge (electron) transfer state from HTM to PVK, corresponding to the hole injection from PVK to HTM. In evaluation of the electronic coupling matrix element, we apply by the generalized Mulliken-Hush model by Newton and Cave.
As HTMs, we herein focus on 4,4'-dimethoxy triphenylamine (DMeOTPA) which is a partial structure of spiro-OMeTAD (N2,N2,N2’,N2’,N7,N7,N7’,N7’-octakis(4-methoxyphenyl)-9,9’-spirobi[9H-fluorene]-2,2’,7,7’-tetramine). For comparison, we also study on 4,4'-dimethlthio triphenylamine (DMeSTPA) and 4,4'-dimethlseleno triphenylamine (DMeSeTPA). On the basis of the computational analysis, we will suggest a compound with higher efficiency in the photo-energy conversion, and will discuss important electronic properties of the materials in the interfacial hole transfer in PSC.
Electrocatalysis of Oxygen Reduction with Elctropolymerized Metallo-Corroles
Authors: Elbaz Lior , Friedman Ariel , Gross Zeev 
Published: February 2020

In recent years we have shown very high electrocatalytic activity with metallo-corroles, specifically with cobalt- and iron-2,3,7,8,12,13,17,18-octabromo-5,10,15-tris(pentafluorophenyl) corrole [M(tpfcBr8)]. Both showed activity comparable with some of the stat-of-the-art molecular catalysts for ORR in acid and alkaline solutions. These very promising results encouraged us to continue developing other corrole-based catalysts in order to enhance the overall activity and shift the reaction mechanism towards the desirable direct 4-electron mechanism. In this work we have taken the bio-mimetic approach of joining catalytic centers together in order to obtain synergistic effects which could be translated to improved activity, selectivity and stability. Cobalt tris (4-aminophenyl) corrole (CoTAPC) were synthesized. The aminophenyl substituents on the corrole ring allowed us to polymerize these corroles using electrochemistry. The CoTAPC was electropolymerized at various polymerization conditions directly on glassy carbon electrodes. We have shown that we can control the growth, structure and density of this polymer by changing the conditions at which the polymerization reaction takes place. The final product was fully characterized using, FTIR, Raman spectroscopy and microscopic techniques. In agreement with previous studies with amino-substituted porphyrins, the obtained polymerization mechanism is similar to that of polyaniline. Indeed, FTIR-ATR analysis shows transition of the primary amine substitutes to secondary and tertiary amine, indicating the formation of dihydrophenazine and phenazine unit linkage respectively.
The electrocatalytic oxygen reduction reaction activity of the polyCoTAPC was studied in both acidic and alkaline conditions. In acidic solution, the number of electrons participating in the reaction (n) was improved by 0.3 electrons and the half-wave potential (E1/2) shifted by 120 mV more positive when compared to the monomer (CoTAPC), while in alkaline solution the n increased by 0.43 electrons and the E1/2 shifted by 200 mV more positive compared to CoTAPC. These shifts are attributed to the unique polymeric structure which allows both sharing of electrons and tandem electrocatalysis by at least two catalytic sites. Another outcome of these unique structures, is the catalytic site density which can possibly compensate for the inherently low turn-over frequency usually associated with non-precious metal catalysts in general.
A Novel Fabrication of Vertically Stacked Gate-all-around Silicon Nanowire Arrays
Authors: Meng Lingkuan , Xu Qiuxia , Yan Jiang 
Published: February 2020

It is well known that the top-down fabricated gate-all-around (GAA) silicon nanowire transistor with vertically stacked arrays is promising candidates to replace Finfet devices in sub-10nm nodes. The structure offers optimal electrostatic control, thereby enabling ultimate CMOS device scalability. Silicon nanowire (SiNW) transistors have shown promising potential to revolutionize the area of electronic, optical, chemical, and biological device applications. However, the fabrication of vertically stacked SiNW arrays in a controllable manner remains challenging due to complex topography and geometry characteristics.
Top-down controlled nanowire patterning methods have been developed mostly by Bosch-based process combined with successive stress-limited oxidation. Recently, a more controllable method has been demonstrated to fabricate stacked horizontal nanowires using an epitaxial growth such as Si/SiGe/Si/SiGe structures, but the process requires careful heteromaterial interface handling.
In this work, we propose a simple top-down method to fabricate vertically stacked nanowires arrays on bulk silicon substrates by originally developed process based on a conventional etch tool. Then, the stress-limited oxidation process can be introduced to achieve a uniform shape in a controllable fashion from a bulk silicon wafer. And also, we will discuss some challenges and innovations associated to such structure fabrications.

Figure 1
Copper Oxide Nanowire Plasma-Assisted Growth Dynamics and Role of Underlying Oxide Layers
Authors: Cvelbar Uros , Baranov Oleg , Filipič Gregor 
Published: February 2020

The plasma-assisted growth of nanowires is gaining importance in recent years due to many potential applications in harvesting renewable energy including nanowire arrays embedded on electrodes for solar fuel harvesting. This growth of metal oxide nanowires on electrodes can be done in plasma by either top-down approach or bottom-up one. However, when depositing or growing nanowires, one has to take into account what is occurring with underlying surface layers. The underlying or interfacial layers between electrode and nanowires have to be as thin as possible in order not to present a barrier during operation. In case of top down approach like in plasma enhanced chemical vapor depositions (PECVD) this is not that big issue, since interfacial layers are reasonably thin. This becomes more important in bottom-up approach, when nanowires are grown directly on the metallic surface or by so-called direct nanowire growth on the substrate. The direct plasma growth process is rather fast and yields large arrays of nanowires on surface of metallic substrate, but the growth and the role of oxide layer created during the plasma process is unknown. The process that involves oxygen plasma and surface oxidation doesn’t only produce nanowires, but also certain oxide layers beneath the nanowire arrays. Herein, the role of underlying oxide layer to growth of nanowires as well as its own dynamics are unrevealed.
The special interest of the presented research are copper oxide nanowires due to their applications in solar fuel cells for water molecule splitting. For this reason, copper samples were treated in low-pressure RF ICP oxygen-argon plasma in order to grow copper oxide nanowires. The result of this time resolved growth is observation of oxide layer saturation mode. These results differ from the copper oxide nanowire growth by thermal oxidation methods where a parabolic kinetics describe all stages of the NW growth. To meaningfully explain these observations a theoretical model was developed. The model explained this phenomenon and revealed a mechanism of the oxide layer growth with respect to the formation of the oxide nanowire arrays. The results of the investigation were confirmed by the experiments and vice versa. The results demonstrated that the density of the ion flux extracted from the plasma to the sample is one of key parameters to tailor the number density of the nanowires and is directly related to underlying oxide growth.