bluuebunny/crossref_metadata_2025 huggingface dataset:
Invited Presentation: Chemical Strain Kinetics in Epitaxial Thin Films Measured By Time-Resolved X-Ray Diffraction
Authors: Santiso Jose , Moreno Roberto , Zapata James , Roqueta Jaume , Garcia Pablo
Published: February 2020

The study of the chemical strain kinetics induced by oxygen surface exchange in transition metal oxides is of increasing relevance for understanding the fundamental mechanisms for oxygen reduction and evolution reactions (ORR/OER) of oxide catalysts as well as for novel cathode materials for intermediate-temperature solid oxide fuel cell (SOFC) technology.

In most transition metal oxide materials the variation in the oxygen stoichiometry produced by oxygen exchange with the atmosphere is often accompanied by subtle cell volume changes, the so-called chemical strain. Generally, the incorporation of charged defects (oxygen vacancies or interstitials) is expected to cause a cell expansion from the equilibrium intrinsic cell because of variations in the radii of the transition metal ions as well as Coulomb repulsion between those defects. Any slight variation in the oxygen content would proportionally result in a measurable volume increase. The ability to dynamically follow the cell volume variations allows establishing a direct correlation with oxidation/reduction kinetics.

In this talk we will describe recent development of a new methodology to analyze chemical strain kinetics in epitaxial thin films after redox cycling by using X-ray diffraction time-resolved measurements in conventional lab diffractometer [1], as depicted in Fig 1(a). With this technique we have been able to measure average cell parameter changes as small as 0.1 ppm in a time scale of a few seconds in a wide variety of SOFC cathode materials like La2NiO4+δ, Ba0.5Sr0.5Co0.8Fe0.3O3-δ, La0.8Sr0.2CoO3-δ, and GdBaCo2O5+δ, as well as in epitaxial bilayers. Some of the results of the oxidation kinetics for the different cathode materials are depicted in the Arrhenius plot in Figure 1(b).

We will analyze the suitability of those materials for their application as cathode materials in intermediate-temperature SOFC. We will also describe the usefulness of this methodology as complementary to other well-established techniques such as Electric Conductivity Relaxation (ECR) and 18O Isotopic Exchange Depth Profiling (IEDP) experiments.

[1] R. Moreno, P. García, J. Zapata, J. Roqueta, J. Chaigneau and J. Santiso, Chem. Mater. 25 (2013) 3640-3647
Invited Presentation: Charge Generation and Recombination in SWCNT Photovoltaic Active Layers
Authors: Blackburn Jeff , Mistry Kevin S. , Dowgiallo Anne-Marie , Avery Azure D. , Reid Obadiah , Ferguson Andrew , Arnold Michael S
Published: February 2020

Single-walled carbon nanotubes (SWCNTs) have many attractive properties for conversion of sunlight into electricity or solar fuels. In solar conversion schemes where SWCNTs are used as absorptive charge donors, it is critical to understand the processes by which initially created excitons are dissociated to produce free charges. In this presentation, I’ll discuss time-resolved spectroscopy studies exploring how photogenerated excitons produce charges in both neat SWCNT films and bilayer heterojunctions designed to dissociate photogenerated SWCNT excitons. In neat SWCNT films, we find charge generation yields of several percent even in the absence of an intentional exciton dissociation interface. We use a thin film of C60 to dissociate SWCNT excitons by interfacial electron transfer from films containing a variety of SWCNT chirality combinations. In these “bilayer” PV active layers, exciton dissociation efficiency varies with the thermodynamic driving force for electron transfer, as well as a number of morphological bilayer properties. Charge mobility and recombination also vary dramatically with bilayer morphology and the diameter distribution of SWCNTs within the film. I will discuss our current understanding of the mechanisms for charge generation and recombination in both neat and bilayer films, and how this understanding helps us envision ways to improve upon SWCNT PV active layers.
Invited Presentation: The Role of Dispersing Molecules on the Separation and Optical Properties of Carbon Nanotubes
Authors: Subbaiyan Navaneetha K , Cambre Sofie , Parra-Vasquez A. Nicholas , Haroz Erik , Crochet Jared , Lounis Brahim , Cognet Laurent , Doorn Steven , Duque Juan G
Published: February 2020

When studying the optical properties of single-walled carbon nanotubes (SWCNTs), it is known that the dispersing agent(s) play an important role in the observed optical and electronic properties as well as in the separation of tubes. However, fundamental and applied reports are hindered by poor control over the interaction between the dispersant molecules and the nanotubes. Here I will discuss how interfacial chemistry affects the separation of SWCNTs and their optical properties. Compelling spectroscopic evidence has shown that surfactant composition, concentration, and structure are crucial factors to separate SWCNTs and obtain highly stable and fluorescent nanotube dispersions.
Invited Presentation: Controlling Carbon Nanotube Properties with Defects
Authors: Wang YuHuang
Published: February 2020

Defects can rule the properties of a crystal. This phenomenon is particularly intriguing in atom-thick materials such as single-walled carbon nanotubes and graphene, where new chemical and physical phenomena may arise due to strong coupling of electrons, excitons, phonons, and spin with defects in reduced dimensions. In this talk, we will discuss novel chemical strategies to address the challenges of understanding and controlling covalent sp3 defects in sp2 carbon lattices. Examples for applications also will be discussed.
Invited Presentation: On the Viability of Helical Arrangement of Carbon Nanotube Via Supported Catalyst Structure: Graphene Embryo As a Precursor for Symmetry Formation
Authors: Harutyunyan Avetik R
Published: February 2020

Understanding of controlled growth of carbon nanotubes (CNTs) is critical for their broader applications and for catalysis in general. The problem remains elusive owing to complex interplay between nanotube nucleation and catalyst morphology reconstruction in the early stages during which the symmetry is set. Exploitation of in situ transmission electron microscopy for studies of carbon nanotube cap formation reveals that the nucleation begins by the creation of a graphene embryo bounded between opposite step edges on the catalyst surface. The embryo evolves into a cap when at least one of the steps flows and crosses the edges of adjacent facets on the catalyst tip. Further motion of the steps away from the catalyst tip with attached rims of carbon cap generates the tubular wall of the nanotube. Hence, CNT nucleation at low temperatures is a result of dynamic rearrangement of the graphene embryo edge-catalyst step interface structure. This implies that the symmetry formation concept driven by catalyst facet structure is very simplified, whereas the interrelationship between the structures of adjacent facets that introduces the curvature on graphene embryo plays the dominant role in the cap and thereby symmetry formation via self consistent manner. The roles of catalyst composition, size, structures of facets and corresponding step/terraces on the tube nucleation and symmetry formation will be presented in light of these new developments.
Invited Presentation: Application and Thermodynamics of Aqueous Two-Phase Partitioning for Chirality Separation of Single-Wall Carbon Nanotubes Using Surfactants
Authors: Fagan Jeffrey
Published: February 2020

The recent development of aqueous two-phase extraction (ATPE) as a method for separating single-wall carbon nanotubes (SWCNTs) provides a scalable method for isolating many individual species of SWCNT via solution processing. Systematic investigation of ATPE separation utilizing different combinations of surfactants, co-surfactants, polymers, and salts has revealed methods for isolating individual species of nanotubes up to > 1.2 nm in diameter. In this presentation I will provide an update on our separation results using surfactant(s) and on understanding achieved through temperature controlled partitioning experiments on pre-separated samples.
Specific DNA Sequences for the Purification of Single-Wall Carbon Nanotube Species in Polymer Aqueous Two-Phase Systems
Authors: Ao Geyou , Zheng Ming
Published: February 2020

A systematic purification of single-chirality species of single-wall carbon nanotubes (SWCNT) from their synthetic mixture provides foundation for many fundamental studies and technological applications of SWCNT. Previous study demonstrated a robust separation of SWCNT dispersed in bile salt surfactants according to their diameter and metallicity in a polymer aqueous two-phase (ATP) system. In this work, specific DNA sequences were utilized as an effective approach for recognition of specific SWCNT chirality and their subsequent purification using the ATP separation method. We show that many single chirality SWCNTs in a synthetic mixture can be obtained in very high purity.

The combination of DNA sequence recognition of specific SWCNT structure and the rapid and tunable ATP separation method open a new route for sorting nanotube into each and every single-chirality species. In addition, the feasibility of volume scale-up in ATP separation allows sufficient materials to be obtained for fundamental studies and application development. Further exploration of DNA recognition sequences in ATP separation method and new polymer ATP systems will be the main focus of our future studies in carbon nanotube sorting.
On the Structures and Growing Mechanisms of the Ti@C2n (2n = 26 - 50) Endohedral Fullerenes
Authors: Poblet Josep M. , Mulet Marc , Abella Laura , Rodríguez-Fortea Antonio , Dunk Paul , Kroto Harry
Published: February 2020

During the last years, several mechanisms have been suggested in relation to the formation of fullerenes. One of them involves the ingestion of a C2 unit by an already formed fullerene. In this communication, we summarize the theoretical investigations carried out for the series of Ti@C2n endohedral fullerenes, with 2n = 26 to 50. After a thorough exploration of the most favorable isomers, potential energy surfaces associated with the C2 addition, and the topology of the involved structures we have concluded that in contrast to large endohedral metallofullerenes (2n>60) in which the empty cage is different to the optimal cage that hosts a metal ion or a small cluster, in small endohedral fullerenes encapsulating a tetravalent ion the empty and hosting cage often coincides. The addition of a C2 unit to an already formed Ti@C2n fullerene is always an exergonic reaction. Most of the lowest in energy isomers are formally linked by a C2 addition and a Stone-Wales transformation. Car-Parrinello Molecular Dynamics calculations show that after the attack of a C2 unit to one of the C atoms of the Ti@C2n system, the formation of the second C-C bond that closes the cage is an improbable event and must be accelerated using Metadynamics or via an external collision, for example with He atoms that are present in the sample.
Consideration of the Electronic Structure of Endohedral Fullerenes from a View Point of the Fullerene Cage Size and Cage Structure
Authors: Hino Shojun
Published: February 2020

We have been measuring the photoelectron spectra of endohedral fullerenes and clarified the transfer of electrons from the entrapped species to the cage as well as the amounts of transferred electrons. Now we have an accumulation of ultraviolet photoelectron spectroscopic data of endohedral fullerenes, which enables us to consider the effects of the cage size and cage geometry to their electronic structure systematically. I am going to present our recently obtained photoelectron spectra of various sized endohedral fullerenes encapsulating two lutetium atoms, a cluster of two lutetium and carbon atoms and a Sc3N cluster, and discuss the cage size effect to the electron transfer from the entrapped species to the cage and geometry of the entrapped species. Ultraviolet photoelectron spectra of I
h- and C
2v-C80 caged endohedral fullerenes will also be given and their electronic structure difference will be discussed with an aid of DFT calculation.
Novel Terbium-Based Endohedral Clusterfullerenes: Synthesis, Isolation and Characterization
Authors: Yang Shangfeng
Published: February 2020

Fupin Liu1, Tao Wei1, Song Wang1, Jian Guan1, Xing Lu2, and Shangfeng Yang1*

1 Hefei National Laboratory for Physical Sciences at Microscale, CAS Key Laboratory of Materials for Energy Conversion & Department of Materials Science and Engineering, University of Science and Technology of China (USTC), Hefei 230026, China

Email: sfyang@ustc.edu.cn

2 State Key Laboratory of Materials Processing and Die & Mould Technology, College of Materials Science and Engineering, Huazhong University of Science and Technology (HUST), Wuhan 430074, China

Clusterfullerenes as a special branch of endohedral fullerenes are characteristic in the encapsulation of an unstable metal cluster by a robust fullerene cage.[1,2] We present here several novel Tb-based endohedral clusterfullerenes isolated successfully recently. Tb2C84 was isolated by multistep HPLC. According to the UV-vis-NIR spectroscopic characterization and comparison with the reported analogous M2C84 (M = Sc, Y) metallofullerenes, the molecular structure of Tb2C84 is proposed to be Tb2C2@Cs
(6)-C82 featuring a metal carbide clusterfullerene (CCF) structure, which is unambiguously confirmed by X-ray crystallographic study. A detailed analysis of the crystal structure of a cocrystal of Tb2C2@Cs
(6)-C82·NiII(OEP)·2C6H6 (NiII(OEP) = nickel (II) octaethylporphyrin) reveals that a bent Tb2C2 carbide cluster is encaged rigidly inside a Cs
(6)-C82 cage.[3] More recently we also successfully isolated the first Tb-based monometallic cyanide clusterfullerene (CYCF), TbCN@C82. The UV-vis-NIR spectrum and cyclic voltammetry of TbCN@C82 show high resemblance to those of the recently reported analogous CYCF YCN@Cs
(6)-C82,[4] suggesting that TbCN@C82 has the same monometallic cyanide clusterfullerene structure and Cs
(6)-C82 isomeric cage, and the electronic property of monometallic cyanide clusterfullerene MCN@C82is insensitive on the encapsulated metal.

REFERENCES

a) S. F. Yang, F. P. Liu, C. B. Chen, M. Z. Jiao, T. Wei, Chem. Commun.
2011, 47, 11822-11839. b) X. Lu, L. Feng, T. Akasaka, S. Nagase, Chem. Soc. Rev.
2012, 41, 7723-7760.

a) A. A. Popov, S. F. Yang, L. Dunsch, Chem. Rev.
2013, 113, 5989-6113; d) S. F. Yang, C. R. Wang (eds), “Endohedral Fullerenes: From Fundamentals to Applications”, World Scientific Publishing Co., Singapore, 2013 (ISBN: 978-9814489836); c) S. F. Yang, Curr. Org. Chem.
2012, 16, 1079-1094; d) A. Rodriguez-Fortea, A. L. Balch, J. M. Poblet, Chem. Soc. Rev.
2011, 40, 3551-3563.

F. P. Liu, T. Wei, S. Wang, J. Guan, X. Lu, S. F. Yang, Fullerenes, Nanotubes and Carbon Nanostructures
2013, 21, in press (DOI: 10.1080/1536383X.2013.801839).

S. F. Yang, C. B. Chen, F. P. Liu, Y. P. Xie, F. Y. Li, M. Z. Jiao, M. Suzuki, T. Wei, S. Wang, Z. F. Chen, X. Lu, T. Akasaka, Sci. Rep.
2013, 3, 1487.
Magnetic Properties of Endohedral Metallofullerenes: Single-Molecular Magnetism and Anisotropy
Authors: Popov Alexey A. , Zhang Yang , Dunsch Lothar , Greber Thomas , Westerstöm Rasmus , Yang Shangfeng
Published: February 2020

Endohedral metallofullerenes (EMFs) encapsulating lanthanide ions (Ln) are of particular interest because of the specific magnetic properties resulting from the combination of the partially filled 4f shell of metal ions, their exchange interactions in endohedral clusters, and shielding role of the carbon cage, which protects endohedral spin states from the outer environment. Inhomogeneous environment of Ln ions inside clusterfullerenes induces magnetic anisotropy and results in a number of magnetic phenomena. In particular, Dy-based nitride clusterfullerenes are the first EMFs to exhibit single molecular magnet (SMM) behaviour.1 Furthermore, completely different SMM behaviour of DySc2N@C80, Dy2ScN@C80, and Dy3N@C80 molecules shows that exchange interactions between Ln ions in EMFs has strong influence on the magnetic properties.2 Results of the SQUID and XMCD studies of different EMFs at low temperatures will be discussed in this contribution. Whereas SQUID and XMCD are of particular use for the study of the low-temperature effects, magnetic properties of EMFs at room-temperature are conveniently addressed by paramagnetic NMR spectroscopy,3 since paramagnetic chemical shift is proportional to the anisotropy of magnetic susceptibility. New results on the NMR studies for a series of LnSc2N@C80molecules will be reported.

1. R. Westerström, J. Dreiser, C. Piamonteze, M. Muntwiler, S. Weyeneth, H. Brune, S. Rusponi, F. Nolting, A. Popov, S. Yang, L. Dunsch and T. Greber, J. Am. Chem. Soc., 2012, 134, 9840-9843.

2. R. Westerström, J. Dreiser, C. Piamonteze, M. Muntwiler, S. Weyeneth, K. Krämer, S.-X. Liu, S. Decurtins, A. Popov, S. Yang, L. Dunsch and T. Greber, arXiv:cond-mat/0604365v1, 2013, 1310.5040.

3. Y. Zhang, A. A. Popov, S. Schiemenz and L. Dunsch, Chem.-Eur. J., 2012, 18, 9691-9698.
Endohedral Metallofullerenes – Filled Fullerene Derivatives Towards Multifunctional Reaction Center Mimics
Authors: Guldi D. M.
Published: February 2020

In recent years, endohedral metallofullerenes have attracted tremendous interest not only in physics and chemistry, but also in interdisciplinary areas such as materials and biological sciences. In this concept article we highlight recent results on different endohedral metallofullerenes based on lanthanides and their derivatives. The chemical and excited state reactivities of endohedral metallofullerenes are discussed for various endohedral clusters. Most important is the part that covers spectroscopic and kinetic assays of reductive and oxidative charge transfer evolving from photoexcited electron donors and electron acceptors, respectively, in a variety of electron donor-acceptor conjugates. Towards the end, we refer to the applications of endohedral metallofullerenes in photovoltaic devices that feature greater efficiency than devices fabricated with empty fullerenes. Herein, we focus mainly on results obtained in the groups of Akasaka, Echegoyen, and Guldi.
Photophysical and Electrochemical Properties of Functionalized Benzo[ghi]perylene and Coronene Derivatives
Authors: Hasobe Taku
Published: February 2020

Planar polycyclic aromatic hydrocarbons (PAHs) such as benzo[ghi]perylene (Bp) and coronene (Cor) are expected for electronic device applications and solar energy conversion because of their π-conjugated structures and ordered aggregate properties. In this work, a series of Bp and Cor derivatives substituted by methoxycarbonyl (COOMe: electron-withdrawing unit) and methoxy (MeO: electron-donating unit) groups were systematically synthesized considering the differences in types and numbers of substituent groups (Figure 1).

The electrochemical, spectroscopic and photophysical properties of these molecules were investigated in full detail by cyclic voltammetry, steady-state and time-resolved spectroscopy and quantum yield measurements of fluorescence and intersystem crossing. The synthetic introduction of proper substituents on the aromatic ring therefore enables us to successfully control the electrochemical behavior. For example, with increasing the number of COOMe groups, the reduction and oxidation potentials are significantly shifted to positive direction. On the other hand, the steady-state absorption and fluorescence spectra also become red-shifted and broadened as compared to those of unsubstituted Bp and Cor.

Additionally, a systematic comparison of quantum yields and rate constants of the excited-state dynamics also reveals that the fluorescence quantum yields dramatically increase with an increase of the number of COOMe groups in both Bp and Cor derivatives. The fabrication and measurement of filed effect transistors (FET) utilizing these derivatives are also discussed in this presentation.
A Supramolecular Photosynthetic Model Made of a Multi-Porphyrinic Array Constructed Around a C60 Core and a C60-Imidazole Derivative
Authors: Armaroli Nicola , Nierengarten Jean-François , Yoosaf K. , Iehl Julian , Nierengarten Iwona , Hmadeh Mohamed , Albrecht-Gary Anne-Marie
Published: February 2020

The photophysical properties of a supramolecular fullerene-porphyrin ensemble resulting from the self-assembly of a pyrrolidinofullerene-imidazole derivative (F1) with a multi-metalloporphyrin array constructed around a hexa-substituted fullerene core (F(ZnP)12
) have been investigated. The fullerene hexa-adduct core of the host system does not play any active role in the cascade of photoinduced events of the supramolecular ensemble, indeed no intercomponent photoinduced processes could be observed in host F(ZnP)12
. In contrast, upon axial coordination with the mono-substituted fullerene guest F1, a quantitative quenching of the fluorescence signal of the metalloporphyrins was observed for the supramolecular complex [F(ZnP)12 (F1)n] both in polar and non polar solvents. In toluene, the supramolecular ensemble exhibits a charge transfer emission centered around 930 nm suggesting the occurrence of intramolecular face-to-face interactions of F1 with neighboring metalloporphyrin moieties within the self-assembled photoactive array. This mechanism is supported by the fact that a one order of magnitude increase in the binding constant was observed for the supramolecular complex [F(ZnP)12 (F1)n] when compared to a reference system lacking the pyrrolidino-fullerene unit. In benzonitrile, a long-lived charge separated state (τ = 0.3 μs) has been detected for the supramolecular adduct.

References

K. Yoosaf, J. Iehl, I. Nierengarten, M. Hmadeh, A.-M. Albrecht-Gary, J.-F. Nierengarten, N. Armaroli, Chem. Eur. J., 2014, in press
Graphene Growth on Electrodeposited Polycrystalline Metals and Alloys
Authors: Pigliafreddo Dario , Tocchio Marco , Livolsi Federica , Nobili Luca , Carraro Carlo , Maboudian Roya , Magagnin Luca
Published: February 2020

Graphene grown by CVD on Cu foils has generated interest due to low cost and the prospect of large-area monolayer coverage. The initial nucleation and growth dynamics of graphene play a critical role in determining the final film quality. However, such characteristics are dependent on Cu surface structure, suggesting that the underlying Cu substrate has a detailed influence on the nucleating carbon species during growth [1,2]. Graphene synthesis on freestanding metallic foils was carried out in a hot-wall tube furnace with CH4 and H2 gases at about 1000 °C.

In this work, we investigate the effects of the electrochemical synthesis onto graphene quality, showing the influence of the Cu-Ru interdiffusion. Copper (about 40 mm thick) and ruthenium coated (about 1 mm thick) copper foils were prepared by electrodeposition in acid electrolyte. The growth of good quality graphene layers is also discussed in terms of the role played by grain boundaries and diffusion at the grain boundaries. Our results demonstrate the synthesis of graphene on Cu with presence of the D-peak and with the 2D-peak not higher than the G-peak (shifting of the 2D-peak) and on Ru with a high D-peak but with the 2D-peak still higher than the G-peak. Graphene on Ru coated copper has a negligible D-peak and the 2D-peak is higher than the G-peak. As alternative substrate, graphene was grown on Ni-Cu electrodeposited alloys with increasing copper content, showing a different behavior from the Cu-Ru system and function of the amount of copper. The Ni-Cu system was used to grow graphene layers on porous substrates obtained by electrochemical de-alloying of copper.

References

[1] X. Li, W. Cai, J. An, S. Kim, J. Nah, D. Yang, R. Piner, A. Velamakanni, I. Jung, E. Tutuc, S.K. Banerjee, L. Colombo, R.S. Ruoff, Science 2009, 1312–1314.

[2] J.D. Wood, S.W. Schmucker, A.S. Lyons, E. Pop, J.W. Lyding, Nano Lett. 2011, 11, 4547–4554.
Hydrogen Incorporation and Reaction with Graphene on SiO2
Authors: Soares Gabriel Vieira , Bom Nicolau Molina , Oliveira Myriano , Lopes João Marcelo , Riechert Henning , Radtke Cláudio
Published: February 2020

Owing to its unique properties with respect to charge transport, graphene is one of the most promising candidates for future nanoelectronic devices. However, the processing and modification of graphene properties for technological purposes is still a challenge. In this context, gases adsorption in graphene is of central importance. It has been already reported that oxygen (O) and hydrogen (H) incorporation in graphene layers have a strong influence in their transport and structural characteristics [1,2]. For instance, hydrogenation of graphene can give rise to a bang gap around 1 eV, where in some cases H incorporation leads to a reduction in carrier mobility. Therefore, understanding the interaction of H with these structures and related chemical modifications are fundamental issues. In the present work, we investigate the incorporation of H in graphene layers upon hydrogen annealing.

Starting samples consisted of monolayer graphene grown by chemical vapor deposition (CVD) on copper and then transferred to SiO2 films (285 nm thick) on Si. Bare SiO2 films of the same thickness on Si were also submitted to the same experiments for the sake of comparison. Samples were loaded in a static pressure and resistively heated quartz tube furnace, which was initially pumped down to 2 x 10-7 mbar. Hereafter, they were annealed at temperatures ranging from 100 up to 1000 ºC, for 1 h, in a 1000 mbar H2 atmosphere enriched in the 2H (D) rare isotope. This rare isotope was chosen in order to distinguish H incorporated during experiment from those incorporated due to air exposure. As references, samples annealed at the same temperatures but in ultra high vacuum (UHV) were also investigated. D quantification was accomplished by nuclear reaction analyses (NRA), using the D(3He,p)4He nuclear reaction at 700 keV (1012 D/cm2 sensitivity and 5% accuracy). In addition, Raman scattering and X-ray photoelectron spectroscopy (XPS) were used for the characterization of the graphene.

Distinct D incorporation behavior was observed for samples with and without graphene overlayer. For annealing temperature above 100ºC, we observed a higher incorporation of species in graphene when compared to bare SiO2 samples. This incorporation reaches saturation for temperature around 400ºC. XPS measurements suggest the formation of C-H on graphene, increasing its relative concentration with temperature until 800ºC. At higher annealing temperatures, the etching of graphene layer takes place introducing bonding configurations related to defective states. Mechanisms of hydrogen reaction and incorporation based on the observed results will be discussed.

References

[1] S. Ryu, L. Liu, S. Berciaud, Y. You, H. Liu, P. Kim, G. W. Flynn, and L. E. Brus, Nano Lett. 10, (2010) 4944.

[2] D. C. Elias, R. R. Nair, T. M. G. Mohiuddin, S. V. Morozov, P. Blake, M. P. Halsall, A. C. Ferrari, D. W. Boukhvalov, M. I. Katnelson, A. K. Geim, and K. S. Novoselov, Science 233 (2009), 610.
Design and Characterization of High-Performance Electrodes for Dye-Sensitized Solar Cells
Authors: Diau Eric Wei-Guang
Published: February 2020

Dye-sensitized solar cells (DSSC) have attracted much attention recently due to its potential as a cost-effective alternative for silicon-based solar cells. Three major components are involved to make a highly efficient DSSC: a working electrode containing dye-sensitized nanostructured TiO2 layers, a counter electrode containing platinum-coated TCO substrate, and a composite electrolyte solution to fill between the two electrodes. In this lecture, I will present our recent developments on novel electrodes for highly efficient DSSC. For the counter electrodes, novel platinum nanostructures were fabricated according to a cyclic electro-deposition (CED) method for the Pt films with uniform nanograss structure having great electro-catalytic performance and intrinsic light-scattering, perfectly suitable for use as counter electrodes for DSSC. we have developed a strategy of nanofabrication to prepare monolayers of platinum nanoparticles self-assembled on a rough surface of TCO in two steps: first, preparation of a well dispersed Pt NP solution from polyol reduction at a pH well controlled on adding NaOH; second, dipping the SAM-functionalized TCO substrate, prepared beforehand using ‘piranha’ and MPTMS surface treatments in turn, into the Pt NP solution near 295 K to complete the fabrication of the SAM-Pt CE for DSSC. The uniform SAM-Pt film with a narrow distribution of size can be produced on TCO without a stabilizer, so that the traditional thermal treatment at high temperatures is no longer necessary. The uniform nature of the SAM-Pt film has the advantages of minimizing the amounts of Pt loading and optimizing the catalytic function on the TCO surface. The DSSC devices prepared according to this SAM-Pt approach attained notable photovoltaic performance (η = 9.2 %) comparable to those fabricated with a conventional TD method (η = 9.1 %) or a CED method (η = 9.3 %) under the same experimental conditions. For the working electrodes, we constructed photoanodes, containing titania nanostructures of varied types – spherical nanoparticles (NP), one-dimensional nanorods (NR), and octahedron-like nanocrystals of varied size (HD1-HD3), in either a bi-layer (BL) or a multi-layer (ML) film configuration. The ML devices were fabricated based on the NP-BL system with additional HDP layers inserted between the two components, NP and SL, to enhance J
SC so as to attain the best performance, with efficiency of power conversion (PCE) = 10.1 %, at film thickness (L) 26 mm. Because of the robust structural feature of the HD films, the devices fabricated with a simple BL film configuration, HD1/SL = 6/3, exhibited the best performance, PCE = 10.2 % at L = 29 mm, which is a promising advance for Z907-based solar cells with a superior and enduring stability of performance for commercialization.
Visible Plasmon-Enhanced Water Splitting
Authors: Misawa Hiroaki
Published: February 2020

The interaction between photon and molecule is weak. The probability of interaction between photon and molecule is roughly estimated as low as 10-7 because the focal spot size of visible light (~1×10-8 cm2) is 107 times larger than the general molecular absorption cross-section (~1×10-15 cm2) due to the relationship between the diffraction limit of the light and the molecular size. Thus far, the number of excited-state molecules has been increased by photon density using a laser as an excitation source, although there is a loss of energy since the probability of interaction does not change. We have recently found that metallic nanostructures exhibiting localized plasmon resonance are promising in the photochemical reaction field, which make it possible to increase the interaction between photons and molecules. As one of the most important achievements, we have observed significant photopolymerization via two-photon absorption in photoinitiator molecules of negative photoresists in the nanogaps of closely spaced gold nanoparticles irradiated by a weak incoherent light source [1]. The key technology and outstanding feature of our photochemical reaction fields is the fabrication of nanogap metallic nanostructures with nanometric accuracy and use of the localization of electromagnetic waves within nanogaps. Near-field enhancement effects localized on nanogap gold structures were studied by two-photon photoluminescence from gold [2], surface-enhanced Raman scattering [3] and plasmon-enhanced photochemical reactions [4,5]. Thus, gold nanostructures are useful in photochemical reaction fields, which make it possible to promote strong coupling between photons and molecules with the aim of effectively using photons. From this standpoint, we have recently demonstrated plasmonic photoelectric conversion from visible to near-infrared wavelengths using electrodes in which gold nanorods are arrayed on TiO2single-crystal and photocatalytic water splitting [6,7].

References

[1] K. Ueno, H. Misawa et al. J. Am. Chem. Soc.
2008, 130, 6928.

[2] K. Ueno, H. Misawa et al. Adv. Mater.
2008, 20, 26.

[3] Y. Yokota, K. Ueno, H. Misawa, Chem. Commun.
2011, 3505.

[4] K. Ueno, H. Misawa et al. J. Phys. Chem. Lett.
2010, 1, 657.

[5] B. Wu, K. Ueno, H. Misawa et al. J. Phys. Chem. Lett.
2012, 3, 1443.

[6] Y. Nishijima, K. Ueno, H. Misawa et al. J. Phys. Chem. Lett.
2010, 1, 2031.

[7] Y. Nishijima, K. Ueno, H. Misawa et al. J. Phys. Chem. Lett.
2012, 3, 1248.
Nanostructured Palladium-Graphene Materials for Energy Conversion
Authors: Serov Alexey , Andersen Nalin , Artyushkova Kateryna , Atanassov Plamen
Published: February 2020

Carbon nanostructured materials are widely used in different energy applications: fuel cells, supercapacitors, Li-ion batteries etc [1, 2]. Several synthetic approaches can be used for preparation of CNTs, graphene etc, such as: CVD, exfoliation. At the present work we adopted the sacrificial support method (SSM) developed at UNM group [3-12].

Several types of 3D structured graphene materials were synthesized by modified SSM. The morphology control was achieved by variation of silica types, graphene oxide to silica ratio etc. After successful synthesis of graphenes the sacrificial support was leatched by means of concentrated HF.

Figure 1 represents SEM image of 3D structured graphene synthesized by SSM.

Figure 1: SEM image of 3D structured graphene.

TEM analysis confirmed the formation of multi-stacks of graphene layers (Fig. 2).

The later step involved the deposition on the graphene surface Pd-based materials. Two methods: thermal or chemical reduction of Pd-precursors was used in order to synthesize highly active catalysts for alcohols electrooxidation.

It has been observed that Pd-Cu was evenly dispersed on the graphene sheets (Fig.3).

Electrochemical performance of Pd-based catalysts in the reaction of alcohols electrooxidation is shown on Figure 4. It was found that addition of second oxophilic metal to the palladium substantially improved it is activity. Peak current generated by Pd-Cu deposited onto the surface of 3D structured graphene was found to be ~1800 A gpd
-1.

Figure 2: TEM image of 3D structured graphene.

Figure 3: TEM image of Pd-Cu/3D structured graphene.

Figure 4: Electrooxidation of EtOH in alkaline media by Pd-based catalysts.

References:

E. Antolini Appl. Catal. B. 88 (2009) 1.

G. Kucinskis, G. Bajars, J. Kleperis J. Power Sources 240 (2013) 66–79.

A. Serov, U. Martinez, A. Falase, P. Atanassov, Electrochem. Comm. 22 (2012) 193-196.

A. Falase, M. Main, K. Garcia, A. Serov, C. Lau, P. Atanassov, Electrochim. Acta 66 (2012) 295-301.

S. Pylypenko, S. Mukherjee, T. S. Olson, P. Atanassov, Electrochim. Acta 53 (2008) 7875-7883.

M. H. Robson, A. Serov, K. Artyushkova, P. Atanassov Electrochim. Acta, 90 (2013) 656–665.

S. Brocato, A. Serov, P. Atanassov Electrochim. Acta, 87 (2013) 361-365

A. Serov, M. H. Robson, K. Artyushkova, P. Atanassov Appl. Catal. B 127 (2012) 300-306.

A. Serov, M. H. Robson, M. Smolnik, P. Atanassov Electrochim. Acta 80 (2012) 213-218.

A. Serov, M. H. Robson, B. Halevi, K. Artyushkova, P. Atanassov Electrochem. Comm. 22 (2012) 53-56.

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A. Serov, M. H. Robson, M. Smolnik, P. Atanassov, Electrochim. Acta 109 (2013) 433-439.
Nickel Oxide Carbon Nanofiber Composite for Electrochemical Oxidation of Methanol
Authors: Abdullah Aboubakr Moustafa , Al-Enizi Abdullah M , El-Zatahry Ahmed A , Al-Theyab Salem S
Published: February 2020

The electrospinning of polyvinyl polyvinylpyrrolidone (PVP) with a polyaniline (PANI) and graphene sol mixture produced uniform, smooth fibers. These electrospun fibers were stabilized for 2 h at 200 °C and then carbonized at 800 °C for 5 h. Composites were prepared by depositing Ni(OH)2 on the carbon nanofibers (CNFs) and calcining them at different temperatures. The composites were characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The effect of the calcination temperatures on the electrochemical catalytic properties towards methanol oxidation was studied using cyclic voltammetry and electrochemical impedance spectroscopy. The optimum calcination temperature for the CNF/NiO composite that yielded highest oxidation peak currents for the MeOH oxidation reaction was found to be 500 oC. The analysis of the chronoamperometry measurements confirmed a significant increase in the real surface area for the CNF/NiO composite as the calcination temperature increases. The real surface area is increased at calcination temperatures of 400 and 500 oC more than 20 times higher than that calcined at 300 oC. This explains the higher electrocatalytic properties for the CNF/NiO composite as the calcined temperatures increases. The oxidation of MeOH was not found to be a purely diffusion controlled process where the square root of the scan rate followed a linear relationship with the currents of the anodic peaks. The CNF/NiO composite has shown, not only, a good stability as the potential was cycled between a large potential window, but also, the electrocatalytic properties was enhanced. This occurred as a result of the surface activation during the cyclic process. The impedance parameters were calculated from the EIS measurements proved that this system has two time constants; one for adsorption and the other for the charge transfer.

Figure . Nyquist plots of the experimental impedance data (scattering dots) measured potentiostatically at 0.5 V (SCE) in a frequency range between 100K and 0.1 Hz with an AC perturbation of 5 mV and the fitting results (solid lines) for CNF-supported Ni oxide composite calcined at 500 oC in (A) 6 M KOH and (B) 6M KOH + 1 M MeOH aqueous solutions at 25 oC. The inset image is the electrical equivalent circuit used for fitting the impedance spectra.
Phenolic Porphyrins Assembled at Surfaces: Hydrogen-Bonding and Binary Systems
Authors: Hill Jonathan P. , Wakayama Yutaka , Xie Yongshu , Ji Qingmin , Ariga Katsuhiko
Published: February 2020

Supramolecular arrangement of porphyrins and other molecules has great potential in the fields of molecular information storage and sensing due to their ease of deposition and good chemical and thermal stabilities. In particular, porphyrins of relatively large molecular weights can be applied in thermal deposition while tetrapyrrole molecules have had an extensive synthetic chemistry developed, which enables synthesis of complex derivatives. In this work, we present complementary examples of porphyrin nanoarchitectonics. Starting from simple symmetrical phenol derivatives, we describe the effects of steric hindrance about the respective hydroxyl groups1,2 and also the effects of conformational variation on the self-assembly structures.3 We also investigated fabrication of binary molecular monolayers using two different porphyrin molecules tetrakis(3,5-di-t-butyl-4-hydroxyphenyl) porphyrin and tetrakis(4-pyridyl) porphyrin by deposition in ultrahigh vacuum.4 This leads to two unusual heteromolecular monolayer structures were observed with one exhibiting good separation of molecules within the monolayer. Meanwhile, a synthetic nanoarchitectonic approach was used to prepare self-assembled molecular nanowires at a mica substrate. The nanowires could be observed growing using atomic force microscopy (AFM) and the network structures of the nanowires can be influenced by manipulation using the AFM probe tip.4,5Formation of molecular monolayers with chromophores positioned remote from the substrate surface will also be discussed.

References

(1) J. P. Hill, Y. Wakayama, W. Schmitt, T. Tsuruoka, T. Nakanishi, P. A. Karr, M. L. Zandler, A. L. McCarty, F. D’Souza, L. R. Milgrom, K. Ariga, Chem. Commun. 2006, 2320–2322 (2) J. P. Hill, Y. Wakayama, M. Akada, Katsuhiko Ariga, J. Phys. Chem. C. 2007, 111, 16174–16180 (3) J. P. Hill, Y. Wakayama, K. Ariga, Phys. Chem. Chem. Phys. 2006, 8, 5034–5037 (4) J. P. Hill, Y. Xie, M. Akada, Y. Wakayama, L. K. Shrestha, Q. Ji, K. Ariga, Langmuir (2013) 29(24), 7291–7299 (5) Y. Xie, M. Akada, J. P. Hill, Q. Ji, R. Charvet K. Ariga, Chem. Commun. 2011, 47, 2285–2287.

Figure. Self-assembled phenol-substituted porphyrins on Cu(111) surface.
Electronic Transport Properties of Molecular Graphyne
Authors: Borguet Eric
Published: February 2020

Thirty years ago there were two classic forms of carbon (diamond and graphite). Since then, three new carbon allotropes (buckyballs, carbon nanotubes and graphene), all involving only sp2 carbons, have been discovered. While there is much excitement about graphene, another interesting carbon-based material, graphyne, has been suggested.

Graphyne is a two dimensional network of sp and sp2 carbon centers. While this material is not known in nature, it has been the subject of theoretical calculations which suggest exciting properties for graphynes beyond those of graphene. While macroscopic samples of graphyne are not currently available, molecular units of graphyne, called carbo-benzenes, have been synthesized by our collaborators in Toulouse.

We report the single molecule electrical measurements on molecular carbo-benzenes, connected to gold electrodes via amine anchoring groups, determined using scanning tunneling microscope break junction (STM-BJ) methods. Our results show that these highly conjugated macro-aromatics with NH2 metal-anchoring functions are superior in conductivity (~100 nS) compared with molecules of similar length (1.94 nm). These experimental results are rationalized by high level calculations performed by our colleagues at Northwestern. Cutting one side of the macro-aromatic circuit results in a two orders of magnitude smaller junction conductance. Furthermore, single carbo-benzene-mediated junctions exhibit field-effect transistor behavior when an electrochemical gate potential is applied, opening the way for device applications.
Allosteric Regulation of Redox Potential and Enzyme Activity of Tryptophan Dioxygenase
Authors: Yeh Syun-Ru , Lewis-Ballester Ariel , Karkashon Shay
Published: February 2020

Human tryptophan dioxygenase (hTDO) is a tetrameric heme-containing enzyme that is responsible for metabolizing 95% of our dietary Trp, the least abundant essential amino acid. It catalyzes the first and rate-limiting step of the kynurenine pathway by dioxygenation of Trp to N-formylkynurenine. hTDO is mostly expressed in the liver. In addition to be crucial for Trp homeostasis, hTDO has been implicated in a variety of human diseases including cancer, neurological and immunological diseases. hTDO is hence considered as an important drug target. Here we show that hTDO contains two Trp binding sites: an active site, where the dioxygenation reaction takes place, and an exo site, where Trp, or other effector molecules, binds. Mutagenesis, biochemical and biophysical studies indicate that the L-Trp affinity towards the exo site is 15-fold higher than that towards the active site; in addition, the occupation of the exo site by L-Trp changes the conformation of the enzyme, thereby perturbing the redox potential of the heme as well as the activity of the enzyme. The data will be discussed in the context of the structural and functional relationships of the enzyme.
Properties of Porphyrin- and Phthalocyanin-Monolayers at Metal-Electrolyte Interfaces
Authors: Wandelt Klaus R.
Published: February 2020

The adsorption of organic layers on solid surfaces is a promising route to produce surfaces of designed functionality. In this lecture an overview will be given about state-of-the-art investigations of the structural and chemical properties of porphyrin- and phthalocyanin-monolayers adsorbed electrochemically in the form of their molecular cations on anion-modified single-crystal metal electrode surfaces as a function of the nature of the metal (copper, gold), the kind of the pread-sorbed anions (chloride, iodide, sulfate), the symmetry of the surface ((100), (111)), and the electro-chemical potential, using besides classical electrochemical methods Electrochemical Scanning Tunneling Microscopy (EC-STM), and ex-situ Synchrotron X-Ray Photoelectron Spectroscopy (S-XPS). Particular attention will be paid to the self-assembly- vs. template-effects in the structure formation process, to structural phase transitions as a function of electrochemical potential, as well as to the chemical reactivity of selected porphyrins and phthalocyanins. Fig. 1b shows 5,10,15,20-Tetrakis(4-trimethylammonio-phenyl)porphyrin molecules adsorbed on a Cl-precovered Cu(111) surface. Instead of the threefold symmetry of the substrate (Fig. 1a) the molecules self-assemble into a square molecular superlattice (Fig.1b) [1]. Fig.2 shows coexisting square and hexagonal structure domains of 3-pyridyloxy-appended phthalocyanine on iodide precovered Cu(100) [2].

References

[1] Thanh Hai Phan, Tomasz Kosmala, and Klaus Wandelt, in preparation

[2] Thanh Hai Phan, Stephan Breuer, Uwe Hahn, DucThanh Pham, Tomás Torres, and Klaus Wandelt,

J.Phys.Chem.C, submitted

Fig. 1 5,10,15,20-Tetrakis(4-trimethylammonio-phenyl)porphyrin Fig. 2 3-pyridyloxy-phthalocyanine

on Cl-precovered Cu(111) [1] on iodide precovered Cu(100) [2].