bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Binders on the Performance of Silicon Oxide
Authors: Huang Haijun , Han Guangshuai , Xie Jingying , Zhang Quansheng
Published: February 2020

The higher specific capacity and richness in natural resources makes SiOx-based become a research focus by international scholar in recent years. A lot volume changes of material in the process of cycling which affects the batteries’ cycling performance, thereby limiting its development and usage. While choosing suitable binder is critical to effectively enhance the performance of the silicon oxide (SiOx) that has high specific capacity and easy pulverization. Researched the lithium insertion/extraction properties of SiOx composite electrode which prepared with polyvinylidene fluoride (PVDF), LA132 (which major copolymerization chain is polyacrylonitrile-polyacrylic acid (PAN-PAA)), polyacrylic acid (PAA). Electrochemical cycling tests with a current density of 160mA/g shows that SiOx electrode with conventional binder PVDF results in rapid capacity loss, while aqueous binder LA132 and PAA could dramatically improve cycle performance of SiOx. SiOx with PAA electrode exhibits reversible capacity still up to 1090mAh/g after 50 cycles. The analysis and characterization methods of SEM, EIS, XRD and differential capacity plots, it is prove that amorphous or little crystalline binder have physical or chemical reaction with –OH of SiOx and formed class network constitute. The expansion pulverization of SiOx power limited in original domain and maintained electronic and ionic conductivity effectively, improved cycle performance of materials.

Acknowledgements

The project was supported by the Shanghai Science and Technology Development Fund (15DZ2282000).

References

[1] J. Li, L. Christensen, M. N. Obrovac, K. C. Hewitt and J. R. Dahn. J. Electrochem. Soc., 155(2008): A234-A238.

[2] N. S. Hochgatterer, M. R. Schweiger, S. Koller, P. R. Raimann, T. Wöhrle, C.Wurm and M. Winter. Electrochem. Solid-State Lett. 11(2008): A76-A80.

[3] X. J. Feng, J. Yang, X. L. Yu, Wang J L, Y. N. Nuli. J. Solid State Electrochem, 17(2013):2461-2469.

[4] I. Kovalenko, B. Zdyrko, A. Magasinski, B. Hertzberg, Z. Milicev, R. Burtovyy, I. Luzinov, G. Yushin. Scicence, 334(2011):76-79.

Figure 1
All-Solid-State Rechargeable Battery with Rubidium Silver Iodide Electrolyte
Authors: Wang Yuchen , Zhang Chen , Qiao Xiaoyao , Zhou Xiangyang
Published: February 2020

All-solid-state electrochemical devices have drawn tremendous attention in recent years. Solid electrolytes are advantageous over liquid electrolytes because solid electrolytes have wider operation temperature range and are leakage free, non-flammable, thermally stable, and easy for fabrication. However, one of the major issues of all-solid-state electrochemical devices is the low ionic conductivity of the solid electrolyte. Rubidium silver iodide (RbAg4I5) has very high ionic conductivity because the iodide tetrahedral arrangement provides diffusion paths for the silver ions. In this work, a novel all-solid-state structural rechargeable battery with RbAg4I5 electrolyte was developed. A four-electrode method was used to evaluate the ionic conductivity of RbAg4I5 electrolyte. The values of the ionic conductivity of RbAg4I5 are in the range of 0.15-0.24 S cm-1. The electrodes of all-solid-state rechargeable batteries were prepared with high surface activated carbon, conductive carbon, RbAg4I5 and AgI. The independently made components were pressed together using a clipper. The cyclic voltammetry (CV) curves and galvanostatic charge/discharge (GCD) curves are shown as Figure 1 and Figure 2, respectively. The charge and discharge efficiency is 95%. The power density can reach 0.2 kW/kg and the energy density can reach 10 Wh/kg. Also, the operational temperature range of this all solid rechargeable battery is -40-100°C. The electrochemical processes during the charge/discharge processes are discussed.

Figure 1
Understanding the Effects of Cell Temperature Gradients on Battery Performance with Mathematical Modeling
Authors: Deshpande Rutooj , Shaffer Christian , Moore William
Published: February 2020

With wide acceptance of lithium ion batteries for electric and hybrid vehicle applications, precise understanding of cell performance at different operating conditions is increasingly important. Cell temperature is often a critical variable determining the cell performance during the vehicle operation. For automotive applications, various cooling/heating strategies are used to keep the cell operating temperature within the predetermined limits. This ensures safety during cell operations as well as helps cells meet the cell warranty targets. Heat generation and heat rejection by a cell during the operation may result in non-uniform temperature distribution within a cell. These effects are pronounced in large format cells. The variation in local temperature affects the kinetic and transport rates and therefore, may result in non-uniformities in the current distribution across the length/breadth of the electrodes. Widely used, Pseudo 2D (P2D) porous electrode models may not be able to accurately predict cell performance with temperature distribution. Here a simple Pseudo 3D model is developed as an extension to the P2D model to understand the implications of the temperature gradient on the cell performance and eventually on the cell life. Differences in cell performance at uniform temperature operation and with cell temperature gradients are highlighted.
Modeling Intercalation Driven Volume Change in Porous Electrodes
Authors: Garrick Taylor R , Higa Kenneth , Srinivasan Venkat , Weidner John W.
Published: February 2020

In order to accurately predict the behavior of electrochemical devices, it is necessary to develop sophisticated models that take into consideration transport processes, electrochemical phenomena, mechanical stresses, and structural deformations on the operation of an electrochemical system. Many different models exist that can predict the electrochemical performance of these devices under a variety of operating and design conditions. In many of these models, the porosity of a porous electrode is often assumed constant since the volume changes seen during the intercalation reaction can be small. However, electrode materials developed in recent years show significant volume changes during intercalation, which are unable to be accurately predicted using these constant porosity models.

Porosity and dimensional changes in an electrode can significantly affect the resistance of the battery during cycling and can cause premature failure of the battery due to generated stresses. Previously, we have shown the ability to incorporate dimensional and porosity changes in a porous electrode into a model to predict volume changes in the active material of a single electrode during intercalation through the coupling of porous rock mechanics and porous electrode theory. There were many assumptions used to obtain an analytical solution, including the assumption of bulk stress, bulk strain, uniform porosity, and uniform concentration across the electrode. Here, we present a model that removes these assumptions and illustrates the coupling of porous electrode theory and rock mechanics in order to predict stress, strain gradients, and porosity gradients across a porous electrode during cycling.
Three Dimensional Interconnected Nanopores Current Collector for Drastically Enhanced Pseudocapacitive Performance
Authors: Gao Yuan , Lin Yuanjing , Fan Zhiyong
Published: February 2020

Three dimensional (3-D) nanopores array has been widely regarded as the promising current collector for fabrication of pseudocapacitor electrodes, mainly due to its large surface area, efficient electron and ion transport, and strong structural stability. Typically, anodization of high purity aluminium (Al) is the facile method to achieve highly packed nanopores with straight channels, of which the structural parameters could be facilely tuned by anodization voltage and etching time. By deposition of conductive and active materials, each channel could serve as the unit cell to store the energy. Nevertheless, the drawbacks still exist in such structure from the following aspects: i) Each channel has the electronic connection only at the top of the nanopores, leading to long pathway for electron transport. ii) The ions diffusion pathway is cut off by the side walls of anodized aluminium oxide (AAO), resulting in the one dimensional diffusion way along the channel. iii) The volume/space occupied by AAO side walls has no contribution to the capacitance, resulting in the low efficient utilization of the nanostructure. To address above issues, we have engineered the 3-D interconnected nanopores array by anodization of unique Al alloy. In such an architecture, the side pores are uniformly distributed along the main channel of AAO, forming more porous and mechanically stable nanopores array. By controllable deposition of fluorine doped tin oxide (FTO) with the cost-effective method of ultrasonic spray pyrolysis, and electrochemical deposition of MnO2, the as-built pseudocapacitor electrode renders the highest areal capacitance of 322.6 mF cm-2 and volumetric capacitance of 80.65 F cm-3 at the discharging current density of 0.1 mA cm-2, and still maintains 236 mF cm-2 and 59 F cm-3 at the discharging current density of 1.5 mA cm-2. By contrast, the values for the pseudocapacitor electrode fabricated based on the traditional nanopores array current collector are 273.8 mF cm-2 and 68.45 F cm-3, respectively, and drastically degrade to 50 mF cm-2 and 12.5 F cm-3. The performance enhancement is much larger when the comparison falls on planar pseudocapacitor electrode. We ascribe the largely enhanced rate capability to two reasons: i) The interconnected nanopores structure offers more space, which benefits for loading of nanostructured MnO2. ii) The side pores allow ions to move freely into neighbouring channels, resulting in the faster ion diffusion. In this case, we regard such interconnected nanopores array as the superior current collector in pursuit of high performance pseudocapacitor electrode.

Figure 1
Mesoporous Nb2O5 Nanofibers with Pseudocapacitive Properties for Lithium and Sodium Storage
Authors: Wang Liu , Bi Xiaofang , Yang Shubin
Published: February 2020

Mesoporous Nb2O5 nanofibers were scalable fabricated via a typical electrospinning method and a specific vapor hydrolysis, followed by an annealing treatment. The uniformly distributed mesopores of ~10 nm are generated through the controllable vapor-phase hydrolysis process without any addition of either hard template or surfactant, which is proved to be a contamination-free and environment-friendly method to obtain mesoporous Nb2O5. According to the merits of layered structure of orthorhombic Nb2O5 (T-Nb2O5) and large scale of mesopores for fast Li and Na ions transportation, the resulting Nb2O5 nanofibers exhibit outstanding electrochemical performance for both lithium and sodium storage, especially show an excellent capacitor-like high-rate performance. In order to explore the origin of these ultrafast charge storage properties, the charge storage kinetics was investigated by cyclic voltammetry. The analytic results reveal a surface-controlled kinetics, which is characteristic of capacitive behavior. Due to the pseudocapacitive charge storage properties, mesoporous Nb2O5 fibers display both high energy density and power density. The facile fabrication of high quality mesoporous Nb2O5 nanofibers and the demonstration of good pseudocapacitive behavior show the great potential of mesoporous Nb2O5 for applications in fast energy storage fields.
New Catalysts Prepared By Co-Sputter Deposition for Direct Oxidation of Methanol
Authors: Fang Dan , Narayanan S. R.
Published: February 2020

Direct methanol fuel cells (DMFCs) are attractive because of the high energy density of methanol, the overall simplicity of the fuel cell system and the easy refueling.[1] The state-of-art DMFC systems are based on the use of platinum-ruthenium catalyst at the anode, platinum catalyst at the cathode, and a polymer electrolyte membrane separating the two electrodes.[2] Although fuel cell power source products are now available in the range of 50 Watt to 2 kW, the commercialization has not occurred in the anticipated large-scale mainly because of the high precious metal catalyst loadings and durability of ruthenium-based catalysts. Our present study is focused on the study of anode catalysts, specifically to improve durability and reduce its cost. To this end, we have examined binary catalysts consisting of platinum and a second metal M (M=niobium, tantalum and titanium) prepared by co-sputter-deposition.

Platinum and the metal M were co-sputtered from separate cathode targets simultaneously using a high-voltage direct current on a Toray paper substrate. The atomic composition of metal M to platinum was varied between 0.1-2 by fixing the sputtering power to the platinum target and varying the sputtering power to the target containing metal M. The structure, morphology and composition of the catalyst were investigated by SEM, EDX and XPS. The results of quasi-steady state voltammetry suggested that the well-known bi-functional mechanism for methanol oxidation was operative on Pt-Nb and Pt-Ta catalysts. With the same amount of platinum, the methanol oxidation current of Pt-Ta and Pt-Nb catalyst was significantly improved compared to a sputtered platinum catalyst (Figure 1). The methanol oxidation current of Pt-Ta and Pt-Nb catalyst was 11.1 times and 8.3 times of platinum catalyst at -0.1 V vs. mercury/mercury sulfate reference electrode. We will present our understanding of the interaction between Pt and M (M=Nb, Ta) in enhancing the electro-oxidation of methanol and report on our efforts towards optimization of the catalyst composition to lower the noble metal content and enable practical use of these new catalyst materials in fuel cells

Figure 1
Over Lithiation Technique to Prevent Irreversible Lithium Loss Due to SEI Formation
Authors: Blaser Rachel , Karulkar Mohan
Published: February 2020

High-capacity materials such as Si and C-Si composites are popular candidates for next generation anodes. However, these materials consume significant amounts of lithium during the formation of Solid Electrolyte Interface (SEI), leading to a large irreversible loss of lithium for cycling and loss of overall cell capacity. One approach to offsetting this effect is to overload the cathode to provide additional lithium. However, this approach reduces the overall cell energy density and reduces the benefits of using a higher capacity anode material. To enable better full cell implementation of Si based anodes, an additional source of sacrificial lithium for SEI formation would be desirable if it could be added to the cell without a significant weight penalty.

We have demonstrated the use of the dual cast technique to incorporate additional Li into the battery cell system using existing slurry casting procedures. The dual cast of NMC and Li2O2 has shown an increase in first cycle capacity up to 2.2x the capacity of traditional NMC cathodes under the same cycling conditions. Characteristic voltage profile curves were confirmed to be present only when Li2O2 was included in the cell. To achieve the full benefit of the additional lithium the voltage maximum must be increased to 4.6V during the initial break-in cycles. The capacity increase due to the Li2O2 was beyond the increase due to the overcharging that can occur when NMC is cycled beyond 4.3V to 4.6V. It was also shown that the dual cast electrodes with Li2O2 could tolerate being cycled in the presence of a carbonate solvent base electrolyte.

Figure 1
Electric and Hybrid-Electric Marine Ferries for Public Transportation Networks
Authors: Patey Timothy John
Published: February 2020

Coastal cities and regions rely on marine vessels to ensure safe and timely transport of people within their public transportation networks. Local emissions of particulate matter and noise pollution are of increasing concern for growing cities. The UN forecasts the percentage of people living in cities will rise from 54 percent in 2014 to 66 percent in 2050 [1] when global population is forecast to reach 9.7 billion. Hence, the infrastructure built today will have to serve the growing communities of tomorrow.

Li-ion battery systems within electric and hybrid-electric marine vessels offer a low cost to greatly reduce local and global emissions of particulate matter and harmful gases within vessels which are traditionally powered by combustion of fossil fuels. In this work, design considerations of Li-ion batteries within marine vessels are presented, including cathode/anode requirements, safety, and thermal management considerations. Use of a thermal, electric, aging model is implemented for a first assessment of the dimensioning of a Li-ion battery system within a marine vessel, with a specific focus on the choice of lithium titanate as anode versus the conventional graphitic anode.

1. World Population Prospects, 2014, United Nations.

Figure 1
(Invited) New Developments in Single Molecule Magnetism of Endohedral Metallofullerenes
Authors: Krylov Denis , Chen Chia-Hsiang , Liu Fupin , Avdoshenko Stanislav , Brandenburg Ariane , Kostanyan Aram , Greber Thomas , Popov Alexey A.
Published: February 2020

Encapsulation of metal clusters within the fullerene cage has multiple structural and physical consequences for the properties of endohedral metallofullerenes (EMFs). In particular, when encapsulated metals are lanthanides, unusual magnetic properties can be achieved. Interaction of lanthanide ions with negatively-charged non-metals (nitride, carbide) create large magnetic anisotropy of the former, which facilitates single molecule magnetism in EMFs. At the same time, carbon cage protects the endohedral species from the environment allowing formation of rather exotic combinations of metal and non-metal ions. Exchange and dipolar interaction between endohedral lanthanides also dramatically affects the magnetism of EMFs. This contribution will present an overview of the recent developments in the single molecule magnetism of EMFs.
(Invited) Actinide Endohedral Fullerenes: Uranium-Based Systems with Unique Bonding Motifs
Authors: Echegoyen Luis , Cai Wenting , Murillo Jesse , Chen Ning , Najera Daniel , Fortier Skie
Published: February 2020

Endohedral fullerenes, which are carbon cages that encapsulate atoms, ions or clusters have been known since the early days immediately following the discovery of the fullerenes in 1985 by Smalley, Kroto and Curl. A wide range of cages, varying in size, shape and electronic properties have been observed which encapsulate individual atomic or ionic species or clusters that possess complementary characteristics. Of the many endohedral fullerenes that have been characterized and reported, lanthanide endofullerenes have received a lot of attention but the corresponding actinide systems have not been extensively investigated experimentally, although theoretical calculations have been reported, especially after the original report by Smalley et al in 1992 of the mass spectral observation of mono- and di-metallic Uranium endohedrals with formulas U@C2n (n=14-36) and U2@C2m (m=25-30). The latter species containing two U ions inside have been the subject of multiple theoretical calculations using multiple cages, mainly C60, C70, C80 and C90. However, experimental reports of these exotic compounds are limited to three and only one involved purification using a two-stage HPLC protocol and presented the UV-Vis spectra for U@C82 and U2@C80.

We have undertaken a systematic study of U endohedrals and have succeeded in identifying many different compounds using HRMS, and have succeeded in purifying and characterizing several mono-metallic endohedrals, including their x-ray single crystal structures, specifically U@C74 and two different isomers of U@C82.

Of particular interest for this presentation are totally unexpected Uranium endohedrals with formula U2C(2n+1), where n=39, 40 which correspond to carbides containing single C atoms encapsulated with two Us inside C78 and C80 cages. More interestingly, U2X@C2n compounds have also been detected, where X=N and O, besides C. These latter compounds will be described and their properties will be presented and discussed.
(Invited) Synthesis and Structural Elucidation of Y2C2@C2n (2n = 86, 88 and 90)
Authors: Pan Changwang , Lu Xing
Published: February 2020

Carbide cluster metallofullerenes (CCMFs) have drawn more and more attention during recent years due to their special structures and properties1
-
3. Herein, we found that some unprecedented medium-sized carbon cages ranging from C86 to C90 can be stabilized by choosing suitable metal atoms (yttrium). Our single-crystal crystallographic results unambiguously showed that they are carbide cluster metallofullerenes Y2C2@C2n (2n=86,88 and 90). It is proposed that the size of the encapsulated metallic units plays a crucial role in stabilization of these medium-sized fullerene cages.

Reference

(1) Lu, X.; Akasaka, T.; Nagase, S. Carbide Cluster Metallofullerenes: Structure, Properties, and Possible Origin. Acc. Chem. Res.
2013, 47 (7), 1627–1635.

(2) Cai, W.; Bao, L.; Zhao, S.; Xie, Y.; Akasaka, T.; Lu, X. Anomalous Compression of D5(450)-C100 by Encapsulating La2C2 Cluster instead of La2. J. Am. Chem. Soc.
2015, 137 (32), 10292–10296.

(3) Cai, W.; Li, F.-F.; Bao, L.; Xie, Y.; Lu, X. Isolation and Crystallographic Characterization of La2C2@Cs(574)-C102 and La2C2@C2(816)-C104: Evidence for the Top-Down Formation Mechanism of Fullerenes. J. Am. Chem. Soc.
2016, 138 (20), 6670–6675.
(Invited) Recent Crystallographic Studies of Endohedral Fullerenes
Authors: Balch Alan L. , Olmstead Marilyn M. , Powers Xian B. , Bowles Faye L.
Published: February 2020

Recent single crystal X-ray diffraction studies of endohedral fullerenes will be reported. These studies are aimed at identifying the particular shape of carbon cage and the positioning of the metal ions inside. A case of external modification of an endohedral fullerene will be described where the cage plays an unusual role in determining the reactivity of the external appendage.
(Invited) Extending the Spiral Algorithm to Non-Classical Isomers and Metallofullerenes
Authors: Gan Li-Hua , Fowler P.W.
Published: February 2020

The face-spiral algorithm proposed by Manolopoulos et al.1 has been extensively used to construct classical fullerenes, 2 and the corresponding numbering of isomers has been recommended as a systematic nomenclature. The spiral algorithm is an important help in clarifying the structures of fullerenes, endohedral fullerenes and fullerene derivatives. Recent and accumulating evidence shows that non-classical fullerene cages with heptagon(s) or square(s) may be competitive with their classical counterparts in some situations; non-classical fullerene cages may be favored parent cages of metallofullerenes and fullerene derivatives. It is desirable to make a systematic examination of the effect of heptagon(s) and/or square(s) on the structures and properties of bare fullerenes, fullerene ions, metallofullerenes and fullerene derivatives. The original spiral algorithm does not generate non-classical fullerene isomers, but can be adapted to do so. An extended spiral algorithm can selectively generate non-classical fullerenes with one or two heptagon(s) or square(s) in the size range of interest, and has been used [3-5] to identify favored non-classical fullerenes and metallofullerenes. Energetic arguments suggest that non-classical fullerene cages may play a significant role in the formation of fullerenes and metallofullerenes.

References

[1] D. E. Manolopoulos, J.C. May, S.E. Down, Chem. Phys. Lett, 1991, 181, 105-111.

[2] P. W. Fowler, D. E. Manolopoulos, an Atlas of Fullerenes, Clarendon Press, 1995.

[3] L. H. Gan, D. Lei, P. W. Fowler, J. Comput. Chem. 2016, 37, 1907-1913

[4] L.-H. Gan, R. Wu, J.-L. Tian, J. Clarke, C. Gibson, P. W. Fowler, 2017, 38, 144–151

[5] L.-H. Gan, R. Wu, J.-L. Tian and P. W. Fowler, Phys. Chem. Chem. Phys., 2017, DOI: 10.1039/C6CP07370K.
(Invited) Tailoring 2D Material-Based Aerogels for Energy Storage and Sensing Applications
Authors: Worsley Marcus A.
Published: February 2020

Aerogels are nanoporous solids used in electrochemical processes relevant to a number of applications including, catalysis, batteries, supercapacitors, and sensing due to their high internal surface, composition, and small pore/particle size. Two-dimensional (2D) nanomaterials, such as graphene, boron nitride, transition metal dichalcogenides, also exhibit a range of distinct electronic and chemical properties, but are typically limited to thin films and coatings. Assembling 2D nanomaterials into monolithic aerogels expands their application space to include technologies and manufacturing processes that require a macroscopic 3D form factor. Furthermore, realizing the unique inherent qualities of 2D materials in a low-density, high surface area architecture creates new materials with novel properties and features only displayed within an aerogel framework. Here, we demonstrate recent work on assembling and tailoring various properties of aerogels made from several different 2D materials, (e.g. boron nitride, graphene, dichalcogenides, etc.). In particular, methods of controlling the composition via doping or hybrid aerogels (e.g. combining two or more layered materials), crystallinity, and macroscale architecture will be presented. The impact of those changes on aerogel properties and performance in energy storage and sensing devices will be discussed.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Graphene and Graphene Oxide in Low Temperature Fuel Cells for Enhanced Performance.
Authors: Holmes Stuart Martin , Balakrishnan Prabhuraj , Perez Page Maria , Ozdincer Baki , Al Batty Sirhan
Published: February 2020

The barrier and electrical properties of graphene and graphene oxide have been well documented with significant discussion around their efficacy as additives in low temperature PEM fuel cells. Graphene oxide has been demonstrated to be an ionic conductor but impermeable to dry gases and electrons. Graphene is an excellent in-plane electronic conductor but impermeable to all species apart from protons through the plane.

Here we will describe the work carried out at Manchester University incorporating Graphene, Reduced Graphene Oxide (RGO) and Graphene Oxide into PEM fuel cell Membrane Electrode Assemblies (MEA’s).

Reduced Graphene Oxide and boron and nitrogen doped RGO has been added to/replaced the carbon in the microporous layer adjacent to the cathode catalyst and provides enhanced fuel cell performance (up to 84% improvement in power density) due to greater electrical conductivity.

Graphene Oxide (GO) has been added to the Nafion binding layer in a Direct Methanol Fuel Cell (DMFC) providing additional tortuosity and hence reduced methanol permeability, the optimisation of the GO loading has led to superior performance(up to 50% improvement in power density) when compared to a standard DMFC.

The addition of CVD graphene (above 50oC) and hBN (at all temperatures) into the MEA has demonstrated no change in proton conductivity but lower fuel permeability [1], supporting the hypothesis of CVD graphene as a proton conductor and again increasing the power density achievable (30% in the initial experiment) by a DMFC. Figure 1

1. Holmes, S., Balakrishnan, P., Kalangi, V. S., Zhang, X., Ajayan, P. M., Lozada Hidalgo, M., & Raveendran Nair, R. (2016). 2-D Crystals Significantly Enhance the Performance of a Working Fuel Cell. Advanced Energy Materials. .

Figure 1
Phonon and Defect Induced Transparencies in the Mid-Infrared Spectrum of Grafted Single Layer Graphene
Authors: Lapointe François , Rousseau Bruno , Nguyen Minh , Aymong Vincent , Biron Maxime , Gaufrès Étienne , Desjardins Patrick , Côté Michel , Martel Richard
Published: February 2020

The Drude-like response of graphene in the terahertz and infrared region of the spectrum has made it attractive for optoelectronic applications in this range, because the response can be controlled by gating and doping. [1] Graphene infrared response can further be tailored for photonics and plasmonics, as the patterned material harbors low energy plasmon modes. [2] However, the infrared spectrum of pristine single layer graphene (SLG) is monotonous; in contrast to Raman, there are no infrared-active phonon modes, while bilayer graphene displays a Fano resonance in the infrared at ~1600 cm-1. [3]

In a first time, we show experimentally that grafting SLG with halogenophenyl moieties induces optical transparencies at two specific energies: 1250 and 1600 cm-1 [4], in close similarity to the bands that can also be observed in carbon nanotubes as Fano resonances. [5] Unlike bands caused by the absorption of light by vibrational modes, these antiresonances show a decrease of the absorbance, an optical transparency effect. Moreover, we show that the amplitude of the transparencies can be modulated by changing the charge carrier density through doping, and by the defect density through controlled grafting.  

In as second time, we will present a theory based on quantum mechanics to calculate the optical conductivity of grafted SLG. [4] The model puts into play phonon modes with momenta different from Γ that can be addressed through scattering on defects. Numerical simulations reproduce the experimental data with good agreement. The theory also captures the dependence of the signal on charge carrier density and defect density.  

Our findings bring a new understanding for the physics behind the infrared activity of nanostructures, while opening new capabilities for tailoring the optical spectrum of nanomaterials.

References

[1] Horng et al. (2011) Phys Rev B 83:165113

[2] Low & Avouris (2014) ACS Nano 8:1086

[3] Kuzmenko et al. (2009) Phys Rev Lett 103:116804

[4] Rousseau et al. (2014) arXiv preprint arxiv:1407.8141

[5] Lapointe et al. (2012) Phys Rev Lett 109:097402
Doping of Graphene By Atomic Layer Deposition of Ruthenium
Authors: Kim Minsu , Kim Ki-Ju , Lee Seung-Joon , Kim Hyun-Mi , Cho Seong-Yong , Kim Min-Sik , Kim Soo-Hyun , Kim Ki-Bum
Published: February 2020

Graphene has received enormous attention from both academia and industry owing to its excellent electrical, optical, chemical, and mechanical properties. A combination of properties makes graphene a strong candidate for the next generation of flexible and transparent conductive electrode (TCE) materials, but in practice the sheet resistance of a single, as-grown layer of graphene is still not sufficient for this purpose. One of the methods for creating highly conductive graphene films is to increase the charge carrier density through doping.

Here, we propose a novel method of graphene doping based on atomic layer deposition (ALD). Ideally, adsorption of precursor should be suppressed on clean surface of graphene since the surface is inert without dangling bonds and chemically active functional group. Defects (e.g., grain boundaries, wrinkles, cracks, holes and residual material) work as selective nucleation sites. Ru is selected due to it having a well-established precursor and recipe and the difference in work function between graphene and Ru can also allow for work function tuning and carrier generation.

The sheet resistance of graphene synthesized by chemical vapor deposition is found to be significantly reduced by the selective atomic layer deposition (ALD) of Ru onto defect sites such as wrinkles and grain boundaries. With 200 ALD cycles, the sheet resistance is reduced from ~500 Ω/sq to <50 Ω/sq and the p-type carrier density is drastically increased from 1013 cm-2 to 1015 cm-2. At the same time, the carrier mobility is reduced from ~670 cm2V-1s-1 to less than 100 cm2V-1s-1. This doping of graphene proved to be very stable, with the electrical properties remaining unchanged over 8 weeks of measurement. The selective deposition of Ru on defect sites also makes it possible to obtain a graphene film that is both highly transparent and electrically conductive (e.g., a sheet resistance of 125 Ω/sq with 92 % optical transmittance at 550 nm). The increase in the work function of graphene from 4.6 to 5.1 eV with Ru ALD provides clear evidence of hole carrier generation as a result of an electronic interaction between graphene and Ru. This demonstration of strong and stable doping of graphene with a high optical transmittance is therefore expected to contribute to the use of graphene as a TCE, and in other fields.

Figure 1. Ru ALD on graphene. (a) TEM images of graphene after 20 cycles of Ru ALD. (b) Sheet resistance of graphene as a function of the number of ALD cycles. Inset of (b) shows sheet resistance as a function of time.

Reference

Minsu Kim et al, ACS Appl. Mater. Interfaces, Article ASAP

Figure 1
(Invited) Colloidal Gold Nanoparticles Stabilized By Hydroxylated Fullerenes
Authors: Kokubo Ken , Sato Nozomi , Sakurai Hidehiro
Published: February 2020

Since bare gold nanoparticles are unstable, they have to be stabilized by protecting with ligands, stabilizing with polymers or immobilizing on solids. Properties of gold nanoparticles depends on the design of their protecting ligands. Fullerene C60, a polyhedral carbon allotrope, possesses unique physical and chemical properties such as electron accepting character, high reactivity to radical species, low electrical conductivity, high thermal stability and so on, therefore utilization of fullerene derivatives to metal particles might be interesting, indeed, there are some reports on Au nanocomposites with C60. In order to prepare the colloidal dispersion of the Au and fullerene composites, soluble fullerene derivatives should be used. We have developed a series of polyhydroxylated fullerenes, C60(OH)n, and among them, C60(OH)36exhibits high water solubility up to 58.9 mg/mL and high dispersion on a molecular level.

Au:C60(OH)36 was synthesized by reduction with excess amount of NaBH4 from HAuCl4 aqueous solution in the presence of C60(OH)36. The colloidal particles are homogeneously dispersed in water and are stable for months. Its core size (measured by Transmission Electron Microscope) and colloid size (measured by Induced Grating Method) are 3.7 nm and 12.2 nm, respectively. X-rays photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) measurements revealed that the nanogold is negatively charged in total, but rather positively charged on the surface due to the interface interaction with C60(OH)36.

In this presentation, the catalytic activity of the thus-prepared gold nanoparticles will also be discussed.
(Invited) Thermoelectric Energy Conversion Optimized By Electrolyte Gating
Authors: Takenobu Taishi
Published: February 2020

Thermoelectric energy conversion is one of the key technologies for energy harvesting devices to convert waste heat into electric power, and vice versa. In these devices, the Seebeck coefficient (= thermopower, S), which is the proportional constant to the voltage generation against an induced temperature gradient, is a significant factor in designing thermoelectric devices. Importantly, according to the Mott equation, Sis proportional to the energy derivative of the electronic density of states at around Fermi energy; therefore, it is critically important to control the energy band filling. Conventionally, the band filling is tuned by chemical doping and, in most materials, it is very difficult to establish precisely controllable doping methods.

Another important factor for thermoelectric energy conversion devices is the thermoelectric power factor S
2
·σ (σ
is conductivity). It should be strongly emphasized that the power factor has to be optimized to maximize the electric power output of thermoelectric devices. Consequently, this is a key parameter for applications. However, it is widely known that there is a trade-off between |S| and σ in terms of carrier density, n. Although σ is almost linearly proportional to n, |S| decreases with increasing n. Therefore, it is necessary to maximize S
2
·σ
by tuning n.

Here, we optimized thermoelectric energy conversion efficiency using the electrolyte gating technique. Importantly, owing to the high specific capacitance of electric double-layers (EDLs) (1−10 μF cm-2), we can continuously control the carrier density up to 1014 cm-2, which results in the tuning of the carrier polarity between p-type and n-type [1-6]. Based on this technique, we investigated the thermoelectric properties of transition metal dichalcogenide monolayers [7], single-walled carbon nanotubes [8,9], organic Mott insulators [10], organic molecules and organic polymers.

[1] J. Pu, L.-J. Li, T. Takenobu, et al., Nano Lett. 12, 4013 (2012).

[2] J.-K. Huang, T. Takenobu, L.-J. Li, et al., ACS Nano. 8, 923 (2014).

[3] J. Pu, L.-J. Li, T. Takenobu, et al., Adv. Mater. 12, 4013 (2016).

[4] H. Shimotani, T. Takenobu, et al., Adv. Funct. Mater. 24, 3305 (2014).

[5] Y. Kawasugi, T. Takenobu, et al., Nat. Commun. 7, 12356 (2016).

[6] Y. Yomogida, T. Takenobu, et al., Adv. Mater. 24, 4392 (2012).

[7] J. Pu, L.-J. Li, T. Takenobu, et al., Phys. Rev. B 94, 014312 (2016).

[8] K. Yanagi, T. Takenobu, et al., Nano Lett. 14, 6437-6442 (2014)

[9] S. Shimizu, T. Takenobu, et al., SMALL 12, 3388 (2016)

[10] Y. Kawasugi, T. Takenobu, et al., Appl. Phys. Lett. 109, 233301 (2016).
Impact of Carbon Addition on 1D Oxide – Chalcogenide Heterostructures
Authors: Subramanian Vaidyanathan
Published: February 2020

Mother Nature and our surroundings always inspire us with new Ideas to purse science. An outcome of one such motivation is the development of a family of 1D oxide chalcogenide composites with interesting architectures and their properties.

As a case study, I will present our recent contributions on the topic of titanium dioxide (TiO2) as a façade for the deposition of visible light agents for light absorbance and charge generation. We know that chalcogenides can aid in improving light harvesting properties of oxides. To this end, the synthesis of the 1D oxide followed by the deposition of a chalcogenide is presented. Of particular focus will be the role of carbon additives. The main insights presented in this talk is the method to integrate carbon, the type of carbon additives and their impact, and what are the possible benefits of the carbon presence in a oxide-chalcogenide system.
Visible Light-Driven Water Oxidation with Porphyrin Sensitizers and Water Oxidation Catalysts
Authors: Imahori Hiroshi
Published: February 2020

Finding renewable energy sources is a crucial task in making our society sustainable. In this regard, exploitation of sunlight as an infinite energy source is attractive. Specifically realizing artificial photosynthesis, i.e., integration of light-harvesting, multi-step electron and proton transfer, and water oxidation for the efficient production of fuels, is a great challenge in chemistry. For the purpose, dye-sensitized photoelectrosynthesis cells (DSPSC) have been investigated, as the heterogeneous water splitting on inorganic semiconductor is promising for the upcoming large scale device operation. In DSPSC a molecular sensitizer adsorbed on a semiconducting electrode harvests visible light and injects an electron from the sensitizer excited-state (S*) to a conduction band (CB) of the electrode. Then, the sensitizer radical cation (S•
+) extracts an electron from a water oxidation catalyst (WOC) to regenerate the sensitizer and one-electron oxidized WOC. After repeating the cycle, high oxidation states of the WOC are generated, eventually transforming two water molecules into four protons and one oxygen molecule. As the sensitizer bis(2,2’-bipyridine)(4,4’-diphosphonato-2,2’-bipyridine)ruthenium(II) (RuP) has been frequently employed for the construction of molecular artificial photosynthetic systems, due to its sufficient first oxidation potential for water oxidation and a long lifetime of its excited state for electron injection. However, the light-harvesting ability of RuP is rather low in visible region beyond 500 nm. Given that yellow to red photons mainly shower down on the earth from sun, utilization of photons in visible region is important for efficient chemical conversion by sunlight. Along this line, porphyrins are promising as the sensitizer because of their excellent light-harvesting in visible region and facile tuning of their excited-states and redox properties by their peripheral functionalization. Nevertheless, molecular artificial photosynthetic systems with porphyrins as the sensitizer are so far limited owing to their low performance. One plausible reason is the occurrence of fast charge recombination (CR) between the electron injected into the CB of TiO2 (denoted as TiO2(e−)) and S•
+. CR from TiO2(e−) to the oxidized WOC is also reported to take place within a few microsecond. Undesirable CR from TiO2(e−) to water is also suggested. Therefore, to overcome the drawbacks, it is crucial to modulate the electron transfer (ET) properties at the interfaces. In this talk, I will give an overview of our recent initiatives on visible light-driven water oxidation with porphyrin sensitizers and water oxidation catalysts.

[1] M. Yamamoto, L. Wang, F. Li, T. Fukushima, K. Tanaka, L. Sun and H. Imahori, Chem. Sci., 7, 1430-1439 (2016).

[2] M. Yamamoto, Y. Nishizawa, P. Chábera, F. Li, T. Pascher, V. Sundström, L. Sun, and H. Imahori, Chem. Commun., 52, 13702-13705 (2016).
Bioinspired Vitamin B12 Catalysis
Authors: Gryko Dorota
Published: February 2020

Vitamin B12 catalysis is inspired by the ultimate chemist Nature, as methylcobalamin and adenosylcobalamin are involved in numerous biocatalytic reactions including isomerization, methylation and dehalogenation.[1,2] This type of catalysis has been successfully translated into the laboratory and used in a small collection of reactions.[2, 3] The advantage of using vitamin B12 as a catalyst lays in the complete stability of the central cobalt ion, whereas most catalytic reactions require the addition of toxic metals plus complex ligands into a cocktail of reagents, vitamin B12in itself is a package deal. It has also been well documented that the reaction mechanism usually follows a radical pathway, bringing a new dimension to this already interesting field.

Along this line, we have proposed vitamin B12
photochemical activation in bond forming and cleavage reactions.[4] Our results show that TiO2 can be utilized in a catalytic system with vitamin B12, allowing for the efficient photocatalytic reduction of Co(III) to Co(I). Under light irradiation vitamin B12 derivative unusually catalyzes a new olefinic sp2 C-H alkylation reaction, with diazo reagents as a carbene source, instead of the expected cyclopropanation. Furthermore, we also use challenging acyl radicals in C-C bond forming reactions. Light-induced vitamin B12-catalyzed methods are also suitable for C-O bond cleavage. Our studies showed that reduced cyanocobalamin catalyzes C-O bond cleavage in allyloxyarenes.

These key findings emphasize the unique feature of vitamin B12as a catalyst to achieve something unachievable with other methodologies or to find a greener approach.

1. Banerjee, R. Chemistry and Biochemistry of B12, John Wiley & Sons, Inc, 1999

2. K. ó Proinsias, M. Giedyk, D. Gryko, Chem. Soc. Rev.
2013, 42, 6605-6619.

3. Giedyk, M.; Fedosov, S.; Gryko, D. Chem.
Commun.
2014, 50, 4674-4676.

4. a) Shimakoshi, H.; Nishi, M.; Tanaka, A.; Chikama, K.; Hiseada, Y. Chem. Commun. 2011, 47, 6548-6550. b) K. Tahara, Y. Hisaeda, Green Chem.
2011, 13, 558-561. H. Shimakoshi, L. Li, M. Nishi, Y. Hisaeda, Chem.
Commun.
2011, 47, 10921-10923.

Figure 1
Structural Characterization of Heme Uptake System in Corynebacteria
Authors: Aono Shigetoshi
Published: February 2020

Heme uptake machinery of Corynebacteria including Corynebacteria glutamicum and Corynebacterium diphtheriae consists of heme binding proteins, HtaA and HtaB, and the ABC-type heme transporter HmuTUV. In this work, we have studied the structural and functional relationships of HtaA, HtaB and HmuT in Corynebacterium glutamicum.

Sequence analysis identified a conserved region (CR) of approximately 150 amino acids that is duplicated in HtaA and present in a single copy in HtaB [1]. HtaA consists of two homologous CRs in the N- and C-terminal regions. We have determined the crystal structures of the N-, and C-terminal CR of HtaA (HtaA-N and HtaA-C, respectively) and HtaB at the resolution of 2.0, 1.3, and 1.7 Å, respectively. HtaA-N consists of 11 β strands and two short α helices and accommodates one heme molecule with Tyr58 located in the first α helix as the heme axial ligand. Tyr58 forms a hydrogen bond with His111. A heme propionate forms hydrogen bonds with Ser54 and Tyr201. Heme is accommodated in an open pocket formed by hydrophobic amino acid residues.

HtaA-C and HtaB show similar global structures to HtaA-N. The key residues for heme-binding and recognition including the axial ligand of heme and residues involved in the hydrogen bonding interactions with heme are conserved among HtaA-N, HtaA-C, and HtaB.

We also determined the crystal structure of HmuT at the resolution of 1.4 Å [2]. HmuT consists of structurally similar two domains located in the N-terminal and C-terminal regions connected a long α helix. A single heme molecule is bound in the cleft between these domains. Heme iron is ligated by His141 and Tyr240, and Tyr240 forms a hydrogen bond with Arg242. Intriguingly, HmuT binds a heme with two different orientations.

References

[1] C. E. Allen, M. P. Schmitt. (2011) J. Bacteriol.
193, 5374-5385.

[2] N. Muraki, S. Aono. (2016) Chem. Lett. 45, 24-26.
Linearly- and Cross-Conjugated Porphyrin Dimers: Synthesis and Characterization
Authors: Wang Hong , Jinadasa R.G. Waruna , Thomas Michael , Hu Yi , D'Souza Francis
Published: February 2020

Acenes consisting of linearly fused benzene rings have been of great interest of study due to their unique electronic properties, in particular, their exceptionally high charge mobility, as well as their close relation to graphene.1-4 Although larger acenes are predicted to have even better electron mobility, larger acenes are not stable and soluble. Much effort has been devoted to the synthesis, stabilization/functionalization and characterization of acenes longer than pentacene in recent years.5-7 The fusion of an acene with two or more chromophores will greatly extend the pi-conjugation, and will likely produce electronically highly interactive multiporphyrinic systems. In this presentation, we present the synthesis and characterization of the pentacene-fused (linearly conjugated) and pentaquinone-fused (cross-conjugated) porphyrin oligomers. These pentacene-fused porphyrins are much more stable than their corresponding pentacene derivatives. The electronic absorption spectra and transit spectroscopy of these porphyrins indicate highly interactive multiple pi-systems. The electronic and optical properties of these i-extended porphyrins were measured using UV-Vis spectroscopy, life-time and steady state fluorescence spectroscopy, and cyclic voltammetry. DFT calculations were also performed for these porphyrins.

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M. Bendikov, F. Wudl, D. F. Perepichka, Chem. Rev.
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Z. Sun, J. S. Wu, Aust. J. Chem.
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2008, 47, 452-483

S. S. Zade, M. Bendikov, J. Phys. Org. Chem.
2012, 25, 452-461

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2010, 22, 3876-3892

Figure 1