bluuebunny/crossref_metadata_2025 huggingface dataset:
Three-Dimensional Graphene Network As a Highly Macro-Porous, Flexible and Large-Scale Electrode for Supercapacitor Application
Authors: Lin Che-Hsien , Tsai Chuen-Horng , Tseng Fan-Gang , Hsieh Chien-Kuo
Published: February 2020

Graphene, a two-dimensional (2D) carbon nanomaterial, was widely used in many electrochemical applications due to their high mechanical strength, good chemical stability, high specific surface area, and excellent electrical conductivity. However, the major concern for those applications was the activity reaction surface area of the 2D plane structure of graphene. Therefore, in order to enhance the reaction surface area of graphene, the development of a highly porous network-macrostructure with large surface area three-dimensional graphene is an effective strategy to be achieved for electrochemical applications.

In this study, we reported an effective and simple method to prepare highly macro-porous, large-scale and flexible three-dimensional graphene foam (3D GF) which was synthesized on the commercial nickel network via the chemical vapor deposition (CVD) method. The quality of 3D GF was investigated by using a Raman spectroscopy. A field-emission scanning electron microscopy was used to examine the surface morphology of 3D GF. A high-resolution transmission electron microscopy was utilized to analyze the inter-layer distance and the number of layers of graphene. Raman results revealed the highly uniform performance of the large-scale 3D GFs. The cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS) were carried out to examine the electrochemical properties. Compared with the traditional 2D plane-structure graphene synthesized on the Ni foil, the CV and EIS results measured by the 3D GF confirmed its superior capacitive behavior, higher specific surface area, and also demonstrated the excellent power capabilities with a low solution resistance and charge transfer resistance. It was found that the specific capacitance of 3D GF was three times larger than the traditional 2D plane-structure graphene. In this study, a tube furnace thermal CVD was utilized to synthesize the large-scale 3D GF. The Ni forms can be curled and loaded into the tube furnace for CVD processes to fabricate the large-scale 3D GFs easily. We provided an easy method to fabricate the highly macro-porous, large-scale and flexible 3D GFs for the future graphene-based potential applications.
Understanding of Capacity Loss/Fading of Li-Rich Layer-Structured Cathode Materials Based on Structural/Electrochemical Analyses
Authors: Fung Kuan-Zong , Tsai Shu-Yi , Ni Chung-Ta , Lin Wei-Zhi , Huang Bo-Yuan
Published: February 2020

Li-rich layer-structured cathode materials formulated as xLi2MnO3 -(1-x)LiMO2(M = Mn, Ni, Co, etc.) have received much attention due to their surprisingly high reversible capacity for Li-ion battery applications. For the understanding of these materials, a systematic study on complicated crystal structures and reaction mechanisms during electrochemical charge/discharge cycles is employed. Although Li-rich layer-structured cathode material show a reversible capacity as high as 250 mAh/g at low rate, its electrochemical properties such as capacity loss at first cycle, rate capability and capacity fading still need to be examined and characterized. In this study, several compositions of xLi2MnO3 -(1-x)LiMO2 (M = Mn, Ni, Co, etc.) were investigated.

The TEM structural analysis shows that the evidence of spinel phase after cycling. It is believed that the transition from layered structure to spinel structure may induce a large lattice distortion resulting in lattice breakdown and capacity. In additions, the phase transition is caused by the redox reaction of transition metal ions through charging/discharging tests. Thus, the cycling behavior of Li-rich layer-structured oxides is studied by changing the oxidation state of transition metal ions in the layered structures. XRD, SEM, TEM will be used for characterization of cycled cathode materials.
Modified Separator Using Inactive Materials from the Cathode for Advanced Lithium Sulfur Batteries
Authors: Liu Naiqiang , Huang Yaqin
Published: February 2020

Lithium sulfur batteries become the promising candidate to develop the high-energy density rechargeable battery for electric vehicles and energy storage systems. The theoretical specific energy of the lithium-sulfur battery is 2600 W h/kg, which is much higher than lithium-ion batteries. 1 However, the commercialization of the lithium sulfur batteries has been hindered by its poor cyclability, short cycle life and low coulombic efficiency.2-3 The carbon interlayer modified separator provided a promising method to improve the electrochemical performance of lithium-sulfur battery. The carbon layer faced to the cathode blocks polysulfides in the cathode side and restrains the polysulfide shuttling during electrochemical reaction.4-5

We describe in this work a carbon interlayer modified separator design by the inactive materials from the cathode. The carbon layer coated on the separator is thin and lightweight. In addition, the method using the redistributed inactive materials avoid the added weights of the battery involved. This design will be beneficial to ensure the high-energy density of lithium sulfur batteries. After 150 cycles, the batteries retain a reversible capacity of 644 mAh g-1at the rate of 0.5 C, showing a low capacity decay of about 0.11% per circle (Figure 1).

Figure 1  Long cycle performance of Li-S batteries with modified separator at 0.5C.

Reference

1. Peled, E.; Gorenshtein, A.; Segal, M.; Sternberg, Y. Rechargeable Lithium-Sulfur Battery. J. Power Sources 1989, 26, 269-271.

2. Mikhaylik, V. Y.; James, R. A. Polysulfide shuttle study in the Li/S battery system. J. Electrochem. Soc. 2004, 151, A1969-A1976.

3. Diao, Y.; Xie, K.; Xiong, S.; Hong, X. Analysis of polysulfide dissolved in electrolyte in discharge-charge process of Li-S battery. J. Electrochem. Soc. 2012, 159, A421-A425.

4. Chung, S. H.; Manthiram, A. Bifunctional Separator with a Light‐Weight Carbon‐Coating for Dynamically and Statically Stable Lithium‐Sulfur Batteries. Adv. Funct. Mater. 2014, 24, 5299-5306.

5. Zhou, G.; Li, L.; Wang, D. W.; Shan, X. Y.; Pei, S.; Li, F.; Cheng, H. M. A Flexible Sulfur‐Graphene‐Polypropylene Separator Integrated Electrode for Advanced Li–S Batteries. Adv. Mater. 2015, 27, 641-647

Acknowledgement: Financial support from the National Science Foundation of China (no. 51272017) is gratefully appreciated.

Figure 1
High Lithium Storage Properties of MnFe2O4 Mesoporous Microspheres As an Anode Material for Li-Ion Batteries
Authors: Sunkara Satyendar
Published: February 2020

Lithium-ion batteries (LIBs) have attracted tremendous attention because of their sustai-nability, high energy density, long cycle life and environmental benignity. Apart from these, LIBs have great potential applications in electric vehicles, potable electronics, solar and wind-based electricity generation systems and renewable energy storage. LIBs became prominent power sources as the non-renewable fossil-fuels result in massive air pollution and depleting very fast. Considering the scarcity, environmental benignity and cost, it is important to develop low cost, high abundance and eco-friendly electrode materials for LIBs which can deliver high energy and power densities with long cycle lives. Manganese ferrite, MnFe2O4 is one of the binary metal oxides and belongs to iron spinel which has been studied widely for its application in drug delivery supercapacitors and in magnetic devices. However, to the best of our knowledge, there have been only a few studies on the application of MnFe2O4 as anode materials for LIBs although it possesses a high theoretical capacity of 930 mA g-1, which is much higher than that of commercial graphite anode. But MnFe2O4 suffers from poor cycling stability because of the large volume changes during lithiation/delithiation. Here, mesoporous microspheres of MnFe2O4 have been successfully synthesized by a facile method followed by a post heat treatment. The mesoporous MnFe2O4 electrodes exhibit high reversible capacity of 733 mA h g-1 after 50 cycles at the current density of 100 mA g-1 indicating the excellent cycling stability. The cell delivered discharge capacities of 1371, 1008, 876, 625, 523, 380 mA h g−1 at current densities of 100, 200, 400, 800, 1000, 1500 mA g−1, respectively. Even at a high current density of 1000 mA g−1, the electrode could deliver a discharge capacity of 523 mA h g−1, which is much higher than the theoretical capacity of graphite. Interestingly, even after stepwise increment in the current densities while measuring the rate capability, the electrode retains a capacity of 812 mA h g−1 when the current rate reverts back to 100 mA g−1.  We believe that such good performance results from the mesoporous nature of MnFe2O4 microspheres, which can substantially absorb large volume changes due during Li+ insertion/extraction.

Figure 1
Electrochemical Reaction and Direct Energy Conversion of Fucose By Functional Nanomaterial-Modified Electrodes
Authors: VU Huong THI , Yoshikawa Hiroyuki , Le Hoa Quynh , Toake Hitoshi , Tamiya Eiichi
Published: February 2020

Biomass extracted from brown macro-algae promises as a future renewable energy because of non-toxicity, natural availability, and greenhouse gas free and do not interfere with the human food chain. Here, we first show the extraction of energy from brown macro-algae by via direct oxidation of fucose by using the novel materials combination of gold nanoparticles (AuNPs), titania (TiO2) and functionalized multi-walled carbon nanotubes (f-MWCNTs). The catalytic activity for fucose oxidation of composites materials was tested by both of cyclic voltammetry and chronoamperometry methods. In all experiments, TiO2/Au/CNT nanocomposites exhibited better electrochemical performance than TiO2/CNT composites; AuNPs/CNT composite or CNTs only. Enhanced current response can be attributed to the synergic effect of nano-TiO2, nano-Au and f-MWCNTs. Further more, the new materials showed improvement on direct fucose fuel cell performance. The results from this research open possibility for practical application of our fuel cell by using the cheap catalytic material of TiO2 with high efficiency on conversion of energy from brown macroalgae biomass.
Novel Cobalt-Rich Composite (CRC) Cathode and Siox Anodes for High-Energy Li-Ion Batteries
Authors: Lopez Herman , Bowling Charles , Hernandez Pedro , Karthikeyan Deepak , Kumar Sujeet , Li Bing , Sharma Sanjeev , Venkatachalam Subramanian
Published: February 2020

The increasing sophistication and functionality of mobile devices coupled with the human dependence for the devices leads to a strong demand for high performance batteries. Over the years, improvements in battery performance have taken place with minor enhancements resulting from improvement in cell design such as increasing the active material content, increasing the electrode density and reducing the weight and thickness of the inactive cell components. Further improvements by cell optimization are quickly reaching their limits creating a shift in focus to new active electrode material that are expected to result in the next leap in cell performance.

In this work, Cobalt-Rich Composite (CRC) cathodes have been developed by modifying standard low voltage LiCoO2 (LCO) and stabilizing the structure by forming high Nickel and Manganese containing composites. The resulting CRC cathode shows surprisingly stable high voltage performance compared to LCO as shown in Figure 1. Traditionally the structure of LCO cathode falls apart at high charge voltages (>4.35V) when >0.5 moles of Li are extracted from the structure. The CRC cathode enables high electrode active content (>97%) and density (>4.0g/cc), high average voltage and high specific capacity required for high-energy cells. To complement the CRC cathode, a high capacity SiOx-based anode electrode has been developed. Current lithium ion cells continue to use graphite as the anode of choice. Si-based anodes have been widely studied as a possible replacement to graphite due to their high specific capacity (~4000mAh/g). Unfortunately Si-based materials suffer from large volume expansion resulting in pulverization and poor cycle life. However, by precise engineering the anode electrode formulation, binder and active material, high capacity SiOx-based anode electrodes with high percent active content (>80%) have been developed and shown to cycle well.

Figure 2 shows 1Ah pouch cell data from cells integrating CRC cathode and SiOx anode, showing high specific energy of 285Wh/Kg and cycle life of ~450 cycles before reaching 80% capacity retention at C/5 rate. Swelling and abuse testing of the cells meet consumer electronics specifications and results will be presented. Figure 3 shows that by engineering the cell design and increasing the cell footprint, 10Ah capacity pouch cells integrating CRC cathode and SiOx anode with specific energy of ~350Wh/Kg have been made enabling automotive and drone applications. This presentation will also cover remaining challenges associated with CRC cathode and SiOx anode with respect to synthesis, performance and cell manufacturing to bring these materials and cell technology from prototypes to large-scale manufacturing.

Figure 1
Binder-Free Freestanding Flexible Si Nanoparticles-Multi-Walled Carbon Nanotubes Composite Anodes for Li-Ion Batteries
Authors: Yao Kang , Zheng Jim P. , Liang Richard
Published: February 2020

Binder-free freestanding flexible Si nanoparticles-multi-walled carbon nanotubes (SiNPs-MWNTs) composite paper anodes have been prepared by the simple, inexpensive, and scalable approach of ultra-sonication and pressure filtration. The 3D network of MWNTs forms a continuous conductive pathway within the composite structure, which ensures sufficient electrical conductivity, holds the particles together, and alleviates the volume expansion of Si. Through control of Si/C weight ratio in the composite, we found out the SiNPs-MWNTs electrode with 3:2 Si/C ratio exhibits the optimal balance between the high capacity of SiNPs and the high electrical conductivity and structural stabilization quality of MWNTs, leading to high rate capability as well as cycle performance superior to the conventional slurry-cast SiNPs electrode using binder and Cu current collector. The reversible capacity can be recovered to 1790 mAh/g (based on the total composite weight, the same below) when the current rate returns to 100 mA/g. After 100 cycles, the electrode retains capacity of 1170 mAh/g at 100 mA/g and 750 mAh/g at 500 mA/g. The freestanding feature of our electrode eliminates the non-active mass, which is promising for enhanced capacity and energy density of Li-ion cells.

Figure 1
In Situ AFM Study of Solid Electrolyte Interface in Lithium-Ion Batteries
Authors: Shen Cai
Published: February 2020

Chemical and morphological structure of solid electrolyte interphase (SEI) plays a vital role in lithium-ion battery (LIB), especially for its cycleability and safety. To date, research on SEI is quite limited due to the complexity of SEI and lack of effective in situ characterization techniques. Here, we present real-time views of SEI morphological evolution using electrochemical atomic force microscopy (EC-AFM). Complemented by an ex situ XPS analysis, fundamental differences of SEI formation from ethylene carbonate (EC) and fluoroethylene carbonate (FEC)-based electrolytes during first lithiation/delithiation cycle on HOPG as well as Fe3O4 electrode surfaces were revealed. Our results showed that SEI layer formed by reductive decomposition of the EC/DMC electrolyte was principally composed of alkyl carbonates ROCO2Li, while the SEI layer formed by FEC/DMC electrolyte was mainly composed of LiF. Only trace of Li2CO3was found in the SEI layer formed from FEC/DMC electrolyte. The dense and hard nature of SEI formed by FEC/DMC electrolyte can protect the graphite against dendrite formation and could be the reason for better cyclability of FEC/DMC electrode as compared to those of EC/DMC based electrolyte. For the  Fe3O4 anode, it was found that Fe3O4 electrode was unable to form a stable SEI layer on the electrode surface which resulting in electrolyte decomposition. FEC-based electrolyte can help to improve the performance of Fe3O4 anodes in lithium ion batteries but its protective effects are far from perfect. To accelerate the application of Fe3O4 or other metal oxide anodes in lithium ion batteries, better electrolytes and sophisticated carbon coating techniques are needed warrant formation of a stable SEI layer. 

Conventional method to evaluate electrolytes are usually complex and tedious procedures. Thus, combination of in situ electrochemical AFM and ex situ XPS could potentially serve as a fast diagnostic tool to evaluate the properties and quality of SEI formed on different electrodes from diverse electrolytes and additives.
(Invited) On the Way to Molecular Building Blocks for Next Gen OPV
Authors: Hummelen Jan
Published: February 2020

We have recently predicted that when the dielectric constant of organic semiconductors is increased from 2-4 to >10, a dramatic increase in (maximal) power conversion efficiency of organic solar cells, based on these materials as active layer constituents, can be achieved.1-3 Binding energies of initial excitons, of charge transfer excitons, and between charges in any type of recombination process are diminished with increasing electric permittivity of the medium.

In order to design and develop new molecular materials with higher dielectric constant, the next challenge is to make the connection between the dielectric constant, as a macroscopic property, and molecular structure.

One approach is to connect suitable substituents to known (opto)electronically functional molecular moieties. We report here on the design and preparation of molecules bearing substituents that are to enhance the dielectric properties without diminishing other crucial parameters (like charge carrier mobility, bandgap, stability, etc.).4,5 Another approach is to design inherently more polarizable/polar chromophores. A new class of conjugated polymers, based on this principle is presented.6

Through a computational chemistry approach, we investigate the influence of molecular moieties on the relative energies of various charge separated states resulting from photo-induced charge transfer between molecular donors and acceptors. We report on a system in which the energies of the charge separated states are tuned to a favorable situation by proper placement of dipolar substituents.7

1. L. J. A. Koster, S.E. Shaheen, J.C. Hummelen, Adv. Energy Mater. 2012, 2, 1246.

2. R.C. Chiechi, J.C. Hummelen, ACS Macro Lett. 2012, 1, 1180.

3. R. C. Chiechi, R. W. A. Havenith, J. C. Hummelen, L. J. A. Koster, M. A. Loi, Materials Today 2013, 16, 281.

4. F.Jahani, S. Torabi, R.C. Chiechi, L. J. A. Koster, J. C. Hummelen Chem. Commun. 2014, 50, 10645.

5. S. Torabi, F.J.Bahnamiri, I. Van Severen, C. Kanimozhi, S. Patil, R.W.A. Havenith, R.C. Chiechi, L. Lutsen, D.J.M. Vanderzande, T.J. Cleij, J.C.Hummelen, L.J.A.Koster, Adv. Funct. Mater. DOI 10.1002/adfm.201402244 (2014)

6. T. P. Voortman, H. D. de Gier, R.W. A. Havenith, R. C. Chiechi, J. Mater. Chem. C, 2014, 2, 3407

7. H. De Gier, R. Broer, R.W.A. Havenith, Phys.Chem.Chem.Phys., 2014, 16, 12454
(Invited) Sumanene: A C3-Symmetric Fragment Structure of C60
Authors: Sakurai Hidehiro
Published: February 2020

Bowl-shaped pi-conjugated compounds including partial structure of fullerenes, which are called "buckybowls", are of importance not only as model compounds of fullerenes but also as their own chemical and physical properties.  Two pristine structure are known, C5v-symmetric corranulene and C3v-symmetric sumanane. One of the characteristic features of buclybowls is that they possess terminal C-H structure, which can be chemically transfered to the functional groups to control the chemical/physical structure of the bowls with ease. In particular, three benzylic positions of sumanene are highly expected to functionalize to other groups such as carbonyl group, which can tune the electrochemical character of the bowls. For example, sumanenetrione exhibits stepwise multi-electron reduction process.  Cyclic voltammograms of the stepwise first and second one-electron reduction showed reversible waves with associated reduction potentials which were almost equivalent to those of C60.
(Invited) Long-Lived Charge Separated States Exclusively from the Triplet Excited States in Palladium Porphyrin-Fullerene Conjugates
Authors: D'Souza Francis , Obondi Christopher , Churchill Brittani , Lim Gary N. , Poddutoori Prashanth , van der Est Art
Published: February 2020

Molecular engineering of donor-acceptor conjugates to control their photoinduced processes to yield the much desired long-lived charge separated states has been one of the major goals in artificial photosynthesis.  The charge separated states of sufficient lifetime and stored energy are key in ultimately driving the photocatalytic processes of either light-to-electricity conversion or light-to-fuel production.  In simple donor-acceptor dyads, charge separation from the singlet excited donor or acceptor due to rapid charge recombination process results in a short-lived charge separated state of singlet spin character.  Utilization of high energy triplet sensitizers instead of the traditionally employed singlet sensitizers could be an elegant approach to generate long-lived charge separated states.  The radical ion-pairs of triplet spin character charge recombine to the ground state slowly due to spin forbidden nature of the process.  However, witnessing such a process purely from the triplet excited state without the interference of the singlet excited state and other competing photochemical events such as excitation energy transfer has been challenging to establish. 

Here, we report our strategy to observe electron transfer exclusively from the triplet excited state of the donor in PdP-C60 dyads (see figure below). Using transient absorption spectral studies operating at different timescales and time-resolved electron paramagnetic resonance (TR-EPR) studies, photoinduced electron transfer from 1PdP* to C60 leading to the formation of PdP•+-C60
•- charge separated state of singlet spin character has been witnessed in 2 (instead of triplet-triplet energy transfer observed in 1
1) due to the close proximity of the donor and acceptor entities.  In contrast, by lowering the energy of the [(TPA)3PdP]•+-C60
•- state owing to the presence of electron rich TPA entities (facile oxidation) compared to that of 3C60*, electron transfer from 3(TPA)3PdP* to C60 leading to [(TPA)3PdP]•+-C60
•- charge separated state of triplet spin character with lifetime in the microsecond range has been observed in 3 in polar solvents.  Results of these findings and its significance will be highlighted.

C. Obondi, G. N. Lim, F. D’Souza, Triplet-Triplet Excitation Transfer in Palladium Porphyrin – Fullerene and Platinum Porphyrin – Fullerene Dyads’ J. Phys. Chem. C 2015, 119, 176-185.

Figure 1
(Invited) Decorating Nanocarbons with Perylenediimide Systems
Authors: Sastre-Santos Ángela , Pla Sara , Martin-Gomis Luis , Fernández-Lázaro Fernando
Published: February 2020

Carbon-based nanostructured materials (fullerenes, carbon nanotubes or graphene, to name a few) are known to show electron-acceptor properties at the molecular scale, together with high values of electron mobilities in bulk. Thus, its implementation in active materials is an important issue in order to develop organic efficient full optoelectronic devices. One of the strategies employed in the improvement of the interesting optoelectronic properties of carbon nanostructures, is the doping, either in a covalent or a non-covalent way, with specially designed electron-donor/light harvesting moieties. These moieties act like light collectors, exciting themselves and promoting an electron to a higher energy state, which is rapidly deactivated through electron and/or energy transfer processes to the carbon-based nanostructure.

Here we present different strategies for the covalent and non-covalent functionalization of nanocarbon materials. In these examples, the decorating agents, specially designed perylenediimides[1-4] (Figure 1) and others, whose electronic character has been modulated through the introduction of different substituents, are successfully employed to improve the light absorption behaviour in the UV and NIR regions of the, in principle, unabsorbing carbon nanoforms, thus yielding hybrid materials with potential applicability like active layers in organic photovoltaic devices.

Acknowledgements. This work has been supported by the Spanish Ministerio de Economía y Competitividad, Generalitat Valenciana and the European FEDER funds (grants CTQ2011-26455, CTQ2014-55798-R, PROMETEO 2012/010 and ISIC/2012/008)

 References

Martín-Gomis, L.; Rotas, G.; Ohkubo, K.; Fernández-Lázaro, F.; Fukuzumi, S.; Tagmatarchis, N.; Sastre-Santos, Á. Nanoscale
2015, 7, 7437-7444..

Barrejón, M.; Pla, S.; Berlanga, I.; Gómez-Escalonilla, M. J.; Martín-Gomis, L.; Fierro, J. L.; Zhang, M.; Yudasaka, M.; Iijima, S.; Gobeze, H. B.; D’Souza, F.; Sastre-Santos, Á.; Langa, F. J. Mater.Chem. C.
2015, 3, 10215-10224.

Pla, S.; Niemi, M.; Martín-Gomis, L.; Fernández-Lázaro, F.; Lemmetyinen, H.; Tkachenko, N. V.; Sastre-Santos, Á. Phys.Chem. Chem. Phys. Accepted.

Martín-Gomis, L.; Karousis, N.; Petsalakis, I. D.; Ohkubo, K.; Fernández-Lázaro, F.; Tagmatarchis, N.; Fukuzumi, S.; Sastre-Santos Á. Submitted.

Figure 1.
Chemical structures of a) [60]Fullerene-Perylenediimide (C60-PDI, DB-1,7-Pyr-PDI-C60) and b) Double Wall Carbon Nanotube-Perylenedimide (DWCNT-PDI).

Figure 1
(Invited) Transition Metal Dichalcogenides: Growth and Characterization
Authors: Bartels Ludwig
Published: February 2020

I will present the growth of transition metal dichalcogenides films (MoS2, MoSe2, WS2, WSe2, MoTe2) and their alloys via chemical vapor deposition and high vacuum techniques.[1] I will highlight the growth of the material on different substrate and the ensuing variation of properties before describing how post-growth processing allows chalcogen exchange towards local change of bandgap.[2] Deposition onto functional substrates - such as ferroelectrics - permits further local modification of the material properties toward device applications.[3]

[1]          J. Mann, et al., Advanced Materials 26 1399 (2014).

[2]          Q. Ma, et al., Acs Nano 8 4672 (2014).

[3]          A. Nguyen, et al., Nano Lett 15 3364 (2015).
(Invited) Towards Large Scale Growth of Two-Dimensional Transition Metal Dichalcogenides
Authors: Grossman Jeffrey C , Ferralis Nicola
Published: February 2020

Investigations of 2D materials have increased substantially, as they have been shown to exhibit a wide range of novel electronic properties. Transition metal dichalcogenides (TMDCs), depending on the polytype and number of d-electrons, can exhibit metallic, semi-metallic, and semiconducting behavior. In addition, enhancements to optical behavior, especially in the form of absorption, have been observed in these 2D materials.  In contrast to the well-known 2D material graphene, the presence of a bandgap, as well as device performance on transistors fabricated using certain TDMCs, indicate that they could serve as possible successor materials to Si. The successful, industrial deployment of such materials however relies on the ability of large scale synthesis of high quality TMDCs.

Large scale, high quality growth of graphene has been enabled by successful application of vapor deposition techniques such as chemical vapor deposition (CVD). In extending the quest for high quality, large scale synthesis of 2D TMDCs, similar vapor deposition techniques have been explored, mainly CVD. Yet, high quality extended 2D TMDCs are still lacking.

Atomic Layer Deposition (ALD) can be instrumental to the production of large area, two-dimensional materials, and simultaneously offer superior alternatives to exfoliating methods. In this work we consider the transition metal dichalcogenide MoS2 – specifically its growth starting from an ALD route comprised of  (tBuN)2(NMe2)2Mo and O3 to produce MoO3, followed by subsequent sulfurization steps to produce MoS2. Data from a variety of direct measurement techniques, including atomic force microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence spectroscopy, for determining the existence and optical properties of monolayer MoS2 will be presented.
(Nanocarbons Division SES Young Investigator Award) Making Graphene Resist Aggregation
Authors: Luo Jiayan
Published: February 2020

Graphene-based sheets have stimulated great interest in many scientific disciplines and shown promise for wide potential applications. Among various ways of creating single atomic layer carbon sheets, a promising route for bulk production is to first chemically exfoliate graphite powders to graphene oxide (GO) sheets, followed by reduction to form chemically modified graphene (CMG). Due to the strong van der Waals attraction between graphene sheets, CMG tends to aggregate. The restacking of sheets is largely uncontrollable and irreversible, thus it reduces their processability and compromises properties such as accessible surface area. Strategies based on colloidal chemistry have been applied to keep CMG dispersed in solvents by introducing electrostatic repulsion to overcome the van der Waals attraction or adding spacers to increase the inter-sheet spacing. In this dissertation, two very different ideas that can prevent CMG aggregation without extensively modifying the material or introducing foreign spacer materials are introduced.

The van der Waals potential decreases with reduced overlapping area between sheets. For CMG, reducing the lateral dimension from micrometer to nanometer scale should greatly enhance their colloidal stability with additional advantages of increased charge density and decreased probability to interact. The enhanced colloidal stability of GO and CMG nanocolloids makes them especially promising for spectroscopy based bio-sensing applications.

For potential applications in a compact bulk solid form, the sheets were converted into paper-ball like structure using capillary compression in evaporating aerosol droplets. The crumpled graphene balls are stabilized by locally folded π-π stacked ridges, and do not unfold or collapse during common processing steps. They can tightly pack without greatly reducing the surface area. This form of graphene leads to scalable performance in energy storage. For example, planer sheets tend to aggregate and lose surface area. So their capacitive performance tends to decrease with increased loading level. But the crumpled balls can resist aggregation and retain high capacitance at high loading level. The crumpled graphene balls can be also used as expandable shells for wrapping lithium ion battery anode materials such as Si nanoparticles, which can accommodate their expansion/contraction without facture, and thus greatly improve the coulombic efficiency of the anode.
Synthesis and Characterization of Graphene Flakes to be Used in the Development of Electrodes for Li-Ion Batteries
Authors: Díaz Francisco , Campo Teresa , Cotto María , Márquez Francisco , Morant Carmen , Elizalde Eduardo
Published: February 2020

One of the main problems in our society is the energy production and storage.  Ion-Li batteries are commonly used as an alternative for energy production but have the disadvantages of a poor recharged cycles and the possibility of fire.  Researches are done to develop efficient anodes and cathodes for batteries and one of the possible alternatives is the use of graphene.  Due to its unique planar structure, transparency, mechanical strength, thermal properties, and electronic conductivity, graphene is a very promising material for nanoelectronic devices, sensors, energy-storage and/or transparent conducting electrodes applications. The exceptional properties of graphene are a consequence of the continuous network of hexagonally arranged sp2-bonded carbon atoms in a 2D-structure. Among the different synthesis processes to obtain graphene (i.e. chemical exfoliation, mechanical cleavage, epitaxial growth or chemical vapor deposition-CVD), the last one (CVD) is considered as the most promising procedure to obtain continuous graphene flakes, with very low level of defects. Although the presence of unwanted byproducts and structural damages is unavoidable, this method is one of the most suitable for large-scale and controllable synthesis of graphene. Commonly, the synthesis of graphene by CVD requires a copper or nickel sheet as substrate, and alcohols or methane as carbon source.

In this research, a CVD method, slightly modified with respect to the standard procedure, has been used to obtain graphene flakes (see Figure 1). Thus, a mixture of ethanol:N2:H2 was used to obtain a blue plasma at high temperature, responsible for the synthesis of graphene. A complete analysis of the as-synthesized graphene flakes has been performed using a combination of tools including scanning and transmission electron microscopies (SEM and TEM), Raman spectroscopy, X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM) and infrared spectroscopy (FT-IR).

Figure 1
Electrochemical Water Treatment Using Graphene, Graphene Foam and Graphene / Metal Oxide Composites
Authors: Roberts Edward , Sharif Farbod , Gagnon Luke
Published: February 2020

Combining adsorption with electrochemical oxidation has been shown to be effective for the removal and oxidation of dissolved and dispersed organic contaminants from water, using a graphite flake adsorbent.  In order to increase the adsorption capacity, we have investigated the use of graphene based adsorbents, which have high specific surface area combined with electrochemical activity.  We have prepared and tested reduced graphene oxide (RGO), graphene foam and graphene metal oxide composite materials.  RGO offer significantly higher adsorptive capacity than graphite flake.  Similarly graphene foam was found to have a high adsorption capacity, although the adsorption kinetics were poor due to the slow diffusion of conatminants into the foam pores.  A graphene foam would be more readily separated from the treated water and further work is planned to determine whether a flow through treatment process can be used to overcome the slow adsorption kinetics.  However, during electrochemical oxidation, the structural integrity of the foam was compromised after only 1 or 2 cycles, presumably due to oxidation of the graphene.  A graphene / iron oxide composite was preapred with ferromagnetic characteristics to enable separation from the treated water.  The adsorption capcity was slightly reduced, but the electrochemcial regeneration performance was good.  Oxidation of graphene remains a challenge, and work is ongoing to explore the use of graphene / titanium dioxide composites.  The TiO2 will catalyse the organic oxidation and may also protect the graphene from oxidation.
Understanding the Binding Mechanism for Catalysis and Energy Storage
Authors: Liu Yuanyue , Wood Brandon , Lou Jun , Ajayan Pulickel M , Yakobson Boris I. , Goddard William A
Published: February 2020

Many catalytic and energy-storing reactions occur through the binding of substances. Understanding the binding mechanism could help design better materials/devices. Using atomistic theory, we show that (i) the Li capacity of pristine graphene is lower than that of graphite, despite its higher surface area [1]; (ii) the binding between Li and C can be described by a ‘states-filling’ model [2]; (iii) This model is used to study the electrochemical hydrogen production, and leads to the discovery of a self-optimizing and highly-active metal dichalcogenide catalyst, whose extraordinary performance relies on the surface-activity, different from conventional Mo and W dichacogenides which have only edge active [3]; (iv) why graphite has a low capacity for Na while high capacities for other alkali-metals, an important question for the development of Na-ion batteries [4]. These progresses demonstrate the power of atomistic theory in aiding the understanding and designing materials.  

[1]          Y. Liu, V. I. Artyukhov, M. Liu, A. R. Harutyunyan, B. I. Yakobson, J. Phys. Chem. Lett.
2013, 4, 1737-1742.

[2]          Y. Liu, Y. M. Wang, B. I. Yakobson, B. C. Wood, Phys. Rev. Lett.
2014, 113, 028304.

[3]          Y. Liu, K. P. Hackenberg, J. Wu et al, submitted.

[4]          Y. Liu, B. Merinov, W. A. Goddard, submitted.
(Invited) Functionalization of Graphene By Oxo-Addents As Performance Boost
Authors: Eigler Siegfried
Published: February 2020

Graphene derivatives are expected to be crucial for finding new properties beyond pure graphene. Selectively sensing of molecules or macromolecules is one exciting example. However, the chemical toolbox giving control over the type and degree of functionalization of graphene, on the single layer level, is far from being developed and understood. Functionalization of graphene by oxo-addends is one possibility to provide soluble graphene. With that oxo-functionalized graphene, post-functionalization reactions can be studies without the reactivity being influenced by defect sites, as it is the case for graphene oxide, a class of materials that’s properties is dominated by defects. We demonstrate in selective examples controlled chemistry of oxo-functionalized graphene, with respect to the degree of functionalization, the ability to form graphene with very little defects and the performance in devices. One example will be about the storage of charge, and therefore information, in an oxo-functionalized graphene composite that was formed by exploiting the electrostatic interaction of alkylammonium ions and sulfatesters bound on the surface of the graphene material. In this special example the benefit of controlled chemistry ,combined with state-of-the-art analysis, will be demonstrated.
(Invited) Conjugated Polymer Spherical Microcavities for Energy Conversion
Authors: Yamamoto Yohei
Published: February 2020

Optical microcavities play an important role for the next-generation light technology. Recently, we succeeded in fabricating spherical microcavities from conjugated polymers (CPs) by simple self-assembly process and found that the microcavities show whispering gallery mode (WGM) resonant photoemission [1-4]. The CP-based microcavities are superior to conventional microcavities in points of simple fabrication process, function as both cavity and emitter, high photo-stability and optical gain, and potent use for electrically-driven WGM and lasers. In this presentation, we demonstrate the WGM-mediated intersphere light propagation and cascade-like energy conversion, in which the confined modes realize directional light energy transport between adjacent spheres and subsequent color conversion.

[1] T. Adachi et al., J. Am. Chem. Soc. 2013, 135, 870-876. [2] L. Tong et al., Polym. Chem. 2014, 5, 3583-3587. [3] K. Tabata et al., Sci. Rep.
2014, 4, 5902/1-5. [4] S. Kushida et al., Macromolecules
2015, 48, 3928-3933.
(Invited) Carbon Nanotube-Templated Synthesis of Covalent Porphyrin Network for Oxygen Reduction Reaction
Authors: Campidelli Stephane , Hijazi Ismail , Bourgeteau Tiphaine , Cornut Renaud , Morozan Adina , Jousselme Bruno
Published: February 2020

The fabrication of functional hybrid materials that preserves and combines the properties of their building blocks is a central issue of nanosciences. Among the different classes of nanomaterials, carbon nanotubes are promising for electronics, catalysis and composite applications. Within the context of sustainable development and renewable energy, we and others envisioned the use of functionalized or doped carbon nanotubes in electrocatalytic systems.1
,
2 In such systems, the catalytic sites need to be supported on conducting materials. Carbon nanotubes, thanks to their electrical conductivity and their high surface area appear as the ideal material for that purpose.

In actual proton exchange membrane fuel cell devices (PEMFC), the reactions at the electrodes and in particular the reduction of oxygen is performed by platinum nanoparticles. The cost of platinum encourages the development of new catalysts based on non-noble metals. In nature, the reduction of oxygen is performed by iron porphyrins in the active center of enzymes. Thus bio-inspired catalysts based on cobalt or iron macrocycles have been extensively studied for oxygen reduction reaction (ORR).3
,
4

Here, we describe the formation of a covalent network of porphyrins around MWNTs. Our approach is based on adsorption of ethynylporphyrins followed by the dimerization of the triple bonds. The nanotube acts as a template for the formation of the polymeric layer. The nanotube hybrids were characterized and tested for the ORR in a series of electrochemical measurements in acidic conditions. Compared to similar systems in which monomeric porphyrins are simply physisorbed, the nanotube hybrib showed a higher activity, a higher current density, a lower overpotential and a four electrons reaction pathway.5

References

(1)    Zhang, W.; Sherrell, P.; Minett, A. I.; Razal, J. M.; Chen, J. Energy Environ. Sci.
2010,
3, 1286-1293.

(2)    Morozan, A.; Jousselme, B.; Palacin, S. Energy Environ. Sci.
2011,
4, 1238-1254.

(3)    Zagal, J. H.; Griveau, S.; Silva, J. F.; Nyokong, T.; Bedioui, F. Coord. Chem. Rev.
2010,
254, 2755-2791.

(4)    Morozan, A.; Campidelli, S.; Filoramo, A.; Jousselme, B.; Palacin, S. Carbon
2011,
49, 4839-4847.

(5)    Hijazi, I.; Bourgeteau, T.; Cornut, R.; Morozan, A.; Filoramo, A.; Leroy, J.; Derycke, V.; Jousselme, B.; Campidelli, S. J. Am. Chem. Soc.
2014,
136, 6348-6354.

Figure 1
(Invited) Purification of a Non-Precious Metal Oxygen Reduction Catalyst to Reveal the Active Species
Authors: Gewirth Andrew A. , Varnell Jason A. , Tse Edmund C. M.
Published: February 2020

Despite substantial efforts to understand the structure of the active site in Fe-based non-precious metal (NPM) catalysts for the oxygen reduction reaction (ORR) in fuel cells, the identification of the active species remains elusive, impeding progress towards the development of highly active and cost efficient catalysts.  We report the isolation and identification of the active Fe species in an NPM catalyst using Cl2 and H2 treatments which decrease the heterogeneity of the catalyst. The Cl2 treatment decreases catalyst activity as shown by a negative shift in the ORR onset of ca. 170 mV.  Subsequent treatment with H2 restores the initial activity of the catalyst.  Mössbauer spectroscopy and X-ray absorption spectroscopy show many Fe species in the as-prepared catalyst while the catalyst after the Cl2 and H2 treatments contains only reduced Fe species encapsulated by C which are highly active for the ORR.
(Invited) Kinetics of Photocatalytic Multielectron Transfer By Nanoparticles of Bare or Catalyst-Loaded Titania
Authors: Ohtani Bunsho , Takeuchi Shugo , Takase Mai , Takashima Mai
Published: February 2020

For heterogeneous photocatalysis, it is well known that photocatalytic oxidation of water into oxygen (O2) is induced by particulate photocatalysts in the presence of electron acceptors.  This reaction has been presumed to proceed through a four-electron (hole) process, and therefore it is expected that reaction rate depends on light intensity and particle size of photocatalyst, which influence the number of photons absorbed by one photocatalyst particle.  However such dependences have rarely been reported and discussed so far. In this study, we report light-intensity and particle-size dependences of rate of oxygen evolution from suspensions of commercial titania samples using iodate (IO3
-) and iron(III) (Fe3+) ions as an electron acceptor under intense UV-LED irradiation (365 nm; < 300 mW).

Figure 1 shows the light-intensity dependence of rate of O2 evolution from a suspension of rutile (Tayca MT-150A; 13 nm) with Fe3+.  A higher-order non-linear dependence was observed in the relatively lower (< 190 mW = threshold intensity, I
thr), while the rate was almost proportional to the intensity (with slope, a) in the higher intensity range, and those dependences could be reproduced by second and first-order equations, respectively.  Similar bimodal dependences, with different a and I
thr, were also observed when the other titania samples were used in the presence of IO3
- or Fe3+.  Assuming a kinetic model (Scheme 1) in which second-photon absorption by a one photon-absorbing particle (TiO2(h+)) within its lifetime leads to oxygen evolution, a rate equation (eq. 1) was derived using parameters of lifetime of TiO2(h+), secondary photon-absorption efficiency and rate constant of oxygen evolution by a two-photon absorbing particle(TiO2*), and further derivation for lower and higher intensity limits to eqs. 2 and 3, respectively, reproduced the bimodal light-intensity dependences.  Threshold intensity (I
thr) at which order of light-intensity dependence formally changes from second to first is defined as intensity for the equal rates of eq. 1 and 2 are equal.   Differences in I
thr and a depending on the kind of electron acceptors, crystalline structure (anatase or rutile) and particle size are discussed.

Figure 1
(Invited) ­­­Stable and Durable CH3NH3PbI3 Perovskite Solar Cells at Ambient Conditions
Authors: Sunkara Mahendra Kumar , Kumari Sudesh , Vendra Venkat Kalyan , Druffel Thad , Spurgeon Joshua M , Lavery Brandon Wayne
Published: February 2020

Organic-inorganic halide perovskites have created a breakthrough in the field of solar cells because of their low cost, low temperature processibility and  excellent optoelectronic properties. However, the instability of  organic-inorganic halide perovskites to moisture is currently a huge challenge in the  field of  perovskite solar cells and needs to be addressed to translate the perovskite technology from the laboratory bench to large scale industrial practice.  Currently, all the lab scale perovskite cells are fabricated in controlled glove box atmosphere with less than 1 % relative humidity to prevent their deterioration under moisture.

In this work, a novel concept of protecting the perovskite using a highly conductive composite of a layered material and a hole transporting polymer is presented. The excellent charge transport properties of the composite coating allow the  use of thick coating on the perovskite, creating extremely high length scales for moisture diffusion through composite. The composite coating developed in our work, could be extended to lead-free organometallic perovskites that are both moisture and oxygen sensitive.  The deposition of gold as a counter electrode for the lab scale perovskite cells is usually performed by thermal evaporation in a bell jar evaporator. This process is time consuming, energy intensive and not viable to scale up. Our approach involving lamination of individual electrodes, enables a much facile low cost process for fabricating perovskite solar cells.

Our results and observation on polymer composites as protective coatings for perovskite and on  laminating electrodes show high promise for the  scalability and low cost fabrication of perovskite cells under atmospheric conditions  (60 -70 % relative humidity). In addition, the degradation mechanisms involving both moisture and oxygen in the presence of UV light irradiation will be discussed.